github.com/rogpeppe/go-internal v1.3.0: semver.Major

# semver.Major verification

This sample verifies `github.com/rogpeppe/go-internal/semver.Major` in `pkg:golang/github.com/rogpeppe/go-internal@v1.3.0`.

## Verified Behaviors

1. `semver.Major` returns the major version prefix with leading 'v' for standard semantic versions.
2. `semver.Major` returns the major version prefix for prerelease and build metadata versions.
3. `semver.Major` supports shorthand version strings without minor or patch numbers.
4. `semver.Major` returns an empty string for invalid semantic versions or versions lacking the leading 'v' prefix.

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 github.com/rogpeppe/go-internal/semver.Major in pkg:golang/github.com/rogpeppe/go-internal@v1.3.0
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/github.com/rogpeppe/go-internal@v1.3.0
Demonstrate these symbols/APIs:
  - github.com/rogpeppe/go-internal/semver.Major

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:ab2d82f2e9d07e4b8072ae6109f914f04d4a9cf638a000c9648979d587221e62","contract":["semver.Major returns the major version prefix with leading 'v' for standard semantic versions.","semver.Major returns the major version prefix for prerelease and build metadata versions.","semver.Major supports shorthand version strings without minor or patch numbers.","semver.Major returns an empty string for invalid semantic versions or versions lacking the leading 'v' prefix."],"goal":"verify github.com/rogpeppe/go-internal/semver.Major in pkg:golang/github.com/rogpeppe/go-internal@v1.3.0","kind":"HOW","packages":["pkg:golang/github.com/rogpeppe/go-internal@v1.3.0"],"schemaVersion":1,"symbols":["github.com/rogpeppe/go-internal/semver.Major"]},"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/github.com/rogpeppe/go-internal@v1.3.0"],"schemaVersion":1,"subject":"pkg:golang/github.com/rogpeppe/go-internal@v1.3.0","symbols":["github.com/rogpeppe/go-internal/semver.Major"],"verifierAdapter":"golang@1"}

module example.com/sample

go 1.26.6

require github.com/rogpeppe/go-internal v1.3.0

github.com/kr/pretty v0.1.0/go.mod h1:dAy3ld7l9f0ibDNOQOHHMYYIIbhfbHSm3C4ZsoJORNo=
github.com/kr/pty v1.1.1/go.mod h1:pFQYn66WHrOpPYNljwOMqo10TkYh1fy3cYio2l3bCsQ=
github.com/kr/text v0.1.0/go.mod h1:4Jbv+DJW3UT/LiOwJeYQe1efqtUx/iVham/4vfdArNI=
github.com/rogpeppe/go-internal v1.3.0 h1:RR9dF3JtopPvtkroDZuVD7qquD0bnHlKSqaQhgwt8yk=
github.com/rogpeppe/go-internal v1.3.0/go.mod h1:M8bDsm7K2OlrFYOpmOWEs/qY81heoFRclV5y23lUDJ4=
gopkg.in/check.v1 v1.0.0-20180628173108-788fd7840127/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
gopkg.in/errgo.v2 v2.1.0/go.mod h1:hNsd1EY+bozCKY1Ytp96fpM3vjJbqLJn88ws8XvfDNI=

package main

import (
	"fmt"

	"github.com/rogpeppe/go-internal/semver"
)

func main() {
	versions := []string{
		"v1.2.3",
		"v2.0.0-alpha.1",
		"v3.4.0+build123",
		"v4",
		"invalid-version",
	}

	for _, v := range versions {
		major := semver.Major(v)
		if major == "" {
			fmt.Printf("%s -> (invalid semantic version)\n", v)
		} else {
			fmt.Printf("%s -> major: %s\n", v, major)
		}
	}
}

{
  "schemaVersion": 1,
  "goal": "verify github.com/rogpeppe/go-internal/semver.Major in pkg:golang/github.com/rogpeppe/go-internal@v1.3.0",
  "kind": "HOW",
  "packages": [
    "pkg:golang/github.com/rogpeppe/go-internal@v1.3.0"
  ],
  "symbols": [
    "github.com/rogpeppe/go-internal/semver.Major"
  ]
}

package main

import (
	"fmt"
	"os"

	"github.com/rogpeppe/go-internal/semver"
)

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. semver.Major returns the major version prefix with leading 'v' for standard semantic versions.
	standardCases := []struct {
		input string
		want  string
	}{
		{"v1.2.3", "v1"},
		{"v2.0.0", "v2"},
		{"v0.1.2", "v0"},
		{"v10.20.30", "v10"},
	}
	for _, tc := range standardCases {
		got := semver.Major(tc.input)
		if got != tc.want {
			return fmt.Errorf("standard version mismatch for %q: expected %q, got %q", tc.input, tc.want, got)
		}
	}

	// 2. semver.Major returns the major version prefix for prerelease and build metadata versions.
	prereleaseCases := []struct {
		input string
		want  string
	}{
		{"v1.5.0-alpha.1", "v1"},
		{"v2.1.0-beta.1", "v2"},
		{"v3.2.1+build100", "v3"},
		{"v0.9.0-rc.2", "v0"},
	}
	for _, tc := range prereleaseCases {
		got := semver.Major(tc.input)
		if got != tc.want {
			return fmt.Errorf("prerelease/build metadata mismatch for %q: expected %q, got %q", tc.input, tc.want, got)
		}
	}

	// 3. semver.Major supports shorthand version strings without minor or patch numbers.
	shorthandCases := []struct {
		input string
		want  string
	}{
		{"v1", "v1"},
		{"v2.1", "v2"},
		{"v0", "v0"},
	}
	for _, tc := range shorthandCases {
		got := semver.Major(tc.input)
		if got != tc.want {
			return fmt.Errorf("shorthand version mismatch for %q: expected %q, got %q", tc.input, tc.want, got)
		}
	}

	// 4. semver.Major returns an empty string for invalid semantic versions or versions lacking the leading 'v' prefix.
	invalidCases := []string{
		"1.2.3",
		"2.0",
		"v",
		"v-alpha",
		"v01.2.3",
		"not-a-version",
		"",
	}
	for _, input := range invalidCases {
		got := semver.Major(input)
		if got != "" {
			return fmt.Errorf("invalid version %q expected empty string, got %q", input, got)
		}
	}

	return nil
}