docs(api): use an inline table sample that really breaks

Assisted-by: DeepSeek V4.1 Flash

.gitea/workflows/test.yml

@@ -105,6 +105,8 @@ jobs:
         run: go build -o bin/interpres-decode ./cmd/interpres-decode
 
       - name: Compliance suite
-        # interpres implements TOML 1.0 and 1.1; the mode is pinned so an upstream
-        # default change cannot silently move the corpus.
-        run: bin/toml-test test -decoder=bin/interpres-decode -toml=1.1
+        # interpres implements TOML 1.1, and the suite runs both directions: the decoder
+        # on the valid and invalid corpora, the encoder on the tagged JSON of the valid
+        # one. The mode is pinned so an upstream default change cannot silently move the
+        # corpus.
+        run: bin/toml-test test -decoder=bin/interpres-decode -encoder='bin/interpres-decode -encode' -toml=1.1

CHANGELOG.md

@@ -9,7 +9,53 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Added
 
--
+- `encoding.TextMarshaler` and `encoding.TextUnmarshaler` are honoured by
+  default, with no option to switch them off. A type that implements them is
+  encoded as a TOML string and decoded from one: `net.IP` becomes
+  `"192.0.2.1"`, and a user type with `MarshalText` or `UnmarshalText` follows.
+  `MarshalTOML` and `UnmarshalTOML` still win over the text methods, and the
+  four date-time types keep their bare timestamp form instead of becoming a
+  quoted string. A struct type that implements the interface now encodes as a
+  string where it was a table before, which is the breaking part of the change.
+- `time.Duration` is encoded in its canonical Go form as a TOML string,
+  `1h30m0s`, because TOML has no duration type; the decoder reads that string
+  back and still accepts a bare integer as the nanosecond count.
+- `interpres-decode -encode`, the adapter's other direction: it reads the
+  toml-test tagged JSON from stdin and writes the TOML document it describes.
+  The compliance suite now runs the encoder as well as the decoder, 214
+  encoder cases against the tagged JSON of the valid corpus.
+- `Encoder.InlineTables(threshold)`: a sub-table whose single-line rendering is
+  at most `threshold` bytes is written as an inline table instead of a header
+  section, which shortens a document of small tables. An array of tables keeps
+  its header form, because its inline form would re-parse as a value array.
+
+### Changed
+
+- The output takes the TOML 1.1 form. A date-time writes its seconds only when
+  the value carries them and drops the trailing zeros of a fractional second,
+  so `07:32:00` is written `07:32` and half a second as `00.5`. Both are the
+  same value, and a document written without seconds now comes back without
+  them. `LocalDateTime.String()`, `LocalTime.String()` and the offset date-time
+  rendering follow the same rule.
+- An inline table that would pass the hundredth column is written across lines
+  with a trailing comma and one tab of indentation per nesting level, the shape
+  TOML 1.1 allows an inline table to take.
+- TOML 1.1 is the acceptance contract, and TOML 1.0 is not. The compliance
+  suite runs the 1.1 corpus alone, and the promise that every 1.0 document
+  parses exactly as before is withdrawn. Nothing that parses today stops
+  parsing: the 1.0 valid corpus still passes in full. The documents whose
+  verdict changes are the ones 1.1 relaxed, such as the `\xHH` escape
+  sequences 1.0 rejected.
+- The module path carries the /v2 suffix the Go toolchain requires of
+  every major version 2 module: imports change to
+  `sourcedock.dev/petrbalvin/interpres/v2`.
+
+### Fixed
+
+- Decoding into a defined type whose underlying kind is string or bool, such
+  as `type Name string`, panicked instead of storing the value, because a
+  value of the predeclared type is not assignable to a defined type and the
+  decoder assigned it without a conversion.
 
 ## [1.1.0] - 2026-09-18
 

CONTRIBUTING.md

@@ -45,8 +45,8 @@ just test
    formatting pass are three commits, never one.
 4. Record every user-visible change in `CHANGELOG.md` under `## [development]`.
 5. Add or update tests. Coverage stays at 80 percent or more; it is a hard
-   gate. Parser and decoder changes must also keep the toml-test suite at zero
-   failures, checked with `just toml-test`.
+   gate. Parser, decoder and encoder changes must also keep both directions of
+   the toml-test suite at zero failures, checked with `just toml-test`.
 6. Update the documentation when the public API, the configuration or the
    behaviour changes; the documents move in the same commit as the behaviour
    they describe.

README.md

@@ -1,14 +1,14 @@
 # interpres
 
-A TOML 1.0 and 1.1 parser and encoder for Go, written with the standard
-library alone. `interpres` (Latin for *interpreter*) gives zero-dependency
+A TOML 1.1 parser and encoder for Go, written with the standard library
+alone. `interpres` (Latin for *interpreter*) gives zero-dependency
 programs an `encoding/json`-style API for reading and writing TOML, and passes
 the entire official [toml-test](https://github.com/toml-lang/toml-test) suite:
-214 valid and 467 invalid cases, zero failures.
+214 valid, 467 invalid and 214 encoder cases, zero failures.
 
 ## Features
 
-- **Full TOML 1.0 and 1.1**: bare, quoted and dotted keys; tables and arrays of
+- **Full TOML 1.1**: bare, quoted and dotted keys; tables and arrays of
   tables; basic and literal strings including multiline, with the 1.1 `\e` and
   `\xHH` escapes; integers in the four radixes with `_` separators; floats with
   exponents, `inf` and `nan`; booleans; the four date-time kinds, seconds
@@ -18,18 +18,21 @@ the entire official [toml-test](https://github.com/toml-lang/toml-test) suite:
 - **Strict decoding**: `NewDecoder().DisallowUnknownFields()` rejects keys that
   match no destination field, at every struct depth.
 - **Custom types**: `Marshaler` and `Unmarshaler` let a type control its own
-  TOML representation in both directions.
+  TOML representation in both directions, and `encoding.TextMarshaler` and
+  `TextUnmarshaler` are honoured by default, so `net.IP`, `time.Duration` and
+  user types with text methods need no configuration.
 - **Cancellation**: every entry point has a `*Context` sibling that honours a
   `context.Context`.
 - **Configurable emission**: `Encoder` options for declaration-order output,
-  omitting empty arrays, and literal multiline strings.
+  omitting empty arrays, literal multiline strings, and inlining small
+  sub-tables.
 
 ## Install
 
 As a library:
 
 ```sh
-go get sourcedock.dev/petrbalvin/interpres
+go get sourcedock.dev/petrbalvin/interpres/v2
 ```
 
 Requires Go 1.27.1 or newer. The module imports only the standard library.
@@ -161,7 +164,7 @@ See [docs/DEVELOPMENT.md](docs/DEVELOPMENT.md) for the full workflow, and
 
 - [docs/ARCHITECTURE.md](docs/ARCHITECTURE.md): components and data flow
 - [docs/API.md](docs/API.md): the API reference, decoding and encoding rules
-- [docs/CLI.md](docs/CLI.md): the interpres-decode toml-test adapter and validator
+- [docs/CLI.md](docs/CLI.md): the interpres-decode adapter and validator
 
 ## Licence
 

SECURITY.md

@@ -7,7 +7,7 @@ releases do not receive them.
 
 | Version | Supported |
 |---|---|
-| 1.0.0 | yes |
+| 1.1.0 | yes |
 | older releases | no |
 
 ## Reporting a vulnerability

cmd/interpres-decode/main.go

@@ -4,14 +4,16 @@
 // Command interpres-decode is the toml-test harness adapter and a TOML
 // validator. Without flags it reads a TOML document from standard input and
 // writes the toml-test "tagged JSON" representation to standard output. With
-// -validate it checks the named documents, or standard input when none are
-// named, and exits non-zero on the first invalid one:
+// -encode it is the reverse: it reads tagged JSON and writes the TOML document
+// it describes. With -validate it checks the named documents, or standard
+// input when none are named, and exits non-zero on the first invalid one:
 //
 //	interpres-decode -validate config.toml
+//	interpres-decode -encode < case.json
 //
-// Run the official suite against the adapter with:
+// Run the official suite in both directions against the adapter with:
 //
-//	toml-test ./interpres-decode
+//	toml-test test -decoder=./interpres-decode -encoder='./interpres-decode -encode'
 package main
 
 import (
@@ -25,7 +27,7 @@ import (
 	"strconv"
 	"time"
 
-	"sourcedock.dev/petrbalvin/interpres"
+	"sourcedock.dev/petrbalvin/interpres/v2"
 )
 
 func main() {
@@ -39,12 +41,17 @@ func Run(args []string, stdin io.Reader, stdout, stderr io.Writer) int {
 	fs := flag.NewFlagSet("interpres-decode", flag.ContinueOnError)
 	fs.SetOutput(stderr)
 	validate := fs.Bool("validate", false, "validate the documents instead of emitting tagged JSON")
+	encode := fs.Bool("encode", false, "read tagged JSON from stdin and write TOML instead")
 	if err := fs.Parse(args); err != nil {
 		if errors.Is(err, flag.ErrHelp) {
 			return 0
 		}
 		return 2
 	}
+	if *validate && *encode {
+		fmt.Fprintln(stderr, "interpres-decode: -validate and -encode cannot be combined")
+		return 2
+	}
 	if *validate {
 		return validatePaths(fs.Args(), stdin, stderr)
 	}
@@ -52,6 +59,9 @@ func Run(args []string, stdin io.Reader, stdout, stderr io.Writer) int {
 		fmt.Fprintln(stderr, "interpres-decode: the adapter mode takes no arguments; name files with -validate")
 		return 2
 	}
+	if *encode {
+		return encodeJSON(stdin, stdout, stderr)
+	}
 	data, err := io.ReadAll(stdin)
 	if err != nil {
 		fmt.Fprintln(stderr, "read stdin:", err)
@@ -109,6 +119,187 @@ func validatePaths(paths []string, stdin io.Reader, stderr io.Writer) int {
 	return 0
 }
 
+// encodeJSON reads a toml-test tagged JSON description from standard input and
+// writes the TOML document it describes to standard output.
+func encodeJSON(stdin io.Reader, stdout, stderr io.Writer) int {
+	data, err := io.ReadAll(stdin)
+	if err != nil {
+		fmt.Fprintln(stderr, "read stdin:", err)
+		return 2
+	}
+	var desc any
+	if err := json.Unmarshal(data, &desc); err != nil {
+		fmt.Fprintln(stderr, "decode JSON:", err)
+		return 2
+	}
+	tree, err := untag(desc)
+	if err != nil {
+		fmt.Fprintln(stderr, err)
+		return 2
+	}
+	doc, ok := tree.(map[string]any)
+	if !ok {
+		fmt.Fprintln(stderr, "interpres-decode: the description must be a JSON object at the top level")
+		return 2
+	}
+	out, err := interpres.Marshal(doc)
+	if err != nil {
+		fmt.Fprintln(stderr, err)
+		return 2
+	}
+	if _, err := stdout.Write(out); err != nil {
+		fmt.Fprintln(stderr, "write stdout:", err)
+		return 2
+	}
+	return 0
+}
+
+// untag converts a toml-test JSON description into the value tree Marshal
+// expects: a JSON object becomes a map[string]any, a JSON array becomes a
+// []any, and an object carrying exactly the keys "type" and "value" becomes
+// the Go value for that TOML type.
+func untag(v any) (any, error) {
+	switch x := v.(type) {
+	case map[string]any:
+		if typ, val, ok := taggedValue(x); ok {
+			return decodeTagged(typ, val)
+		}
+		out := make(map[string]any, len(x))
+		for k, e := range x {
+			u, err := untag(e)
+			if err != nil {
+				return nil, fmt.Errorf("%s: %w", k, err)
+			}
+			out[k] = u
+		}
+		return out, nil
+	case []any:
+		out := make([]any, len(x))
+		for i, e := range x {
+			u, err := untag(e)
+			if err != nil {
+				return nil, fmt.Errorf("[%d]: %w", i, err)
+			}
+			out[i] = u
+		}
+		return asTables(out), nil
+	default:
+		return nil, fmt.Errorf("unsupported JSON value %T", v)
+	}
+}
+
+// asTables returns the elements as a []map[string]any when there is at least
+// one and every element is a table, the shape the encoder renders as an array
+// of tables. The tagged JSON cannot tell an array of tables from a value array
+// of inline tables, and both parse back to the same value, so the header form
+// is chosen because it is the one the encoder otherwise never exercises. An
+// empty array stays a []any, because TOML has no empty array of tables.
+func asTables(items []any) any {
+	if len(items) == 0 {
+		return items
+	}
+	tbls := make([]map[string]any, len(items))
+	for i, e := range items {
+		tbl, ok := e.(map[string]any)
+		if !ok {
+			return items
+		}
+		tbls[i] = tbl
+	}
+	return tbls
+}
+
+// taggedValue reports whether m is a toml-test value object: a JSON object of
+// exactly the two string keys "type" and "value", carrying a type this adapter
+// knows. Any other object is a table.
+func taggedValue(m map[string]any) (typ, val string, ok bool) {
+	if len(m) != 2 {
+		return "", "", false
+	}
+	ts, ok := m["type"].(string)
+	if !ok || !knownType(ts) {
+		return "", "", false
+	}
+	vs, ok := m["value"].(string)
+	if !ok {
+		return "", "", false
+	}
+	return ts, vs, true
+}
+
+func knownType(typ string) bool {
+	switch typ {
+	case "string", "integer", "float", "bool",
+		"datetime", "datetime-local", "date-local", "time-local":
+		return true
+	}
+	return false
+}
+
+// decodeTagged returns the Go value for one tagged JSON value. Every type but
+// string is parsed by the library itself, so the adapter and the library agree
+// on what an integer, a float or a date-time is.
+func decodeTagged(typ, val string) (any, error) {
+	if typ == "string" {
+		return val, nil
+	}
+	v, err := parseAtom(val)
+	if err != nil {
+		return nil, fmt.Errorf("%s %q: %w", typ, val, err)
+	}
+	// A float with no fractional part and no exponent is described by a bare
+	// integer literal, so here the tag decides and not the literal.
+	if n, ok := v.(int64); ok && typ == "float" {
+		return float64(n), nil
+	}
+	if !typeMatches(typ, v) {
+		return nil, fmt.Errorf("%s %q parsed as %T", typ, val, v)
+	}
+	return v, nil
+}
+
+// parseAtom parses one bare TOML value, by handing `v = <val>` to the library's
+// parser and requiring the result to hold exactly that one statement, so a
+// value carrying a newline or a comment cannot smuggle a second one in.
+func parseAtom(val string) (any, error) {
+	tree, err := interpres.Parse([]byte("v = " + val + "\n"))
+	if err != nil {
+		return nil, err
+	}
+	if len(tree) != 1 {
+		return nil, errors.New("not a single bare value")
+	}
+	return tree["v"], nil
+}
+
+// typeMatches reports whether v is the Go value the tagged type names.
+func typeMatches(typ string, v any) bool {
+	switch typ {
+	case "integer":
+		_, ok := v.(int64)
+		return ok
+	case "float":
+		_, ok := v.(float64)
+		return ok
+	case "bool":
+		_, ok := v.(bool)
+		return ok
+	case "datetime":
+		_, ok := v.(time.Time)
+		return ok
+	case "datetime-local":
+		_, ok := v.(interpres.LocalDateTime)
+		return ok
+	case "date-local":
+		_, ok := v.(interpres.LocalDate)
+		return ok
+	case "time-local":
+		_, ok := v.(interpres.LocalTime)
+		return ok
+	}
+	return false
+}
+
 // tag converts an interpres value into its toml-test tagged-JSON form. Tables
 // become JSON objects and arrays become JSON arrays; scalars are wrapped in a
 // {"type", "value"} object. An error is returned for value types the encoder

