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

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/module.CheckPathMajor in 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
Demonstrate these symbols/APIs:
  - golang.org/x/mod/module.CheckPathMajor
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:sha256:27b09e8c61489d4bc0ca760ab7f2507781d664535b84357a72664a340b9f2530","contract":["module.CheckPathMajor accepts v0 and v1 versions when path major is empty","module.CheckPathMajor accepts higher major versions when path major is empty if marked +incompatible","module.CheckPathMajor accepts versions matching slash-prefixed major version path","module.CheckPathMajor rejects versions whose major version does not match path major","module.CheckPathMajor accepts gopkg.in dot-prefixed major path versions including unstable suffixes"],"goal":"verify golang.org/x/mod/module.CheckPathMajor in pkg:golang/golang.org/x/mod@v0.39.0","kind":"HOW","packages":["pkg:golang/golang.org/x/mod@v0.39.0"],"schemaVersion":1,"symbols":["golang.org/x/mod/module.CheckPathMajor"]},"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":["golang.org/x/mod/module.CheckPathMajor"],"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"
	"os"

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

func main() {
	cases := []struct {
		version   string
		pathMajor string
	}{
		{"v1.2.3", ""},
		{"v2.0.0", "/v2"},
		{"v2.0.0+incompatible", ""},
		{"v3.1.0", ".v3"},
	}

	for _, c := range cases {
		if err := module.CheckPathMajor(c.version, c.pathMajor); err != nil {
			fmt.Fprintf(os.Stderr, "CheckPathMajor(%q, %q) error: %v\n", c.version, c.pathMajor, err)
			os.Exit(1)
		}
		fmt.Printf("CheckPathMajor(%q, %q) -> valid\n", c.version, c.pathMajor)
	}
}

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

package main

import (
	"fmt"
	"os"

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

func main() {
	if err := runTests(); err != nil {
		fmt.Fprintf(os.Stderr, "Contract test failed: %v\n", err)
		os.Exit(1)
	}
	fmt.Println("All contract assertions passed.")
}

func runTests() error {
	// 1. module.CheckPathMajor accepts v0 and v1 versions when path major is empty
	if err := module.CheckPathMajor("v0.1.0", ""); err != nil {
		return fmt.Errorf("expected CheckPathMajor(v0.1.0, \"\") to accept: %w", err)
	}
	if err := module.CheckPathMajor("v1.5.2", ""); err != nil {
		return fmt.Errorf("expected CheckPathMajor(v1.5.2, \"\") to accept: %w", err)
	}

	// 2. module.CheckPathMajor accepts higher major versions when path major is empty if marked +incompatible
	if err := module.CheckPathMajor("v2.0.0+incompatible", ""); err != nil {
		return fmt.Errorf("expected CheckPathMajor(v2.0.0+incompatible, \"\") to accept: %w", err)
	}

	// 3. module.CheckPathMajor accepts versions matching slash-prefixed major version path
	if err := module.CheckPathMajor("v2.3.1", "/v2"); err != nil {
		return fmt.Errorf("expected CheckPathMajor(v2.3.1, \"/v2\") to accept: %w", err)
	}
	if err := module.CheckPathMajor("v3.0.0", "/v3"); err != nil {
		return fmt.Errorf("expected CheckPathMajor(v3.0.0, \"/v3\") to accept: %w", err)
	}

	// 4. module.CheckPathMajor rejects versions whose major version does not match path major
	if err := module.CheckPathMajor("v2.0.0", ""); err == nil {
		return fmt.Errorf("expected CheckPathMajor(v2.0.0, \"\") to fail, got nil")
	}
	if err := module.CheckPathMajor("v1.0.0", "/v2"); err == nil {
		return fmt.Errorf("expected CheckPathMajor(v1.0.0, \"/v2\") to fail, got nil")
	}
	if err := module.CheckPathMajor("v3.0.0", "/v2"); err == nil {
		return fmt.Errorf("expected CheckPathMajor(v3.0.0, \"/v2\") to fail, got nil")
	}

	// 5. module.CheckPathMajor accepts gopkg.in dot-prefixed major path versions including unstable suffixes
	if err := module.CheckPathMajor("v2.1.0", ".v2"); err != nil {
		return fmt.Errorf("expected CheckPathMajor(v2.1.0, \".v2\") to accept: %w", err)
	}
	if err := module.CheckPathMajor("v3.0.0", ".v3-unstable"); err != nil {
		return fmt.Errorf("expected CheckPathMajor(v3.0.0, \".v3-unstable\") to accept: %w", err)
	}
	if err := module.CheckPathMajor("v0.0.0-20161208181325-20d25e280405", ".v1"); err != nil {
		return fmt.Errorf("expected CheckPathMajor pseudo-version for .v1 to accept: %w", err)
	}

	return nil
}