golang.org/x/net v0.61.0: atom.H2

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 golang.org/x/net/html/atom.H2 in pkg:golang/golang.org/x/net@v0.61.0
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/golang.org/x/net@v0.61.0
Demonstrate these symbols/APIs:
  - golang.org/x/net/html/atom.H2

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:a6ab89dc549c695fa4ae41b27bc763834b1b989b8e6639c11a95d95b5c88b568","contract":["atom.H2 is a non-zero Atom constant whose String() method returns \"h2\"","atom.Lookup on byte slice \"h2\" returns atom.H2","atom.String on byte slice \"h2\" returns \"h2\"","atom.H2 is distinct from other heading atoms such as atom.H1 and atom.H3","html.Parse on HTML containing \u003ch2\u003e tag yields an ElementNode with DataAtom equal to atom.H2","explicitly created html.Node with DataAtom atom.H2 and Data \"h2\" renders as an \u003ch2\u003e element"],"goal":"verify golang.org/x/net/html/atom.H2 in pkg:golang/golang.org/x/net@v0.61.0","kind":"HOW","packages":["pkg:golang/golang.org/x/net@v0.61.0"],"schemaVersion":1,"symbols":["golang.org/x/net/html/atom.H2"]},"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/net@v0.61.0"],"schemaVersion":1,"subject":"pkg:golang/golang.org/x/net@v0.61.0","symbols":["golang.org/x/net/html/atom.H2"],"verifierAdapter":"golang@1"}

module sample

go 1.26.0

require golang.org/x/net v0.61.0

golang.org/x/net v0.61.0 h1:RR+6j/BTBCrggOLugxa+66R8FvoN6MHlzDlZIbN9YFw=
golang.org/x/net v0.61.0/go.mod h1:WgDCOTH8iwtB66T4/GfI94AHo/hhdb7Hah9NDseQfiI=

package main

import (
	"bytes"
	"fmt"
	"strings"

	"golang.org/x/net/html"
	"golang.org/x/net/html/atom"
)

// IsH2Element reports whether n is an HTML <h2> element.
func IsH2Element(n *html.Node) bool {
	return n != nil && n.Type == html.ElementNode && n.DataAtom == atom.H2
}

// CreateH2Element constructs a new <h2> DOM element containing text.
func CreateH2Element(text string) *html.Node {
	h2 := &html.Node{
		Type:     html.ElementNode,
		DataAtom: atom.H2,
		Data:     atom.H2.String(),
	}
	if text != "" {
		h2.AppendChild(&html.Node{
			Type: html.TextNode,
			Data: text,
		})
	}
	return h2
}

// FindFirstH2 searches the node tree for the first <h2> element.
func FindFirstH2(n *html.Node) *html.Node {
	if IsH2Element(n) {
		return n
	}
	for c := n.FirstChild; c != nil; c = c.NextSibling {
		if found := FindFirstH2(c); found != nil {
			return found
		}
	}
	return nil
}

func main() {
	// Demonstrating atom.H2 constant and string representation
	fmt.Printf("atom.H2 integer value: %d, string: %q\n", atom.H2, atom.H2.String())

	// Resolving atom from byte slice
	resolved := atom.Lookup([]byte("h2"))
	fmt.Printf("Lookup(\"h2\"): %d (matches atom.H2: %t)\n", resolved, resolved == atom.H2)

	// Creating an explicit <h2> element using atom.H2
	node := CreateH2Element("Sample Section Heading")
	var buf bytes.Buffer
	if err := html.Render(&buf, node); err != nil {
		panic(err)
	}
	fmt.Printf("Rendered element: %s\n", buf.String())

	// Parsing HTML document and identifying <h2> by DataAtom
	doc, err := html.Parse(strings.NewReader("<html><body><h2>Section Subtitle</h2></body></html>"))
	if err != nil {
		panic(err)
	}
	found := FindFirstH2(doc)
	if found != nil {
		fmt.Printf("Found <h2> in parsed document with DataAtom == atom.H2\n")
	}
}