cmd/interpres-decode/main_test.go

@@ -8,11 +8,12 @@ import (
 	"encoding/json"
 	"errors"
 	"os"
+	"reflect"
 	"strings"
 	"testing"
 	"time"
 
-	"sourcedock.dev/petrbalvin/interpres"
+	"sourcedock.dev/petrbalvin/interpres/v2"
 )
 
 func TestRunParsesValidTOML(t *testing.T) {
@@ -283,3 +284,165 @@ func TestUnknownFlagReturnsTwo(t *testing.T) {
 		t.Fatalf("Run returned %d, want 2; stderr = %q", code, stderr.String())
 	}
 }
+
+// --- encoder mode ----------------------------------------------------------
+
+func TestRunEncoderScalars(t *testing.T) {
+	in := `{
+    "s":   {"type": "string", "value": "quote \" and backslash \\"},
+    "nl":  {"type": "string", "value": "line1\nline2"},
+    "i":   {"type": "integer", "value": "-9223372036854775808"},
+    "g":   {"type": "float", "value": "1.5"},
+    "f":   {"type": "float", "value": "inf"},
+    "b":   {"type": "bool", "value": "false"},
+    "dt":  {"type": "datetime", "value": "1979-05-27T07:32:00-07:00"},
+    "ldt": {"type": "datetime-local", "value": "1979-05-27T07:32:00"},
+    "ld":  {"type": "date-local", "value": "1979-05-27"},
+    "lt":  {"type": "time-local", "value": "07:32:00.999"}
+}
+`
+	var stdout, stderr bytes.Buffer
+	code := Run([]string{"-encode"}, strings.NewReader(in), &stdout, &stderr)
+	if code != 0 {
+		t.Fatalf("Run returned %d, stderr = %q", code, stderr.String())
+	}
+	want := "b = false\n" +
+		"dt = 1979-05-27T07:32-07:00\n" +
+		"f = inf\n" +
+		"g = 1.5\n" +
+		"i = -9223372036854775808\n" +
+		"ld = 1979-05-27\n" +
+		"ldt = 1979-05-27T07:32\n" +
+		"lt = 07:32:00.999\n" +
+		"nl = \"line1\\nline2\"\n" +
+		"s = \"quote \\\" and backslash \\\\\"\n"
+	if stdout.String() != want {
+		t.Errorf("output mismatch:\ngot:  %q\nwant: %q", stdout.String(), want)
+	}
+}
+
+func TestRunEncoderNested(t *testing.T) {
+	in := `{
+    "tbl": {"x": {"type": "bool", "value": "true"},
+            "sub": {"y": {"type": "integer", "value": "1"}}},
+    "items": [{"n": {"type": "string", "value": "a"}},
+              {"n": {"type": "string", "value": "b"}}],
+    "list": [{"type": "integer", "value": "1"}, {"type": "string", "value": "two"}],
+    "emptyTbl": {},
+    "emptyArr": []
+}
+`
+	var stdout, stderr bytes.Buffer
+	code := Run([]string{"-encode"}, strings.NewReader(in), &stdout, &stderr)
+	if code != 0 {
+		t.Fatalf("Run returned %d, stderr = %q", code, stderr.String())
+	}
+	want := "emptyArr = []\n" +
+		"list = [1, \"two\"]\n" +
+		"\n[emptyTbl]\n" +
+		"\n[tbl]\nx = true\n" +
+		"\n[tbl.sub]\ny = 1\n" +
+		"\n[[items]]\nn = \"a\"\n" +
+		"\n[[items]]\nn = \"b\"\n"
+	if stdout.String() != want {
+		t.Errorf("output mismatch:\ngot:  %q\nwant: %q", stdout.String(), want)
+	}
+}
+
+func TestRunEncoderFloatTagDecides(t *testing.T) {
+	// A float with no fraction is described by a bare integer literal, so the
+	// tag decides the type; the output must stay a float.
+	var stdout, stderr bytes.Buffer
+	in := `{"whole": {"type": "float", "value": "1"}, "exp": {"type": "float", "value": "5e+22"}}`
+	code := Run([]string{"-encode"}, strings.NewReader(in), &stdout, &stderr)
+	if code != 0 {
+		t.Fatalf("Run returned %d, stderr = %q", code, stderr.String())
+	}
+	if want := "exp = 5e+22\nwhole = 1.0\n"; stdout.String() != want {
+		t.Errorf("output mismatch:\ngot:  %q\nwant: %q", stdout.String(), want)
+	}
+}
+
+func TestRunEncoderRejectsBadInput(t *testing.T) {
+	cases := []struct {
+		name string
+		in   string
+		want string
+	}{
+		{"not-json", "not json", "decode JSON"},
+		{"top-level-array", `[{"type": "integer", "value": "1"}]`, "must be a JSON object"},
+		{"untagged-scalar", `{"x": 1}`, "unsupported JSON value"},
+		{"literal-mismatch", `{"x": {"type": "integer", "value": "1.5"}}`, "parsed as float64"},
+		{"offset-for-local", `{"x": {"type": "datetime-local", "value": "1979-05-27T07:32:00Z"}}`, "parsed as time.Time"},
+		{"bad-literal", `{"x": {"type": "date-local", "value": "nope"}}`, "date-local"},
+		{"smuggled-statement", `{"x": {"type": "integer", "value": "1\nx = 2"}}`, "not a single bare value"},
+	}
+	for _, c := range cases {
+		var stdout, stderr bytes.Buffer
+		code := Run([]string{"-encode"}, strings.NewReader(c.in), &stdout, &stderr)
+		if code != 2 {
+			t.Errorf("%s: Run returned %d, want 2; stderr = %q", c.name, code, stderr.String())
+			continue
+		}
+		if !strings.Contains(stderr.String(), c.want) {
+			t.Errorf("%s: stderr = %q, want it to mention %q", c.name, stderr.String(), c.want)
+		}
+		if stdout.Len() != 0 {
+			t.Errorf("%s: stdout should be empty, got %q", c.name, stdout.String())
+		}
+	}
+}
+
+func TestRunEncoderFlagConflicts(t *testing.T) {
+	var stdout, stderr bytes.Buffer
+	if code := Run([]string{"-encode", "-validate"}, strings.NewReader(""), &stdout, &stderr); code != 2 {
+		t.Errorf("Run returned %d, want 2 for the two modes together", code)
+	}
+	if !strings.Contains(stderr.String(), "cannot be combined") {
+		t.Errorf("stderr = %q, want it to explain the conflict", stderr.String())
+	}
+
+	stdout.Reset()
+	stderr.Reset()
+	if code := Run([]string{"-encode", "file.json"}, strings.NewReader(""), &stdout, &stderr); code != 2 {
+		t.Errorf("Run returned %d, want 2 for an argument", code)
+	}
+}
+
+func TestEncodeAfterDecodeRoundTrip(t *testing.T) {
+	doc := `title = "x"
+flt = 1.5
+whole = 7.0
+big = 9223372036854775807
+when = 1979-05-27T07:32:00-07:00
+day = 1979-05-27
+clock = 07:32:00.999
+list = [1, "two"]
+multi = "a\nb"
+
+[tbl]
+x = true
+
+[[items]]
+n = "a"
+`
+	var tagged, stderr bytes.Buffer
+	if code := Run(nil, strings.NewReader(doc), &tagged, &stderr); code != 0 {
+		t.Fatalf("decode returned %d, stderr = %q", code, stderr.String())
+	}
+	var out bytes.Buffer
+	if code := Run([]string{"-encode"}, bytes.NewReader(tagged.Bytes()), &out, &stderr); code != 0 {
+		t.Fatalf("encode returned %d, stderr = %q", code, stderr.String())
+	}
+	want, err := interpres.Parse([]byte(doc))
+	if err != nil {
+		t.Fatalf("parse of the original: %v", err)
+	}
+	got, err := interpres.Parse(out.Bytes())
+	if err != nil {
+		t.Fatalf("parse of the encoder output (%q): %v", out.String(), err)
+	}
+	if !reflect.DeepEqual(want, got) {
+		t.Errorf("round trip changed the document:\noriginal: %#v\nencoded:  %#v\noutput: %q", want, got, out.String())
+	}
+}

datetime.go

@@ -28,29 +28,42 @@ type LocalDate struct{ time.Time }
 type LocalTime struct{ time.Time }
 
 // String returns the TOML-canonical rendering of the local date-time, e.g.
-// "1979-05-27T07:32:00" or "...:00.000000123" when the time has a fractional
-// second. The fractional component is zero-padded to nanosecond precision.
+// "1979-05-27T07:32" or "1979-05-27T07:32:00.5" when the time carries a
+// fractional second. TOML 1.1 makes the seconds optional, so they appear only
+// when they are non-zero, and a fraction drops its trailing zeros.
 func (ldt LocalDateTime) String() string {
-	base := ldt.Format("2006-01-02T15:04:05")
-	if ns := ldt.Nanosecond(); ns > 0 {
-		return base + "." + fmt.Sprintf("%09d", ns)
-	}
-	return base
+	return ldt.Format("2006-01-02T") + clockString(ldt.Time)
 }
 
 // String returns the TOML-canonical rendering of the local date, e.g.
 // "1979-05-27".
 func (ld LocalDate) String() string { return ld.Format("2006-01-02") }
 
