fix(chat): preserve #file reference when editing text before it

src/vs/workbench/contrib/chat/browser/attachments/chatDynamicVariables.ts

@@ -102,13 +102,23 @@ export class ChatDynamicVariableModel extends Disposable implements IChatWidgetC
 						change.rangeOffset <= data.rangeOffset
 						&& change.rangeOffset + change.rangeLength >= data.rangeOffset + data.text.length
 					);
-					const preservedRange = replacement && this.findReferenceRangeInReplacement(model, e.changes, replacement, data);
+
+					const touchesReference = e.changes.some(change =>
+						change.rangeOffset < data.rangeOffset + data.text.length
+						&& change.rangeOffset + change.rangeLength > data.rangeOffset
+					);
+
+					const preservedRange = replacement
+						? this.findReferenceRangeInReplacement(model, e.changes, replacement, data)
+						: !touchesReference
+							? this.findReferenceRangeForNonOverlappingEdit(model, e.changes, data)
+							: undefined;
 					if (preservedRange) {
 						didChange = true;
 						return { ...ref, range: preservedRange };
 					}
 
-					if (!replacement) {
+					if (!replacement && touchesReference) {
 						this.widget.inputEditor.executeEdits(this.id, [{
 							range: newRange,
 							text: '',
@@ -176,6 +186,25 @@ export class ChatDynamicVariableModel extends Disposable implements IChatWidgetC
 		return model.getValueInRange(range) === data.text ? range : undefined;
 	}
 
+	private findReferenceRangeForNonOverlappingEdit(
+		model: ITextModel,
+		changes: readonly IModelContentChange[],
+		data: { text: string; rangeOffset: number }
+	): Range | undefined {
+		if (!data.text) {
+			return undefined;
+		}
+
+		const precedingChangesDelta = changes.reduce((delta, change) =>
+			change.rangeOffset < data.rangeOffset ? delta + change.text.length - change.rangeLength : delta, 0);
+		const startOffset = data.rangeOffset + precedingChangesDelta;
+		const range = Range.fromPositions(
+			model.getPositionAt(startOffset),
+			model.getPositionAt(startOffset + data.text.length)
+		);
+		return model.getValueInRange(range) === data.text ? range : undefined;
+	}
+
 	getInputState(contrib: Record<string, unknown>): void {
 		contrib[ChatDynamicVariableModel.ID] = [...this._variables];
 	}

src/vs/workbench/contrib/chat/test/browser/attachments/chatVariables.test.ts

@@ -435,4 +435,84 @@ suite('ChatDynamicVariableModel', () => {
 			hasImageDecorationHover: false,
 		});
 	});
+
+	test('recovers a reference range after a delete strictly before it', () => {
+		const { editor, model } = createDynamicVariableModel('explain #sym:example ');
+		model.addReference(createMockVariable({
+			range: new Range(1, 9, 1, 21),
+		}));
+
+		editor.executeEdits('test', [{
+			range: new Range(1, 8, 1, 9),
+			text: '',
+		}]);
+
+		assert.deepStrictEqual({
+			text: editor.getValue(),
+			variables: model.variables.map(variable => variable.range),
+		}, {
+			text: 'explain#sym:example ',
+			variables: [new Range(1, 8, 1, 20)],
+		});
+	});
+
+	test('recovers a reference range after a replace strictly before it', () => {
+		const { editor, model } = createDynamicVariableModel('explain #sym:example ');
+		model.addReference(createMockVariable({
+			range: new Range(1, 9, 1, 21),
+		}));
+
+		editor.executeEdits('test', [{
+			range: new Range(1, 1, 1, 8),
+			text: 'describe',
+		}]);
+
+		assert.deepStrictEqual({
+			text: editor.getValue(),
+			variables: model.variables.map(variable => variable.range),
+		}, {
+			text: 'describe #sym:example ',
+			variables: [new Range(1, 10, 1, 22)],
+		});
+	});
+
+	test('removes the reference when a delete touches its first character', () => {
+		const { editor, model } = createDynamicVariableModel('explain #sym:example ');
+		model.addReference(createMockVariable({
+			range: new Range(1, 9, 1, 21),
+		}));
+
+		editor.executeEdits('test', [{
+			range: new Range(1, 9, 1, 10),
+			text: '',
+		}]);
+
+		assert.deepStrictEqual({
+			text: editor.getValue(),
+			variables: model.variables,
+		}, {
+			text: 'explain  ',
+			variables: [],
+		});
+	});
+
+	test('recovers a reference range across edits before and after it', () => {
+		const { editor, model } = createDynamicVariableModel('explain #sym:example please');
+		model.addReference(createMockVariable({
+			range: new Range(1, 9, 1, 21),
+		}));
+
+		editor.executeEdits('test', [
+			{ range: new Range(1, 1, 1, 8), text: 'describe' },
+			{ range: new Range(1, 22, 1, 28), text: 'now' },
+		]);
+
+		assert.deepStrictEqual({
+			text: editor.getValue(),
+			variables: model.variables.map(variable => variable.range),
+		}, {
+			text: 'describe #sym:example now',
+			variables: [new Range(1, 10, 1, 22)],
+		});
+	});
 });