fix(vertexai): pass GenerativeModel's BaseParams to ChatSession

.changeset/fast-mangos-chew.md

@@ -0,0 +1,5 @@
+---
+'@firebase/vertexai': patch
+---
+
+Pass `GenerativeModel`'s `BaseParams` to created chat sessions. This fixes an issue where `GenerationConfig` would not be inherited from `ChatSession`.

packages/vertexai/src/models/generative-model.test.ts

@@ -165,6 +165,35 @@ describe('GenerativeModel', () => {
     );
     restore();
   });
+  it('passes base model params through to ChatSession when there are no startChatParams', async () => {
+    const genModel = new GenerativeModel(fakeVertexAI, {
+      model: 'my-model',
+      generationConfig: {
+        topK: 1
+      }
+    });
+    const chatSession = genModel.startChat();
+    expect(chatSession.params?.generationConfig).to.deep.equal({
+      topK: 1
+    });
+    restore();
+  });
+  it('overrides base model params with startChatParams', () => {
+    const genModel = new GenerativeModel(fakeVertexAI, {
+      model: 'my-model',
+      generationConfig: {
+        topK: 1
+      }
+    });
+    const chatSession = genModel.startChat({
+      generationConfig: {
+        topK: 2
+      }
+    });
+    expect(chatSession.params?.generationConfig).to.deep.equal({
+      topK: 2
+    });
+  });
   it('passes params through to chat.sendMessage', async () => {
     const genModel = new GenerativeModel(fakeVertexAI, {
       model: 'my-model',

packages/vertexai/src/models/generative-model.ts

@@ -132,6 +132,13 @@ export class GenerativeModel extends VertexAIModel {
         tools: this.tools,
         toolConfig: this.toolConfig,
         systemInstruction: this.systemInstruction,
+        generationConfig: this.generationConfig,
+        safetySettings: this.safetySettings,
+        /**
+         * Overrides params inherited from GenerativeModel with those explicitly set in the
+         * StartChatParams. For example, if startChatParams.generationConfig is set, it'll override
+         * this.generationConfig.
+         */
         ...startChatParams
       },
       this.requestOptions