-// String returns the TOML-canonical rendering of the local time, e.g.
-// "07:32:00" or "...:00.000000123" when the time has a fractional second.
-// The fractional component is zero-padded to nanosecond precision.
-func (lt LocalTime) String() string {
-	base := lt.Format("15:04:05")
-	if ns := lt.Nanosecond(); ns > 0 {
-		return base + "." + fmt.Sprintf("%09d", ns)
+// String returns the TOML-canonical rendering of the local time, e.g. "07:32"
+// or "07:32:00.5" when the time carries a fractional second.
+func (lt LocalTime) String() string { return clockString(lt.Time) }
+
+// clockString renders a time of day the way TOML writes it: the seconds appear
+// only when the value carries them, and a fractional second drops its trailing
+// zeros, so half a second is "00.5" and not "00.500000000". Both are the same
+// value either way; the shorter form is the one TOML 1.1 allows.
+func clockString(t time.Time) string {
+	out := t.Format("15:04")
+	ns := t.Nanosecond()
+	if t.Second() != 0 || ns != 0 {
+		out += t.Format(":05")
 	}
-	return base
+	if ns > 0 {
+		out += "." + strings.TrimRight(fmt.Sprintf("%09d", ns), "0")
+	}
+	return out
+}
+
+// offsetString renders an offset date-time, the fourth TOML kind, in the same
+// shape: no zero seconds, no trailing zeros in the fraction, and the offset
+// written as "Z" when it is zero.
+func offsetString(t time.Time) string {
+	return t.Format("2006-01-02T") + clockString(t) + t.Format("Z07:00")
 }
 
 var (

decode.go

@@ -4,6 +4,7 @@
 package interpres
 
 import (
+	"encoding"
 	"fmt"
 	"reflect"
 	"slices"
@@ -63,6 +64,19 @@ func (d *decoder) assign(data any, dst reflect.Value) error {
 		}
 	}
 
+	// A TOML string fills a destination that implements
+	// encoding.TextUnmarshaler, the rule encoding/json follows. Every other
+	// value kind keeps its own rule, so an integer still reaches a numeric
+	// destination.
+	if s, isString := data.(string); isString {
+		if tu, ok := textUnmarshalerOf(dst); ok {
+			if err := tu.UnmarshalText([]byte(s)); err != nil {
+				return fmt.Errorf("unmarshal text: %w", err)
+			}
+			return nil
+		}
+	}
+
 	switch v := data.(type) {
 	case map[string]any:
 		return d.assignTable(v, dst)
@@ -71,6 +85,9 @@ func (d *decoder) assign(data any, dst reflect.Value) error {
 	case []any:
 		return d.assignSlice(v, dst)
 	case string:
+		if dst.Type() == durationType {
+			return setDuration(dst, v)
+		}
 		return setBasic(dst, reflect.ValueOf(v), "string")
 	case bool:
 		return setBasic(dst, reflect.ValueOf(v), "bool")
@@ -94,6 +111,26 @@ func (d *decoder) assign(data any, dst reflect.Value) error {
 	}
 }
 
+// textUnmarshalerOf finds the encoding.TextUnmarshaler for dst: on the value
+// itself, or on its address, so a pointer-receiver UnmarshalText is invoked on
+// an addressable struct field. The TOML date-time types are excluded, because
+// they carry time.Time's UnmarshalText through an embedded field while their
+// only accepted form is a bare timestamp.
+func textUnmarshalerOf(dst reflect.Value) (encoding.TextUnmarshaler, bool) {
+	if !dst.CanInterface() || isDateTimeType(dst.Type()) {
+		return nil, false
+	}
+	if u, ok := dst.Interface().(encoding.TextUnmarshaler); ok {
+		return u, true
+	}
+	if dst.CanAddr() {
+		if u, ok := dst.Addr().Interface().(encoding.TextUnmarshaler); ok {
+			return u, true
+		}
+	}
+	return nil, false
+}
+
 func (d *decoder) assignTable(tbl map[string]any, dst reflect.Value) error {
 	switch dst.Kind() {
 	case reflect.Struct:
@@ -202,7 +239,23 @@ func setBasic(dst, val reflect.Value, kind string) error {
 	if dst.Kind() != val.Kind() {
 		return fmt.Errorf("interpres: cannot assign %s to %s", kind, dst.Type())
 	}
-	dst.Set(val)
+	// Convert rather than assign: a value of the predeclared type is not
+	// assignable to a defined type of the same kind, so a plain Set panics on
+	// a destination such as `type Name string`.
+	dst.Set(val.Convert(dst.Type()))
+	return nil
+}
+
+// setDuration reads a duration literal into a time.Duration destination. TOML
+// has no duration type, so the encoder writes the canonical Go form and the
+// decoder reads that back; a bare integer stays the nanosecond count it has
+// always been, and reaches the destination through setInt.
+func setDuration(dst reflect.Value, s string) error {
+	d, err := time.ParseDuration(s)
+	if err != nil {
+		return fmt.Errorf("interpres: invalid duration %q", s)
+	}
+	dst.SetInt(int64(d))
 	return nil
 }
 

decode_test.go

@@ -8,9 +8,11 @@ import (
 	"errors"
 	"fmt"
 	"math"
+	"net"
 	"slices"
 	"strings"
 	"testing"
+	"time"
 )
 
 func TestSyntaxErrorMessage(t *testing.T) {
@@ -725,3 +727,227 @@ func TestDecodeErrorOnMapDestination(t *testing.T) {
 		t.Fatalf("Path = %v", de.Path)
 	}
 }
+
+func TestUnmarshalIntoDefinedScalarTypes(t *testing.T) {
+	// A defined type whose underlying kind is string or bool takes the value.
+	// A bare reflect Set panics on such a type, because a string is not
+	// assignable to a defined string type without a conversion.
+	type Name string
+	type Flag bool
+	type Cfg struct {
+		N Name `toml:"n"`
+		F Flag `toml:"f"`
+	}
+	var cfg Cfg
+	if err := Unmarshal([]byte("n = \"x\"\nf = true\n"), &cfg); err != nil {
+		t.Fatalf("unmarshal: %v", err)
+	}
+	if cfg.N != "x" {
+		t.Errorf("N = %q, want \"x\"", cfg.N)
+	}
+	if !cfg.F {
+		t.Error("F = false, want true")
+	}
+}
+
+// --- encoding.TextUnmarshaler and time.Duration ----------------------------
+
+// textReceiver implements encoding.TextUnmarshaler on the pointer receiver.
+type textReceiver struct{ Text string }
+
+func (t *textReceiver) UnmarshalText(text []byte) error {
+	t.Text = "got:" + string(text)
+	return nil
+}
+
+// upperText is a defined string type whose UnmarshalText transforms the
+// content, so a plain string assignment would leave the wrong value behind.
+type upperText string
+
+func (u *upperText) UnmarshalText(text []byte) error {
+	*u = upperText(strings.ToUpper(string(text)))
+	return nil
+}
+
+// failingTextUnmarshaler fails the decode from UnmarshalText.
+type failingTextUnmarshaler struct{}
+
+func (f *failingTextUnmarshaler) UnmarshalText(_ []byte) error { return errors.New("text boom") }
+
+// textAndTOMLReceiver implements both decode interfaces; the TOML method wins.
+type textAndTOMLReceiver struct{ From string }
+
+func (t *textAndTOMLReceiver) UnmarshalTOML(any) error { t.From = "toml"; return nil }
+
+func (t *textAndTOMLReceiver) UnmarshalText([]byte) error { t.From = "text"; return nil }
+
+func TestTextUnmarshalerByPointer(t *testing.T) {
+	type Cfg struct {
+		R textReceiver `toml:"r"`
+	}
+	var cfg Cfg
+	if err := Unmarshal([]byte(`r = "hello"`), &cfg); err != nil {
+		t.Fatalf("unmarshal: %v", err)
+	}
+	if cfg.R.Text != "got:hello" {
+		t.Errorf("Text = %q, want \"got:hello\"", cfg.R.Text)
+	}
+}
+
+func TestTextUnmarshalerWinsOverKindAssignment(t *testing.T) {
+	type Cfg struct {
+		U upperText `toml:"u"`
+	}
+	var cfg Cfg
+	if err := Unmarshal([]byte(`u = "abc"`), &cfg); err != nil {
+		t.Fatalf("unmarshal: %v", err)
+	}
+	if cfg.U != "ABC" {
+		t.Errorf("U = %q, want \"ABC\"", cfg.U)
+	}
+}
+
+func TestTextUnmarshalerForNetIP(t *testing.T) {
+	type Cfg struct {
+		V4  net.IP   `toml:"v4"`
+		V6  net.IP   `toml:"v6"`
+		IPs []net.IP `toml:"ips"`
+	}
+	in := "v4 = \"192.0.2.1\"\nv6 = \"2001:db8::68\"\nips = [\"198.51.100.7\", \"203.0.113.9\"]\n"
+	var cfg Cfg
+	if err := Unmarshal([]byte(in), &cfg); err != nil {
+		t.Fatalf("unmarshal: %v", err)
+	}
+	if got := cfg.V4.String(); got != "192.0.2.1" {
+		t.Errorf("V4 = %q, want \"192.0.2.1\"", got)
+	}
+	if got := cfg.V6.String(); got != "2001:db8::68" {
+		t.Errorf("V6 = %q, want \"2001:db8::68\"", got)
+	}
+	if len(cfg.IPs) != 2 || cfg.IPs[0].String() != "198.51.100.7" || cfg.IPs[1].String() != "203.0.113.9" {
+		t.Errorf("IPs = %v, want two addresses", cfg.IPs)
+	}
+}
+
+func TestTextUnmarshalerSeesStringsOnly(t *testing.T) {
+	// An integer keeps its own rule: the text method is not consulted, and the
+	// value does not reach the receiver.
+	type Cfg struct {
+		R textReceiver `toml:"r"`
+	}
+	var cfg Cfg
+	err := Unmarshal([]byte("r = 1\n"), &cfg)
+	if err == nil {
+		t.Fatal("expected an integer to be rejected for a text receiver")
+	}
+	if cfg.R.Text != "" {
+		t.Errorf("Text = %q, want it untouched", cfg.R.Text)
+	}
+}
+
+func TestUnmarshalTOMLWinsOverTextUnmarshaler(t *testing.T) {
+	type Cfg struct {
+		B textAndTOMLReceiver `toml:"b"`
+	}
+	var cfg Cfg
+	if err := Unmarshal([]byte(`b = "x"`), &cfg); err != nil {
+		t.Fatalf("unmarshal: %v", err)
+	}
+	if cfg.B.From != "toml" {
+		t.Errorf("From = %q, want \"toml\"", cfg.B.From)
+	}
+}
+
+func TestTextUnmarshalerErrorCarriesPath(t *testing.T) {
+	type Inner struct {
+		F failingTextUnmarshaler `toml:"f"`
+	}
+	type Cfg struct {
+		Inner Inner `toml:"inner"`
+	}
+	var cfg Cfg
+	err := Unmarshal([]byte("[inner]\nf = \"x\"\n"), &cfg)
+	if err == nil {
+		t.Fatal("expected an error from UnmarshalText")
+	}
+	if !strings.Contains(err.Error(), "unmarshal text: text boom") {
+		t.Errorf("err = %v, want the text error wrapped", err)
+	}
+	de, ok := errors.AsType[*DecodeError](err)
+	if !ok {
+		t.Fatalf("expected a *DecodeError, got %T: %v", err, err)
+	}
+	if !slices.Equal(de.Path, []string{"inner", "f"}) {
+		t.Fatalf("Path = %v, want [inner f]", de.Path)
+	}
+}
+
+func TestTextUnmarshalerReportsBadText(t *testing.T) {
+	var cfg struct {
+		IP net.IP `toml:"ip"`
+	}
+	err := Unmarshal([]byte(`ip = "not-an-ip"`), &cfg)
+	if err == nil {
+		t.Fatal("expected an error for a malformed address")
+	}
+	if !strings.Contains(err.Error(), "unmarshal text:") {
+		t.Errorf("err = %v, want it wrapped as a text error", err)
+	}
+}
+
+func TestUnmarshalDurations(t *testing.T) {
+	type Cfg struct {
+		FromText time.Duration `toml:"from_text"`
+		FromInt  time.Duration `toml:"from_int"`
+		Fraction time.Duration `toml:"fraction"`
+	}
+	in := "from_text = \"1h30m\"\nfrom_int = 5400000000000\nfraction = \"1.5s\"\n"
+	var cfg Cfg
+	if err := Unmarshal([]byte(in), &cfg); err != nil {
+		t.Fatalf("unmarshal: %v", err)
+	}
+	if cfg.FromText != 90*time.Minute {
+		t.Errorf("FromText = %v, want %v", cfg.FromText, 90*time.Minute)
+	}
+	if cfg.FromInt != 90*time.Minute {
+		t.Errorf("FromInt = %v, want %v", cfg.FromInt, 90*time.Minute)
+	}
+	if cfg.Fraction != 1500*time.Millisecond {
+		t.Errorf("Fraction = %v, want %v", cfg.Fraction, 1500*time.Millisecond)
+	}
+}
+
+func TestUnmarshalDurationRejectsMalformedText(t *testing.T) {
+	var cfg struct {
+		D time.Duration `toml:"d"`
+	}
+	err := Unmarshal([]byte("d = \"90\"\n"), &cfg)
+	if err == nil {
+		t.Fatal("expected an error for a duration without a unit")
+	}
+	if !strings.Contains(err.Error(), "invalid duration") {
+		t.Errorf("err = %v, want an invalid-duration message", err)
+	}
+}
+
+func TestQuotedStringNeverBecomesDateTime(t *testing.T) {
+	// The date-time types take a bare timestamp only, so the text path is
+	// excluded for them and a quoted string stays a string.
+	var stamp struct {
+		S time.Time `toml:"s"`
+	}
+	err := Unmarshal([]byte("s = \"2026-06-26T10:00:00Z\"\n"), &stamp)
+	if err == nil {
+		t.Fatal("expected a quoted string to be rejected for time.Time")
+	}
+	if !strings.Contains(err.Error(), "cannot assign string") {
+		t.Errorf("err = %v, want a cannot-assign message", err)
+	}
+
+	var day struct {
+		D LocalDate `toml:"d"`
+	}
+	if err := Unmarshal([]byte("d = \"1979-05-27\"\n"), &day); err == nil {
+		t.Fatal("expected a quoted string to be rejected for LocalDate")
+	}
+}

docs/API.md

@@ -1,16 +1,15 @@
 # API
 
-The library exports the surface below from the `sourcedock.dev/petrbalvin/interpres`
+The library exports the surface below from the `sourcedock.dev/petrbalvin/interpres/v2`
 package. The snippets assume:
 
 ```go
-import "sourcedock.dev/petrbalvin/interpres"
+import "sourcedock.dev/petrbalvin/interpres/v2"
 ```
 
-The parser accepts TOML 1.0 documents plus the TOML 1.1 extensions: date-times
-and times without seconds, the `\e` and `\xHH` escape sequences, and
-multi-line inline tables with comments and trailing commas. The encoder emits
-TOML 1.0, which is valid under both versions.
+The parser implements TOML 1.1: date-times and times without seconds, the
+`\e` and `\xHH` escape sequences, and multi-line inline tables with comments
+and trailing commas. The encoder emits TOML 1.1.
 
