feat(ask): start chat from selected code range

packages/web/src/app/(app)/components/editorContextMenu.tsx

@@ -2,6 +2,7 @@
 
 import { useToast } from "@/components/hooks/use-toast";
 import { Button } from "@/components/ui/button";
+import { useCreateNewChatThread } from "@/features/chat/useCreateNewChatThread";
 import useCaptureEvent from "@/hooks/useCaptureEvent";
 import { createPathWithQueryParams } from "@/lib/utils";
 import { autoPlacement, computePosition, offset, shift, VirtualElement } from "@floating-ui/react";
@@ -28,6 +29,7 @@ export const EditorContextMenu = ({
     const ref = useRef<HTMLDivElement>(null);
     const { toast } = useToast();
     const captureEvent = useCaptureEvent();
+    const { createChatFromSource } = useCreateNewChatThread();
     useEffect(() => {
         if (selection.empty) {
             ref.current?.classList.add('hidden');
@@ -126,19 +128,47 @@ export const EditorContextMenu = ({
         )
     }, [selection.from, selection.to, repoName, revisionName, path, toast, captureEvent, view]);
 
+    const onAskSourcebot = useCallback(() => {
+        if (selection.empty) {
+            return;
+        }
+
+        const startLine = view.state.doc.lineAt(selection.from).number;
+        const endLine = view.state.doc.lineAt(selection.to - 1).number;
+
+        void createChatFromSource({
+            type: 'file',
+            repo: repoName,
+            path,
+            name: path.split('/').pop() ?? path,
+            revision: revisionName,
+            range: { startLine, endLine },
+        });
+    }, [createChatFromSource, path, repoName, revisionName, selection, view]);
+
     return (
-        <div
-            ref={ref}
-            className="absolute z-10 flex flex-col gap-2 bg-background border border-gray-300 dark:border-gray-700 rounded-md shadow-lg p-2"
-        >
-            <Button
-                variant="ghost"
-                size="sm"
-                onClick={onCopyLinkToSelection}
-            >
-                <Link2Icon className="h-4 w-4 mr-1" />
-                Share selection
-            </Button>
-        </div>
+<div
+  ref={ref}
+  className="absolute z-10 flex items-center gap-1 rounded-lg border border-border bg-popover p-1 shadow-xl"
+>
+  <Button
+    variant="secondary"
+    size="sm"
+    onClick={onCopyLinkToSelection}
+    className="h-8 px-3 hover:bg-black/50"
+  >
+    <Link2Icon className="mr-2 h-4 w-4" />
+    Share selection
+  </Button>
+
+  <Button
+    variant="secondary"
+    size="sm"
+    onClick={onAskSourcebot}
+    className="h-8 px-3 hover:bg-black/50"
+  >
+    Ask SourceBot
+  </Button>
+</div>
     )
-}
+}

packages/web/src/ee/features/chat/agent.test.ts

@@ -121,7 +121,7 @@ vi.mock('ai', async (importOriginal) => {
     };
 });
 
-const { createMessageStream } = await import('./agent');
+const { createMessageStream, sliceFileSourceForPrompt } = await import('./agent');
 const { getPromptCacheStrategy } = await import('./promptCaching');
 
 // Strategies reused across the prompt-caching tests below.
@@ -135,6 +135,33 @@ const listReposInput = {
     direction: 'asc',
 } as const;
 
+describe('sliceFileSourceForPrompt', () => {
+    test('slices an inclusive range and preserves its original line offset', () => {
+        expect(sliceFileSourceForPrompt('one\ntwo\nthree\nfour', {
+            startLine: 2,
+            endLine: 3,
+        })).toEqual({
+            source: 'two\nthree',
+            lineOffset: 2,
+        });
+    });
+
+    test('keeps the full file when there is no selected range', () => {
+        expect(sliceFileSourceForPrompt('one\ntwo', undefined)).toEqual({
+            source: 'one\ntwo',
+            lineOffset: 1,
+        });
+    });
+
+    test.each([
+        { startLine: 0, endLine: 1 },
+        { startLine: 3, endLine: 2 },
+        { startLine: 1, endLine: 4 },
+    ])('ignores invalid ranges safely', (range) => {
+        expect(sliceFileSourceForPrompt('one\ntwo\nthree', range)).toBeUndefined();
+    });
+});
+
 const dynamicApprovalRespondedPart = {
     type: 'dynamic-tool',
     toolName: 'mcp_linear__save_issue',

