github.com/ianlancetaylor/demangle v0.0.0-20250417193237-f615e6bd150b: AST

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/ianlancetaylor/demangle.AST in pkg:golang/github.com/ianlancetaylor/demangle@v0.0.0-20250417193237-f615e6bd150b
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/github.com/ianlancetaylor/demangle@v0.0.0-20250417193237-f615e6bd150b
Demonstrate these symbols/APIs:
  - github.com/ianlancetaylor/demangle.AST

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:sha256:380ddb769d7026148c0e946ac0feb370b533a839c217812bd0bead23c1742d7c","contract":["demangle.ToAST parses a valid C++ mangled symbol into an AST representation","demangle.ToAST returns an error for invalid mangled symbol names","demangle.AST Traverse visits all nodes within the AST tree","demangle.AST GoString produces a formatted debug representation of the tree","demangle.AST Copy transforms the AST tree using copy and skip functions","demangle.ASTToString formats an AST with options such as NoTemplateParams"],"goal":"verify github.com/ianlancetaylor/demangle.AST in pkg:golang/github.com/ianlancetaylor/demangle@v0.0.0-20250417193237-f615e6bd150b","kind":"HOW","packages":["pkg:golang/github.com/ianlancetaylor/demangle@v0.0.0-20250417193237-f615e6bd150b"],"schemaVersion":1,"symbols":["github.com/ianlancetaylor/demangle.AST"]},"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/ianlancetaylor/demangle@v0.0.0-20250417193237-f615e6bd150b"],"schemaVersion":1,"subject":"pkg:golang/github.com/ianlancetaylor/demangle@v0.0.0-20250417193237-f615e6bd150b","symbols":["github.com/ianlancetaylor/demangle.AST"],"verifierAdapter":"golang@1"}

module sample

go 1.24

require github.com/ianlancetaylor/demangle v0.0.0-20250417193237-f615e6bd150b

github.com/ianlancetaylor/demangle v0.0.0-20250417193237-f615e6bd150b h1:ogbOPx86mIhFy764gGkqnkFC8m5PJA7sPzlk9ppLVQA=
github.com/ianlancetaylor/demangle v0.0.0-20250417193237-f615e6bd150b/go.mod h1:gx7rwoVhcfuVKG5uya9Hs3Sxj7EIvldVofAWIUtGouw=

package main

import (
	"fmt"

	"github.com/ianlancetaylor/demangle"
)

func main() {
	mangled := "_Z3fooi"
	ast, err := demangle.ToAST(mangled)
	if err != nil {
		fmt.Printf("Failed to parse mangled symbol %s: %v\n", mangled, err)
		return
	}

	fmt.Printf("Demangled symbol: %s\n", demangle.ASTToString(ast))
	fmt.Printf("AST debug representation:\n%s\n", ast.GoString())
}

{
  "schemaVersion": 1,
  "goal": "verify github.com/ianlancetaylor/demangle.AST in pkg:golang/github.com/ianlancetaylor/demangle@v0.0.0-20250417193237-f615e6bd150b",
  "kind": "HOW",
  "packages": [
    "pkg:golang/github.com/ianlancetaylor/demangle@v0.0.0-20250417193237-f615e6bd150b"
  ],
  "symbols": [
    "github.com/ianlancetaylor/demangle.AST"
  ]
}

package main

import (
	"fmt"
	"os"
	"strings"

	"github.com/ianlancetaylor/demangle"
)

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

func runTests() error {
	// 1. demangle.ToAST parses a valid C++ mangled symbol into an AST representation
	{
		ast, err := demangle.ToAST("_Z3fooi")
		if err != nil {
			return fmt.Errorf("test 1 (parse valid symbol) failed: %w", err)
		}
		if ast == nil {
			return fmt.Errorf("test 1: expected non-nil AST")
		}
		str := demangle.ASTToString(ast)
		if str != "foo(int)" {
			return fmt.Errorf("test 1: expected 'foo(int)', got %q", str)
		}
	}

	// 2. demangle.ToAST returns an error for invalid mangled symbol names
	{
		_, err := demangle.ToAST("not_a_mangled_name")
		if err == nil {
			return fmt.Errorf("test 2: expected error for invalid mangled symbol, got nil")
		}
	}

	// 3. demangle.AST Traverse visits all nodes within the AST tree
	{
		ast, err := demangle.ToAST("_Z3barPKc")
		if err != nil {
			return fmt.Errorf("test 3 (ToAST) failed: %w", err)
		}
		var visitedCount int
		ast.Traverse(func(a demangle.AST) bool {
			visitedCount++
			return true
		})
		if visitedCount == 0 {
			return fmt.Errorf("test 3: expected AST Traverse to visit at least one node, visited %d", visitedCount)
		}
	}

	// 4. demangle.AST GoString produces a formatted debug representation of the tree
	{
		ast, err := demangle.ToAST("_Z3fooi")
		if err != nil {
			return fmt.Errorf("test 4 (ToAST) failed: %w", err)
		}
		goStr := ast.GoString()
		if len(goStr) == 0 {
			return fmt.Errorf("test 4: expected non-empty GoString output")
		}
		if !strings.Contains(goStr, "foo") {
			return fmt.Errorf("test 4: expected GoString to contain symbol name 'foo', got %q", goStr)
		}
	}

	// 5. demangle.AST Copy transforms the AST tree using copy and skip functions
	{
		ast, err := demangle.ToAST("_Z3fooi")
		if err != nil {
			return fmt.Errorf("test 5 (ToAST) failed: %w", err)
		}
		transformed := ast.Copy(func(a demangle.AST) demangle.AST {
			if n, ok := a.(*demangle.Name); ok && n.Name == "foo" {
				return &demangle.Name{Name: "bar"}
			}
			return nil
		}, func(a demangle.AST) bool {
			return false
		})
		if transformed == nil {
			return fmt.Errorf("test 5: expected non-nil transformed AST")
		}
		transformedStr := demangle.ASTToString(transformed)
		if transformedStr != "bar(int)" {
			return fmt.Errorf("test 5: expected transformed AST to format as 'bar(int)', got %q", transformedStr)
		}

		skipped := ast.Copy(func(a demangle.AST) demangle.AST {
			return nil
		}, func(a demangle.AST) bool {
			return true
		})
		if skipped != nil {
			return fmt.Errorf("test 5: expected nil AST when skip returns true for root, got %v", skipped)
		}
	}

	// 6. demangle.ASTToString formats an AST with options such as NoTemplateParams
	{
		ast, err := demangle.ToAST("_Z3fooIiEvv")
		if err != nil {
			return fmt.Errorf("test 6 (ToAST) failed: %w", err)
		}
		fullStr := demangle.ASTToString(ast)
		if !strings.Contains(fullStr, "<int>") {
			return fmt.Errorf("test 6: expected full demangled string to contain '<int>', got %q", fullStr)
		}
		noTParamsStr := demangle.ASTToString(ast, demangle.NoTemplateParams)
		if strings.Contains(noTParamsStr, "<int>") {
			return fmt.Errorf("test 6: expected '<int>' to be omitted with NoTemplateParams, got %q", noTParamsStr)
		}
	}

	return nil
}