golang.org/x/text v0.3.2: cases.Fold

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 cases.Fold in pkg:golang/golang.org/x/text@v0.3.2
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/golang.org/x/text@v0.3.2
Demonstrate these symbols/APIs:
  - cases.Fold

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:sha256:600a34f42e6708f0df89f971bb8723762fb08b163173be7688e341ceeb4bc533","contract":["cases.Fold returns a Caser that maps uppercase ASCII characters to lowercase equivalents","cases.Fold folds German sharp S character ß to ss","cases.Fold normalizes Greek letters to their folded lowercase counterparts","cases.Fold Bytes method produces folded byte sequences matching String method results","cases.Fold preserves strings that contain no case distinction or are already lowercase","cases.Fold returns equal folded strings for case-varied representations of the same word"],"goal":"verify cases.Fold in pkg:golang/golang.org/x/text@v0.3.2","kind":"HOW","packages":["pkg:golang/golang.org/x/text@v0.3.2"],"schemaVersion":1,"symbols":["cases.Fold"]},"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/text@v0.3.2"],"schemaVersion":1,"subject":"pkg:golang/golang.org/x/text@v0.3.2","symbols":["cases.Fold"],"verifierAdapter":"golang@1"}

module example.com/sample

go 1.26.6

require golang.org/x/text v0.3.2

golang.org/x/text v0.3.2 h1:tW2bmiBqwgJj/UpqtC8EpXEZVYOwU0yG4iWbprSVAcs=
golang.org/x/text v0.3.2/go.mod h1:bEr9sfX3Q8Zfm5fL9x+3itogRgK3+ptLWKqgva+5dAk=
golang.org/x/tools v0.0.0-20180917221912-90fa682c2a6e/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=

package main

import (
	"fmt"

	"golang.org/x/text/cases"
)

func main() {
	folder := cases.Fold()

	asciiResult := folder.String("HELLO WORLD")
	fmt.Printf("Folded ASCII: %s\n", asciiResult)

	germanResult := folder.String("Straße")
	fmt.Printf("Folded German: %s\n", germanResult)

	greekResult := folder.String("ὈΔΥΣΣΕΎΣ")
	fmt.Printf("Folded Greek: %s\n", greekResult)
}

{
  "schemaVersion": 1,
  "goal": "verify cases.Fold in pkg:golang/golang.org/x/text@v0.3.2",
  "kind": "HOW",
  "packages": [
    "pkg:golang/golang.org/x/text@v0.3.2"
  ],
  "symbols": [
    "cases.Fold"
  ]
}

package main

import (
	"bytes"
	"fmt"
	"os"

	"golang.org/x/text/cases"
)

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 {
	folder := cases.Fold()

	// 1. cases.Fold returns a Caser that maps uppercase ASCII characters to lowercase equivalents
	asciiInput := "HELLO WORLD 123"
	expectedASCII := "hello world 123"
	if got := folder.String(asciiInput); got != expectedASCII {
		return fmt.Errorf("expected folded ASCII %q, got %q", expectedASCII, got)
	}

	// 2. cases.Fold folds German sharp S character ß to ss
	germanInput := "Straße"
	expectedGerman := "strasse"
	if got := folder.String(germanInput); got != expectedGerman {
		return fmt.Errorf("expected folded German %q, got %q", expectedGerman, got)
	}
	if gotUpper := folder.String("STRASSE"); gotUpper != expectedGerman {
		return fmt.Errorf("expected folded STRASSE %q, got %q", expectedGerman, gotUpper)
	}

	// 3. cases.Fold normalizes Greek letters to their folded lowercase counterparts
	greekInput := "ὈΔΥΣΣΕΎΣ"
	foldedGreek := folder.String(greekInput)
	if foldedGreek == "" || foldedGreek == greekInput {
		return fmt.Errorf("expected folded Greek text, got %q", foldedGreek)
	}

	// 4. cases.Fold Bytes method produces folded byte sequences matching String method results
	srcBytes := []byte("GOLANG CASES FOLD")
	expectedBytes := []byte("golang cases fold")
	gotBytes := folder.Bytes(srcBytes)
	if !bytes.Equal(gotBytes, expectedBytes) {
		return fmt.Errorf("expected folded bytes %q, got %q", expectedBytes, gotBytes)
	}
	if string(gotBytes) != folder.String(string(srcBytes)) {
		return fmt.Errorf("folder.Bytes result %q does not match folder.String %q", gotBytes, folder.String(string(srcBytes)))
	}

	// 5. cases.Fold preserves strings that contain no case distinction or are already lowercase
	stableInput := "already folded text 12345 !@#"
	if got := folder.String(stableInput); got != stableInput {
		return fmt.Errorf("expected preserved text %q, got %q", stableInput, got)
	}

	// 6. cases.Fold returns equal folded strings for case-varied representations of the same word
	v1 := folder.String("MicroSoft")
	v2 := folder.String("MICROSOFT")
	v3 := folder.String("microsoft")
	if v1 != v2 || v2 != v3 {
		return fmt.Errorf("expected case folding equality across variants, got %q, %q, %q", v1, v2, v3)
	}

	return nil
}