feat: add the -validate mode to interpres-decode

Assisted-by: GLM 5.3 Flash

cmd/interpres-decode/main.go

@@ -1,17 +1,23 @@
 // Copyright (c) 2026 Petr Balvín <opensource@petrbalvin.org> (https://petrbalvin.org)
 // SPDX-License-Identifier: MIT
 
-// Command interpres-decode reads a TOML document from standard input and writes
-// the toml-test "tagged JSON" representation to standard output.
+// 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:
 //
-// It exits non-zero on a parse error, which is how the toml-test harness checks
-// that invalid documents are rejected. Run the official suite against it with:
+//	interpres-decode -validate config.toml
+//
+// Run the official suite against the adapter with:
 //
 //	toml-test ./interpres-decode
 package main
 
 import (
 	"encoding/json"
+	"errors"
+	"flag"
 	"fmt"
 	"io"
 	"math"
@@ -23,13 +29,29 @@ import (
 )
 
 func main() {
-	os.Exit(Run(os.Stdin, os.Stdout, os.Stderr))
+	os.Exit(Run(os.Args[1:], os.Stdin, os.Stdout, os.Stderr))
 }
 
-// Run reads a TOML document from stdin, emits the toml-test tagged-JSON form
-// on stdout, and returns the process exit code (0 success, 1 parse error,
-// 2 I/O, encoding, or unsupported-value error).
-func Run(stdin io.Reader, stdout, stderr io.Writer) int {
+// Run runs the command line and returns the process exit code: 0 success,
+// 1 an invalid document, 2 a usage, reading, encoding, or
+// unsupported-value error.
+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")
+	if err := fs.Parse(args); err != nil {
+		if errors.Is(err, flag.ErrHelp) {
+			return 0
+		}
+		return 2
+	}
+	if *validate {
+		return validatePaths(fs.Args(), stdin, stderr)
+	}
+	if fs.NArg() > 0 {
+		fmt.Fprintln(stderr, "interpres-decode: the adapter mode takes no arguments; name files with -validate")
+		return 2
+	}
 	data, err := io.ReadAll(stdin)
 	if err != nil {
 		fmt.Fprintln(stderr, "read stdin:", err)
@@ -54,6 +76,39 @@ func Run(stdin io.Reader, stdout, stderr io.Writer) int {
 	return 0
 }
 
+// validatePaths parses every named file, or standard input when none are
+// named, and reports each invalid document on stderr. It returns 0 when all
+// documents parse, 1 when one does not, and 2 on a usage or read failure.
+func validatePaths(paths []string, stdin io.Reader, stderr io.Writer) int {
+	if len(paths) == 0 {
+		paths = []string{"-"}
+	}
+	valid := true
+	for _, p := range paths {
+		name := p
+		var data []byte
+		var err error
+		if p == "-" {
+			data, err = io.ReadAll(stdin)
+			name = "<stdin>"
+		} else {
+			data, err = os.ReadFile(p)
+		}
+		if err != nil {
+			fmt.Fprintf(stderr, "interpres-decode: %s: %v\n", name, err)
+			return 2
+		}
+		if _, err := interpres.Parse(data); err != nil {
+			fmt.Fprintf(stderr, "%s: %v\n", name, err)
+			valid = false
+		}
+	}
+	if !valid {
+		return 1
+	}
+	return 0
+}
+
 // 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