golang.org/x/mod v0.40.0: modfile.File

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 golang.org/x/mod/modfile.File in pkg:golang/golang.org/x/mod@v0.40.0
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/golang.org/x/mod@v0.40.0
Demonstrate these symbols/APIs:
  - golang.org/x/mod/modfile.File
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:d8582dbfeb8e67c5c40526c9cc109dbb3c0a03046a207ef9d8c815310ae64f94","contract":["modfile.Parse parses valid go.mod bytes into *modfile.File and exposes Module and Go version directives","modfile.File.AddRequire adds new require directives and modfile.File.DropRequire removes existing ones","modfile.File.AddReplace and modfile.File.DropReplace manage replace directives with module paths and versions","modfile.File.Format cleans up and formats the abstract syntax tree into standard go.mod formatting","modfile.Parse returns an error when parsing malformed or syntactically invalid go.mod content"],"goal":"verify golang.org/x/mod/modfile.File in pkg:golang/golang.org/x/mod@v0.40.0","kind":"HOW","packages":["pkg:golang/golang.org/x/mod@v0.40.0"],"schemaVersion":1,"symbols":["golang.org/x/mod/modfile.File"]},"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@v0.40.0"],"schemaVersion":1,"subject":"pkg:golang/golang.org/x/mod@v0.40.0","symbols":["golang.org/x/mod/modfile.File"],"verifierAdapter":"golang@1"}

module example.com/sample

go 1.25.0

require golang.org/x/mod v0.40.0

golang.org/x/mod v0.40.0 h1:hUv+3cXcdRHz08UmSiOob7sadHig73uo5bkXxQ/tvUs=
golang.org/x/mod v0.40.0/go.mod h1:0/weTWkPWGBikyTWAX3dkjVztMmBA5hM0DH6BElSupE=

package main

import (
	"fmt"
	"os"

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

// ParseAndModifyModfile parses a go.mod file content, adds a require directive,
// and returns the formatted modfile content along with the parsed module path.
func ParseAndModifyModfile(content []byte, reqPath, reqVersion string) (string, []byte, error) {
	f, err := modfile.Parse("go.mod", content, nil)
	if err != nil {
		return "", nil, fmt.Errorf("failed to parse go.mod: %w", err)
	}

	if f.Module == nil {
		return "", nil, fmt.Errorf("missing module statement")
	}

	modPath := f.Module.Mod.Path

	if err := f.AddRequire(reqPath, reqVersion); err != nil {
		return "", nil, fmt.Errorf("failed to add require %s@%s: %w", reqPath, reqVersion, err)
	}

	f.Cleanup()

	formatted, err := f.Format()
	if err != nil {
		return "", nil, fmt.Errorf("failed to format modfile: %w", err)
	}

	return modPath, formatted, nil
}

func main() {
	sampleGoMod := []byte(`module example.com/myapp

go 1.24.0

require (
	golang.org/x/sync v0.10.0
)
`)

	modPath, formatted, err := ParseAndModifyModfile(sampleGoMod, "golang.org/x/text", "v0.22.0")
	if err != nil {
		fmt.Fprintf(os.Stderr, "Error: %v\n", err)
		os.Exit(1)
	}

	fmt.Printf("Parsed module: %s\n", modPath)
	fmt.Printf("Updated go.mod:\n%s\n", string(formatted))
}

{
  "schemaVersion": 1,
  "goal": "verify golang.org/x/mod/modfile.File in pkg:golang/golang.org/x/mod@v0.40.0",
  "kind": "HOW",
  "packages": [
    "pkg:golang/golang.org/x/mod@v0.40.0"
  ],
  "symbols": [
    "golang.org/x/mod/modfile.File"
  ],
  "constraints": {
    "executionContext": "node"
  },
  "runtimeConditions": {
    "ecosystem": "npm",
    "language": "javascript",
    "moduleSystem": "cjs",
    "packageManager": "npm@10.9.8",
    "runtime": "node@22.23.2"
  }
}

package main

import (
	"fmt"
	"os"

