github.com/russross/blackfriday/v2 v2.1.0: Heading

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/russross/blackfriday/v2.Heading in pkg:golang/github.com/russross/blackfriday/v2@v2.1.0
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/github.com/russross/blackfriday/v2@v2.1.0
Demonstrate these symbols/APIs:
  - github.com/russross/blackfriday/v2.Heading
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:sha256:339e1c55510d99dce46b37555d0ef73f884aaa03698736cdc75bd00b7d7851b3","constraints":{"executionContext":"go"},"contract":["blackfriday.Heading identifies heading AST nodes parsed from ATX and setext Markdown headers.","blackfriday.Heading nodes carry HeadingData with Level corresponding to the header depth (1-6).","blackfriday.Heading nodes can be traversed with Node.Walk with entering true and false states.","blackfriday.Heading nodes populate HeadingID in HeadingData when AutoHeadingIDs or HeadingIDs extensions are enabled.","blackfriday.NewNode with blackfriday.Heading creates an AST node of Type Heading with configurable HeadingData."],"goal":"verify github.com/russross/blackfriday/v2.Heading in pkg:golang/github.com/russross/blackfriday/v2@v2.1.0","kind":"HOW","packages":["pkg:golang/github.com/russross/blackfriday/v2@v2.1.0"],"schemaVersion":1,"symbols":["github.com/russross/blackfriday/v2.Heading"]},"contractCommand":["go","test","./..."],"environment":{"arch":"x64","distro":"ubuntu","ecosystem":"golang","executionContext":"go","language":"go","libc":"glibc","libcVersion":"2.39","os":"linux","osVersionBucket":"24","packageManager":"go","runtime":"go","schemaVersion":1},"license":"MIT-0","packages":["pkg:golang/github.com/russross/blackfriday/v2@v2.1.0"],"schemaVersion":1,"subject":"pkg:golang/github.com/russross/blackfriday/v2@v2.1.0","symbols":["github.com/russross/blackfriday/v2.Heading"],"verifierAdapter":"golang@1"}

module example.com/heading

go 1.26.6

require github.com/russross/blackfriday/v2 v2.1.0

github.com/russross/blackfriday/v2 v2.1.0 h1:JIOH55/0cWyOuilr9/qlrm0BSXldqnqwMsf35Ld67mk=
github.com/russross/blackfriday/v2 v2.1.0/go.mod h1:+Rmxgy9KzJVeS9/2gXHxylqXiyQDYRxCVz55jmeOWTM=

package main

import (
	"fmt"

	"github.com/russross/blackfriday/v2"
)

func main() {
	markdown := []byte("# Main Title\n\n## Subtitle\n\nSection content.\n")
	p := blackfriday.New(blackfriday.WithExtensions(blackfriday.AutoHeadingIDs))
	doc := p.Parse(markdown)

	doc.Walk(func(node *blackfriday.Node, entering bool) blackfriday.WalkStatus {
		if node.Type == blackfriday.Heading && entering {
			var text string
			if node.FirstChild != nil {
				text = string(node.FirstChild.Literal)
			}
			fmt.Printf("Heading Level: %d, ID: %s, Text: %s\n",
				node.HeadingData.Level,
				node.HeadingData.HeadingID,
				text,
			)
		}
		return blackfriday.GoToNext
	})
}

{
  "schemaVersion": 1,
  "goal": "verify github.com/russross/blackfriday/v2.Heading in pkg:golang/github.com/russross/blackfriday/v2@v2.1.0",
  "kind": "HOW",
  "packages": [
    "pkg:golang/github.com/russross/blackfriday/v2@v2.1.0"
  ],
  "symbols": [
    "github.com/russross/blackfriday/v2.Heading"
  ],
  "constraints": {
    "executionContext": "node"
  },
  "runtimeConditions": {
    "ecosystem": "npm",
    "language": "javascript",
    "moduleSystem": "cjs",
    "packageManager": "npm@10.9.8",
    "runtime": "node@22.23.2"
  }
}

package test

import (
	"testing"

	"github.com/russross/blackfriday/v2"
)

func TestHeadingNodeParsingATX(t *testing.T) {
	tests := []struct {
		input string
		level int
		text  string
	}{
		{"# Heading 1\n", 1, "Heading 1"},
		{"## Heading 2\n", 2, "Heading 2"},
		{"### Heading 3\n", 3, "Heading 3"},
		{"#### Heading 4\n", 4, "Heading 4"},
		{"##### Heading 5\n", 5, "Heading 5"},
		{"###### Heading 6\n", 6, "Heading 6"},
	}

	for _, tc := range tests {
		p := blackfriday.New()
		doc := p.Parse([]byte(tc.input))
		var headingNode *blackfriday.Node
		doc.Walk(func(node *blackfriday.Node, entering bool) blackfriday.WalkStatus {
			if node.Type == blackfriday.Heading && entering {
				headingNode = node
				return blackfriday.Terminate
			}
			return blackfriday.GoToNext
		})

