perf(vscode): replace fast-diff with custom character-by-character alignment algorithm

extensions/vscode/lib/rangeFormatting.ts

@@ -1,5 +1,4 @@
 import type * as vscode from 'vscode';
-import diff = require('fast-diff');
 
 /** for test unit */
 export type FormatableTextDocument = Pick<vscode.TextDocument, 'getText' | 'offsetAt' | 'positionAt'>;
@@ -61,72 +60,60 @@ function getTrimmedNewText(
 		return;
 	}
 
-	const map = createOffsetMap(oldText, edit.newText);
-	const newStart = map[overlapStart];
-	const newEnd = map[overlapEnd];
-	return {
-		start: editStart + overlapStart,
-		end: editStart + overlapEnd,
-		newText: edit.newText.slice(newStart, newEnd),
-	};
-}
+	let oldTextIndex = 0;
+	let newTextIndex = 0;
+	let newStart!: number;
+	let newEnd!: number;
 
-function createOffsetMap(oldText: string, newText: string) {
-	const length = oldText.length;
-	const map = new Array<number>(length + 1);
-	let oldIndex = 0;
-	let newIndex = 0;
-	map[0] = 0;
-
-	for (const [op, text] of diff(oldText, newText)) {
-		if (op === diff.EQUAL) {
-			for (let i = 0; i < text.length; i++) {
-				oldIndex++;
-				newIndex++;
-				map[oldIndex] = newIndex;
-			}
+	while (true) {
+		if (oldTextIndex === overlapStart) {
+			newStart = newTextIndex;
+			break;
+		}
+		const oldCharCode = oldText.charCodeAt(oldTextIndex);
+		const newCharCode = edit.newText.charCodeAt(newTextIndex);
+		if (oldCharCode === newCharCode || (!isWhitespaceChar(oldCharCode) && !isWhitespaceChar(newCharCode))) {
+			oldTextIndex++;
+			newTextIndex++;
+			continue;
 		}
-		else if (op === diff.DELETE) {
-			for (let i = 0; i < text.length; i++) {
-				oldIndex++;
-				map[oldIndex] = Number.NaN;
-			}
+		if (isWhitespaceChar(oldCharCode)) {
+			oldTextIndex++;
 		}
-		else {
-			newIndex += text.length;
+		if (isWhitespaceChar(newCharCode)) {
+			newTextIndex++;
 		}
 	}
 
-	map[length] = newIndex;
-
-	let lastDefinedIndex = 0;
-	for (let i = 1; i <= length; i++) {
-		if (map[i] === undefined || Number.isNaN(map[i])) {
+	oldTextIndex = oldText.length - 1;
+	newTextIndex = edit.newText.length - 1;
+	while (true) {
+		if (oldTextIndex + 1 === overlapEnd) {
+			newEnd = newTextIndex + 1;
+			break;
+		}
+		const oldCharCode = oldText.charCodeAt(oldTextIndex);
+		const newCharCode = edit.newText.charCodeAt(newTextIndex);
+		if (oldCharCode === newCharCode || (!isWhitespaceChar(oldCharCode) && !isWhitespaceChar(newCharCode))) {
+			oldTextIndex--;
+			newTextIndex--;
 			continue;
 		}
-		interpolate(map, lastDefinedIndex, i);
-		lastDefinedIndex = i;
-	}
-	if (lastDefinedIndex < length) {
-		interpolate(map, lastDefinedIndex, length);
+		if (isWhitespaceChar(oldCharCode)) {
+			oldTextIndex--;
+		}
+		if (isWhitespaceChar(newCharCode)) {
+			newTextIndex--;
+		}
 	}
 
-	return map;
+	return {
+		start: editStart + overlapStart,
+		end: editStart + overlapEnd,
+		newText: edit.newText.slice(newStart, newEnd),
+	};
 }
 
-function interpolate(map: number[], startIndex: number, endIndex: number) {
-	const startValue = map[startIndex] ?? 0;
-	const endValue = map[endIndex] ?? startValue;
-	const gap = endIndex - startIndex;
-	if (gap <= 1) {
-		return;
-	}
-	const delta = (endValue - startValue) / gap;
-	for (let i = 1; i < gap; i++) {
-		const index = startIndex + i;
-		if (map[index] !== undefined && !Number.isNaN(map[index])) {
-			continue;
-		}
-		map[index] = Math.floor(startValue + delta * i);
-	}
+function isWhitespaceChar(charCode: number) {
+	return charCode === 32 || charCode === 9 || charCode === 10 || charCode === 13;
 }

extensions/vscode/package.json

@@ -490,7 +490,6 @@
 		"@vue/language-core": "3.1.8",
 		"@vue/language-server": "3.1.8",
 		"@vue/typescript-plugin": "3.1.8",
-		"fast-diff": "^1.3.0",
 		"laplacenoma": "^0.0.3",
 		"reactive-vscode": "^0.2.9",
 		"rolldown": "1.0.0-beta.8",

