github.com/pmezard/go-difflib v1.0.0: difflib.GetUnifiedDiffString

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/pmezard/go-difflib/difflib.GetUnifiedDiffString in pkg:golang/github.com/pmezard/go-difflib@v1.0.0
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/github.com/pmezard/go-difflib@v1.0.0
Demonstrate these symbols/APIs:
  - github.com/pmezard/go-difflib/difflib.GetUnifiedDiffString
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:acba9058baf2fb88b0d5018de726acb8001303c10d3143bb7c2a10900788d44f","contract":["ComputeUnifiedDiff returns empty diff for identical inputs","ComputeUnifiedDiff generates unified diff string with file headers and hunk markers","difflib.GetUnifiedDiffString produces expected unified diff from UnifiedDiff struct"],"goal":"verify github.com/pmezard/go-difflib/difflib.GetUnifiedDiffString in pkg:golang/github.com/pmezard/go-difflib@v1.0.0","kind":"HOW","packages":["pkg:golang/github.com/pmezard/go-difflib@v1.0.0"],"schemaVersion":1,"symbols":["github.com/pmezard/go-difflib/difflib.GetUnifiedDiffString"]},"contractCommand":["go","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/pmezard/go-difflib@v1.0.0"],"schemaVersion":1,"subject":"pkg:golang/github.com/pmezard/go-difflib@v1.0.0","symbols":["github.com/pmezard/go-difflib/difflib.GetUnifiedDiffString"],"verifierAdapter":"golang@1"}

package sample

import (
	"github.com/pmezard/go-difflib/difflib"
)

// ComputeUnifiedDiff calculates the unified diff string between original and modified text.
func ComputeUnifiedDiff(fromFile, toFile, textA, textB string, context int) (string, error) {
	diff := difflib.UnifiedDiff{
		A:        difflib.SplitLines(textA),
		B:        difflib.SplitLines(textB),
		FromFile: fromFile,
		ToFile:   toFile,
		Context:  context,
	}
	return difflib.GetUnifiedDiffString(diff)
}

module sample

go 1.20

require github.com/pmezard/go-difflib v1.0.0

github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=

{
  "schemaVersion": 1,
  "goal": "verify github.com/pmezard/go-difflib/difflib.GetUnifiedDiffString in pkg:golang/github.com/pmezard/go-difflib@v1.0.0",
  "kind": "HOW",
  "packages": [
    "pkg:golang/github.com/pmezard/go-difflib@v1.0.0"
  ],
  "symbols": [
    "github.com/pmezard/go-difflib/difflib.GetUnifiedDiffString"
  ],
  "constraints": {
    "executionContext": "node"
  },
  "runtimeConditions": {
    "ecosystem": "npm",
    "language": "javascript",
    "moduleSystem": "cjs",
    "packageManager": "npm@10.9.8",
    "runtime": "node@22.23.2"
  }
}

package test

import (
	"strings"
	"testing"

	"github.com/pmezard/go-difflib/difflib"
	"sample"
)

func TestContract_IdenticalInputs(t *testing.T) {
	text := "apple\nbanana\ncherry\n"
	diff, err := sample.ComputeUnifiedDiff("file_a.txt", "file_b.txt", text, text, 3)
	if err != nil {
		t.Fatalf("unexpected error: %v", err)
	}
	if diff != "" {
		t.Fatalf("expected empty diff, got: %q", diff)
	}
}

func TestContract_ModifiedInputs(t *testing.T) {
	textA := "apple\nbanana\ncherry\n"
	textB := "apple\nblueberry\ncherry\n"
	diff, err := sample.ComputeUnifiedDiff("file_a.txt", "file_b.txt", textA, textB, 1)
	if err != nil {
		t.Fatalf("unexpected error: %v", err)
	}
	if !strings.Contains(diff, "--- file_a.txt") {
		t.Errorf("expected header '--- file_a.txt', got: %s", diff)
	}
	if !strings.Contains(diff, "+++ file_b.txt") {
		t.Errorf("expected header '+++ file_b.txt', got: %s", diff)
	}
	if !strings.Contains(diff, "-banana") {
		t.Errorf("expected deleted line '-banana', got: %s", diff)
	}
	if !strings.Contains(diff, "+blueberry") {
		t.Errorf("expected added line '+blueberry', got: %s", diff)
	}
}

func TestContract_DirectGetUnifiedDiffString(t *testing.T) {
	ud := difflib.UnifiedDiff{
		A:        difflib.SplitLines("line one\nline two\n"),
		B:        difflib.SplitLines("line one\nline changed\n"),
		FromFile: "original.txt",
		ToFile:   "modified.txt",
		Context:  0,
	}
	result, err := difflib.GetUnifiedDiffString(ud)
	if err != nil {
		t.Fatalf("unexpected error: %v", err)
	}
	if !strings.Contains(result, "--- original.txt") || !strings.Contains(result, "+++ modified.txt") {
		t.Fatalf("missing headers: %s", result)
	}
	if !strings.Contains(result, "-line two") || !strings.Contains(result, "+line changed") {
		t.Fatalf("missing diff content: %s", result)
	}
}