 ## Functions
 
@@ -146,8 +145,12 @@ variants decode into `LocalDateTime`, `LocalDate` and `LocalTime`, whose
 embedded `time.Time` is normalised to UTC (midnight UTC for a local date, the
 zero date for a local time). Every kind may omit the seconds as of TOML 1.1
 (`07:32`, `1979-05-27T07:32`); such a value carries a zero second, and the
-canonical rendering writes full seconds. There is no implicit conversion
-between the offset and local kinds; assigning one to the other is an error.
+encoder writes the seconds only when the value carries them, so a document
+written without seconds comes back without them. There is no implicit
+conversion between the offset and local kinds; assigning one to the other is an
+error. The four types take a bare timestamp and never a quoted string, so a
+document that writes a date-time with quotes does not decode into them, and
+neither `encoding.TextUnmarshaler` nor the embedded `time.Time` changes that.
 
 ### Arrays of tables
 
@@ -178,6 +181,38 @@ automatically, and a nil pointer destination is allocated first. An error
 returned from `UnmarshalTOML` halts the decode and propagates wrapped with the
 key path, for example `addr: unmarshal: not a string`.
 
+### Custom decoding: `encoding.TextUnmarshaler`
+
+A destination type that implements `encoding.TextUnmarshaler` receives a TOML
+string as its text content, the rule `encoding/json` follows:
+
+```go
+func (ip *IP) UnmarshalText(text []byte) error
+```
+
+The decoder looks for the method on the destination and on its address, so a
+pointer-receiver `UnmarshalText` is invoked on an addressable struct field, and
+the elements of a slice destination are reached the same way. The text path
+applies to TOML strings only: every other value kind keeps its own rule, so
+`r = 1` does not reach a receiver that expects text. An error from
+`UnmarshalText` halts the decode and propagates with the key path and the
+prefix `unmarshal text:`, for example `addr: unmarshal text: not an address`.
+
+[`UnmarshalTOML`](#custom-decoding-unmarshaler) wins over `UnmarshalText` when
+a type implements both, and the four [date-time
+types](#date-time-values) are excluded: a quoted string stays a string and
+never becomes a `time.Time` or one of the local wrappers.
+
+### Durations
+
+TOML has no duration type, so `time.Duration` has a rule of its own. The
+encoder writes the canonical Go form in a TOML string, `1h30m0s`, and the
+decoder reads that string back with `time.ParseDuration`. A bare integer is
+still the nanosecond count it has always been, so `from_int = 5400000000000`
+and `from_text = "1h30m"` decode to the same duration. Text that
+`time.ParseDuration` rejects, `d = "90"` among it, fails with
+`interpres: invalid duration "90"`.
+
 ### Strict decoding
 
 By default unknown keys are dropped silently. A `Decoder` built with
@@ -330,6 +365,27 @@ func (p Port) MarshalTOML() (any, error) {
 }
 ```
 
+### Custom encoding: `encoding.TextMarshaler`
+
+A type that implements `encoding.TextMarshaler` is encoded as a TOML string
+holding the text the method returns, which is the rule `encoding/json` follows:
+
+```go
+func (ip IP) MarshalText() ([]byte, error)
+```
+
+The encoder looks for the method on the value and on its address, so a
+pointer-receiver `MarshalText` is found on a struct field of an addressable
+value (pass a pointer to `Marshal`) and always on a slice element. `net.IP`,
+`netip.Addr` and user types follow this rule, and a struct that implements the
+interface becomes a string rather than a table. `MarshalTOML` wins when a type
+implements both, the four [date-time types](#date-time-values) keep their bare
+timestamp form, and text that is not valid UTF-8 is an error rather than a
+replacement character.
+
+A duration carries no text method of its own; see [Durations](#durations) for
+its rule.
+
 ### Arrays
 
 An array whose every element is a table (`[]struct`, `[]map[string]V`, after
@@ -357,10 +413,9 @@ omitted, because TOML forbids an empty `[[a]]`. Other empty arrays emit as
 ### Long strings
 
 By default every string is emitted as a basic `"..."` string with the escapes
-TOML requires, and a string containing a newline is emitted as an escaped
-multi-line basic string. `UseLiteralMultiline(threshold)` switches strings that
-contain a newline and are at least `threshold` bytes long to the literal
-`'''...'''` form, which carries the newlines verbatim:
+TOML requires, a newline among them as `\n`. `UseLiteralMultiline(threshold)`
+switches strings that contain a newline and are at least `threshold` bytes long
+to the literal `'''...'''` form, which carries the newlines verbatim:
 
 ```go
 out, err := interpres.NewEncoder().UseLiteralMultiline(80).Marshal(cfg)
@@ -372,6 +427,48 @@ carry verbatim (an embedded run of three single quotes, a control character
 other than tab or newline, or a carriage return outside a CRLF pair) also keeps
 the basic form, so the output always re-parses to the same value.
 
+### Inline tables
+
+A table element of a value array, and a sub-table inlined by
+[`InlineTables`](#compact-documents), is written as one `{a = 1, b = 2}` line
+while it fits. An inline table that would pass the hundredth column carries
+newlines and a trailing comma instead, which TOML 1.1 allows:
+
+```toml
+arr = [1, {
+	n = 1,
+	name = "a value long enough to push this line well past the one hundred column limit",
+}]
+```
+
+The closing brace and the entries are indented one tab per nesting level, a
+nested table is measured on its own line, and the output re-parses to the same
+value either way.
+
+### Compact documents
+
+`InlineTables(threshold)` writes a sub-table as an inline table when its
+single-line rendering is at most `threshold` bytes, and as a table header
+section when it is longer. A document of small tables therefore grows shorter:
+
+```go
+out, err := interpres.NewEncoder().InlineTables(60).Marshal(cfg)
+```
+
+With `60` and a table of three short entries, the same value is written
+
+```toml
+server = {host = "127.0.0.1", port = 9090, tls = {on = false}}
+```
+
+instead of three lines under a `[server]` header and a `[server.tls]` section.
+A nested sub-table takes part in the same way, and the whole option is off at
+`0` or less. Two limits are deliberate. An array of tables keeps the `[[a]]`
+header form, because its inline form re-parses as a value array and would change
+the value's Go type. And because an inlined table is a value line, every one of
+them precedes the first header of its document, so a table inlined next to a
+header is not read back as part of that header's section.
+
 ### Cancellation
 
 `MarshalContext` and `(*Encoder).MarshalContext` accept a `context.Context`. The
@@ -386,6 +483,8 @@ The output is not byte-identical to any document that produced the value:
 - map keys are emitted in sorted order
 - the choice between `[table]` headers and inline tables is not preserved
 - strings use the basic quoted form unless the literal option above applies
+- a date-time drops its zero seconds and the trailing zeros of its fraction, so
+  `07:32:00` is written `07:32`; both are the same value
 - floats always carry a `.` or an exponent, so a float `1` is emitted as `1.0`
   and stays distinguishable from the integer `1` across a round-trip; negative
   zero is normalised to `0.0`
@@ -462,12 +561,14 @@ encoder:
 | `GroupByKind(v bool)` | `true` | group entries as scalars, then sub-tables, then arrays of tables; `false` preserves declaration order |
 | `OmitEmptyArrays()` | off | skip `key = []` for empty scalar arrays |
 | `UseLiteralMultiline(threshold int)` | `0` | emit multi-line strings of at least `threshold` bytes as literal `'''...'''` |
+| `InlineTables(threshold int)` | `0` | write a sub-table inline when its single-line form is at most `threshold` bytes |
 
 ```go
 out, err := interpres.NewEncoder().
 	GroupByKind(false).
 	OmitEmptyArrays().
 	UseLiteralMultiline(80).
+	InlineTables(60).
 	MarshalContext(ctx, cfg)
 ```
 
@@ -491,9 +592,11 @@ type LocalDate     struct{ time.Time } // 1979-05-27
 type LocalTime     struct{ time.Time } // 07:32:00.999999
 ```
 
-Each carries a `String()` method returning the TOML-canonical rendering, with
-the fractional second zero-padded to nanosecond precision when present. The
-types are produced by `Parse` and accepted by `Marshal`.
+Each carries a `String()` method returning the TOML-canonical rendering: the
+seconds appear only when the value carries them, and a fractional second drops
+its trailing zeros, so `07:32:00` renders as `07:32` and a half second as
+`00.5`. The types are produced by `Parse` and accepted by `Marshal`, which
+writes them through `String()`.
 
 ## Errors
 

docs/ARCHITECTURE.md

@@ -6,10 +6,10 @@ source tree; nothing is aspirational.
 ## Overview
 
 interpres is one public library package, one command, and one example. The
-library implements the whole of TOML 1.0 and 1.1, decoding and encoding, in the
-standard library alone; the command wraps the parser for the toml-test
-compliance harness, against which it stands at 214 valid and 467 invalid cases
-with zero failures; the example demonstrates the API.
+library implements the whole of TOML 1.1, decoding and encoding, in the
+standard library alone; the command wraps the parser and the encoder for the
+toml-test compliance harness, against which it stands at 214 valid, 467 invalid
+and 214 encoder cases with zero failures; the example demonstrates the API.
 
 ```mermaid
 flowchart TD
@@ -36,14 +36,14 @@ strict validation.
 | Path | Responsibility |
 |---|---|
 | `.` (package `interpres`) | The whole library. `interpres.go` declares the exported surface (`Parse`, `Unmarshal`, `Marshal`, the `*Context` variants, `Decoder`, `Encoder`, `Marshaler`, `Unmarshaler`, `SyntaxError`, the local date-time types); everything below it is unexported. |
-| `cmd/interpres-decode` | The toml-test adapter. Reads TOML on stdin, writes tagged JSON on stdout. Owns no parsing logic. |
+| `cmd/interpres-decode` | The toml-test adapter, both directions. Reads TOML on stdin, writes tagged JSON on stdout; with `-encode` it reads tagged JSON and writes TOML. Owns no parsing logic and no emission logic. |
 | `examples/basic` | A runnable tour of the API. Documentation in executable form, not part of the library. |
 
 Inside the library package, one file owns one concern:
 
 | File | Responsibility |
 |---|---|
-| `parser.go` | The recursive-descent parser. Produces the `map[string]any` tree and enforces the structural rules of TOML 1.0 and 1.1 (table redefinitions, dotted keys, arrays of tables, multi-line inline tables). Reports a 1-based line on failure. |
+| `parser.go` | The recursive-descent parser. Produces the `map[string]any` tree and enforces the structural rules of TOML 1.1 (table redefinitions, dotted keys, arrays of tables, multi-line inline tables). Reports a 1-based line on failure. |
 | `number.go` | Strict numeric tokens: integers in the four radixes with `_` separators, and floats including `inf` and `nan`. Rejects leading zeros, misplaced underscores and malformed fractions. |
 | `datetime.go` | The three local date-time wrapper types and `parseDateTime`, which classifies a token into the four date-time kinds under the strict TOML grammar. |
 | `decode.go` | Maps the parsed tree onto Go values by reflection: struct fields, maps, slices, scalar conversion with overflow checks, `Unmarshaler` dispatch. |

docs/CLI.md

@@ -1,25 +1,32 @@
 # Command line
 
 The reference below is taken from the program itself. `interpres-decode` is
-the toml-test harness adapter, and it also validates documents. Install it
-with Go itself, no release assets involved:
+the toml-test harness adapter in both directions, decoding TOML into tagged
+JSON and encoding tagged JSON back into TOML, and it also validates documents.
+Install it with Go itself, no release assets involved:
 
 ```sh
-go install sourcedock.dev/petrbalvin/interpres/cmd/interpres-decode@latest
+go install sourcedock.dev/petrbalvin/interpres/v2/cmd/interpres-decode@latest
 ```
 
 ## Synopsis
 
 ```sh
 interpres-decode [flags]
+interpres-decode -encode
 interpres-decode -validate [file ...]
 ```
 
-Without `-validate` the program is the toml-test adapter: it takes no
-arguments, reads one TOML document from stdin, and writes the toml-test
-tagged-JSON form to stdout. Build it locally with `just build`, which
-compiles it into `bin/interpres-decode`, or run it straight from the module
-directory with `just run`.
+Without `-validate` or `-encode` the program is the decoding half of the
+toml-test adapter: it takes no arguments, reads one TOML document from stdin,
+and writes the toml-test tagged-JSON form to stdout. Build it locally with
+`just build`, which compiles it into `bin/interpres-decode`, or run it
+straight from the module directory with `just run`.
+
+With `-encode` the direction is reversed: the program reads a tagged-JSON
+description from stdin and writes the TOML document it describes to stdout,
+which is the shape toml-test expects of an encoder command. It takes no
+arguments either, and `-validate` and `-encode` cannot be combined.
 
