golang.org/x/mod v0.39.0: module.Check

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/golang.org/x/mod@v0.39.0
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/golang.org/x/mod@v0.39.0

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:sha256:53ac1a7291547c9d3cbe36765484965ee64f88e19965f3e771131a443f941bfe","contract":["module.Check returns nil for a valid module path and semantic version","module.Check returns nil for major version \u003e= 2 when path includes the matching /vN suffix","module.Check returns InvalidVersionError when major version \u003e= 2 is used without a matching /vN path suffix","module.Check returns InvalidVersionError when version string is not a semantic version","module.Check returns InvalidPathError when module path contains invalid syntax such as a leading dash","module.Check returns InvalidPathError when module path is empty","module.Check returns InvalidPathError when module path contains an invalid /v0 major version suffix"],"goal":"verify pkg:golang/golang.org/x/mod@v0.39.0","kind":"HOW","packages":["pkg:golang/golang.org/x/mod@v0.39.0"],"schemaVersion":1,"symbols":["module.Check"]},"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@v0.39.0"],"schemaVersion":1,"subject":"pkg:golang/golang.org/x/mod@v0.39.0","symbols":["module.Check"],"verifierAdapter":"golang@1"}

module example.com/sample

go 1.26.6

require golang.org/x/mod v0.39.0

golang.org/x/mod v0.39.0 h1:UF5zwQdCRRUpHfyPwr7d4UrGiVeldIsogtzWVnczL74=
golang.org/x/mod v0.39.0/go.mod h1:bvIbwjQ0HUFFf5AKukeeYQG4ZBUG9yxQbR9aEweIwYY=

package main

import (
	"fmt"
	"log"

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

func main() {
	modulePath := "example.com/pkg/demo"
	version := "v1.2.3"
	if err := module.Check(modulePath, version); err != nil {
		log.Fatalf("Unexpected check failure for %s@%s: %v", modulePath, version, err)
	}
	fmt.Printf("Validated module %s@%s successfully.\n", modulePath, version)

	v2Path := "example.com/pkg/demo/v2"
	v2Version := "v2.0.0"
	if err := module.Check(v2Path, v2Version); err != nil {
		log.Fatalf("Unexpected check failure for %s@%s: %v", v2Path, v2Version, err)
	}
	fmt.Printf("Validated v2 module %s@%s successfully.\n", v2Path, v2Version)

	if err := module.Check(modulePath, v2Version); err != nil {
		fmt.Printf("Correctly rejected mismatched major version: %v\n", err)
	}
}

{
  "schemaVersion": 1,
  "goal": "verify pkg:golang/golang.org/x/mod@v0.39.0",
  "kind": "HOW",
  "packages": [
    "pkg:golang/golang.org/x/mod@v0.39.0"
  ]
}

package main

import (
	"errors"
	"fmt"
	"os"

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

func main() {
	// 1. module.Check returns nil for a valid module path and semantic version
	if err := module.Check("example.com/pkg/foo", "v1.2.3"); err != nil {
		fmt.Fprintf(os.Stderr, "Check(example.com/pkg/foo, v1.2.3) failed: %v\n", err)
		os.Exit(1)
	}

	// 2. module.Check returns nil for major version >= 2 when path includes the matching /vN suffix
	if err := module.Check("example.com/pkg/foo/v2", "v2.0.0"); err != nil {
		fmt.Fprintf(os.Stderr, "Check(example.com/pkg/foo/v2, v2.0.0) failed: %v\n", err)
		os.Exit(1)
	}

	// 3. module.Check returns InvalidVersionError when major version >= 2 is used without a matching /vN path suffix
	errV2Mismatch := module.Check("example.com/pkg/foo", "v2.0.0")
	if errV2Mismatch == nil {
		fmt.Fprintf(os.Stderr, "Check(example.com/pkg/foo, v2.0.0) expected error, got nil\n")
		os.Exit(1)
	}
	var verErr *module.InvalidVersionError
	if !errors.As(errV2Mismatch, &verErr) {
		fmt.Fprintf(os.Stderr, "Check(example.com/pkg/foo, v2.0.0) expected InvalidVersionError, got %T (%v)\n", errV2Mismatch, errV2Mismatch)
		os.Exit(1)
	}

	// 4. module.Check returns InvalidVersionError when version string is not a semantic version
	errNotSemver := module.Check("example.com/pkg/foo", "1.2.3")
	if errNotSemver == nil {
		fmt.Fprintf(os.Stderr, "Check(example.com/pkg/foo, 1.2.3) expected error, got nil\n")
		os.Exit(1)
	}
	if !errors.As(errNotSemver, &verErr) {
		fmt.Fprintf(os.Stderr, "Check(example.com/pkg/foo, 1.2.3) expected InvalidVersionError, got %T (%v)\n", errNotSemver, errNotSemver)
		os.Exit(1)
	}

	// 5. module.Check returns InvalidPathError when module path contains invalid syntax such as a leading dash
	errLeadingDash := module.Check("-invalid/path", "v1.0.0")
	if errLeadingDash == nil {
		fmt.Fprintf(os.Stderr, "Check(-invalid/path, v1.0.0) expected error, got nil\n")
		os.Exit(1)
	}
	var pathErr *module.InvalidPathError
	if !errors.As(errLeadingDash, &pathErr) {
		fmt.Fprintf(os.Stderr, "Check(-invalid/path, v1.0.0) expected InvalidPathError, got %T (%v)\n", errLeadingDash, errLeadingDash)
		os.Exit(1)
	}

	// 6. module.Check returns InvalidPathError when module path is empty
	errEmptyPath := module.Check("", "v1.0.0")
	if errEmptyPath == nil {
		fmt.Fprintf(os.Stderr, "Check(\"\", v1.0.0) expected error, got nil\n")
		os.Exit(1)
	}
	if !errors.As(errEmptyPath, &pathErr) {
		fmt.Fprintf(os.Stderr, "Check(\"\", v1.0.0) expected InvalidPathError, got %T (%v)\n", errEmptyPath, errEmptyPath)
		os.Exit(1)
	}

	// 7. module.Check returns InvalidPathError when module path contains an invalid /v0 major version suffix
	errV0Path := module.Check("example.com/pkg/foo/v0", "v0.1.0")
	if errV0Path == nil {
		fmt.Fprintf(os.Stderr, "Check(example.com/pkg/foo/v0, v0.1.0) expected error, got nil\n")
		os.Exit(1)
	}
	if !errors.As(errV0Path, &pathErr) {
		fmt.Fprintf(os.Stderr, "Check(example.com/pkg/foo/v0, v0.1.0) expected InvalidPathError, got %T (%v)\n", errV0Path, errV0Path)
		os.Exit(1)
	}

	fmt.Println("All contract assertions passed.")
}