From 93e3d5dc5f2af317c874fd61cbd354409ea9fd33 Mon Sep 17 00:00:00 2001
From: Mateusz Poliwczak <mpoliwczak34@gmail.com>
Date: Thu, 1 May 2025 12:20:45 +0000
Subject: [PATCH] go/parser: use non-adjusted position while parsing
 CommentGroups

Line directives should not affect the way Comments get grouped
into CommentGroups.

Change-Id: I9aa4b558cb1333b32be692e8720291d0e6961cae
GitHub-Last-Rev: de867b27bff28983716ba9126329d75f456a2b5a
GitHub-Pull-Request: golang/go#69133
Reviewed-on: https://go-review.googlesource.com/c/go/+/609515
Reviewed-by: Alan Donovan <adonovan@google.com>
Reviewed-by: Carlos Amedee <carlos@golang.org>
Auto-Submit: Alan Donovan <adonovan@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
---
 src/go/parser/parser.go      | 17 +++++++++++------
 src/go/parser/parser_test.go | 37 ++++++++++++++++++++++++++++++++++++
 2 files changed, 48 insertions(+), 6 deletions(-)

diff --git a/src/go/parser/parser.go b/src/go/parser/parser.go
index c31b65bb53..38ee0de3bb 100644
--- a/src/go/parser/parser.go
+++ b/src/go/parser/parser.go
@@ -161,11 +161,16 @@ func (p *parser) next0() {
 	}
 }
 
+// lineFor returns the line of pos, ignoring line directive adjustments.
+func (p *parser) lineFor(pos token.Pos) int {
+	return p.file.PositionFor(pos, false).Line
+}
+
 // Consume a comment and return it and the line on which it ends.
 func (p *parser) consumeComment() (comment *ast.Comment, endline int) {
 	// /*-style comments may end on a different line than where they start.
 	// Scan the comment for '\n' chars and adjust endline accordingly.
-	endline = p.file.Line(p.pos)
+	endline = p.lineFor(p.pos)
 	if p.lit[1] == '*' {
 		// don't use range here - no need to decode Unicode code points
 		for i := 0; i < len(p.lit); i++ {
@@ -187,8 +192,8 @@ func (p *parser) consumeComment() (comment *ast.Comment, endline int) {
 // empty lines terminate a comment group.
 func (p *parser) consumeCommentGroup(n int) (comments *ast.CommentGroup, endline int) {
 	var list []*ast.Comment
-	endline = p.file.Line(p.pos)
-	for p.tok == token.COMMENT && p.file.Line(p.pos) <= endline+n {
+	endline = p.lineFor(p.pos)
+	for p.tok == token.COMMENT && p.lineFor(p.pos) <= endline+n {
 		var comment *ast.Comment
 		comment, endline = p.consumeComment()
 		list = append(list, comment)
@@ -225,11 +230,11 @@ func (p *parser) next() {
 		var comment *ast.CommentGroup
 		var endline int
 
-		if p.file.Line(p.pos) == p.file.Line(prev) {
+		if p.lineFor(p.pos) == p.lineFor(prev) {
 			// The comment is on same line as the previous token; it
 			// cannot be a lead comment but may be a line comment.
 			comment, endline = p.consumeCommentGroup(0)
-			if p.file.Line(p.pos) != endline || p.tok == token.SEMICOLON || p.tok == token.EOF {
+			if p.lineFor(p.pos) != endline || p.tok == token.SEMICOLON || p.tok == token.EOF {
 				// The next token is on a different line, thus
 				// the last comment group is a line comment.
 				p.lineComment = comment
@@ -242,7 +247,7 @@ func (p *parser) next() {
 			comment, endline = p.consumeCommentGroup(1)
 		}
 
-		if endline+1 == p.file.Line(p.pos) {
+		if endline+1 == p.lineFor(p.pos) {
 			// The next token is following on the line immediately after the
 			// comment group, thus the last comment group is a lead comment.
 			p.leadComment = comment
diff --git a/src/go/parser/parser_test.go b/src/go/parser/parser_test.go
index 714a6e0237..2516cedc88 100644
--- a/src/go/parser/parser_test.go
+++ b/src/go/parser/parser_test.go
@@ -9,6 +9,7 @@ import (
 	"go/ast"
 	"go/token"
 	"io/fs"
+	"reflect"
 	"strings"
 	"testing"
 )
@@ -859,3 +860,39 @@ func TestEmptyFileHasValidStartEnd(t *testing.T) {
 		}
 	}
 }
+
+func TestCommentGroupWithLineDirective(t *testing.T) {
+	const src = `package main
+func test() {
+//line a:15:1
+	//
+}
+`
+	fset := token.NewFileSet()
+	f, err := ParseFile(fset, "test.go", src, ParseComments|SkipObjectResolution)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	wantCommentGroups := []*ast.CommentGroup{
+		{
+			List: []*ast.Comment{
+				{
+					Slash: token.Pos(28),
+					Text:  "//line a:15:1",
+				},
+				{
+					Slash: token.Pos(43),
+					Text:  "//",
+				},
+			},
+		},
+	}
+
+	if !reflect.DeepEqual(f.Comments, wantCommentGroups) {
+		var got, want strings.Builder
+		ast.Fprint(&got, fset, f.Comments, nil)
+		ast.Fprint(&want, fset, wantCommentGroups, nil)
+		t.Fatalf("unexpected f.Comments got:\n%v\nwant:\n%v", got.String(), want.String())
+	}
+}
-- 
2.51.0