 With `-validate` the program parses each named file instead, or stdin when no
 file is named, and prints one line per invalid document to stderr. It is
@@ -31,15 +38,16 @@ means stdin.
 | Flag | Effect |
 |---|---|
 | `-validate` | validate the documents instead of emitting tagged JSON |
+| `-encode` | read tagged JSON from stdin and write TOML instead |
 | `-h` | print the usage |
 
 ## Exit codes
 
 | Code | Meaning |
 |---|---|
-| `0` | adapter: the document parsed and the tagged JSON was written; validate: every document parsed |
+| `0` | adapter: the document parsed and the tagged JSON was written; encode: the TOML was written; validate: every document parsed |
 | `1` | adapter: parse error; validate: at least one document is invalid |
-| `2` | a usage error, a read failure, or a value with no tagged representation |
+| `2` | a usage error, a read failure, malformed tagged JSON, or a value with no TOML representation |
 
 ## Wire format
 
@@ -66,6 +74,14 @@ wrapped in an object with a `type` and a `value`:
 | local date | `date-local` | `1979-05-27` |
 | local time | `time-local` | `07:32:00.999999` |
 
+The `-encode` mode reads exactly this form back. Two properties of it are
+worth knowing. A float whose value has no fraction and no exponent is written
+as a bare integer string, `{"type": "float", "value": "1"}`, so there the tag
+decides the type and not the literal. And the form cannot tell an array of
+tables from a value array of inline tables, so the adapter writes the header
+form, `[[a]]`, for an array whose every element is a JSON object; a mixed
+array keeps the value form.
+
 ## Examples
 
 Echo a small document through the adapter:
@@ -78,8 +94,18 @@ port = 9090
 ' | ./bin/interpres-decode
 ```
 
-The output is the equivalent value tree as one JSON object. Validate the
-TOML files of another repository in CI:
+The output is the equivalent value tree as one JSON object. Turn a description
+back into TOML with `-encode`:
+
+```sh
+echo '{"title": {"type": "string", "value": "hello"}}' | ./bin/interpres-decode -encode
+```
+
+```toml
+title = "hello"
+```
+
+Validate the TOML files of another repository in CI:
 
