modernc.org/gc/v2 v2.6.5: NewScanner, ParseSourceFile

Clean-room public code sample — generation instructions

Write a brand-new, minimal, self-contained code sample in this clean-room directory.
Do not copy, paraphrase, or reference any existing project source. Work only from this spec.

A csx.json manifest scaffold already exists. Do not recreate it from memory. Preserve its case.goal, packages and symbols; fill its empty case.contract with exact assertions and correct its environment, commands and verifierAdapter for the files you generate.

Goal: verify pkg:golang/modernc.org/gc/v2@v2.6.5
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/modernc.org/gc/v2@v2.6.5
Demonstrate these symbols/APIs:
  - modernc.org/gc/v2.NewScanner
  - modernc.org/gc/v2.ParseSourceFile

Rules:
  - One focused purpose; the smallest project that proves the goal.
  - Include a contract test (test/contract.*) that runs OFFLINE and exits 0 exactly when the goal behavior works.
  - Pin every dependency with a lockfile so resolution is reproducible.
  - No secrets, credentials, or tokens. No real URLs (only example.com or localhost). No absolute paths.
  - No personal names, emails, company names, or project identifiers of any kind.
  - No binaries and no generated output (node_modules, dist, target, venv, .git, .env).
  - Keep it under 200 files and 256KB packed.

{"case":{"caseId":"case:sha256:08358a339769d5f6e170f1d336aad7ce3045f72afe346b9af5b8f885cc04fb1e","contract":["gc.ParseSourceFile parses valid Go source code and returns a SourceFile AST with the matching package name","gc.ParseSourceFile returns a non-nil error when given invalid Go syntax","gc.NewScanner tokenizes Go source code into sequential tokens","gc.ParseSourceFile aborts parsing early with an error when ParseSourceFileConfig.Accept returns an error"],"goal":"verify pkg:golang/modernc.org/gc/v2@v2.6.5","kind":"HOW","packages":["pkg:golang/modernc.org/gc/v2@v2.6.5"],"schemaVersion":1,"symbols":["modernc.org/gc/v2.NewScanner","modernc.org/gc/v2.ParseSourceFile"]},"contractCommand":["go","run","./test"],"environment":{"arch":"x64","distro":"ubuntu","ecosystem":"golang","libc":"glibc","libcVersion":"2.39","os":"linux","osVersionBucket":"24","packageManager":"go","schemaVersion":1},"license":"MIT-0","packages":["pkg:golang/modernc.org/gc/v2@v2.6.5"],"schemaVersion":1,"subject":"pkg:golang/modernc.org/gc/v2@v2.6.5","symbols":["modernc.org/gc/v2.NewScanner","modernc.org/gc/v2.ParseSourceFile"],"verifierAdapter":"golang@1"}

module sample

go 1.26.6

require (
	modernc.org/gc/v2 v2.6.5 // indirect
	modernc.org/token v1.1.0 // indirect
)

modernc.org/gc/v2 v2.6.5 h1:nyqdV8q46KvTpZlsw66kWqwXRHdjIlJOhG6kxiV/9xI=
modernc.org/gc/v2 v2.6.5/go.mod h1:YgIahr1ypgfe7chRuJi2gD7DBQiKSLMPgBQe9oIiito=
modernc.org/token v1.1.0 h1:Xl7Ap9dKaEs5kLoOQeQmPWevfnk/DM5qcLcYlA8ys6Y=
modernc.org/token v1.1.0/go.mod h1:UGzOrNV1mAFSEB63lOFHIpNRUVMvYTc6yu1SMY/XTDM=

package main

import (
	"fmt"
	"os"

	"modernc.org/gc/v2"
)

func main() {
	src := []byte("package main\n\nfunc main() {}\n")

	sf, err := gc.ParseSourceFile(&gc.ParseSourceFileConfig{}, "main.go", src)
	if err != nil {
		fmt.Fprintf(os.Stderr, "ParseSourceFile error: %v\n", err)
		os.Exit(1)
	}
	fmt.Printf("Parsed package: %s\n", sf.PackageClause.PackageName.Src())

	s, err := gc.NewScanner("main.go", src)
	if err != nil {
		fmt.Fprintf(os.Stderr, "NewScanner error: %v\n", err)
		os.Exit(1)
	}
	for s.Scan() {
		fmt.Printf("Token: %s\n", s.Tok.Src())
	}
}

