Add full-file context to experimental plugin diffs

apps/app/src/components/code/DiffHost.test.tsx

@@ -3,7 +3,10 @@ import { cleanup, render, screen } from "@testing-library/react";
 import { createStore, Provider as JotaiProvider } from "jotai";
 import { act } from "react";
 import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
-import type { PluginDiffRendererProps } from "@get-bb/plugin-sdk";
+import type {
+  ExperimentalDiffFullFileContents,
+  PluginDiffRendererProps,
+} from "@get-bb/plugin-sdk";
 import { defaultResolvedCodeTheme } from "@bb/domain";
 import { applyResolvedCodeTheme } from "@/lib/code-theme";
 import {
@@ -58,6 +61,29 @@ const PATCH = [
   "",
 ].join("\n");
 
+const FULL_FILE_CONTENTS = {
+  old: {
+    path: "src/app.ts",
+    content: [
+      "const a = 1;",
+      "const b = 2;",
+      "const c = 4;",
+      "const oldTail = true;",
+      "",
+    ].join("\n"),
+  },
+  new: {
+    path: "src/app.ts",
+    content: [
+      "const a = 1;",
+      "const b = 3;",
+      "const c = 4;",
+      "const newTail = true;",
+      "",
+    ].join("\n"),
+  },
+} satisfies ExperimentalDiffFullFileContents;
+
 function parseFixture() {
   const file = parseGitDiffFiles(PATCH)[0];
   if (file === undefined) throw new Error("fixture patch did not parse");
@@ -77,9 +103,7 @@ function registerDiffRenderer(
     sidebarFooterActions: [],
     fileOpeners: [],
     messageDirectives: [],
-    diffRenderers: [
-      { id: "diffs", title: "Demo diffs", component },
-    ],
+    diffRenderers: [{ id: "diffs", title: "Demo diffs", component }],
   });
 }
 
@@ -106,7 +130,12 @@ describe("DiffHost", () => {
     });
 
     render(
-      <DiffHost file={parseFixture()} patchText={PATCH} view="split" />,
+      <DiffHost
+        file={parseFixture()}
+        patchText={PATCH}
+        fullFileContents={null}
+        view="split"
+      />,
     );
 
     expect(await screen.findByTestId("plugin-diff")).toBeDefined();
@@ -128,6 +157,7 @@ describe("DiffHost", () => {
       <DiffHost
         file={parseFixture()}
         patchText={PATCH}
+        fullFileContents={FULL_FILE_CONTENTS}
         view="split"
         overflow="wrap"
         showLineNumbers={false}
@@ -142,6 +172,7 @@ describe("DiffHost", () => {
     expect(props?.view).toBe("split");
     expect(props?.overflow).toBe("wrap");
     expect(props?.showLineNumbers).toBe(false);
+    expect(props?.experimental_fullFileContents).toBe(FULL_FILE_CONTENTS);
     expect(Object.keys(props ?? {})).not.toContain("onSelectionAddToChat");
     expect(Object.keys(props ?? {})).not.toContain("file");
   });
@@ -152,7 +183,7 @@ describe("DiffHost", () => {
       return <div data-testid="plugin-diff">plugin diff</div>;
     });
 
-    render(<DiffHost file={parseFixture()} />);
+    render(<DiffHost file={parseFixture()} fullFileContents={null} />);
 
     await screen.findByTestId("plugin-diff");
     const patch = receivedProps.at(-1)?.patch ?? "";
@@ -173,7 +204,13 @@ describe("DiffHost", () => {
       path.endsWith(".ts") ? <Original /> : <div>plugin diff</div>,
     );
 
