feat: scaffold interpres project with TOML parser and CI

interpres.go

@@ -0,0 +1,86 @@
+// Package interpres is a dependency-free TOML parser for Go.
+//
+// interpres reads TOML documents into Go values using only the standard
+// library. It exposes a small, encoding/json-style API:
+//
+//	var cfg Config
+//	err := interpres.Unmarshal(data, &cfg)
+//
+// or, for an untyped tree:
+//
+//	tree, err := interpres.Parse(data)
+//
+// A Decoder allows strict decoding that rejects keys without a matching
+// struct field, mirroring (*json.Decoder).DisallowUnknownFields.
+package interpres
+
+import (
+	"fmt"
+	"unicode/utf8"
+)
+
+// A SyntaxError describes a malformed TOML document, including the 1-based
+// line on which the problem was detected.
+type SyntaxError struct {
+	Line int
+	Msg  string
+}
+
+func (e *SyntaxError) Error() string {
+	return fmt.Sprintf("interpres: line %d: %s", e.Line, e.Msg)
+}
+
+// Parse decodes a TOML document into a nested map[string]any.
+//
+// Values are mapped to Go types as follows: strings to string, integers to
+// int64, floats to float64, booleans to bool, date-times to time.Time, arrays
+// to []any, and tables (including inline tables) to map[string]any.
+func Parse(data []byte) (map[string]any, error) {
+	if !utf8.Valid(data) {
+		return nil, &SyntaxError{Line: 1, Msg: "input is not valid UTF-8"}
+	}
+	p := &parser{src: []rune(string(data)), line: 1}
+	return p.parse()
+}
+
+// Unmarshal parses a TOML document and stores the result in the value pointed
+// to by v. v is typically a pointer to a struct or to a map[string]any.
+//
+// Struct fields are matched to TOML keys by the `toml:"name"` tag, or by a
+// case-insensitive match on the field name when no tag is present. A tag of
+// "-" skips the field.
+func Unmarshal(data []byte, v any) error {
+	tree, err := Parse(data)
+	if err != nil {
+		return err
+	}
+	return newDecoder().decode(tree, v)
+}
+
+// A Decoder decodes a TOML document into a Go value with configurable
+// strictness.
+type Decoder struct {
+	disallowUnknown bool
+}
+
+// NewDecoder returns a Decoder.
+func NewDecoder() *Decoder { return &Decoder{} }
+
+// DisallowUnknownFields causes Decode to return an error when the document
+// contains a key with no matching destination struct field.
+func (d *Decoder) DisallowUnknownFields() *Decoder {
+	d.disallowUnknown = true
+	return d
+}
+
+// Decode parses data and stores the result in the value pointed to by v,
+// honouring the decoder's strictness settings.
+func (d *Decoder) Decode(data []byte, v any) error {
+	tree, err := Parse(data)
+	if err != nil {
+		return err
+	}
+	dec := newDecoder()
+	dec.disallowUnknown = d.disallowUnknown
+	return dec.decode(tree, v)
+}