internal/lsp: fix folding range for block comments

Block comments are a single comment that stretches across multiple
lines. The folding range code made assumptions that each comment
was a single line. This change fixes the folding range logic to check for multiline comments and adjust the folding range to start at
the end of the first line.

Fixes golang/go#46253
Fixes golang/vscode-go#1511

Change-Id: I902f6cda7547cb1f8b4cd447152c3cf29a691d3b
Reviewed-on: https://go-review.googlesource.com/c/tools/+/325071
Trust: Suzy Mueller <[email protected]>
Run-TryBot: Suzy Mueller <[email protected]>
gopls-CI: kokoro <[email protected]>
TryBot-Result: Go Bot <[email protected]>
Reviewed-by: Rebecca Stambler <[email protected]>

Author: suzmue

internal/lsp/source/folding_range.go

@@ -9,6 +9,7 @@ import (
 	"go/ast"
 	"go/token"
 	"sort"
+	"strings"
 
 	"golang.org/x/tools/internal/lsp/protocol"
 )
@@ -151,17 +152,27 @@ func validLineFoldingRange(fset *token.FileSet, open, close, start, end token.Po
 }
 
 // commentsFoldingRange returns the folding ranges for all comment blocks in file.
-// The folding range starts at the end of the first comment, and ends at the end of the
+// The folding range starts at the end of the first line of the comment block, and ends at the end of the
 // comment block and has kind protocol.Comment.
 func commentsFoldingRange(fset *token.FileSet, m *protocol.ColumnMapper, file *ast.File) (comments []*FoldingRangeInfo) {
 	for _, commentGrp := range file.Comments {
-		// Don't fold single comments.
-		if len(commentGrp.List) <= 1 {
+		startGrp, endGrp := fset.Position(commentGrp.Pos()), fset.Position(commentGrp.End())
+		if startGrp.Line == endGrp.Line {
+			// Don't fold single line comments.
 			continue
 		}
+
+		firstComment := commentGrp.List[0]
+		startPos, endLinePos := firstComment.Pos(), firstComment.End()
+		startCmmnt, endCmmnt := fset.Position(startPos), fset.Position(endLinePos)
+		if startCmmnt.Line != endCmmnt.Line {
+			// If the first comment spans multiple lines, then we want to have the
+			// folding range start at the end of the first line.
+			endLinePos = token.Pos(int(startPos) + len(strings.Split(firstComment.Text, "\n")[0]))
+		}
 		comments = append(comments, &FoldingRangeInfo{
 			// Fold from the end of the first line comment to the end of the comment block.
-			MappedRange: NewMappedRange(fset, m, commentGrp.List[0].End(), commentGrp.End()),
+			MappedRange: NewMappedRange(fset, m, endLinePos, commentGrp.End()),
 			Kind:        protocol.Comment,
 		})
 	}

internal/lsp/testdata/folding/a.go

@@ -10,6 +10,7 @@ import _ "os"
 // bar is a function.
 // With a multiline doc comment.
 func bar() string {
+	/* This is a single line comment */
 	switch {
 	case true:
 		if true {
@@ -22,6 +23,14 @@ func bar() string {
 	default:
 		fmt.Println("default")
 	}
+	/* This is a multiline
+	block
+	comment */
+
+	/* This is a multiline
+	block
+	comment */
+	// Followed by another comment.
 	_ = []int{
 		1,
 		2,