		if headingNode == nil {
			t.Fatalf("expected Heading node for input %q, found none", tc.input)
		}
		if headingNode.Type != blackfriday.Heading {
			t.Errorf("headingNode.Type = %v, want %v", headingNode.Type, blackfriday.Heading)
		}
		if headingNode.HeadingData.Level != tc.level {
			t.Errorf("headingNode.HeadingData.Level = %d, want %d", headingNode.HeadingData.Level, tc.level)
		}
		if headingNode.FirstChild == nil || string(headingNode.FirstChild.Literal) != tc.text {
			t.Errorf("heading text = %q, want %q", string(headingNode.FirstChild.Literal), tc.text)
		}
	}
}

func TestHeadingNodeParsingSetext(t *testing.T) {
	tests := []struct {
		input string
		level int
		text  string
	}{
		{"Setext Heading 1\n===============\n", 1, "Setext Heading 1"},
		{"Setext Heading 2\n---------------\n", 2, "Setext Heading 2"},
	}

	for _, tc := range tests {
		p := blackfriday.New()
		doc := p.Parse([]byte(tc.input))
		var headingNode *blackfriday.Node
		doc.Walk(func(node *blackfriday.Node, entering bool) blackfriday.WalkStatus {
			if node.Type == blackfriday.Heading && entering {
				headingNode = node
				return blackfriday.Terminate
			}
			return blackfriday.GoToNext
		})

		if headingNode == nil {
			t.Fatalf("expected Heading node for setext input %q, found none", tc.input)
		}
		if headingNode.Type != blackfriday.Heading {
			t.Errorf("headingNode.Type = %v, want %v", headingNode.Type, blackfriday.Heading)
		}
		if headingNode.HeadingData.Level != tc.level {
			t.Errorf("headingNode.HeadingData.Level = %d, want %d", headingNode.HeadingData.Level, tc.level)
		}
		if headingNode.FirstChild == nil || string(headingNode.FirstChild.Literal) != tc.text {
			t.Errorf("heading text = %q, want %q", string(headingNode.FirstChild.Literal), tc.text)
		}
	}
}

func TestHeadingNodeWalkTraversal(t *testing.T) {
	markdown := []byte("# Main Title\n")
	p := blackfriday.New()
	doc := p.Parse(markdown)

	var entered, exited bool
	doc.Walk(func(node *blackfriday.Node, entering bool) blackfriday.WalkStatus {
		if node.Type == blackfriday.Heading {
			if entering {
				entered = true
			} else {
				exited = true
			}
		}
		return blackfriday.GoToNext
	})

	if !entered {
		t.Error("expected Heading node to be entered during Walk")
	}
	if !exited {
		t.Error("expected Heading node to be exited during Walk")
	}
}

func TestHeadingAutoHeadingIDs(t *testing.T) {
	markdown := []byte("# Getting Started Guide\n")
	p := blackfriday.New(blackfriday.WithExtensions(blackfriday.AutoHeadingIDs))
	doc := p.Parse(markdown)

	var headingID string
	doc.Walk(func(node *blackfriday.Node, entering bool) blackfriday.WalkStatus {
		if node.Type == blackfriday.Heading && entering {
			headingID = node.HeadingData.HeadingID
			return blackfriday.Terminate
		}
		return blackfriday.GoToNext
	})

	expectedID := "getting-started-guide"
	if headingID != expectedID {
		t.Errorf("HeadingID = %q, want %q", headingID, expectedID)
	}
}

func TestHeadingExplicitHeadingIDs(t *testing.T) {
	markdown := []byte("# Custom Section {#custom-anchor}\n")
	p := blackfriday.New(blackfriday.WithExtensions(blackfriday.HeadingIDs))
	doc := p.Parse(markdown)

	var headingID string
	doc.Walk(func(node *blackfriday.Node, entering bool) blackfriday.WalkStatus {
		if node.Type == blackfriday.Heading && entering {
			headingID = node.HeadingData.HeadingID
			return blackfriday.Terminate
		}
		return blackfriday.GoToNext
	})

	expectedID := "custom-anchor"
	if headingID != expectedID {
		t.Errorf("HeadingID = %q, want %q", headingID, expectedID)
	}
}

func TestNewNodeHeadingCreation(t *testing.T) {
	node := blackfriday.NewNode(blackfriday.Heading)
	if node.Type != blackfriday.Heading {
		t.Fatalf("node.Type = %v, want %v", node.Type, blackfriday.Heading)
	}

	node.HeadingData.Level = 3
	node.HeadingData.HeadingID = "manual-h3"

	textChild := blackfriday.NewNode(blackfriday.Text)
	textChild.Literal = []byte("Manual Heading Content")
	node.AppendChild(textChild)

	if node.HeadingData.Level != 3 {
		t.Errorf("node.HeadingData.Level = %d, want 3", node.HeadingData.Level)
	}
	if node.HeadingData.HeadingID != "manual-h3" {
		t.Errorf("node.HeadingData.HeadingID = %q, want %q", node.HeadingData.HeadingID, "manual-h3")
	}
	if node.FirstChild != textChild {
		t.Error("expected textChild to be first child of heading node")
	}
	if string(node.FirstChild.Literal) != "Manual Heading Content" {
		t.Errorf("child literal = %q, want %q", string(node.FirstChild.Literal), "Manual Heading Content")
	}
}