{
  "schemaVersion": 1,
  "goal": "verify golang.org/x/net/html/atom.H2 in pkg:golang/golang.org/x/net@v0.61.0",
  "kind": "HOW",
  "packages": [
    "pkg:golang/golang.org/x/net@v0.61.0"
  ],
  "symbols": [
    "golang.org/x/net/html/atom.H2"
  ]
}

package main

import (
	"bytes"
	"fmt"
	"os"
	"strings"

	"golang.org/x/net/html"
	"golang.org/x/net/html/atom"
)

func main() {
	// 1. atom.H2 is a non-zero Atom constant whose String() method returns "h2"
	{
		if atom.H2 == 0 {
			fmt.Fprintf(os.Stderr, "FAIL: expected atom.H2 to be non-zero, got 0\n")
			os.Exit(1)
		}
		if atom.H2.String() != "h2" {
			fmt.Fprintf(os.Stderr, "FAIL: expected atom.H2.String() to be \"h2\", got %q\n", atom.H2.String())
			os.Exit(1)
		}
	}

	// 2. atom.Lookup on byte slice "h2" returns atom.H2
	{
		lookupResult := atom.Lookup([]byte("h2"))
		if lookupResult != atom.H2 {
			fmt.Fprintf(os.Stderr, "FAIL: expected atom.Lookup([]byte(\"h2\")) to be atom.H2, got %v\n", lookupResult)
			os.Exit(1)
		}
	}

	// 3. atom.String on byte slice "h2" returns "h2"
	{
		strResult := atom.String([]byte("h2"))
		if strResult != "h2" {
			fmt.Fprintf(os.Stderr, "FAIL: expected atom.String([]byte(\"h2\")) to be \"h2\", got %q\n", strResult)
			os.Exit(1)
		}
	}

	// 4. atom.H2 is distinct from other heading atoms such as atom.H1 and atom.H3
	{
		otherHeadings := []struct {
			name string
			a    atom.Atom
		}{
			{"H1", atom.H1},
			{"H3", atom.H3},
			{"H4", atom.H4},
			{"H5", atom.H5},
			{"H6", atom.H6},
		}
		for _, oh := range otherHeadings {
			if atom.H2 == oh.a {
				fmt.Fprintf(os.Stderr, "FAIL: atom.H2 unexpectedly matches atom.%s\n", oh.name)
				os.Exit(1)
			}
		}
	}

	// 5. html.Parse on HTML containing <h2> tag yields an ElementNode with DataAtom equal to atom.H2
	{
		doc, err := html.Parse(strings.NewReader("<!DOCTYPE html><html><body><h2>Subheading</h2></body></html>"))
		if err != nil {
			fmt.Fprintf(os.Stderr, "FAIL: html.Parse failed: %v\n", err)
			os.Exit(1)
		}

		var h2Node *html.Node
		var walk func(*html.Node)
		walk = func(n *html.Node) {
			if n.Type == html.ElementNode && n.DataAtom == atom.H2 {
				h2Node = n
				return
			}
			for c := n.FirstChild; c != nil; c = c.NextSibling {
				walk(c)
			}
		}
		walk(doc)

		if h2Node == nil {
			fmt.Fprintf(os.Stderr, "FAIL: expected to find node with DataAtom == atom.H2 in parsed document\n")
			os.Exit(1)
		}
		if h2Node.Data != "h2" {
			fmt.Fprintf(os.Stderr, "FAIL: expected h2Node.Data to be \"h2\", got %q\n", h2Node.Data)
			os.Exit(1)
		}
	}

	// 6. explicitly created html.Node with DataAtom atom.H2 and Data "h2" renders as an <h2> element
	{
		node := &html.Node{
			Type:     html.ElementNode,
			DataAtom: atom.H2,
			Data:     atom.H2.String(),
		}
		node.AppendChild(&html.Node{
			Type: html.TextNode,
			Data: "Contract Subheading",
		})

		var buf bytes.Buffer
		if err := html.Render(&buf, node); err != nil {
			fmt.Fprintf(os.Stderr, "FAIL: html.Render failed: %v\n", err)
			os.Exit(1)
		}
		expected := "<h2>Contract Subheading</h2>"
		if buf.String() != expected {
			fmt.Fprintf(os.Stderr, "FAIL: expected rendered output %q, got %q\n", expected, buf.String())
			os.Exit(1)
		}
	}

	fmt.Println("PASS: all contract assertions passed")
}