{
  "schemaVersion": 1,
  "goal": "verify pkg:golang/modernc.org/gc/v2@v2.6.5",
  "kind": "HOW",
  "packages": [
    "pkg:golang/modernc.org/gc/v2@v2.6.5"
  ],
  "symbols": [
    "modernc.org/gc/v2.NewScanner",
    "modernc.org/gc/v2.ParseSourceFile"
  ]
}

package main

import (
	"errors"
	"fmt"
	"os"

	"modernc.org/gc/v2"
)

func main() {
	// Assertion 1: gc.ParseSourceFile parses valid Go source code and returns a SourceFile AST with the matching package name
	{
		src := []byte("package example\n\nfunc Add(a, b int) int { return a + b }\n")
		sf, err := gc.ParseSourceFile(&gc.ParseSourceFileConfig{}, "example.go", src)
		if err != nil {
			fmt.Fprintf(os.Stderr, "Assertion 1 failed: ParseSourceFile failed: %v\n", err)
			os.Exit(1)
		}
		if sf == nil || sf.PackageClause == nil {
			fmt.Fprintf(os.Stderr, "Assertion 1 failed: nil SourceFile or PackageClause\n")
			os.Exit(1)
		}
		pkgName := sf.PackageClause.PackageName.Src()
		if pkgName != "example" {
			fmt.Fprintf(os.Stderr, "Assertion 1 failed: expected package %q, got %q\n", "example", pkgName)
			os.Exit(1)
		}
	}

	// Assertion 2: gc.ParseSourceFile returns a non-nil error when given invalid Go syntax
	{
		badSrc := []byte("package example\n\nfunc broken( {")
		_, err := gc.ParseSourceFile(&gc.ParseSourceFileConfig{}, "broken.go", badSrc)
		if err == nil {
			fmt.Fprintf(os.Stderr, "Assertion 2 failed: expected error for invalid Go syntax, got nil\n")
			os.Exit(1)
		}
	}

	// Assertion 3: gc.NewScanner tokenizes Go source code into sequential tokens
	{
		src := []byte("package foo\nconst Answer = 42\n")
		s, err := gc.NewScanner("foo.go", src)
		if err != nil {
			fmt.Fprintf(os.Stderr, "Assertion 3 failed: NewScanner failed: %v\n", err)
			os.Exit(1)
		}
		var tokens []string
		for s.Scan() {
			tokens = append(tokens, s.Tok.Src())
		}
		if err := s.Err(); err != nil {
			fmt.Fprintf(os.Stderr, "Assertion 3 failed: scanner error: %v\n", err)
			os.Exit(1)
		}
		if len(tokens) == 0 {
			fmt.Fprintf(os.Stderr, "Assertion 3 failed: expected non-empty token list\n")
			os.Exit(1)
		}
		if tokens[0] != "package" {
			fmt.Fprintf(os.Stderr, "Assertion 3 failed: expected first token 'package', got %q\n", tokens[0])
			os.Exit(1)
		}
	}

	// Assertion 4: gc.ParseSourceFile aborts parsing early with an error when ParseSourceFileConfig.Accept returns an error
	{
		src := []byte("package example\n\nfunc Target() {}\n")
		expectedErr := errors.New("aborted by accept hook")
		cfg := &gc.ParseSourceFileConfig{
			Accept: func(sf *gc.SourceFile) error {
				return expectedErr
			},
		}
		_, err := gc.ParseSourceFile(cfg, "hook.go", src)
		if !errors.Is(err, expectedErr) {
			fmt.Fprintf(os.Stderr, "Assertion 4 failed: expected error %v, got %v\n", expectedErr, err)
			os.Exit(1)
		}
	}

	fmt.Println("PASS: all modernc.org/gc/v2 contract assertions passed")
}