-    render(<DiffHost file={parseFixture()} patchText={PATCH} />);
+    render(
+      <DiffHost
+        file={parseFixture()}
+        patchText={PATCH}
+        fullFileContents={null}
+      />,
+    );
 
     expect(await screen.findByTestId("bb-diff")).toBeDefined();
     expect(bbDiff.loaded).toBe(true);
@@ -191,7 +228,11 @@ describe("DiffHost", () => {
 
     render(
       <JotaiProvider store={store}>
-        <DiffHost file={parseFixture()} patchText={PATCH} />
+        <DiffHost
+          file={parseFixture()}
+          patchText={PATCH}
+          fullFileContents={null}
+        />
       </JotaiProvider>,
     );
 
@@ -230,7 +271,11 @@ describe("DiffHost", () => {
 
     render(
       <JotaiProvider store={store}>
-        <DiffHost file={parseFixture()} patchText={PATCH} />
+        <DiffHost
+          file={parseFixture()}
+          patchText={PATCH}
+          fullFileContents={null}
+        />
       </JotaiProvider>,
     );
 
@@ -245,13 +290,19 @@ describe("DiffHost", () => {
       throw new Error("replacement exploded");
     });
 
-    render(<DiffHost file={parseFixture()} patchText={PATCH} />);
+    render(
+      <DiffHost
+        file={parseFixture()}
+        patchText={PATCH}
+        fullFileContents={null}
+      />,
+    );
 
     expect(await screen.findByTestId("bb-diff")).toBeDefined();
   });
 
   it("uses BB's renderer with resolved presentation defaults when nothing is registered", async () => {
-    render(<DiffHost file={parseFixture()} />);
+    render(<DiffHost file={parseFixture()} fullFileContents={null} />);
 
     await screen.findByTestId("bb-diff");
     expect(bbDiff.lastProps?.view).toBe("unified");
@@ -271,6 +322,7 @@ describe("experimental_Diff", () => {
 
     await screen.findByTestId("plugin-diff");
     expect(receivedProps.at(-1)?.path).toBe("src/app.ts");
+    expect(receivedProps.at(-1)?.experimental_fullFileContents).toBeNull();
     expect(bbDiff.loaded).toBe(false);
   });
 
@@ -296,6 +348,24 @@ describe("experimental_Diff", () => {
     expect(patch).not.toContain("\r");
   });
 
+  it("enriches BB's renderer with complete file contents for context expansion", async () => {
+    render(
+      <PluginDiff
+        patch={PATCH}
+        path="src/app.ts"
+        experimental_fullFileContents={FULL_FILE_CONTENTS}
+      />,
+    );
+
+    await screen.findByTestId("bb-diff");
+    const file = bbDiff.lastProps?.file as ReturnType<
+      typeof parseFixture
+    > | null;
+    expect(file?.isPartial).toBe(false);
+    expect(file?.additionLines).toContain("const newTail = true;\n");
+    expect(bbDiff.lastProps?.expansionLineCount).toBe(30);
+  });
+
   it("degrades to plain text instead of an empty diff when the patch will not parse", () => {
     render(<PluginDiff patch="not a patch at all" path="notes.txt" />);
 

apps/app/src/components/code/DiffHost.tsx

@@ -1,4 +1,5 @@
 import { Suspense, lazy, useMemo, type ReactNode } from "react";
+import type { ExperimentalDiffFullFileContents } from "@get-bb/plugin-sdk";
 import { PluginReplacementSlot } from "@/components/plugin/PluginReplacementSlot";
 import type { ParsedGitDiffFile } from "@/components/git-diff/git-diff-parsing";
 import { buildFileDiffPatchText } from "@/components/git-diff/git-diff-patch-text";
@@ -14,11 +15,14 @@ const DIFF_RENDERER_SLOT_KIND = "diffRenderer";
 
 const BbDiff = lazy(() => import("./BbDiff"));
 
