Extract shared AST utilities into astutil package

internal/rules/astutil/astutil.go

@@ -0,0 +1,77 @@
+package astutil
+
+import (
+	"bytes"
+
+	"github.com/jeduden/mdsmith/internal/lint"
+	"github.com/yuin/goldmark/ast"
+)
+
+// HeadingLine returns the 1-based source line of a heading node.
+// Setext headings expose their line via Lines(); ATX headings are found
+// by walking inline descendants until the first text segment. Returns 1
+// as a safe fallback.
+func HeadingLine(heading *ast.Heading, f *lint.File) int {
+	lines := heading.Lines()
+	if lines.Len() > 0 {
+		return f.LineOfOffset(lines.At(0).Start)
+	}
+
+	line := 1
+	_ = ast.Walk(heading, func(n ast.Node, entering bool) (ast.WalkStatus, error) {
+		if !entering || n == heading {
+			return ast.WalkContinue, nil
+		}
+		t, ok := n.(*ast.Text)
+		if !ok {
+			return ast.WalkContinue, nil
+		}
+		line = f.LineOfOffset(t.Segment.Start)
+		return ast.WalkStop, nil
+	})
+
+	return line
+}
+
+// ParagraphLine returns the 1-based source line of a paragraph node.
+func ParagraphLine(para *ast.Paragraph, f *lint.File) int {
+	lines := para.Lines()
+	if lines.Len() > 0 {
+		return f.LineOfOffset(lines.At(0).Start)
+	}
+	return 1
+}
+
+// IsTable reports whether a paragraph node is actually a GFM table
+// (goldmark parses tables as paragraphs when the table extension is
+// absent).  It checks whether the first line starts with "|".
+func IsTable(para *ast.Paragraph, f *lint.File) bool {
+	lines := para.Lines()
+	if lines.Len() == 0 {
+		return false
+	}
+	seg := lines.At(0)
+	return bytes.HasPrefix(bytes.TrimSpace(f.Source[seg.Start:seg.Stop]), []byte("|"))
+}
+
+// HeadingText returns the plain-text content of a heading by
+// recursively extracting all text segments from its children.
+func HeadingText(heading *ast.Heading, source []byte) string {
+	var buf bytes.Buffer
+	for c := heading.FirstChild(); c != nil; c = c.NextSibling() {
+		ExtractText(c, source, &buf)
+	}
+	return buf.String()
+}
+
+// ExtractText recursively writes the text content of n and its
+// descendants into buf.
+func ExtractText(n ast.Node, source []byte, buf *bytes.Buffer) {
+	if t, ok := n.(*ast.Text); ok {
+		buf.Write(t.Segment.Value(source))
+		return
+	}
+	for c := n.FirstChild(); c != nil; c = c.NextSibling() {
+		ExtractText(c, source, buf)
+	}
+}