golang.org/x/mod v0.24.0: parse and format go.mod files with modfile.Parse and Format

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: parse and format go.mod files with modfile.Parse and Format
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/golang.org/x/mod@v0.24.0
Demonstrate these symbols/APIs:
  - modfile.Parse
Constraints:
  - executionContext: node
Required runtime conditions:
  - ecosystem: npm
  - language: javascript
  - moduleSystem: cjs
  - packageManager: npm@10.9.8
  - runtime: node@22.23.2

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:sha256:3b651738328e747b57da8b3a91dd670b4c90c0363f89b0e539b54f587bd3b87a","contract":["modfile.Parse parses a go.mod file into a File struct with module path and Go version","modfile.File.AddRequire adds a required dependency module path and version to the modfile","modfile.Format formats a modfile.File AST back into standard go.mod formatted bytes","modfile.File.DropRequire removes an existing requirement from the modfile AST","modfile.File.AddReplace adds a module replace directive to the modfile AST","modfile.Parse returns an error when parsing malformed go.mod content"],"goal":"parse and format go.mod files with modfile.Parse and Format","kind":"HOW","packages":["pkg:golang/golang.org/x/mod@v0.24.0"],"schemaVersion":1,"symbols":["modfile.Parse"]},"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/golang.org/x/mod@v0.24.0"],"schemaVersion":1,"subject":"pkg:golang/golang.org/x/mod@v0.24.0","symbols":["modfile.Parse"],"verifierAdapter":"golang@1"}

module sample-golang-mod

go 1.23.0

require golang.org/x/mod v0.24.0

golang.org/x/mod v0.24.0 h1:ZfthKaKaT4NrhGVZHO1/WDTwGES4De8KtWO0SIbNJMU=
golang.org/x/mod v0.24.0/go.mod h1:IXM97Txy2VM4PJ3gI61r1YEk/gAj6zAHN3AdZt6S9Ww=

package main

import (
	"fmt"

	"golang.org/x/mod/modfile"
)

func main() {
	raw := []byte("module example.com/mymodule\n\ngo 1.23.0\n\nrequire github.com/stretchr/testify v1.8.4\n")

	f, err := modfile.Parse("go.mod", raw, nil)
	if err != nil {
		fmt.Printf("parse error: %v\n", err)
		return
	}

	fmt.Printf("Module path: %s\n", f.Module.Mod.Path)
	fmt.Printf("Go version: %s\n", f.Go.Version)

	if err := f.AddRequire("golang.org/x/sync", "v0.10.0"); err != nil {
		fmt.Printf("add require error: %v\n", err)
		return
	}

	formatted, err := f.Format()
	if err != nil {
		fmt.Printf("format error: %v\n", err)
		return
	}

	fmt.Printf("Formatted go.mod:\n%s\n", string(formatted))
}

{
  "schemaVersion": 1,
  "goal": "parse and format go.mod files with modfile.Parse and Format",
  "kind": "HOW",
  "packages": [
    "pkg:golang/golang.org/x/mod@v0.24.0"
  ],
  "symbols": [
    "modfile.Parse"
  ],
  "constraints": {
    "executionContext": "node"
  },
  "runtimeConditions": {
    "ecosystem": "npm",
    "language": "javascript",
    "moduleSystem": "cjs",
    "packageManager": "npm@10.9.8",
    "runtime": "node@22.23.2"
  }
}

package main

import (
	"bytes"
	"fmt"
	"os"

	"golang.org/x/mod/modfile"
)

func main() {
	// Assertion 1: modfile.Parse parses a go.mod file into a File struct with module path and Go version
	{
		raw := []byte("module example.com/app\n\ngo 1.23.0\n\nrequire github.com/stretchr/testify v1.8.4\n")
		f, err := modfile.Parse("go.mod", raw, nil)
		if err != nil {
			fmt.Fprintf(os.Stderr, "FAIL: modfile.Parse returned error: %v\n", err)
			os.Exit(1)
		}
		if f.Module == nil || f.Module.Mod.Path != "example.com/app" {
			fmt.Fprintf(os.Stderr, "FAIL: unexpected module path: %v\n", f.Module)
			os.Exit(1)
		}
		if f.Go == nil || f.Go.Version != "1.23.0" {
			fmt.Fprintf(os.Stderr, "FAIL: unexpected Go version: %v\n", f.Go)
			os.Exit(1)
		}
		if len(f.Require) != 1 || f.Require[0].Mod.Path != "github.com/stretchr/testify" || f.Require[0].Mod.Version != "v1.8.4" {
			fmt.Fprintf(os.Stderr, "FAIL: unexpected require statement: %v\n", f.Require)
			os.Exit(1)
		}
	}

