Cody Web: Fix no embeddings use case (#51082)

Reported here:
https://github.com/sourcegraph/sourcegraph/pull/51072#issuecomment-1521295540

Right now, Cody web simply crashes when encountering a repo that has no
embeddings. This is because it falls back to the keyword based
implementation which throws on the web (we won't have it there for a
while, because the vs code extension uses a native library to implement
that).

Since Cody is now useful even for unindexed repos (because we add the
currently viewed file into the context automatically), I think making it
gracefully handle this situation is better than disabling Cody for these
views.

## Test plan

<img width="593" alt="Screenshot 2023-04-25 at 12 15 13"
src="https://user-images.githubusercontent.com/458591/234247521-281859da-4c34-4c2c-b451-f355d0e7e2f7.png">


<!-- All pull requests REQUIRE a test plan:
https://docs.sourcegraph.com/dev/background-information/testing_principles
-->

client/cody-shared/src/chat/client.ts

@@ -4,7 +4,6 @@ import { Editor } from '../editor'
 import { PrefilledOptions, withPreselectedOptions } from '../editor/withPreselectedOptions'
 import { SourcegraphEmbeddingsSearchClient } from '../embeddings/client'
 import { SourcegraphIntentDetectorClient } from '../intent-detector/client'
-import { KeywordContextFetcher } from '../keyword-context'
 import { SourcegraphBrowserCompletionsClient } from '../sourcegraph-api/completions/browserClient'
 import { SourcegraphGraphQLAPIClient } from '../sourcegraph-api/graphql/client'
 import { isError } from '../utils'
@@ -63,7 +62,7 @@ export async function createClient({
 
     const embeddingsSearch = repoId ? new SourcegraphEmbeddingsSearchClient(graphqlClient, repoId) : null
 
-    const codebaseContext = new CodebaseContext(config, embeddingsSearch, noopKeywordFetcher)
+    const codebaseContext = new CodebaseContext(config, embeddingsSearch, null)
 
     const intentDetector = new SourcegraphIntentDetectorClient(graphqlClient)
 
@@ -142,10 +141,3 @@ export async function createClient({
         },
     }
 }
-
-const noopKeywordFetcher: KeywordContextFetcher = {
-    // eslint-disable-next-line @typescript-eslint/require-await
-    async getContext() {
-        throw new Error('noopKeywordFetcher: not implemented')
-    },
-}

client/cody-shared/src/chat/context.ts

@@ -5,4 +5,5 @@ export interface ChatContextStatus {
     connection?: boolean
     codebase?: string
     filePath?: string
+    supportsKeyword?: boolean
 }

client/cody-shared/src/codebase-context/index.ts

@@ -17,7 +17,7 @@ export class CodebaseContext {
     constructor(
         private config: Pick<Configuration, 'useContext'>,
         private embeddings: EmbeddingsSearch | null,
-        private keywords: KeywordContextFetcher
+        private keywords: KeywordContextFetcher | null
     ) {}
 
     public onConfigurationChange(newConfig: typeof this.config): void {
@@ -81,6 +81,10 @@ export class CodebaseContext {
     }
 
     private async getKeywordContextMessages(query: string, options: ContextSearchOptions): Promise<ContextMessage[]> {
+        if (!this.keywords) {
+            return []
+        }
+
         const results = await this.keywords.getContext(query, options.numCodeResults + options.numTextResults)
         return results.flatMap(({ content, fileName }) => {
             const messageText = populateCodeContextTemplate(content, fileName)

client/cody-ui/src/chat/inputContext/ChatInputContext.tsx

@@ -37,9 +37,12 @@ export const ChatInputContext: React.FunctionComponent<{
 
     return (
         <div className={classNames(styles.container, className)}>
-            <h3 className={styles.badge}>
-                {contextStatus.mode && contextStatus.connection ? 'Embeddings' : 'Keyword'}
-            </h3>
+            {contextStatus.mode && contextStatus.connection ? (
+                <h3 className={styles.badge}>Embeddings</h3>
+            ) : contextStatus.supportsKeyword ? (
+                <h3 className={styles.badge}>Keyword</h3>
+            ) : null}
+
             {items.length > 0 && (
                 <ul className={styles.items}>
                     {items.map(({ icon, text, tooltip }, index) => (

client/cody/src/chat/ChatViewProvider.ts

@@ -326,6 +326,7 @@ export class ChatViewProvider implements vscode.WebviewViewProvider, vscode.Disp
                     connection: this.codebaseContext.checkEmbeddingsConnection(),
                     codebase: this.config.codebase,
                     filePath: editorContext ? vscode.workspace.asRelativePath(editorContext.filePath) : undefined,
+                    supportsKeyword: true,
                 },
             })
         }

client/web/src/stores/codyChat.ts

@@ -187,6 +187,7 @@ export const useChatStoreState = create<CodyChatStore>((set, get): CodyChatStore
         return {
             codebase: config?.codebase,
             filePath: editor?.getActiveTextEditorSelectionOrEntireFile()?.fileName,
+            supportsKeyword: false,
             mode: config?.useContext,
             connection: true,
         }