packages/web/src/ee/features/chat/agent.ts

@@ -21,7 +21,7 @@ import {
 import { randomUUID } from "crypto";
 import _dedent from "dedent";
 import { ANSWER_TAG, FILE_REFERENCE_PREFIX } from "@/features/chat/constants";
-import { Source } from "@/features/chat/types";
+import { FileSource, Source } from "@/features/chat/types";
 import { addLineNumbers, fileReferenceToString, formatAttachmentsForPrompt, getAnswerPartFromAssistantMessage, getTurnProgressState, getUserMessageAttachments, getUserMessageText } from "@/features/chat/utils";
 import { createTools } from "./tools";
 import { getConnectedMcpClients } from "@/ee/features/chat/mcp/mcpClientFactory";
@@ -551,6 +551,29 @@ interface AgentOptions {
     orgId?: number;
 }
 
+export const sliceFileSourceForPrompt = (
+    source: string,
+    range: FileSource['range'],
+): { source: string; lineOffset: number } | undefined => {
+    if (!range) {
+        return { source, lineOffset: 1 };
+    }
+
+    const lines = source.split('\n');
+    if (
+        range.startLine < 1 ||
+        range.endLine < range.startLine ||
+        range.endLine > lines.length
+    ) {
+        return undefined;
+    }
+
+    return {
+        source: lines.slice(range.startLine - 1, range.endLine).join('\n'),
+        lineOffset: range.startLine,
+    };
+};
+
 const createAgentStream = async ({
     model,
     promptCacheStrategy,
@@ -591,12 +614,20 @@ const createAgentStream = async ({
                 return undefined;
             }
 
+            const selectedSource = sliceFileSourceForPrompt(fileSource.source, source.range);
+            if (!selectedSource) {
+                logger.warn(`Ignoring invalid selected range for ${source.repo}:${source.path}`);
+                return undefined;
+            }
+
             return {
                 path: fileSource.path,
-                source: fileSource.source,
+                source: selectedSource.source,
                 repo: fileSource.repo,
                 language: fileSource.language,
                 revision: source.revision,
+                lineOffset: selectedSource.lineOffset,
+                range: source.range,
             };
         }))
     ).filter((source) => source !== undefined);
@@ -999,8 +1030,8 @@ const createPrompt = ({
         <files>
         The user has mentioned the following files, which are automatically included for analysis.
 
-        ${files.map(file => `<file path="${file.path}" repository="${file.repo}" language="${file.language}" revision="${file.revision}">
-            ${addLineNumbers(file.source)}
+        ${files.map(file => `<file path="${file.path}" repository="${file.repo}" language="${file.language}" revision="${file.revision}"${file.range ? ` selected_lines="${file.range.startLine}-${file.range.endLine}"` : ''}>
+            ${addLineNumbers(file.source, file.lineOffset)}
             </file>`).join('\n\n')}
         </files>
         `);

packages/web/src/features/chat/useCreateNewChatThread.ts

@@ -9,7 +9,7 @@ import { useRouter } from "next/navigation";
 import { createChat } from "./actions";
 import { isServiceError } from "@/lib/utils";
 import { createPathWithQueryParams } from "@/lib/utils";
-import { AttachmentData, SearchScope, SetChatStatePayload } from "./types";
+import { AttachmentData, SearchScope, SetChatStatePayload, Source } from "./types";
 import { DISABLED_MCP_SERVER_IDS_LOCAL_STORAGE_KEY, SELECTED_SEARCH_SCOPES_LOCAL_STORAGE_KEY, SET_CHAT_STATE_SESSION_STORAGE_KEY } from "./constants";
 import { useSessionStorage } from "usehooks-ts";
 