internal/lsp/testdata/folding/a.go.golden

@@ -21,7 +21,11 @@ import _ "os"
 // bar is a function.
 // With a multiline doc comment.
 func bar() string {
+	/* This is a single line comment */
 	switch {<>}
+	/* This is a multiline<>
+
+	/* This is a multiline<>
 	_ = []int{<>}
 	_ = [2]string{<>}
 	_ = map[string]int{<>}
@@ -48,11 +52,20 @@ import _ "os"
 // bar is a function.
 // With a multiline doc comment.
 func bar() string {
+	/* This is a single line comment */
 	switch {
 	case true:<>
 	case false:<>
 	default:<>
 	}
+	/* This is a multiline
+	block
+	comment */
+
+	/* This is a multiline
+	block
+	comment */
+	// Followed by another comment.
 	_ = []int{
 		1,
 		2,
@@ -102,6 +115,7 @@ import _ "os"
 // bar is a function.
 // With a multiline doc comment.
 func bar() string {
+	/* This is a single line comment */
 	switch {
 	case true:
 		if true {<>} else {<>}
@@ -110,6 +124,14 @@ func bar() string {
 	default:
 		fmt.Println(<>)
 	}
+	/* This is a multiline
+	block
+	comment */
+
+	/* This is a multiline
+	block
+	comment */
+	// Followed by another comment.
 	_ = []int{
 		1,
 		2,
@@ -162,6 +184,7 @@ import _ "os"
 // bar is a function.
 // With a multiline doc comment.
 func bar() string {
+	/* This is a single line comment */
 	switch {
 	case true:
 		if true {
@@ -174,6 +197,14 @@ func bar() string {
 	default:
 		fmt.Println("default")
 	}
+	/* This is a multiline
+	block
+	comment */
+
+	/* This is a multiline
+	block
+	comment */
+	// Followed by another comment.
 	_ = []int{
 		1,
 		2,
@@ -221,35 +252,37 @@ is not indented`
 3:9-6:0
 10:22-11:32
 12:10-12:9
-12:20-66:0
-13:10-24:1
-14:12-19:3
-15:12-17:2
-16:16-16:21
-17:11-19:2
-18:16-18:22
-20:13-21:22
-21:15-21:21
-22:10-23:24
-23:15-23:23
-25:12-29:1
-30:16-32:1
-33:21-37:1
-38:17-42:1
-43:8-47:1
-48:15-48:23
-48:32-48:40
-49:10-60:1
-50:18-55:3
-51:11-53:2
-52:16-52:28
-53:11-55:2
-54:16-54:29
-56:11-57:18
-57:15-57:17
-58:10-59:24
-59:15-59:23
-61:32-62:30
+12:20-75:0
+14:10-25:1
+15:12-20:3
+16:12-18:2
+17:16-17:21
+18:11-20:2
+19:16-19:22
+21:13-22:22
+22:15-22:21
+23:10-24:24
+24:15-24:23
+26:24-28:11
+30:24-33:32
+34:12-38:1
+39:16-41:1
+42:21-46:1
+47:17-51:1
+52:8-56:1
+57:15-57:23
+57:32-57:40
+58:10-69:1
+59:18-64:3
+60:11-62:2
+61:16-61:28
+62:11-64:2
+63:16-63:29
+65:11-66:18
+66:15-66:17
+67:10-68:24
+68:15-68:23
+70:32-71:30
 
 -- foldingRange-comment-0 --
 package folding //@fold("package")
@@ -263,6 +296,7 @@ import _ "os"
 
 // bar is a function.<>
 func bar() string {
+	/* This is a single line comment */
 	switch {
 	case true:
 		if true {
@@ -275,6 +309,9 @@ func bar() string {
 	default:
 		fmt.Println("default")
 	}
+	/* This is a multiline<>
+
+	/* This is a multiline<>
 	_ = []int{
 		1,
 		2,
@@ -327,6 +364,7 @@ import _ "os"
 // bar is a function.
 // With a multiline doc comment.
 func bar() string {
+	/* This is a single line comment */
 	switch {
 	case true:
 		if true {
@@ -339,6 +377,14 @@ func bar() string {
 	default:
 		fmt.Println("default")
 	}
+	/* This is a multiline
+	block
+	comment */
+
+	/* This is a multiline
+	block
+	comment */
+	// Followed by another comment.
 	_ = []int{
 		1,
 		2,
@@ -407,8 +453,12 @@ import _ "os"
 // bar is a function.
 // With a multiline doc comment.
 func bar() string {
+	/* This is a single line comment */
 	switch {<>
 	}
+	/* This is a multiline<>
+
+	/* This is a multiline<>
 	_ = []int{<>,
 	}
 	_ = [2]string{"d",
@@ -442,11 +492,20 @@ import _ "os"
 // bar is a function.
 // With a multiline doc comment.
 func bar() string {
+	/* This is a single line comment */
 	switch {
 	case true:<>
 	case false:<>
 	default:<>
 	}
+	/* This is a multiline
+	block
+	comment */
+
+	/* This is a multiline
+	block
+	comment */
+	// Followed by another comment.
 	_ = []int{
 		1,
 		2,
@@ -496,6 +555,7 @@ import _ "os"
 // bar is a function.
 // With a multiline doc comment.
 func bar() string {
+	/* This is a single line comment */
 	switch {
 	case true:
 		if true {<>
@@ -506,6 +566,14 @@ func bar() string {
 	default:
 		fmt.Println("default")
 	}
+	/* This is a multiline
+	block
+	comment */
+
+	/* This is a multiline
+	block
+	comment */
+	// Followed by another comment.
 	_ = []int{
 		1,
 		2,
@@ -559,6 +627,7 @@ import _ "os"
 
 // bar is a function.<>
 func bar() string {
+	/* This is a single line comment */
 	switch {
 	case true:
 		if true {
@@ -571,6 +640,9 @@ func bar() string {
 	default:
 		fmt.Println("default")
 	}
+	/* This is a multiline<>
+
+	/* This is a multiline<>
 	_ = []int{
 		1,
 		2,
@@ -624,6 +696,7 @@ import _ "os"
 // bar is a function.
 // With a multiline doc comment.
 func bar() string {
+	/* This is a single line comment */
 	switch {
 	case true:
 		if true {
@@ -636,6 +709,14 @@ func bar() string {
 	default:
 		fmt.Println("default")
 	}
+	/* This is a multiline
+	block
+	comment */
+
+	/* This is a multiline
+	block
+	comment */
+	// Followed by another comment.
 	_ = []int{
 		1,
 		2,