indentMultilineCommentOrJsxText: Fix bug when 'parts' is empty (#25645)

src/services/formatting/formatting.ts

@@ -975,7 +975,6 @@ namespace ts.formatting {
             // split comment in lines
             let startLine = sourceFile.getLineAndCharacterOfPosition(commentRange.pos).line;
             const endLine = sourceFile.getLineAndCharacterOfPosition(commentRange.end).line;
-            let parts: TextRange[];
             if (startLine === endLine) {
                 if (!firstLineIsIndented) {
                     // treat as single line comment
@@ -983,20 +982,21 @@ namespace ts.formatting {
                 }
                 return;
             }
-            else {
-                parts = [];
-                let startPos = commentRange.pos;
-                for (let line = startLine; line < endLine; line++) {
-                    const endOfLine = getEndLinePosition(line, sourceFile);
-                    parts.push({ pos: startPos, end: endOfLine });
-                    startPos = getStartPositionOfLine(line + 1, sourceFile);
-                }
 
-                if (indentFinalLine) {
-                    parts.push({ pos: startPos, end: commentRange.end });
-                }
+            const parts: TextRange[] = [];
+            let startPos = commentRange.pos;
+            for (let line = startLine; line < endLine; line++) {
+                const endOfLine = getEndLinePosition(line, sourceFile);
+                parts.push({ pos: startPos, end: endOfLine });
+                startPos = getStartPositionOfLine(line + 1, sourceFile);
             }
 
+            if (indentFinalLine) {
+                parts.push({ pos: startPos, end: commentRange.end });
+            }
+
+            if (parts.length === 0) return;
+
             const startLinePos = getStartPositionOfLine(startLine, sourceFile);
 
             const nonWhitespaceColumnInFirstPart =

tests/cases/fourslash/refactorAddOrRemoveBracesToArrowFunction_formatBug.ts

@@ -0,0 +1,20 @@
+/// <reference path='fourslash.ts' />
+
+// @Filename: /a.tsx
+////const x = () /*a*/=>/*b*/
+////           <div>:</div>
+
+// This code with this exact indent level used to crash in `indentMultilineCommentOrJsxText`.
+
+goTo.select("a", "b");
+
+edit.applyRefactor({
+    refactorName: "Add or remove braces in an arrow function",
+    actionName: "Add braces to arrow function",
+    actionDescription: "Add braces to arrow function",
+    newContent:
+`const x = () =>
+           {
+        return <div>:</div>;
+    }`,
+});