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

func main() {
	// Assertion 1: modfile.Parse parses valid go.mod bytes into *modfile.File and exposes Module and Go version directives
	initialMod := []byte("module example.com/demo\n\ngo 1.24.0\n\nrequire golang.org/x/sync v0.10.0\n")
	f, err := modfile.Parse("go.mod", initialMod, nil)
	if err != nil {
		fmt.Fprintf(os.Stderr, "FAIL: modfile.Parse initial: %v\n", err)
		os.Exit(1)
	}
	if f.Module == nil || f.Module.Mod.Path != "example.com/demo" {
		fmt.Fprintf(os.Stderr, "FAIL: expected module 'example.com/demo', got %+v\n", f.Module)
		os.Exit(1)
	}
	if f.Go == nil || f.Go.Version != "1.24.0" {
		fmt.Fprintf(os.Stderr, "FAIL: expected go version '1.24.0', got %+v\n", f.Go)
		os.Exit(1)
	}
	if len(f.Require) != 1 || f.Require[0].Mod.Path != "golang.org/x/sync" || f.Require[0].Mod.Version != "v0.10.0" {
		fmt.Fprintf(os.Stderr, "FAIL: unexpected require directives: %+v\n", f.Require)
		os.Exit(1)
	}

	// Assertion 2: modfile.File.AddRequire adds new require directives and modfile.File.DropRequire removes existing ones
	if err := f.AddRequire("golang.org/x/text", "v0.22.0"); err != nil {
		fmt.Fprintf(os.Stderr, "FAIL: f.AddRequire: %v\n", err)
		os.Exit(1)
	}
	if len(f.Require) != 2 {
		fmt.Fprintf(os.Stderr, "FAIL: expected 2 require entries after AddRequire, got %d\n", len(f.Require))
		os.Exit(1)
	}
	if err := f.DropRequire("golang.org/x/sync"); err != nil {
		fmt.Fprintf(os.Stderr, "FAIL: f.DropRequire: %v\n", err)
		os.Exit(1)
	}
	f.Cleanup()
	var remainingRequires []string
	for _, req := range f.Require {
		remainingRequires = append(remainingRequires, req.Mod.Path)
	}
	if len(remainingRequires) != 1 || remainingRequires[0] != "golang.org/x/text" {
		fmt.Fprintf(os.Stderr, "FAIL: expected [golang.org/x/text] after DropRequire, got %+v\n", remainingRequires)
		os.Exit(1)
	}

	// Assertion 3: modfile.File.AddReplace and modfile.File.DropReplace manage replace directives with module paths and versions
	if err := f.AddReplace("golang.org/x/text", "", "example.com/forked/text", "v0.22.1"); err != nil {
		fmt.Fprintf(os.Stderr, "FAIL: f.AddReplace: %v\n", err)
		os.Exit(1)
	}
	if len(f.Replace) != 1 || f.Replace[0].Old.Path != "golang.org/x/text" || f.Replace[0].New.Path != "example.com/forked/text" {
		fmt.Fprintf(os.Stderr, "FAIL: unexpected replace entries: %+v\n", f.Replace)
		os.Exit(1)
	}
	if err := f.DropReplace("golang.org/x/text", ""); err != nil {
		fmt.Fprintf(os.Stderr, "FAIL: f.DropReplace: %v\n", err)
		os.Exit(1)
	}
	f.Cleanup()
	if len(f.Replace) != 0 {
		fmt.Fprintf(os.Stderr, "FAIL: expected 0 replace entries after DropReplace, got %d\n", len(f.Replace))
		os.Exit(1)
	}

	// Assertion 4: modfile.File.Format cleans up and formats the abstract syntax tree into standard go.mod formatting
	formattedBytes, err := f.Format()
	if err != nil {
		fmt.Fprintf(os.Stderr, "FAIL: f.Format: %v\n", err)
		os.Exit(1)
	}
	reparsed, err := modfile.Parse("go.mod", formattedBytes, nil)
	if err != nil {
		fmt.Fprintf(os.Stderr, "FAIL: modfile.Parse reparsed: %v\n", err)
		os.Exit(1)
	}
	if reparsed.Module.Mod.Path != "example.com/demo" || len(reparsed.Require) != 1 || reparsed.Require[0].Mod.Path != "golang.org/x/text" {
		fmt.Fprintf(os.Stderr, "FAIL: formatted output reparsed incorrectly: %s\n", string(formattedBytes))
		os.Exit(1)
	}

	// Assertion 5: modfile.Parse returns an error when parsing malformed or syntactically invalid go.mod content
	malformedGoMod := []byte("module\n invalid syntax !!! {{{")
	_, err = modfile.Parse("go.mod", malformedGoMod, nil)
	if err == nil {
		fmt.Fprintf(os.Stderr, "FAIL: expected error parsing malformed go.mod, got nil\n")
		os.Exit(1)
	}

	fmt.Println("PASS: golang.org/x/mod/modfile.File contract verified")
}