feat: support Go comments within HTML tag attributes

generator/generator.go

@@ -1458,6 +1458,8 @@ func (g *generator) writeElementAttributes(indentLevel int, name string, attrs [
 			err = g.writeSpreadAttributes(indentLevel, attr)
 		case *parser.ConditionalAttribute:
 			err = g.writeConditionalAttribute(indentLevel, name, attr)
+		case *parser.AttributeComment:
+			continue
 		default:
 			err = fmt.Errorf("unknown attribute type %T", attr)
 		}

generator/test-attribute-comments/expected.html

@@ -0,0 +1,6 @@
+<form class="flex" action="javascript:void(0)" method="post" id="test-form">
+  <input type="text" name="field1" />
+</form>
+<div id="main" class="container" data-value="dynamic" hidden>Content</div>
+<button type="button" onclick="handleClick()" disabled="false">Click me</button>
+

generator/test-attribute-comments/render_test.go

@@ -0,0 +1,23 @@
+package testattributecomments
+
+import (
+	_ "embed"
+	"testing"
+
+	"github.com/a-h/templ/generator/htmldiff"
+)
+
+//go:embed expected.html
+var expected string
+
+func Test(t *testing.T) {
+	component := TestAttributeComments()
+
+	_, diff, err := htmldiff.Diff(component, expected)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if diff != "" {
+		t.Error(diff)
+	}
+}

generator/test-attribute-comments/template.templ

@@ -0,0 +1,41 @@
+package testattributecomments
+
+templ TestAttributeComments() {
+	<form
+		class="flex"
+		// This comment here explains why the following attribute is necessary,
+		// namely to prevent submit when hitting the enter key.
+		action="javascript:void(0)"
+		/* This is a multi-line comment
+		   that spans multiple lines
+		   within the attributes */
+		method="post"
+		// Another single line comment
+		id="test-form"
+	>
+		<input type="text" name="field1"/>
+	</form>
+	<div
+		// Comment at the start
+		id="main"
+		/* Multi-line comment */
+		class="container"
+		// Comment before expression
+		data-value={ "dynamic" }
+		// Comment before boolean
+		hidden
+		// Final comment
+	>
+		Content
+	</div>
+	<button
+		type="button"
+		// This explains the onclick handler
+		onclick="handleClick()"
+		/* This is a safety measure
+		   to prevent accidental submits */
+		disabled={ false }
+	>
+		Click me
+	</button>
+}

internal/format/testdata/comments_in_attributes_are_preserved.txt

@@ -0,0 +1,58 @@
+-- in --
+package main
+
+templ test() {
+	<form
+		class="flex"
+		// This comment explains why the action is necessary
+		action="javascript:void(0)"
+		/* Multi-line comment
+		   for detailed explanations */
+		method="post"
+		// Comment before id
+		id="test-form"
+	>
+		<input type="text" />
+	</form>
+	<div
+		// Comment at start
+		id="main"
+		/* Multi-line comment */
+		class="container"
+		// Comment before expression
+		data-value={ "dynamic" }
+		// Comment before boolean
+		hidden
+	>
+		Content
+	</div>
+}
+-- out --
+package main
+
+templ test() {
+	<form
+		class="flex"
+		// This comment explains why the action is necessary
+		action="javascript:void(0)"
+		/* Multi-line comment
+		   for detailed explanations */
+		method="post"
+		// Comment before id
+		id="test-form"
+	>
+		<input type="text"/>
+	</form>
+	<div
+		// Comment at start
+		id="main"
+		/* Multi-line comment */
+		class="container"
+		// Comment before expression
+		data-value={ "dynamic" }
+		// Comment before boolean
+		hidden
+	>
+		Content
+	</div>
+}

parser/v2/elementparser.go

@@ -402,6 +402,30 @@ type attributesParser struct{}
 
 func (attributesParser) Parse(in *parse.Input) (attributes []Attribute, ok bool, err error) {
 	for {
+		// Try to parse and handle any comments first.
+		for {
+			if _, _, err = parse.OptionalWhitespace.Parse(in); err != nil {
+				return
+			}
+
+			commentStart := in.Index()
+			if node, commentOk, commentErr := goComment.Parse(in); commentErr != nil {
+				return attributes, false, commentErr
+			} else if commentOk {
+				// Found a Go comment, add it as an attribute comment
+				if goNode, ok := node.(*GoComment); ok {
+					attributes = append(attributes, &AttributeComment{
+						Comment:   goNode.Contents,
+						Multiline: goNode.Multiline,
+					})
+				}
+				continue
+			}
+
+			in.Seek(commentStart)
+			break
+		}
+
 		var attr Attribute
 		attr, ok, err = attribute.Parse(in)
 		if err != nil {

parser/v2/types.go

@@ -1108,6 +1108,35 @@ func (ca *ConditionalAttribute) Copy() Attribute {
 	}
 }
 
+// AttributeComment represents a comment within element attributes.
+type AttributeComment struct {
+	Comment   string
+	Multiline bool
+}
+
+func (ac *AttributeComment) String() string {
+	if ac.Multiline {
+		return "/*" + ac.Comment + "*/"
+	}
+	return "//" + ac.Comment
+}
+
+func (ac *AttributeComment) Write(w io.Writer, indent int) error {
+	return writeIndent(w, indent, ac.String())
+}
+
+func (ac *AttributeComment) Visit(v Visitor) error {
+	// Comments don't need to be visited.
+	return nil
+}
+
+func (ac *AttributeComment) Copy() Attribute {
+	return &AttributeComment{
+		Comment:   ac.Comment,
+		Multiline: ac.Multiline,
+	}
+}
+
 func CopyAttributes(attrs []Attribute) (copies []Attribute) {
 	copies = make([]Attribute, len(attrs))
 	for i, a := range attrs {