 ```sh
 interpres-decode -validate config.toml deploy/example.toml
@@ -101,5 +127,7 @@ just toml-test
 ```
 
 That recipe needs the `toml-test` binary on `PATH`, installed with
-`go install github.com/toml-lang/toml-test/v2/cmd/toml-test@v2.2.0`. The full
+`go install github.com/toml-lang/toml-test/v2/cmd/toml-test@v2.2.0`. It runs
+the suite in both directions: the decoder against the valid and invalid
+corpora, and the encoder against the tagged JSON of the valid one. The full
 reference for the library itself is [API.md](API.md).

docs/DEVELOPMENT.md

@@ -41,7 +41,7 @@ prints the same list.
 | `just run` | `go run ./cmd/interpres-decode`, reads TOML from stdin |
 | `just dev` | the same run, for iterating |
 | `just example` | `go run ./examples/basic`, the usage tour |
-| `just toml-test` | builds the adapter and runs the official toml-test compliance suite against it |
+| `just toml-test` | builds the adapter and runs the official toml-test compliance suite against it, decoder and encoder |
 | `just coverage-html` | `just test`, then `go tool cover -html` into `coverage.html` |
 | `just install` | builds, then copies the binary into `~/.local/bin` (`BINDIR` overrides) |
 | `just uninstall` | removes the installed binary |

encode.go

@@ -6,6 +6,7 @@ package interpres
 import (
 	"bytes"
 	"context"
+	"encoding"
 	"errors"
 	"fmt"
 	"maps"
@@ -23,20 +24,54 @@ var (
 	localDateType     = reflect.TypeFor[LocalDate]()
 	localTimeType     = reflect.TypeFor[LocalTime]()
 	timeGoType        = reflect.TypeFor[time.Time]()
+	durationType      = reflect.TypeFor[time.Duration]()
+	textMarshalerType = reflect.TypeFor[encoding.TextMarshaler]()
 )
 
+// inlineLimit is the column past which an inline table is written across
+// lines. TOML 1.1 lets an inline table carry newlines and a trailing comma, so
+// a long one stays readable instead of running off the line.
+const inlineLimit = 100
+
+// noInlineBreak is the limit a measuring encoder carries, high enough that the
+// form it renders is always the single-line one.
+const noInlineBreak = 1 << 30
+
 // encoder produces a TOML document from a Go value via a small intermediate
 // representation that preserves the order in which fields were declared.
 type encoder struct {
 	buf  bytes.Buffer
 	ctx  context.Context
 	opts Encoder
+
+	// inlineDepth is the nesting level inside inline tables, which decides
+	// their indentation.
+	inlineDepth int
+
+	// limit is the column at which an inline table is broken; only a
+	// measuring encoder raises it.
+	limit int
 }
 
-func newEncoder() *encoder { return &encoder{} }
+func newEncoder() *encoder { return &encoder{limit: inlineLimit} }
+
+// flat returns an encoder that measures a value by rendering it on one line,
+// so a caller can decide which form to write before writing it.
+func (e *encoder) flat() *encoder {
+	return &encoder{ctx: e.ctx, opts: e.opts, limit: noInlineBreak}
+}
 
 func (e *encoder) bytes() []byte { return e.buf.Bytes() }
 
+// column reports how many bytes the current line already holds, so a form can
+// be measured against the limit before it is written.
+func (e *encoder) column() int {
+	if i := bytes.LastIndexByte(e.buf.Bytes(), '\n'); i >= 0 {
+		return e.buf.Len() - i - 1
+	}
+	return e.buf.Len()
+}
+
 func (e *encoder) checkCtx() error {
 	if e.ctx == nil {
 		return nil
@@ -319,6 +354,15 @@ func addField(doc *tomlDoc, name string, v reflect.Value, ctx string) error {
 			v = reflect.ValueOf(mv)
 		}
 	}
+	// A type that renders itself as text becomes a TOML string, whether it is
+	// a scalar kind or a struct.
+	s, isText, err := textValue(v)
+	if err != nil {
+		return &EncodeError{Path: joinKey(ctx, name), Err: err}
+	}
+	if isText {
+		return doc.appendScalar(name, s, ctx)
+	}
 	v = followPtr(v)
 	if !v.IsValid() {
 		return nil
@@ -500,6 +544,20 @@ func normaliseValue(v reflect.Value) (any, error) {
 	if t := v.Type(); t == timeGoType || isLocalDateType(t) {
 		return v.Interface(), nil
 	}
+	// TOML has no duration type, so a duration goes out in its canonical Go
+	// form, the shape it comes back in.
+	if v.Type() == durationType {
+		return time.Duration(v.Int()).String(), nil
+	}
+	// A type that renders itself as text becomes a TOML string, scalar kinds
+	// and structs alike.
+	s, isText, err := textValue(v)
+	if err != nil {
+		return nil, err
+	}
+	if isText {
+		return s, nil
+	}
 	switch v.Kind() {
 	case reflect.String:
 		return v.String(), nil
@@ -573,10 +631,75 @@ func isLocalDateType(t reflect.Type) bool {
 	return t == localDateTimeType || t == localDateType || t == localTimeType
 }
 
+// isDateTimeType reports whether t is one of the four TOML date-time types,
+// which the encoder emits as bare atoms. Pointers are looked through. The types
+// carry time.Time's text methods through an embedded field, and the atom form
+// takes precedence over them.
+func isDateTimeType(t reflect.Type) bool {
+	for t.Kind() == reflect.Pointer {
+		t = t.Elem()
+	}
+	return t == timeGoType || isLocalDateType(t)
+}
+
+// isTextMarshalerType reports whether t or *t implements
+// encoding.TextMarshaler. An array of such values stays a value array, because
+// each element's TOML form is a string.
+func isTextMarshalerType(t reflect.Type) bool {
+	if isDateTimeType(t) {
+		return false
+	}
+	return t.Implements(textMarshalerType) || reflect.PointerTo(t).Implements(textMarshalerType)
+}
+
+// textValue returns the string a value renders itself as through
+// encoding.TextMarshaler. The date-time types are excluded, because their
+// embedded time.Time would answer with an RFC 3339 string where the TOML form
+// is a bare timestamp. A nil pointer offers no text and is left to the ordinary
+// nil handling, which omits the field.
+func textValue(v reflect.Value) (string, bool, error) {
+	for v.Kind() == reflect.Interface && !v.IsNil() {
+		v = v.Elem()
+	}
+	if !v.IsValid() || isDateTimeType(v.Type()) {
+		return "", false, nil
+	}
+	if v.Kind() == reflect.Pointer && v.IsNil() {
+		return "", false, nil
+	}
+	m, ok := textMarshalerOf(v)
+	if !ok {
+		return "", false, nil
+	}
+	b, err := m.MarshalText()
+	if err != nil {
+		return "", true, err
+	}
+	return string(b), true, nil
+}
+
+// textMarshalerOf finds the encoding.TextMarshaler for v: on the value itself,
+// or on its address, so a pointer-receiver MarshalText is found on an
+// addressable struct field.
+func textMarshalerOf(v reflect.Value) (encoding.TextMarshaler, bool) {
+	if !v.CanInterface() {
+		return nil, false
+	}
+	if m, ok := v.Interface().(encoding.TextMarshaler); ok {
+		return m, true
+	}
+	if v.CanAddr() {
+		if m, ok := v.Addr().Interface().(encoding.TextMarshaler); ok {
+			return m, true
+		}
+	}
+	return nil, false
+}
+
 func isTableElementType(t reflect.Type) bool {
 	switch t.Kind() {
 	case reflect.Struct:
-		return !isScalarStruct(t)
+		return !isScalarStruct(t) && !isTextMarshalerType(t)
 	case reflect.Map:
 		return t.Key().Kind() == reflect.String
 	}
@@ -618,7 +741,20 @@ func (e *encoder) emitDoc(doc *tomlDoc, prefix []string) error {
 				return err
 			}
 		}
+		// An inlined sub-table is a value line, so it has to precede every
+		// header of this document: a line written after a [header] would be
+		// read back as part of that table.
+		headers := make([]entry, 0, len(tables))
 		for _, t := range tables {
+			inlined, err := e.writeInlineSubTableIfSmall(t.key, t.doc)
+			if err != nil {
+				return err
+			}
+			if !inlined {
+				headers = append(headers, t)
+			}
+		}
+		for _, t := range headers {
 			path := append(append([]string{}, prefix...), t.key)
 			e.writeBlankLine()
 			e.buf.WriteByte('[')
@@ -659,6 +795,13 @@ func (e *encoder) emitDoc(doc *tomlDoc, prefix []string) error {
 				return err
 			}
 		case entryTable:
+			inlined, err := e.writeInlineSubTableIfSmall(ent.key, ent.doc)
+			if err != nil {
+				return err
+			}
+			if inlined {
+				continue
+			}
 			path := append(append([]string{}, prefix...), ent.key)
 			e.writeBlankLine()
 			e.buf.WriteByte('[')
@@ -800,7 +943,7 @@ func (e *encoder) writeValue(val any) error {
 	case float64:
 		return e.writeFloat(v)
 	case time.Time:
-		e.buf.WriteString(v.Format(time.RFC3339Nano))
+		e.buf.WriteString(offsetString(v))
 		return nil
 	case LocalDateTime:
 		e.buf.WriteString(v.String())
@@ -824,7 +967,7 @@ func (e *encoder) writeValue(val any) error {
 		e.buf.WriteByte(']')
 		return nil
 	case map[string]any:
-		return e.writeInlineTable(v)
+		return e.writeInlineMap(v)
 	case nil:
 		return fmt.Errorf("interpres: cannot encode nil value")
 	default:
@@ -832,10 +975,24 @@ func (e *encoder) writeValue(val any) error {
 	}
 }
 
-// writeInlineTable renders m as a TOML inline table with sorted keys, the
-// order buildMapDoc uses for header tables. It backs the table elements of a
-// value array, where the [[header]] form is not available.
-func (e *encoder) writeInlineTable(m map[string]any) error {
+// writeInlineMap renders m as a TOML inline table, on one line when it fits
+// there and across lines when it does not.
+func (e *encoder) writeInlineMap(m map[string]any) error {
+	flat := e.flat()
+	if err := flat.writeInlineMapFlat(m); err != nil {
+		return err
+	}
+	if e.column()+flat.buf.Len() <= e.limit {
+		e.buf.Write(flat.buf.Bytes())
+		return nil
+	}
+	return e.writeInlineMapMultiline(m)
+}
+
+// writeInlineMapFlat renders m as a single-line inline table with sorted keys,
+// the order buildMapDoc uses for header tables. It backs the table elements of
+// a value array, where the [[header]] form is not available.
+func (e *encoder) writeInlineMapFlat(m map[string]any) error {
 	keys := slices.Sorted(maps.Keys(m))
 	e.buf.WriteByte('{')
 	for i, k := range keys {
@@ -854,6 +1011,137 @@ func (e *encoder) writeInlineTable(m map[string]any) error {
 	return nil
 }
 
+// writeInlineMapMultiline renders m with one entry per line and a trailing
+// comma, the form TOML 1.1 allows for an inline table too long for one line.
+func (e *encoder) writeInlineMapMultiline(m map[string]any) error {
+	keys := slices.Sorted(maps.Keys(m))
+	e.buf.WriteString("{\n")
+	e.inlineDepth++
+	for _, k := range keys {
+		e.writeInlineIndent()
+		if err := e.writeKey(k); err != nil {
+			return err
+		}
+		e.buf.WriteString(" = ")
+		if err := e.writeValue(m[k]); err != nil {
+			return err
+		}
+		e.buf.WriteString(",\n")
+	}
+	e.inlineDepth--
+	e.writeInlineIndent()
+	e.buf.WriteByte('}')
+	return nil
+}
+
+// writeInlineIndent writes one tab per inline-table nesting level.
+func (e *encoder) writeInlineIndent() {
+	for range e.inlineDepth {
+		e.buf.WriteByte('\t')
+	}
+}
+
+// errInlineArrayOfTables reports an attempt to render an array of tables
+// inline, which has no form that keeps the value's type.
+var errInlineArrayOfTables = errors.New("interpres: an array of tables has no inline form")
+
+// inlinableDoc reports whether doc can be written as an inline table without
+// changing the type of any value: scalars, value arrays and further sub-tables
+// are fine, while an array of tables is not, because its inline form would
+// re-parse as a value array.
+func inlinableDoc(doc *tomlDoc) bool {
+	for _, ent := range doc.entries {
+		switch ent.kind {
+		case entryArray:
+			return false
+		case entryTable:
+			if !inlinableDoc(ent.doc) {
+				return false
+			}
+		}
+	}
+	return true
+}
+
+// writeInlineDocEntry writes one "key = value" binding of an inline table,
+// without the separator that follows it.
+func (e *encoder) writeInlineDocEntry(ent entry) error {
+	if err := e.writeKey(ent.key); err != nil {
+		return err
+	}
+	e.buf.WriteString(" = ")
+	switch ent.kind {
+	case entryTable:
+		return e.writeInlineDoc(ent.doc)
+	case entryArray:
+		return errInlineArrayOfTables
+	default:
+		return e.writeValue(ent.val)
+	}
+}
+
+// writeInlineDoc renders doc as a single-line inline table in entry order, the
+// order the fields were declared in.
+func (e *encoder) writeInlineDoc(doc *tomlDoc) error {
+	e.buf.WriteByte('{')
+	for i, ent := range doc.entries {
+		if i > 0 {
+			e.buf.WriteString(", ")
+		}
+		if err := e.writeInlineDocEntry(ent); err != nil {
+			return err
+		}
+	}
+	e.buf.WriteByte('}')
+	return nil
+}
+
+// writeInlineDocMultiline renders doc with one entry per line and a trailing
+// comma, the form TOML 1.1 allows for an inline table too long for one line.
+func (e *encoder) writeInlineDocMultiline(doc *tomlDoc) error {
+	e.buf.WriteString("{\n")
+	e.inlineDepth++
+	for _, ent := range doc.entries {
+		e.writeInlineIndent()
+		if err := e.writeInlineDocEntry(ent); err != nil {
+			return err
+		}
+		e.buf.WriteString(",\n")
+	}
+	e.inlineDepth--
+	e.writeInlineIndent()
+	e.buf.WriteByte('}')
+	return nil
+}
+
+// writeInlineSubTableIfSmall writes "key = {…}" for a sub-table whose
+// single-line rendering fits the compact threshold, and reports whether it did
+// so. An array of tables is never inlined, because its inline form would
+// re-parse as a value array and change the value's Go type.
+func (e *encoder) writeInlineSubTableIfSmall(name string, doc *tomlDoc) (bool, error) {
+	if e.opts.inlineTablesAt <= 0 || !inlinableDoc(doc) {
+		return false, nil
+	}
+	flat := e.flat()
+	if err := flat.writeInlineDoc(doc); err != nil {
+		return false, err
+	}
+	if flat.buf.Len() > e.opts.inlineTablesAt {
+		return false, nil
+	}
+	if err := e.writeKey(name); err != nil {
+		return false, err
+	}
