fix https://github.com/microsoft/vscode-copilot/issues/9509 (#231926)

src/vs/workbench/api/common/extHostTypes.ts

@@ -4608,30 +4608,34 @@ export class LanguageModelChatMessage implements vscode.LanguageModelChatMessage
 
 	role: vscode.LanguageModelChatMessageRole;
 
-	// Temp to avoid breaking changes
-	content2: (string | LanguageModelToolResultPart | LanguageModelToolCallPart)[] | undefined;
+	content: (LanguageModelTextPart | LanguageModelToolResultPart | LanguageModelToolCallPart)[];
 
-	private _content: (LanguageModelTextPart | LanguageModelToolResultPart | LanguageModelToolCallPart)[];
-	get content(): (LanguageModelTextPart | LanguageModelToolResultPart | LanguageModelToolCallPart)[] {
-		// Temp for back-compat
-		if (this.content2) {
-			return this.content2.map(part => {
+	// Temp to avoid breaking changes
+	set content2(value: (string | LanguageModelToolResultPart | LanguageModelToolCallPart)[] | undefined) {
+		if (value) {
+			this.content = value.map(part => {
 				if (typeof part === 'string') {
 					return new LanguageModelTextPart(part);
 				}
-
 				return part;
 			});
 		}
+	}
 
-		return this._content;
+	get content2(): (string | LanguageModelToolResultPart | LanguageModelToolCallPart)[] | undefined {
+		return this.content.map(part => {
+			if (part instanceof LanguageModelTextPart) {
+				return part.value;
+			}
+			return part;
+		});
 	}
 
 	name: string | undefined;
 
 	constructor(role: vscode.LanguageModelChatMessageRole, content: string | (LanguageModelTextPart | LanguageModelToolResultPart | LanguageModelToolCallPart)[], name?: string) {
 		this.role = role;
-		this._content = typeof content === 'string' ? [new LanguageModelTextPart(content)] : content;
+		this.content = typeof content === 'string' ? [new LanguageModelTextPart(content)] : content;
 		this.name = name;
 	}
 }

src/vs/workbench/api/test/browser/extHostTypes.test.ts

@@ -775,4 +775,20 @@ suite('ExtHostTypes', function () {
 		assert.throws(() => types.FileDecoration.validate({ badge: 'புன்சிரிப்போடு' }));
 		assert.throws(() => types.FileDecoration.validate({ badge: 'ããã' }));
 	});
+
+	test('No longer possible to set content on LanguageModelChatMessage', function () {
+		const m = types.LanguageModelChatMessage.Assistant('');
+		m.content = [new types.LanguageModelToolCallPart('toolCall.tool.name', 'toolCall.call.callId', 'toolCall.call.parameters')];
+
+		assert.equal(m.content.length, 1);
+		assert.equal(m.content2?.length, 1);
+
+
+		m.content2 = ['foo'];
+		assert.equal(m.content.length, 1);
+		assert.ok(m.content[0] instanceof types.LanguageModelTextPart);
+
+		assert.equal(m.content2?.length, 1);
+		assert.ok(typeof m.content2[0] === 'string');
+	});
 });