@@ -64,8 +64,38 @@ export const useCreateNewChatThread = () => {
         router.push(url);
     }, [router, toast, setChatState]);
 
+    const createChatFromSource = useCallback(async (source: Source) => {
+        const inputMessage = createUIMessage(
+            'Explain this selected code.',
+            [],
+            [],
+            [],
+            [],
+            [source],
+        );
+
+        setIsLoading(true);
+        const response = await createChat({ source: 'sourcebot-web-client' });
+        if (isServiceError(response)) {
+            toast({
+                description: `❌ Failed to create chat. Reason: ${response.message}`,
+            });
+            setIsLoading(false);
+            return;
+        }
+
+        setChatState({
+            inputMessage,
+            selectedSearchScopes: [],
+            disabledMcpServerIds: [],
+        });
+
+        router.push(`/chat/${response.id}`);
+    }, [router, setChatState, toast]);
+
     return {
         createNewChatThread,
+        createChatFromSource,
         isLoading,
     };
 }

packages/web/src/features/chat/utils.test.ts

@@ -769,6 +769,29 @@ test('repairReferences handles malformed inline code blocks', () => {
 });
 
 describe('createUIMessage', () => {
+    test('includes an explicit ranged file source', () => {
+        const result = createUIMessage('Explain this selected code.', [], [], [], [], [{
+            type: 'file',
+            repo: 'github.com/sourcebot-dev/sourcebot',
+            path: 'packages/web/src/auth.ts',
+            name: 'auth.ts',
+            revision: 'main',
+            range: { startLine: 12, endLine: 30 },
+        }]);
+
+        expect(result.parts).toContainEqual({
+            type: 'data-source',
+            data: {
+                type: 'file',
+                repo: 'github.com/sourcebot-dev/sourcebot',
+                path: 'packages/web/src/auth.ts',
+                name: 'auth.ts',
+                revision: 'main',
+                range: { startLine: 12, endLine: 30 },
+            },
+        });
+    });
+
     test('includes disabledMcpServerIds in metadata when provided', () => {
         const result = createUIMessage('hello', [], [], ['server1', 'server2']);
 

packages/web/src/features/chat/utils.ts

@@ -200,7 +200,7 @@ export const addLineNumbers = (source: string, lineOffset = 1) => {
     return source.split('\n').map((line, index) => `${index + lineOffset}: ${line}`).join('\n');
 }
 
-export const createUIMessage = (text: string, mentions: MentionData[], selectedSearchScopes: SearchScope[], disabledMcpServerIds: string[] = [], attachments: AttachmentData[] = []): CreateUIMessage<SBChatMessage> => {
+export const createUIMessage = (text: string, mentions: MentionData[], selectedSearchScopes: SearchScope[], disabledMcpServerIds: string[] = [], attachments: AttachmentData[] = [], explicitSources: Source[] = []): CreateUIMessage<SBChatMessage> => {
     // Converts applicable mentions into sources.
     const sources: Source[] = mentions
         .map((mention) => {
@@ -218,6 +218,7 @@ export const createUIMessage = (text: string, mentions: MentionData[], selectedS
             return undefined;
         })
         .filter((source) => source !== undefined);
+    sources.push(...explicitSources);
     const commandInvocation = createCommandInvocationData(
         text,
         mentions.filter((mention) => mention.type === 'command'),

packages/web/src/features/tools/types.ts

@@ -6,6 +6,10 @@ const fileSourceSchema = z.object({
     path: z.string(),
     name: z.string(),
     revision: z.string(),
+    range: z.object({
+        startLine: z.number().int().positive(),
+        endLine: z.number().int().positive(),
+    }).refine(({ startLine, endLine }) => endLine >= startLine).optional(),
 });
 export type FileSource = z.infer<typeof fileSourceSchema>;