+	e.buf.WriteString(" = ")
+	if e.column()+flat.buf.Len() <= e.limit {
+		e.buf.Write(flat.buf.Bytes())
+	} else if err := e.writeInlineDocMultiline(doc); err != nil {
+		return false, err
+	}
+	e.buf.WriteByte('\n')
+	return true, nil
+}
+
 func (e *encoder) writeStringVal(s string) error {
 	if e.opts.literalMultilineAt > 0 && strings.ContainsRune(s, '\n') &&
 		len(s) >= e.opts.literalMultilineAt && canBeLiteralMultiline(s) {

encode_test.go

@@ -8,6 +8,7 @@ import (
 	"context"
 	"errors"
 	"math"
+	"net"
 	"reflect"
 	"strings"
 	"testing"
@@ -325,7 +326,7 @@ func TestMarshalerReturningTime(t *testing.T) {
 	if err != nil {
 		t.Fatalf("marshal: %v", err)
 	}
-	want := "m = 2026-06-26T10:00:00Z\n"
+	want := "m = 2026-06-26T10:00Z\n"
 	if string(out) != want {
 		t.Errorf("output mismatch:\ngot:  %q\nwant: %q", out, want)
 	}
@@ -465,7 +466,7 @@ func TestMarshalEmbeddedScalarStruct(t *testing.T) {
 	if err != nil {
 		t.Fatalf("marshal: %v", err)
 	}
-	want := "name = \"x\"\ns = 2026-06-26T00:00:00\n"
+	want := "name = \"x\"\ns = 2026-06-26T00:00\n"
 	if string(out) != want {
 		t.Errorf("output mismatch:\ngot:  %q\nwant: %q", out, want)
 	}
@@ -540,7 +541,7 @@ func TestMarshalDateTime(t *testing.T) {
 	if err != nil {
 		t.Fatalf("marshal: %v", err)
 	}
-	want := "offset = 2026-06-26T10:00:00Z\nlocal = 2026-06-26T07:32:00\nday = 2026-06-26\nclock = 07:32:00\n"
+	want := "offset = 2026-06-26T10:00Z\nlocal = 2026-06-26T07:32\nday = 2026-06-26\nclock = 07:32\n"
 	if string(out) != want {
 		t.Errorf("output mismatch:\ngot:  %q\nwant: %q", out, want)
 	}
@@ -687,7 +688,7 @@ func TestMarshalInlineTableWithDatetime(t *testing.T) {
 	if err != nil {
 		t.Fatalf("marshal: %v", err)
 	}
-	want := "mix = [1979-05-27T07:32:00Z, {t = 1979-05-27T07:32:00}]\n"
+	want := "mix = [1979-05-27T07:32Z, {t = 1979-05-27T07:32}]\n"
 	if string(out) != want {
 		t.Fatalf("output mismatch:\ngot:  %q\nwant: %q", out, want)
 	}
@@ -906,7 +907,7 @@ func TestMarshalTagOptionOmitZero(t *testing.T) {
 	if err != nil {
 		t.Fatalf("marshal: %v", err)
 	}
-	want = "name = \"x\"\ncount = 1\nratio = 0.5\nwhen = 2026-09-17T12:00:00Z\nalways = \"kept\"\n\n[server]\nhost = \"h\"\n"
+	want = "name = \"x\"\ncount = 1\nratio = 0.5\nwhen = 2026-09-17T12:00Z\nalways = \"kept\"\n\n[server]\nhost = \"h\"\n"
 	if string(out) != want {
 		t.Fatalf("output mismatch:\ngot:  %q\nwant: %q", out, want)
 	}
@@ -1195,6 +1196,8 @@ qty = 2
 
 [meta]
 created = 2026-06-26T10:00:00Z
+
+mixed = [1, {n = 1, name = "a value long enough to push this line well past the one hundred column limit"}]
 `)
 	tree1, err := Parse(src)
 	if err != nil {
@@ -1257,24 +1260,35 @@ func TestLocalDateString(t *testing.T) {
 }
 
 func TestLocalDateTimeString(t *testing.T) {
+	// The rendering drops zero seconds and the trailing zeros of a fraction,
+	// which TOML 1.1 allows and which keeps a value written without seconds
+	// written without them.
 	ldt := LocalDateTime{Time: time.Date(1979, 5, 27, 7, 32, 0, 0, time.UTC)}
-	if got := ldt.String(); got != "1979-05-27T07:32:00" {
-		t.Errorf("LocalDateTime.String() = %q, want 1979-05-27T07:32:00", got)
+	if got := ldt.String(); got != "1979-05-27T07:32" {
+		t.Errorf("LocalDateTime.String() = %q, want 1979-05-27T07:32", got)
 	}
 	ldt2 := LocalDateTime{Time: time.Date(1979, 5, 27, 7, 32, 0, 5, time.UTC)}
 	if got := ldt2.String(); got != "1979-05-27T07:32:00.000000005" {
 		t.Errorf("LocalDateTime.String() = %q, want 1979-05-27T07:32:00.000000005", got)
 	}
 	ldt3 := LocalDateTime{Time: time.Date(1979, 5, 27, 7, 32, 0, 500, time.UTC)}
-	if got := ldt3.String(); got != "1979-05-27T07:32:00.000000500" {
-		t.Errorf("LocalDateTime.String() = %q, want 1979-05-27T07:32:00.000000500", got)
+	if got := ldt3.String(); got != "1979-05-27T07:32:00.0000005" {
+		t.Errorf("LocalDateTime.String() = %q, want 1979-05-27T07:32:00.0000005", got)
+	}
+	ldt4 := LocalDateTime{Time: time.Date(1979, 5, 27, 7, 32, 30, 500000000, time.UTC)}
+	if got := ldt4.String(); got != "1979-05-27T07:32:30.5" {
+		t.Errorf("LocalDateTime.String() = %q, want 1979-05-27T07:32:30.5", got)
 	}
 }
 
 func TestLocalTimeString(t *testing.T) {
 	lt := LocalTime{Time: time.Date(0, 1, 1, 7, 32, 0, 0, time.UTC)}
-	if got := lt.String(); got != "07:32:00" {
-		t.Errorf("LocalTime.String() = %q, want 07:32:00", got)
+	if got := lt.String(); got != "07:32" {
+		t.Errorf("LocalTime.String() = %q, want 07:32", got)
+	}
+	lt2 := LocalTime{Time: time.Date(0, 1, 1, 7, 32, 15, 250000000, time.UTC)}
+	if got := lt2.String(); got != "07:32:15.25" {
+		t.Errorf("LocalTime.String() = %q, want 07:32:15.25", got)
 	}
 }
 
@@ -1372,3 +1386,417 @@ func TestEncodeErrorHeterogeneousArrayPath(t *testing.T) {
 		t.Fatalf("Path = %q, want %q", ee.Path, "items[0]")
 	}
 }
+
+// --- encoding.TextMarshaler and time.Duration ------------------------------
+
+// textTag is a value-receiver encoding.TextMarshaler, so the encoder finds the
+// method on the value itself.
+type textTag string
+
+func (t textTag) MarshalText() ([]byte, error) { return []byte("tag:" + string(t)), nil }
+
+// textPointer carries MarshalText on the pointer receiver only, so the encoder
+// has to look at the address of an addressable field.
+type textPointer struct{ V string }
+
+func (t *textPointer) MarshalText() ([]byte, error) { return []byte(strings.ToUpper(t.V)), nil }
+
+// textAndTOML implements both encoding interfaces; the TOML method wins.
+type textAndTOML struct{}
+
+func (textAndTOML) MarshalTOML() (any, error)    { return "toml", nil }
+func (textAndTOML) MarshalText() ([]byte, error) { return []byte("text"), nil }
+
+// brokenText fails the marshal from MarshalText.
+type brokenText struct{}
+
+func (brokenText) MarshalText() ([]byte, error) { return nil, errors.New("text boom") }
+
+// notUTF8 renders bytes that no TOML string can carry.
+type notUTF8 struct{}
+
+func (notUTF8) MarshalText() ([]byte, error) { return []byte{0xff, 0xfe}, nil }
+
+// textTagBoth renders itself with a prefix and strips it again on decode, so
+// the round trip through a TOML string is lossless.
+type textTagBoth string
+
+func (t textTagBoth) MarshalText() ([]byte, error) { return []byte("tag:" + string(t)), nil }
+
+func (t *textTagBoth) UnmarshalText(text []byte) error {
+	trimmed, ok := strings.CutPrefix(string(text), "tag:")
+	if !ok {
+		return errors.New("textTagBoth: missing the tag prefix")
+	}
+	*t = textTagBoth(trimmed)
+	return nil
+}
+
+func TestMarshalTextValues(t *testing.T) {
+	// The pointer receiver is reachable only through an addressable field, so
+	// the whole value is marshalled through a pointer here.
+	type Cfg struct {
+		IP       net.IP        `toml:"ip"`
+		Duration time.Duration `toml:"duration"`
+		Tag      textTag       `toml:"tag"`
+		Pointer  textPointer   `toml:"pointer"`
+		Both     textAndTOML   `toml:"both"`
+	}
+	out, err := Marshal(&Cfg{
+		IP:       net.IPv4(192, 0, 2, 1),
+		Duration: 90 * time.Minute,
+		Tag:      "x",
+		Pointer:  textPointer{V: "abc"},
+	})
+	if err != nil {
+		t.Fatalf("marshal: %v", err)
+	}
+	want := "ip = \"192.0.2.1\"\nduration = \"1h30m0s\"\ntag = \"tag:x\"\npointer = \"ABC\"\nboth = \"toml\"\n"
+	if string(out) != want {
+		t.Errorf("output mismatch:\ngot:  %q\nwant: %q", out, want)
+	}
+}
+
+func TestMarshalTextValuesInContainers(t *testing.T) {
+	// Slice elements are addressable, so a pointer-receiver MarshalText is used
+	// there too, and an array of such values stays a value array: each element's
+	// TOML form is a string, so the [[header]] form cannot carry it.
+	type Cfg struct {
+		Map   map[string]net.IP `toml:"map"`
+		Durs  []time.Duration   `toml:"durs"`
+		Ptrs  []textPointer     `toml:"ptrs"`
+		Empty []textPointer     `toml:"empty"`
+	}
+	out, err := Marshal(Cfg{
+		Map:   map[string]net.IP{"a": net.IPv4(10, 0, 0, 1)},
+		Durs:  []time.Duration{0, 250 * time.Millisecond},
+		Ptrs:  []textPointer{{V: "a"}, {V: "b"}},
+		Empty: []textPointer{},
+	})
+	if err != nil {
+		t.Fatalf("marshal: %v", err)
+	}
+	want := "durs = [\"0s\", \"250ms\"]\nptrs = [\"A\", \"B\"]\nempty = []\n\n[map]\na = \"10.0.0.1\"\n"
+	if string(out) != want {
+		t.Errorf("output mismatch:\ngot:  %q\nwant: %q", out, want)
+	}
+}
+
+func TestMarshalTextLeavesDateTimesAlone(t *testing.T) {
+	// The four date-time types carry time.Time's text methods through an
+	// embedded field; their TOML form is a bare atom, never a quoted string.
+	stamp := time.Date(2026, 6, 26, 10, 0, 0, 0, time.UTC)
+	type Cfg struct {
+		Stamp time.Time     `toml:"stamp"`
+		Ptr   *time.Time    `toml:"ptr"`
+		Day   LocalDate     `toml:"day"`
+		At    LocalDateTime `toml:"at"`
+		Clock LocalTime     `toml:"clock"`
+	}
+	out, err := Marshal(&Cfg{
+		Stamp: stamp,
+		Ptr:   &stamp,
+		Day:   LocalDate{time.Date(1979, 5, 27, 0, 0, 0, 0, time.UTC)},
+		At:    LocalDateTime{time.Date(1979, 5, 27, 7, 32, 0, 0, time.UTC)},
+		Clock: LocalTime{time.Date(0, 1, 1, 7, 32, 0, 0, time.UTC)},
+	})
+	if err != nil {
+		t.Fatalf("marshal: %v", err)
+	}
+	want := "stamp = 2026-06-26T10:00Z\nptr = 2026-06-26T10:00Z\nday = 1979-05-27\nat = 1979-05-27T07:32\nclock = 07:32\n"
+	if string(out) != want {
+		t.Errorf("output mismatch:\ngot:  %q\nwant: %q", out, want)
+	}
+}
+
+func TestMarshalTextNilPointerOmitted(t *testing.T) {
+	type Cfg struct {
+		P *textPointer `toml:"p"`
+		K string       `toml:"k"`
+	}
+	out, err := Marshal(&Cfg{K: "x"})
+	if err != nil {
+		t.Fatalf("marshal: %v", err)
+	}
+	if want := "k = \"x\"\n"; string(out) != want {
+		t.Errorf("output mismatch:\ngot:  %q\nwant: %q", out, want)
+	}
+}
+
+func TestMarshalTextErrorCarriesPath(t *testing.T) {
+	type Inner struct {
+		F brokenText `toml:"f"`
+	}
+	type Cfg struct {
+		Inner Inner `toml:"inner"`
+	}
+	_, err := Marshal(Cfg{})
+	if err == nil {
+		t.Fatal("expected an error from MarshalText")
+	}
+	if !strings.Contains(err.Error(), "text boom") {
+		t.Errorf("err = %v, want substring \"text boom\"", err)
+	}
+	ee, ok := errors.AsType[*EncodeError](err)
+	if !ok {
+		t.Fatalf("expected an *EncodeError, got %T: %v", err, err)
+	}
+	if ee.Path != "inner.f" {
+		t.Fatalf("Path = %q, want %q", ee.Path, "inner.f")
+	}
+}
+
+func TestMarshalTextRejectsInvalidUTF8(t *testing.T) {
+	// A TOML string holds UTF-8 only, so text that is not gets an error rather
+	// than replacement characters.
+	_, err := Marshal(struct {
+		V notUTF8 `toml:"v"`
+	}{})
+	if err == nil {
+		t.Fatal("expected an error for text that is not valid UTF-8")
+	}
+	if !strings.Contains(err.Error(), "UTF-8") {
+		t.Errorf("err = %v, want a UTF-8 message", err)
+	}
+}
+
+func TestMarshalTextValuesRoundTrip(t *testing.T) {
+	type Cfg struct {
+		Duration time.Duration `toml:"duration"`
+		IP       net.IP        `toml:"ip"`
+		Tag      textTagBoth   `toml:"tag"`
+	}
+	in := Cfg{Duration: 90 * time.Minute, IP: net.IPv4(198, 51, 100, 7), Tag: "y"}
+	out, err := Marshal(&in)
+	if err != nil {
+		t.Fatalf("marshal: %v", err)
+	}
+	var back Cfg
+	if err := Unmarshal(out, &back); err != nil {
+		t.Fatalf("unmarshal: %v", err)
+	}
+	if back.Duration != in.Duration {
+		t.Errorf("Duration = %v, want %v", back.Duration, in.Duration)
+	}
+	if !back.IP.Equal(in.IP) {
+		t.Errorf("IP = %v, want %v", back.IP, in.IP)
+	}
+	if back.Tag != in.Tag {
+		t.Errorf("Tag = %q, want %q", back.Tag, in.Tag)
+	}
+}
+
+// --- TOML 1.1 output forms -------------------------------------------------
+
+func TestMarshalDateTimeRendering(t *testing.T) {
+	// The seconds are written only when the value carries them, and a fraction
+	// drops its trailing zeros. Both are the same value either way; the shorter
+	// form is the one TOML 1.1 allows.
+	base := time.Date(2026, 6, 26, 10, 0, 0, 0, time.UTC)
+	cases := []struct {
+		name string
+		val  any
+		want string
+	}{
+		{"offset-zero-seconds", base, "v = 2026-06-26T10:00Z\n"},
+		{"offset-seconds", base.Add(30 * time.Second), "v = 2026-06-26T10:00:30Z\n"},
+		{"offset-fraction", base.Add(500 * time.Millisecond), "v = 2026-06-26T10:00:00.5Z\n"},
+		{"offset-zone", time.Date(2026, 6, 26, 10, 0, 0, 0, time.FixedZone("", -7*3600)), "v = 2026-06-26T10:00-07:00\n"},
+		{"local-zero-seconds", LocalDateTime{Time: base}, "v = 2026-06-26T10:00\n"},
+		{"local-fraction", LocalDateTime{Time: base.Add(2500 * time.Millisecond)}, "v = 2026-06-26T10:00:02.5\n"},
+		{"date", LocalDate{Time: base}, "v = 2026-06-26\n"},
+		{"time-zero-seconds", LocalTime{Time: base}, "v = 10:00\n"},
+		{"time-seconds", LocalTime{Time: base.Add(15 * time.Second)}, "v = 10:00:15\n"},
+		{"time-nanoseconds", LocalTime{Time: base.Add(123456789 * time.Nanosecond)}, "v = 10:00:00.123456789\n"},
+	}
+	for _, c := range cases {
+		out, err := Marshal(map[string]any{"v": c.val})
+		if err != nil {
+			t.Errorf("%s: marshal: %v", c.name, err)
+			continue
+		}
+		if string(out) != c.want {
+			t.Errorf("%s: output mismatch:\ngot:  %q\nwant: %q", c.name, out, c.want)
+		}
+	}
+}
+
+func TestMarshalInlineTableBreaksWhenLong(t *testing.T) {
+	// A table element of a value array is written inline; a long one carries
+	// newlines and a trailing comma instead of running past the line limit,
+	// which TOML 1.1 allows an inline table to do.
+	const long = "a-very-long-value-that-pushes-the-line-well-past-the-one-hundred-column-limit"
+	type Cfg struct {
+		Arr []any `toml:"arr"`
+	}
+	out, err := Marshal(Cfg{Arr: []any{int64(1), map[string]any{"n": int64(1), "name": long}}})
+	if err != nil {
+		t.Fatalf("marshal: %v", err)