extensions/vscode/tests/rangeFormatting.spec.ts

@@ -30,7 +30,7 @@ describe('provideDocumentRangeFormattingEdits', () => {
 			createTextEdit(
 				selection.start.character - 1,
 				selection.end.character,
-				`  <div>
+				`\n  <div>
     <div>2</div>
   </div>`,
 			),
@@ -75,6 +75,106 @@ describe('provideDocumentRangeFormattingEdits', () => {
 		const result = restrictFormattingEditsToRange(document, selection, edits, createTextEdit);
 		expect(applyEdits(document, result)).toMatchInlineSnapshot(`"01X23456789"`);
 	});
+
+	test('handles deletion where newText is shorter than oldText in selection', () => {
+		const document = createDocument('ab  ');
+		const selection = createRange(1, 3);
+		const edits = [createTextEdit(0, 4, 'ab')];
+		const result = restrictFormattingEditsToRange(document, selection, edits, createTextEdit);
+		expect(applyEdits(document, result)).toMatchInlineSnapshot(`"ab "`);
+	});
+
+	test('handles newText completely exhausted before reaching overlapEnd', () => {
+		const document = createDocument('abcdef');
+		const selection = createRange(1, 5); // select "bcde"
+		const edits = [createTextEdit(0, 6, 'ab')]; // replace all with just "ab"
+		const result = restrictFormattingEditsToRange(document, selection, edits, createTextEdit);
+		expect(applyEdits(document, result)).toMatchInlineSnapshot(`"af"`);
+	});
+
+	test('handles insertion where newText is longer than oldText', () => {
+		const document = createDocument('abc');
+		const selection = createRange(1, 2); // select "b"
+		const edits = [createTextEdit(0, 3, 'aXYZc')]; // insert XYZ in the middle
+		const result = restrictFormattingEditsToRange(document, selection, edits, createTextEdit);
+		expect(applyEdits(document, result)).toMatchInlineSnapshot(`"aXYZc"`);
+	});
+
+	test('handles whitespace-only differences', () => {
+		const document = createDocument('a  b  c');
+		const selection = createRange(1, 6); // select "  b  "
+		const edits = [createTextEdit(0, 7, 'a b c')]; // normalize spaces
+		const result = restrictFormattingEditsToRange(document, selection, edits, createTextEdit);
+		expect(applyEdits(document, result)).toMatchInlineSnapshot(`"a b c"`);
+	});
+
+	test('handles edit range completely before selection', () => {
+		const document = createDocument('0123456789');
+		const selection = createRange(5, 8);
+		const edits = [createTextEdit(0, 3, 'XYZ')];
+		const result = restrictFormattingEditsToRange(document, selection, edits, createTextEdit);
+		expect(applyEdits(document, result)).toMatchInlineSnapshot(`"0123456789"`);
+	});
+
+	test('handles edit range completely after selection', () => {
+		const document = createDocument('0123456789');
+		const selection = createRange(2, 5);
+		const edits = [createTextEdit(7, 10, 'XYZ')];
+		const result = restrictFormattingEditsToRange(document, selection, edits, createTextEdit);
+		expect(applyEdits(document, result)).toMatchInlineSnapshot(`"0123456789"`);
+	});
+
+	test('handles empty selection', () => {
+		const document = createDocument('0123456789');
+		const selection = createRange(5, 5); // empty selection at position 5
+		const edits = [createTextEdit(3, 7, 'ABCD')];
+		const result = restrictFormattingEditsToRange(document, selection, edits, createTextEdit);
+		expect(applyEdits(document, result)).toMatchInlineSnapshot(`"0123456789"`);
+	});
+
+	test('handles empty edit (pure insertion)', () => {
+		const document = createDocument('0123456789');
+		const selection = createRange(3, 7);
+		const edits = [createTextEdit(5, 5, 'XXX')]; // insert at position 5
+		const result = restrictFormattingEditsToRange(document, selection, edits, createTextEdit);
+		expect(applyEdits(document, result)).toMatchInlineSnapshot(`"01234XXX56789"`);
+	});
+
+	test('handles multiple edits within selection', () => {
+		const document = createDocument('0123456789');
+		const selection = createRange(2, 8);
+		const edits = [
+			createTextEdit(3, 4, 'A'),
+			createTextEdit(6, 7, 'B'),
+		];
+		const result = restrictFormattingEditsToRange(document, selection, edits, createTextEdit);
+		expect(applyEdits(document, result)).toMatchInlineSnapshot(`"012A45B789"`);
+	});
+
+	test('handles edit with mixed whitespace and non-whitespace changes', () => {
+		const document = createDocument('a\n\tb\n\tc');
+		const selection = createRange(1, 5); // select "\n\tb\n"
+		const edits = [createTextEdit(0, 7, 'a b c')]; // normalize all whitespace
+		const result = restrictFormattingEditsToRange(document, selection, edits, createTextEdit);
+		expect(applyEdits(document, result)).toMatchInlineSnapshot(`"a b	c"`);
+	});
+
+	test('handles non-ASCII characters', () => {
+		const document = createDocument('你好世界');
+		const selection = createRange(1, 3); // select "好世"
+		const edits = [createTextEdit(0, 4, '你好朋友')];
+		const result = restrictFormattingEditsToRange(document, selection, edits, createTextEdit);
+		expect(applyEdits(document, result)).toMatchInlineSnapshot(`"你好朋界"`);
+	});
+
+	test('handles overlapStart equals overlapEnd', () => {
+		// When edit and selection don't actually overlap in content
+		const document = createDocument('0123456789');
+		const selection = createRange(5, 5);
+		const edits = [createTextEdit(3, 7, 'WXYZ')];
+		const result = restrictFormattingEditsToRange(document, selection, edits, createTextEdit);
+		expect(applyEdits(document, result)).toMatchInlineSnapshot(`"0123456789"`);
+	});
 });
 
 // self implementation of vscode test utils