golang.org/x/exp v0.0.0-20260824195058-e88cd73687aa: ebnf.Parse, ebnf.Verify

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 pkg:golang/golang.org/x/exp@v0.0.0-20260824195058-e88cd73687aa
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/golang.org/x/exp@v0.0.0-20260824195058-e88cd73687aa
Demonstrate these symbols/APIs:
  - golang.org/x/exp/ebnf.Parse
  - golang.org/x/exp/ebnf.Verify

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:d615afb4505c08efd84c41a39fb24a72ddf570aa8298cc0f6c34690a05514aca","contract":["ebnf.Parse parses valid EBNF grammar productions into a Grammar map","ebnf.Verify validates that all referenced productions are defined from the start production","ebnf.Parse reports an error when grammar syntax is malformed","ebnf.Verify reports an error when an undefined production name is referenced"],"goal":"verify pkg:golang/golang.org/x/exp@v0.0.0-20260824195058-e88cd73687aa","kind":"HOW","packages":["pkg:golang/golang.org/x/exp@v0.0.0-20260824195058-e88cd73687aa"],"schemaVersion":1,"symbols":["golang.org/x/exp/ebnf.Parse","golang.org/x/exp/ebnf.Verify"]},"contractCommand":["go","run","./test"],"environment":{"arch":"x64","distro":"ubuntu","ecosystem":"golang","language":"go","libc":"glibc","libcVersion":"2.39","os":"linux","osVersionBucket":"24","packageManager":"go","schemaVersion":1},"license":"MIT-0","packages":["pkg:golang/golang.org/x/exp@v0.0.0-20260824195058-e88cd73687aa"],"schemaVersion":1,"subject":"pkg:golang/golang.org/x/exp@v0.0.0-20260824195058-e88cd73687aa","symbols":["golang.org/x/exp/ebnf.Parse","golang.org/x/exp/ebnf.Verify"],"verifierAdapter":"golang@1"}

package ebnfsample

import (
	"bytes"
	"io"

	"golang.org/x/exp/ebnf"
)

// ParseGrammar parses EBNF grammar text from an io.Reader.
func ParseGrammar(filename string, r io.Reader) (ebnf.Grammar, error) {
	return ebnf.Parse(filename, r)
}

// VerifyGrammar verifies that all productions reachable from start are defined.
func VerifyGrammar(g ebnf.Grammar, start string) error {
	return ebnf.Verify(g, start)
}

// ParseAndVerify combines parsing and verification of EBNF grammar source.
func ParseAndVerify(filename, src, start string) (ebnf.Grammar, error) {
	g, err := ebnf.Parse(filename, bytes.NewBufferString(src))
	if err != nil {
		return nil, err
	}
	if err := ebnf.Verify(g, start); err != nil {
		return nil, err
	}
	return g, nil
}

module example.com/ebnfsample

go 1.26.0

require golang.org/x/exp v0.0.0-20260824195058-e88cd73687aa

golang.org/x/exp v0.0.0-20260824195058-e88cd73687aa h1:QSyA8ishJCyT21kER9KwNt0b7BM3iRK4x9QXhjN5Fdk=
golang.org/x/exp v0.0.0-20260824195058-e88cd73687aa/go.mod h1:zeBbvyFKDaLwa7CH/zI8KXt7gTl14SF7sO08Pl5jBCM=

{
  "schemaVersion": 1,
  "goal": "verify pkg:golang/golang.org/x/exp@v0.0.0-20260824195058-e88cd73687aa",
  "kind": "HOW",
  "packages": [
    "pkg:golang/golang.org/x/exp@v0.0.0-20260824195058-e88cd73687aa"
  ],
  "symbols": [
    "golang.org/x/exp/ebnf.Parse",
    "golang.org/x/exp/ebnf.Verify"
  ]
}

package main

import (
	"bytes"
	"fmt"
	"os"

	"example.com/ebnfsample"
	"golang.org/x/exp/ebnf"
)

func main() {
	validGrammar := `
Program = Statement { ";" Statement } .
Statement = Assign | Print .
Assign = identifier "=" Expression .
Print = "print" Expression .
Expression = Term { ("+" | "-") Term } .
Term = Factor { ("*" | "/") Factor } .
Factor = identifier | number | "(" Expression ")" .
identifier = "a" … "z" .
number = "0" … "9" .
`

	// 1. ebnf.Parse parses valid EBNF grammar productions into a Grammar map
	g, err := ebnf.Parse("calc.ebnf", bytes.NewBufferString(validGrammar))
	if err != nil {
		fmt.Fprintf(os.Stderr, "FAIL: ebnf.Parse valid grammar failed: %v\n", err)
		os.Exit(1)
	}
	if len(g) != 9 {
		fmt.Fprintf(os.Stderr, "FAIL: ebnf.Parse got %d productions, want 9\n", len(g))
		os.Exit(1)
	}
	if _, ok := g["Program"]; !ok {
		fmt.Fprintf(os.Stderr, "FAIL: missing 'Program' production in grammar map\n")
		os.Exit(1)
	}

	// 2. ebnf.Verify validates that all referenced productions are defined from the start production
	if err := ebnf.Verify(g, "Program"); err != nil {
		fmt.Fprintf(os.Stderr, "FAIL: ebnf.Verify failed for valid grammar: %v\n", err)
		os.Exit(1)
	}

	// Also verify via helper function
	gHelper, err := ebnfsample.ParseAndVerify("calc.ebnf", validGrammar, "Program")
	if err != nil || gHelper == nil {
		fmt.Fprintf(os.Stderr, "FAIL: ParseAndVerify helper failed: %v\n", err)
		os.Exit(1)
	}

	// 3. ebnf.Parse reports an error when grammar syntax is malformed
	invalidSrc := `Program = | .`
	if _, err := ebnf.Parse("invalid.ebnf", bytes.NewBufferString(invalidSrc)); err == nil {
		fmt.Fprintf(os.Stderr, "FAIL: ebnf.Parse expected error for malformed grammar, got nil\n")
		os.Exit(1)
	}

	// 4. ebnf.Verify reports an error when an undefined production name is referenced
	undefinedRefSrc := `Root = MissingProduction .`
	gUndef, err := ebnf.Parse("undefined.ebnf", bytes.NewBufferString(undefinedRefSrc))
	if err != nil {
		fmt.Fprintf(os.Stderr, "FAIL: unexpected Parse error for undefined ref: %v\n", err)
		os.Exit(1)
	}
	if err := ebnf.Verify(gUndef, "Root"); err == nil {
		fmt.Fprintf(os.Stderr, "FAIL: ebnf.Verify expected error for undefined production, got nil\n")
		os.Exit(1)
	}

	fmt.Println("PASS: golang.org/x/exp/ebnf contract verified")
}