+/** Unchanged lines revealed by one built-in expand-context action. */
+const DEFAULT_DIFF_EXPANSION_LINE_COUNT = 30;
+
 interface DiffHostProps extends Partial<DiffPresentation> {
   /**
    * The parsed diff to render. Callers parse it anyway for their own header,
-   * and the diff panel additionally enriches it with full file contents so the
-   * renderer can expand context between hunks.
+   * and callers with full file contents additionally enrich it so the renderer
+   * can expand context between hunks.
    */
   file: ParsedGitDiffFile;
   /**
@@ -27,13 +31,9 @@ interface DiffHostProps extends Partial<DiffPresentation> {
    * reconstructs an equivalent single-file patch from `file`.
    */
   patchText?: string;
+  /** Resolved semantic context forwarded to renderer replacements. */
+  fullFileContents: ExperimentalDiffFullFileContents | null;
   className?: string;
-  /**
-   * Forwarded to BB's renderer; see {@link BbDiffProps.expansionLineCount}.
-   * Never reaches a plugin replacement — context expansion is a BB renderer
-   * capability, not part of the semantic contract.
-   */
-  expansionLineCount?: number;
   /** Rendered while BB's renderer chunk loads. */
   fallback?: ReactNode;
   onSelectionAddToChat?: (text: string) => void;
@@ -45,6 +45,8 @@ interface DiffHostProps extends Partial<DiffPresentation> {
  * the environment diff panel's file bodies — and every plugin that calls
  * `experimental_Diff` renders through here, so one
  * `experimental_diffRenderer` registration replaces them all at once.
+ * Resolved full-file text is semantic input: the built-in renderer uses the
+ * enriched parsed file, while a replacement receives the plain text sides.
  *
  * BB's own renderer sits behind `lazy()`. A plugin replacement that never
  * delegates therefore never downloads it, and `experimental_Original` costs
@@ -53,11 +55,11 @@ interface DiffHostProps extends Partial<DiffPresentation> {
 export function DiffHost({
   file,
   patchText,
+  fullFileContents,
   view = DEFAULT_DIFF_VIEW,
   overflow = DEFAULT_CODE_OVERFLOW,
   showLineNumbers = true,
   className,
-  expansionLineCount,
   fallback = null,
   onSelectionAddToChat,
 }: DiffHostProps) {
@@ -66,8 +68,7 @@ export function DiffHost({
   // Only reconstructed when a replacement will actually read it: the walk is
   // proportional to the rendered hunks, and BB's own renderer never needs it.
   const semanticPatch = useMemo(
-    () =>
-      isReplaced ? (patchText ?? buildFileDiffPatchText(file)) : "",
+    () => (isReplaced ? (patchText ?? buildFileDiffPatchText(file)) : ""),
     [file, isReplaced, patchText],
   );
 
@@ -79,7 +80,11 @@ export function DiffHost({
         overflow={overflow}
         showLineNumbers={showLineNumbers}
         className={className}
-        expansionLineCount={expansionLineCount}
+        expansionLineCount={
+          fullFileContents !== null && file.isPartial === false
+            ? DEFAULT_DIFF_EXPANSION_LINE_COUNT
+            : undefined
+        }
         onSelectionAddToChat={onSelectionAddToChat}
       />
     </Suspense>
@@ -99,6 +104,7 @@ export function DiffHost({
             view={view}
             overflow={overflow}
             showLineNumbers={showLineNumbers}
+            experimental_fullFileContents={fullFileContents}
             experimental_Original={BoundOriginal}
           />
         </div>

apps/app/src/components/code/code-rendering.ts

@@ -65,9 +65,9 @@ export interface BbDiffProps extends DiffPresentation {
   className?: string;
   /**
    * How many unchanged lines each expand-context click reveals. Set ONLY by a
-   * caller that can attach full file contents to `file`: pierre renders an
-   * empty diff when it is given an expansion budget for a hunk-only patch,
-   * which is what the timeline supplies.
+   * host that received complete file contents and a successfully enriched
+   * `file`: pierre renders an empty diff when it is given an expansion budget
+   * for a hunk-only patch, which is what the timeline supplies.
    */
   expansionLineCount?: number;
   onSelectionAddToChat?: (text: string) => void;