+	}
+	want := "arr = [1, {\n\tn = 1,\n\tname = \"" + long + "\",\n}]\n"
+	if string(out) != want {
+		t.Errorf("output mismatch:\ngot:  %q\nwant: %q", out, want)
+	}
+
+	// The same values without the long string stay on one line.
+	out, err = Marshal(Cfg{Arr: []any{int64(1), map[string]any{"n": int64(1), "name": "short"}}})
+	if err != nil {
+		t.Fatalf("marshal: %v", err)
+	}
+	if want := "arr = [1, {n = 1, name = \"short\"}]\n"; string(out) != want {
+		t.Errorf("output mismatch:\ngot:  %q\nwant: %q", out, want)
+	}
+
+	// The broken form parses back to the same tree.
+	tree, err := Parse(out)
+	if err != nil {
+		t.Fatalf("parse of the encoder output: %v", err)
+	}
+	if got := len(tree["arr"].([]any)); got != 2 {
+		t.Fatalf("arr has %d elements, want 2", got)
+	}
+}
+
+func TestMarshalNestedInlineTableBreaksIndependently(t *testing.T) {
+	// A nested table breaks on its own measure, so a table whose entries stay
+	// short keeps the one-line form inside a parent that broke.
+	const long = "a-very-long-value-that-pushes-the-line-well-past-the-one-hundred-column-limit"
+	type Cfg struct {
+		Arr []any `toml:"arr"`
+	}
+	out, err := Marshal(Cfg{Arr: []any{int64(1), map[string]any{"n": int64(1), "sub": map[string]any{"name": long}}}})
+	if err != nil {
+		t.Fatalf("marshal: %v", err)
+	}
+	want := "arr = [1, {\n\tn = 1,\n\tsub = {name = \"" + long + "\"},\n}]\n"
+	if string(out) != want {
+		t.Errorf("output mismatch:\ngot:  %q\nwant: %q", out, want)
+	}
+}
+
+type inlineTLS struct {
+	On bool `toml:"on"`
+}
+
+type inlineServer struct {
+	Host string    `toml:"host"`
+	Port int       `toml:"port"`
+	TLS  inlineTLS `toml:"tls"`
+}
+
+type inlineBig struct {
+	A int `toml:"a"`
+	B int `toml:"b"`
+	C int `toml:"c"`
+}
+
+func TestEncoderInlineTables(t *testing.T) {
+	type Cfg struct {
+		Server inlineServer `toml:"server"`
+		Big    inlineBig    `toml:"big"`
+	}
+	cfg := Cfg{Server: inlineServer{Host: "127.0.0.1", Port: 9090}, Big: inlineBig{A: 1, B: 2, C: 3}}
+
+	// The default keeps every sub-table a header section.
+	headerForm, err := Marshal(cfg)
+	if err != nil {
+		t.Fatalf("marshal: %v", err)
+	}
+	want := "[server]\nhost = \"127.0.0.1\"\nport = 9090\n\n[server.tls]\non = false\n\n[big]\na = 1\nb = 2\nc = 3\n"
+	if string(headerForm) != want {
+		t.Errorf("default output mismatch:\ngot:  %q\nwant: %q", headerForm, want)
+	}
+
+	// With the option both fit the threshold and become inline tables, nested
+	// ones included.
+	out, err := NewEncoder().InlineTables(60).Marshal(cfg)
+	if err != nil {
+		t.Fatalf("marshal: %v", err)
+	}
+	want = "server = {host = \"127.0.0.1\", port = 9090, tls = {on = false}}\nbig = {a = 1, b = 2, c = 3}\n"
+	if string(out) != want {
+		t.Errorf("compact output mismatch:\ngot:  %q\nwant: %q", out, want)
+	}
+
+	// A threshold below the rendering keeps the header form.
+	out, err = NewEncoder().InlineTables(10).Marshal(cfg)
+	if err != nil {
+		t.Fatalf("marshal: %v", err)
+	}
+	if string(out) != string(headerForm) {
+		t.Errorf("small threshold output mismatch:\ngot:  %q\nwant: %q", out, headerForm)
+	}
+}
+
+func TestEncoderInlineTablesOrderAndRoundTrip(t *testing.T) {
+	// An inlined sub-table is a value line, so it precedes every header of the
+	// document; written after a header it would be read back as part of that
+	// table. The compact form and the header form parse to the same tree.
+	type Four struct {
+		A int `toml:"a"`
+		B int `toml:"b"`
+		C int `toml:"c"`
+		D int `toml:"d"`
+	}
+	type Cfg struct {
+		Small inlineTLS `toml:"small"`
+		Big   Four      `toml:"big"`
+	}
+	cfg := Cfg{Small: inlineTLS{On: true}, Big: Four{A: 1, B: 2, C: 3, D: 4}}
+
+	headerForm, err := Marshal(cfg)
+	if err != nil {
+		t.Fatalf("marshal: %v", err)
+	}
+	compact, err := NewEncoder().InlineTables(20).Marshal(cfg)
+	if err != nil {
+		t.Fatalf("marshal: %v", err)
+	}
+	want := "small = {on = true}\n\n[big]\na = 1\nb = 2\nc = 3\nd = 4\n"
+	if string(compact) != want {
+		t.Errorf("output mismatch:\ngot:  %q\nwant: %q", compact, want)
+	}
+
+	got, err := Parse(compact)
+	if err != nil {
+		t.Fatalf("parse of the compact output: %v", err)
+	}
+	ref, err := Parse(headerForm)
+	if err != nil {
+		t.Fatalf("parse of the header output: %v", err)
+	}
+	if !reflect.DeepEqual(got, ref) {
+		t.Errorf("the compact form changed the tree:\ncompact: %#v\nheaders: %#v", got, ref)
+	}
+	if _, ok := got["big"].(map[string]any); !ok {
+		t.Errorf("big = %#v, want a table", got["big"])
+	}
+}
+
+func TestEncoderInlineTablesKeepsArraysOfTables(t *testing.T) {
+	// An array of tables has no inline form that keeps the value's type, so the
+	// option leaves it alone and the tree keeps its []map[string]any shape.
+	type Item struct {
+		N int `toml:"n"`
+	}
+	type Cfg struct {
+		Items []Item    `toml:"items"`
+		Small inlineTLS `toml:"small"`
+	}
+	cfg := Cfg{Items: []Item{{N: 1}}, Small: inlineTLS{On: true}}
+	out, err := NewEncoder().InlineTables(60).Marshal(cfg)
+	if err != nil {
+		t.Fatalf("marshal: %v", err)
+	}
+	want := "small = {on = true}\n\n[[items]]\nn = 1\n"
+	if string(out) != want {
+		t.Errorf("output mismatch:\ngot:  %q\nwant: %q", out, want)
+	}
+	tree, err := Parse(out)
+	if err != nil {
+		t.Fatalf("parse: %v", err)
+	}
+	if _, ok := tree["items"].([]map[string]any); !ok {
+		t.Errorf("items = %#v, want []map[string]any", tree["items"])
+	}
+}

examples/basic/main.go

@@ -13,7 +13,7 @@ import (
 	"os"
 	"time"
 
-	"sourcedock.dev/petrbalvin/interpres"
+	"sourcedock.dev/petrbalvin/interpres/v2"
 )
 
 // document is a small but realistic configuration: it has scalars, a

go.mod

@@ -1,3 +1,3 @@
-module sourcedock.dev/petrbalvin/interpres
+module sourcedock.dev/petrbalvin/interpres/v2
 
 go 1.27.1

interpres.go

@@ -123,6 +123,11 @@ func ParseContext(ctx context.Context, data []byte) (map[string]any, error) {
 // case-insensitive match on the field name when no tag is present. A tag of
 // "-" skips the field.
 //
+// A destination implementing Unmarshaler receives the parsed value as it is,
+// a TOML string fills a destination implementing encoding.TextUnmarshaler, and
+// a time.Duration destination takes a duration literal such as `1h30m` or a
+// bare integer as its nanosecond count.
+//
 // Unmarshal is equivalent to UnmarshalContext with context.Background.
 func Unmarshal(data []byte, v any) error {
 	return UnmarshalContext(context.Background(), data, v)
@@ -177,6 +182,10 @@ func (d *Decoder) DecodeContext(ctx context.Context, data []byte, v any) error {
 // then encodes as if the returned value had been passed in its place, which
 // is useful for emitting a Go type as a different TOML shape (for example, a
 // struct as an inline table or a primitive alias as a richer value).
+//
+// MarshalTOML wins over encoding.TextMarshaler when a type implements both.
+// A type that implements only encoding.TextMarshaler is encoded as a TOML
+// string holding its text, and needs no method here.
 type Marshaler interface {
 	MarshalTOML() (any, error)
 }
@@ -194,12 +203,15 @@ type Marshaler interface {
 // UnmarshalTOML is invoked from (*Decoder).Decode / Unmarshal when the
 // destination type implements the interface. The decoder does not need to
 // consult the concrete return value; whatever the receiver stores is kept.
+//
+// UnmarshalTOML wins over encoding.TextUnmarshaler when a type implements
+// both. A type that implements only encoding.TextUnmarshaler is filled from a
+// TOML string holding its text, and needs no method here.
 type Unmarshaler interface {
 	UnmarshalTOML(data any) error
 }
 
-// Marshal returns the TOML encoding of v. The output stays within TOML 1.0,
-// so it is valid under both TOML 1.0 and 1.1.
+// Marshal returns the TOML encoding of v. The output is valid TOML 1.1.
 //
 // Marshal traverses v using reflection and applies the following rules:
 //
@@ -220,9 +232,16 @@ type Unmarshaler interface {
 //     inline table.
 //   - Scalars encode as TOML scalars: bool, int64, float64, string, time.Time
 //     (offset date-time), and LocalDateTime/LocalDate/LocalTime (local
-//     variants).
+//     variants). A date-time writes its seconds only when the value carries
+//     them, and drops the trailing zeros of a fractional second.
+//   - A table element of a value array, and a sub-table inlined by
+//     Encoder.InlineTables, is written as an inline table, across lines when it
+//     does not fit one.
 //   - Values implementing Marshaler are encoded by calling MarshalTOML and
 //     using its result.
+//   - Values implementing encoding.TextMarshaler, and not one of the
+//     date-time types, encode as a TOML string holding the text the method
+//     returns. time.Duration is written in its canonical Go form, `1h30m0s`.
 //   - nil pointer fields are omitted.
 //
 // Marshal cannot encode cyclic data structures; passing one will loop until
@@ -246,14 +265,16 @@ func MarshalContext(ctx context.Context, v any) ([]byte, error) {
 
 // An Encoder encodes Go values into TOML.
 //
-// All options default to behaviour that preserves byte-for-byte compatibility
-// with previous releases and passes the toml-test compliance suite:
+// All options default to the behaviour that passes the toml-test compliance
+// suite in both directions:
 //
 //	GroupByKind:        true  (scalars first, then tables, then arrays of tables)
 //	OmitEmptyArrays:    false (a nil/empty []string slice emits [] as a value;
 //	                          a nil/empty []Item struct slice is still skipped)
-//	LiteralMultilineAt: 0     (always emit basic multi-line strings with
-//	                          escape sequences, never literal ones)
+//	LiteralMultilineAt: 0     (always emit the escaped basic form, never a
+//	                          literal one)
+//	InlineTablesAt:     0     (always emit a table header, never an inline
+//	                          table)
 //
 // Use the chainable option methods to opt out. The option state is private;
 // callers that need the underlying knobs reach for the methods rather than
@@ -262,6 +283,7 @@ type Encoder struct {
 	groupByKind        bool // default true; set via (*Encoder).GroupByKind
 	omitEmptyArrays    bool // default false; set via (*Encoder).OmitEmptyArrays
 	literalMultilineAt int  // default 0; set via (*Encoder).UseLiteralMultiline
+	inlineTablesAt     int  // default 0; set via (*Encoder).InlineTables
 }
 
 // NewEncoder returns an Encoder with default options.
@@ -294,6 +316,24 @@ func (e *Encoder) UseLiteralMultiline(threshold int) *Encoder {
 	return e
 }
 
+// InlineTables sets the size limit, in bytes of the single-line rendering, at
+// which a sub-table is written as an inline table instead of a table header,
+// which makes a document of small tables shorter. Use 0 or any negative value
+// to disable (always emit a header).
+//
+// A sub-table is inlined only when doing so keeps every value's type: an array
+// of tables keeps its header form, because its inline form would re-parse as a
+// value array. An inlined table that does not fit the line is written across
+// lines, which TOML 1.1 allows.
+//
+// With GroupByKind(false) the layout is already for presentation only, and an
+// inlined table follows the same rule as any other value line: it lands in the
+// section of the header that precedes it.
+func (e *Encoder) InlineTables(threshold int) *Encoder {
+	e.inlineTablesAt = threshold
+	return e
+}
+
 // Marshal encodes v to TOML bytes. It is equivalent to calling Marshal with v.
 //
 // Marshal is equivalent to MarshalContext with context.Background.

interpres_test.go

@@ -611,11 +611,13 @@ odt2 = 1979-05-27 07:32-07:00
 	if err != nil {
 		t.Fatalf("parse: %v", err)
 	}
-	if got := tree["t"].(LocalTime).String(); got != "13:37:00" {
-		t.Errorf("t = %q, want %q", got, "13:37:00")
+	// A value written without seconds comes back without them: the seconds are
+	// only written when the value carries them.
+	if got := tree["t"].(LocalTime).String(); got != "13:37" {
+		t.Errorf("t = %q, want %q", got, "13:37")
 	}
-	if got := tree["dt"].(LocalDateTime).String(); got != "1979-05-27T07:32:00" {
-		t.Errorf("dt = %q, want %q", got, "1979-05-27T07:32:00")
+	if got := tree["dt"].(LocalDateTime).String(); got != "1979-05-27T07:32" {
+		t.Errorf("dt = %q, want %q", got, "1979-05-27T07:32")
 	}
 	if got := tree["odt1"].(time.Time).Format(time.RFC3339Nano); got != "1979-05-27T07:32:00Z" {
 		t.Errorf("odt1 = %q", got)

justfile

@@ -92,9 +92,9 @@ run:
 dev:
     go run -buildvcs=true {{package}}
 
-# Runs the official toml-test compliance suite against the built adapter; toml-test must be on PATH (go install github.com/toml-lang/toml-test/v2/cmd/toml-test@v2.2.0); not standard because no canonical recipe covers a domain compliance suite.
+# Runs the official toml-test compliance suite in both directions, decoder and encoder, against the built adapter; toml-test must be on PATH (go install github.com/toml-lang/toml-test/v2/cmd/toml-test@v2.2.0); not standard because no canonical recipe covers a domain compliance suite.
 toml-test: build
-    toml-test test -decoder=bin/interpres-decode -toml=1.1
+    toml-test test -decoder=bin/interpres-decode -encoder='bin/interpres-decode -encode' -toml=1.1
 
 # Coverage report as an HTML map from the gate's profile; not standard because the gate needs only the numeric floor, and a browser artefact is exploration, not a gate.
 coverage-html: test