Fixes #141550.

src/vs/editor/contrib/inlineCompletions/browser/inlineCompletionToGhostText.ts

@@ -143,7 +143,18 @@ function cachingDiff(originalValue: string, newValue: string): readonly IDiffCha
 	if (lastRequest?.originalValue === originalValue && lastRequest?.newValue === newValue) {
 		return lastRequest?.changes;
 	} else {
-		const changes = smartDiff(originalValue, newValue);
+		let changes = smartDiff(originalValue, newValue, true);
+		if (changes) {
+			const deletedChars = deletedCharacters(changes);
+			if (deletedChars > 0) {
+				// For performance reasons, don't compute diff if there is nothing to improve
+				const newChanges = smartDiff(originalValue, newValue, false);
+				if (newChanges && deletedCharacters(newChanges) < deletedChars) {
+					// Disabling smartness seems to be better here
+					changes = newChanges;
+				}
+			}
+		}
 		lastRequest = {
 			originalValue,
 			newValue,
@@ -153,6 +164,14 @@ function cachingDiff(originalValue: string, newValue: string): readonly IDiffCha
 	}
 }
 
+function deletedCharacters(changes: readonly IDiffChange[]): number {
+	let sum = 0;
+	for (const c of changes) {
+		sum += Math.max(c.originalLength - c.modifiedLength, 0);
+	}
+	return sum;
+}
+
 /**
  * When matching `if ()` with `if (f() = 1) { g(); }`,
  * align it like this:        `if (       )`
@@ -161,7 +180,7 @@ function cachingDiff(originalValue: string, newValue: string): readonly IDiffCha
  *
  * The parenthesis are preprocessed to ensure that they match correctly.
  */
-function smartDiff(originalValue: string, newValue: string): (readonly IDiffChange[]) | undefined {
+function smartDiff(originalValue: string, newValue: string, smartBracketMatching: boolean): (readonly IDiffChange[]) | undefined {
 	if (originalValue.length > 5000 || newValue.length > 5000) {
 		// We don't want to work on strings that are too big
 		return undefined;
@@ -191,18 +210,18 @@ function smartDiff(originalValue: string, newValue: string): (readonly IDiffChan
 		let group = 0;
 		const characters = new Int32Array(source.length);
 		for (let i = 0, len = source.length; i < len; i++) {
-			const id = group * 100 + level;
-
 			// TODO support more brackets
-			if (source[i] === '(') {
+			if (smartBracketMatching && source[i] === '(') {
+				const id = group * 100 + level;
 				characters[i] = getUniqueCharCode(2 * id);
 				level++;
-			} else if (source[i] === ')') {
+			} else if (smartBracketMatching && source[i] === ')') {
+				level = Math.max(level - 1, 0);
+				const id = group * 100 + level;
 				characters[i] = getUniqueCharCode(2 * id + 1);
-				if (level === 1) {
+				if (level === 0) {
 					group++;
 				}
-				level = Math.max(level - 1, 0);
 			} else {
 				characters[i] = source.charCodeAt(i);
 			}

src/vs/editor/contrib/inlineCompletions/test/browser/inlineCompletionsProvider.test.ts

@@ -85,11 +85,18 @@ suite('Inline Completions', () => {
 			assert.deepStrictEqual(getOutput('[\tfoo]', '\t\tfoobar'), { prefix: undefined, subword: '\t[\t]foo[bar]' });
 			assert.deepStrictEqual(getOutput('[(y ===)]', '(y === 1) { f(); }'), { prefix: undefined, subword: '(y ===[ 1])[ { f(); }]' });
 			assert.deepStrictEqual(getOutput('[(y ==)]', '(y === 1) { f(); }'), { prefix: undefined, subword: '(y ==[= 1])[ { f(); }]' });
+
+			assert.deepStrictEqual(getOutput('[(y ==)]', '(y === 1) { f(); }'), { prefix: undefined, subword: '(y ==[= 1])[ { f(); }]' });
 		});
 
 		test('Multi Part Diffing 1', () => {
 			assert.deepStrictEqual(getOutput('[if () ()]', 'if (1 == f()) ()'), { prefix: undefined, subword: 'if ([1 == f()]) ()' });
 		});
+
+		test('Multi Part Diffing 2', () => {
+			assert.deepStrictEqual(getOutput('[)]', '())'), ({ prefix: undefined, subword: "[(])[)]" }));
+			assert.deepStrictEqual(getOutput('[))]', '(())'), ({ prefix: undefined, subword: "[((]))" }));
+		});
 	});
 
 	test('Does not trigger automatically if disabled', async function () {