golang.org/x/net v0.41.0: html.ErrorNode

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.ErrorNode in pkg:golang/golang.org/x/net@v0.41.0
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/golang.org/x/net@v0.41.0
Demonstrate these symbols/APIs:
  - golang.org/x/net/html.ErrorNode

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:af5468585d37786007de2d03677e89e93be4d6f2d8a5c81515b030b6b2f8c5f7","contract":["html.ErrorNode is the zero-value NodeType constant equal to uint32(0)","zero-initialized html.Node defaults to Type == html.ErrorNode","explicitly constructed html.Node with Type: html.ErrorNode preserves Type and Data","html.ErrorNode is distinct from TextNode, DocumentNode, ElementNode, CommentNode, DoctypeNode, and RawNode","html.Parse on well-formed HTML yields a node tree containing zero html.ErrorNode nodes","appending an html.ErrorNode child into a tree makes it discoverable by Type == html.ErrorNode"],"goal":"verify golang.org/x/net/html.ErrorNode in pkg:golang/golang.org/x/net@v0.41.0","kind":"HOW","packages":["pkg:golang/golang.org/x/net@v0.41.0"],"schemaVersion":1,"symbols":["golang.org/x/net/html.ErrorNode"]},"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@v0.41.0"],"schemaVersion":1,"subject":"pkg:golang/golang.org/x/net@v0.41.0","symbols":["golang.org/x/net/html.ErrorNode"],"verifierAdapter":"golang@1"}

module sample

go 1.24.0

require golang.org/x/net v0.41.0

golang.org/x/net v0.41.0 h1:vBTly1HeNPEn3wtREYfy4GZ/NECgw2Cnl+nK6Nz3uvw=
golang.org/x/net v0.41.0/go.mod h1:B/K4NNqkfmg07DQYrbwvSluqCJOOXwUjeb/5lOisjbA=

package main

import (
	"fmt"
	"strings"

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

func IsError(n *html.Node) bool {
	return n != nil && n.Type == html.ErrorNode
}

func CollectErrorNodes(root *html.Node) []*html.Node {
	var out []*html.Node
	var visit func(*html.Node)
	visit = func(n *html.Node) {
		if n == nil {
			return
		}
		if n.Type == html.ErrorNode {
			out = append(out, n)
		}
		for c := n.FirstChild; c != nil; c = c.NextSibling {
			visit(c)
		}
	}
	visit(root)
	return out
}

func main() {
	var zeroNode html.Node
	fmt.Printf("Zero-value html.Node is ErrorNode: %v (type=%d)\n", IsError(&zeroNode), zeroNode.Type)

	errNode := &html.Node{
		Type: html.ErrorNode,
		Data: "synthetic html error node",
	}
	fmt.Printf("Explicit ErrorNode: isError=%v data=%q\n", IsError(errNode), errNode.Data)

	doc, err := html.Parse(strings.NewReader("<html><body><p>valid</p></body></html>"))
	if err != nil {
		panic(err)
	}
	fmt.Printf("ErrorNodes in valid parsed HTML: %d\n", len(CollectErrorNodes(doc)))
}

{
  "schemaVersion": 1,
  "goal": "verify golang.org/x/net/html.ErrorNode in pkg:golang/golang.org/x/net@v0.41.0",
  "kind": "HOW",
  "packages": [
    "pkg:golang/golang.org/x/net@v0.41.0"
  ],
  "symbols": [
    "golang.org/x/net/html.ErrorNode"
  ]
}

package main

import (
	"fmt"
	"os"
	"strings"

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

func fail(msg string, args ...any) {
	fmt.Fprintf(os.Stderr, "FAIL: "+msg+"\n", args...)
	os.Exit(1)
}

func main() {
	// 1. html.ErrorNode is the zero-value NodeType constant (uint32(0))
	if html.ErrorNode != html.NodeType(0) || uint32(html.ErrorNode) != 0 {
		fail("expected html.ErrorNode to equal 0, got %v", html.ErrorNode)
	}

	// 2. Zero-initialized html.Node defaults to Type == html.ErrorNode
	var zero html.Node
	if zero.Type != html.ErrorNode {
		fail("expected zero-value html.Node.Type to be html.ErrorNode, got %v", zero.Type)
	}

	// 3. Explicitly constructed html.Node with Type: html.ErrorNode preserves Type and Data
	custom := &html.Node{
		Type: html.ErrorNode,
		Data: "unexpected EOF in token stream",
	}
	if custom.Type != html.ErrorNode {
		fail("expected custom.Type to be html.ErrorNode, got %v", custom.Type)
	}
	if custom.Data != "unexpected EOF in token stream" {
		fail("expected custom.Data to be preserved, got %q", custom.Data)
	}

	// 4. html.ErrorNode is distinct from all other standard html.NodeType constants
	otherTypes := []html.NodeType{
		html.TextNode,
		html.DocumentNode,
		html.ElementNode,
		html.CommentNode,
		html.DoctypeNode,
		html.RawNode,
	}
	for _, nt := range otherTypes {
		if nt == html.ErrorNode {
			fail("expected html.ErrorNode to be distinct from %v", nt)
		}
	}

	// 5. html.Parse on well-formed HTML yields a node tree containing zero html.ErrorNode nodes
	doc, err := html.Parse(strings.NewReader("<!DOCTYPE html><html><head><title>OK</title></head><body><div>Hello</div></body></html>"))
	if err != nil {
		fail("html.Parse failed: %v", err)
	}
	var count int
	var walk func(*html.Node)
	walk = func(n *html.Node) {
		if n.Type == html.ErrorNode {
			count++
		}
		for c := n.FirstChild; c != nil; c = c.NextSibling {
			walk(c)
		}
	}
	walk(doc)
	if count != 0 {
		fail("expected 0 ErrorNode instances in parsed document, got %d", count)
	}

	// 6. Appending an html.ErrorNode child into a tree makes it discoverable by Type == html.ErrorNode
	doc.AppendChild(custom)
	count = 0
	walk(doc)
	if count != 1 {
		fail("expected 1 ErrorNode instance after appending custom ErrorNode, got %d", count)
	}

	fmt.Println("PASS")
}