	// Assertion 2: modfile.File.AddRequire adds a required dependency module path and version to the modfile
	{
		raw := []byte("module example.com/app\n\ngo 1.23.0\n")
		f, err := modfile.Parse("go.mod", raw, nil)
		if err != nil {
			fmt.Fprintf(os.Stderr, "FAIL: modfile.Parse failed: %v\n", err)
			os.Exit(1)
		}
		err = f.AddRequire("golang.org/x/sync", "v0.10.0")
		if err != nil {
			fmt.Fprintf(os.Stderr, "FAIL: AddRequire failed: %v\n", err)
			os.Exit(1)
		}
		found := false
		for _, req := range f.Require {
			if req.Mod.Path == "golang.org/x/sync" && req.Mod.Version == "v0.10.0" {
				found = true
				break
			}
		}
		if !found {
			fmt.Fprintln(os.Stderr, "FAIL: AddRequire did not add the requirement")
			os.Exit(1)
		}
	}

	// Assertion 3: modfile.Format formats a modfile.File AST back into standard go.mod formatted bytes
	{
		raw := []byte("module example.com/app\n\ngo 1.23.0\n\nrequire golang.org/x/sync v0.10.0\n")
		f, err := modfile.Parse("go.mod", raw, nil)
		if err != nil {
			fmt.Fprintf(os.Stderr, "FAIL: modfile.Parse failed: %v\n", err)
			os.Exit(1)
		}
		formatted, err := f.Format()
		if err != nil {
			fmt.Fprintf(os.Stderr, "FAIL: Format failed: %v\n", err)
			os.Exit(1)
		}
		if !bytes.Contains(formatted, []byte("module example.com/app")) ||
			!bytes.Contains(formatted, []byte("go 1.23.0")) ||
			!bytes.Contains(formatted, []byte("require golang.org/x/sync v0.10.0")) {
			fmt.Fprintf(os.Stderr, "FAIL: formatted content mismatch:\n%s\n", string(formatted))
			os.Exit(1)
		}
	}

	// Assertion 4: modfile.File.DropRequire removes an existing requirement from the modfile AST
	{
		raw := []byte("module example.com/app\n\ngo 1.23.0\n\nrequire (\n\tgolang.org/x/sync v0.10.0\n\tgolang.org/x/net v0.34.0\n)\n")
		f, err := modfile.Parse("go.mod", raw, nil)
		if err != nil {
			fmt.Fprintf(os.Stderr, "FAIL: modfile.Parse failed: %v\n", err)
			os.Exit(1)
		}
		err = f.DropRequire("golang.org/x/net")
		if err != nil {
			fmt.Fprintf(os.Stderr, "FAIL: DropRequire failed: %v\n", err)
			os.Exit(1)
		}
		f.Cleanup()
		for _, req := range f.Require {
			if req.Mod.Path == "golang.org/x/net" {
				fmt.Fprintln(os.Stderr, "FAIL: DropRequire did not remove the requirement")
				os.Exit(1)
			}
		}
	}

	// Assertion 5: modfile.File.AddReplace adds a module replace directive to the modfile AST
	{
		raw := []byte("module example.com/app\n\ngo 1.23.0\n\nrequire golang.org/x/sync v0.10.0\n")
		f, err := modfile.Parse("go.mod", raw, nil)
		if err != nil {
			fmt.Fprintf(os.Stderr, "FAIL: modfile.Parse failed: %v\n", err)
			os.Exit(1)
		}
		err = f.AddReplace("golang.org/x/sync", "v0.10.0", "github.com/fork/sync", "v0.10.1")
		if err != nil {
			fmt.Fprintf(os.Stderr, "FAIL: AddReplace failed: %v\n", err)
			os.Exit(1)
		}
		found := false
		for _, rep := range f.Replace {
			if rep.Old.Path == "golang.org/x/sync" && rep.Old.Version == "v0.10.0" &&
				rep.New.Path == "github.com/fork/sync" && rep.New.Version == "v0.10.1" {
				found = true
				break
			}
		}
		if !found {
			fmt.Fprintln(os.Stderr, "FAIL: AddReplace did not add the replace directive")
			os.Exit(1)
		}
	}

	// Assertion 6: modfile.Parse returns an error when parsing malformed go.mod content
	{
		malformed := []byte("invalid syntax here {{{")
		_, err := modfile.Parse("go.mod", malformed, nil)
		if err == nil {
			fmt.Fprintln(os.Stderr, "FAIL: expected error on malformed go.mod, got nil")
			os.Exit(1)
		}
	}

	fmt.Println("PASS: golang.org/x/mod contract passed")
}