fix: show empty docs msg, schema set msg content correctly (#851)

Author: Anemy

src/participant/participant.ts

@@ -792,10 +792,12 @@ export default class ParticipantController {
       // TODO: Remove this when the issue is fixed.
       messagesWithNamespace.messages[
         messagesWithNamespace.messages.length - 1
-      ].content =
+        // eslint-disable-next-line new-cap
+      ] = vscode.LanguageModelChatMessage.User(
         messagesWithNamespace.messages[
           messagesWithNamespace.messages.length - 1
-        ].content.trim() || 'see previous messages';
+        ].content.trim() || 'see previous messages'
+      );
 
       const responseContentWithNamespace = await this.getChatResponseContent({
         modelInput: messagesWithNamespace,
@@ -1359,13 +1361,7 @@ export default class ParticipantController {
         token,
       });
 
-    this._streamResponseReference({
-      reference: {
-        url: MONGODB_DOCS_LINK,
-        title: 'View MongoDB documentation',
-      },
-      stream,
-    });
+    this._streamGenericDocsLink(stream);
 
     this._telemetryService.trackCopilotParticipantResponse({
       command: 'docs/copilot',
@@ -1390,6 +1386,16 @@ export default class ParticipantController {
     stream.markdown(link);
   }
 
+  _streamGenericDocsLink(stream: vscode.ChatResponseStream): void {
+    this._streamResponseReference({
+      reference: {
+        url: MONGODB_DOCS_LINK,
+        title: 'View MongoDB documentation',
+      },
+      stream,
+    });
+  }
+
   async handleDocsRequest(
     ...args: [
       vscode.ChatRequest,
@@ -1400,6 +1406,12 @@ export default class ParticipantController {
   ): Promise<ChatResult> {
     const [request, context, stream, token] = args;
 
+    if (Prompts.isPromptEmpty(request)) {
+      stream.markdown(Prompts.generic.getEmptyRequestResponse());
+      this._streamGenericDocsLink(stream);
+      return emptyRequestChatResult(context.history);
+    }
+
     const chatId = ChatMetadataStore.getChatIdFromHistoryOrNewChatId(
       context.history
     );

src/test/suite/participant/participant.test.ts

@@ -1383,6 +1383,52 @@ suite('Participant Controller Test Suite', function () {
               'What is the name of the database you would like to run against?'
             );
           });
+
+          test('with history, and a blank prompt, it sets a message so it does not cause model error (VSCODE-626)', async function () {
+            const chatRequestMock = {
+              prompt: '',
+              command: 'schema',
+              references: [],
+            };
+            chatContextStub = {
+              history: [
+                Object.assign(Object.create(vscode.ChatRequestTurn.prototype), {
+                  prompt:
+                    'how do I make a find request vs favorite_fruits.pineapple?',
+                  command: 'query',
+                  references: [],
+                  participant: CHAT_PARTICIPANT_ID,
+                }),
+                Object.assign(
+                  Object.create(vscode.ChatResponseTurn.prototype),
+                  {
+                    participant: CHAT_PARTICIPANT_ID,
+                    response: [
+                      {
+                        value: 'some code',
+                      },
+                    ],
+                    command: 'query',
+                    result: {
+                      metadata: {
+                        intent: 'query',
+                        chatId: 'abc',
+                      },
+                    },
+                  }
+                ),
+              ],
+            };
+            await invokeChatHandler(chatRequestMock);
+
+            expect(sendRequestStub.calledOnce).to.be.true;
+            expect(sendRequestStub.firstCall.args[0][0].content).to.include(
+              'Parse all user messages to find a database name and a collection name.'
+            );
+            expect(sendRequestStub.firstCall.args[0][3].content).to.include(
+              'see previous messages'
+            );
+          });
         });
 
         suite(
@@ -1549,7 +1595,26 @@ Schema:
 
         afterEach(function () {
           global.fetch = initialFetch;
-          sinon.restore();
+        });
+
+        test('shows a message and docs link on empty prompt', async function () {
+          fetchStub = sinon.stub().resolves();
+          global.fetch = fetchStub;
+          const chatRequestMock = {
+            prompt: '',
+            command: 'docs',
+            references: [],
+          };
+          const res = await invokeChatHandler(chatRequestMock);
+          expect(fetchStub).to.not.have.been.called;
+          expect(sendRequestStub).to.have.not.been.called;
+          expect(res?.metadata.intent).to.equal('emptyRequest');
+          const defaultEmptyMsg = chatStreamStub.markdown.getCall(0).args[0];
+          expect(defaultEmptyMsg).to.include(
+            'Ask anything about MongoDB, from writing queries to questions a'
+          );
+          const referenceMsg = chatStreamStub.markdown.getCall(1).args[0];
+          expect(referenceMsg.value).to.include('View MongoDB documentation');
         });
 
         test('uses docs chatbot result if available', async function () {