tui: let users review branch changes against main

packages/opencode/src/cli/cmd/tui/feature-plugins/system/diff-viewer.tsx

@@ -33,11 +33,11 @@ const ROUTE = "diff"
 const MIN_SPLIT_WIDTH = 100
 const FILE_TREE_WIDTH = 32
 const PLAIN_TEXT_FILETYPE = "opencode-plain-text"
-const WORKING_TREE_DIFF_CONTEXT_LINES = 12
+const VCS_DIFF_CONTEXT_LINES = 12
 const KV_SHOW_FILE_TREE = "diff_viewer_show_file_tree"
 const KV_SINGLE_PATCH = "diff_viewer_single_patch"
 const KV_VIEW = "diff_viewer_view"
-type DiffMode = "git" | "last-turn"
+type DiffMode = "git" | "branch" | "last-turn"
 type DiffViewerFocus = "patches" | "files"
 type DiffView = "split" | "unified"
 
@@ -75,6 +75,12 @@ function storedView(value: unknown): DiffView | undefined {
   if (value === "split" || value === "unified") return value
 }
 
+function diffSourceLabel(mode: DiffMode) {
+  if (mode === "last-turn") return "last turn"
+  if (mode === "branch") return "main branch"
+  return "working tree"
+}
+
 function DiffViewer(props: { api: TuiPluginApi }) {
   const dimensions = useTerminalDimensions()
   const themeState = useTheme()
@@ -106,7 +112,7 @@ function DiffViewer(props: { api: TuiPluginApi }) {
     }
 
     const result = await props.api.client.vcs.diff(
-      { mode: "git", context: WORKING_TREE_DIFF_CONTEXT_LINES },
+      { mode: input.mode, context: VCS_DIFF_CONTEXT_LINES },
       { throwOnError: true },
     )
     return normalizeDiffs(result.data ?? [])
@@ -609,6 +615,11 @@ function DiffViewer(props: { api: TuiPluginApi }) {
       value: "git" as const,
       description: "Show current git changes",
     },
+    {
+      title: "Main branch",
+      value: "branch" as const,
+      description: "Show changes compared to main branch",
+    },
     {
       title: "Last turn",
       value: "last-turn" as const,
@@ -664,7 +675,7 @@ function DiffViewer(props: { api: TuiPluginApi }) {
       <PanelGroup axis="y" width="100%" height="100%">
         <Panel border="none" flexShrink={0} padding={0} paddingLeft={1}>
           <text fg={theme().text}>Diff </text>
-          <text fg={theme().textMuted}>{mode() === "last-turn" ? "last turn" : "working tree"}</text>
+          <text fg={theme().textMuted}>{diffSourceLabel(mode())}</text>
           <box flexGrow={1} />
           <text fg={theme().textMuted}>
             {files().length} {files().length === 1 ? "file" : "files"}
@@ -874,7 +885,7 @@ function DiffViewerHelpDialog() {
     {
       shortcut: useCommandShortcut("diff.switch_source"),
       action: "Switch source",
-      description: "Choose working tree or last-turn changes",
+      description: "Choose working tree, main branch, or last-turn changes",
     },
     {
       shortcut: useCommandShortcut("diff.toggle_view"),

packages/opencode/test/cli/tui/diff-viewer.test.tsx

@@ -85,6 +85,66 @@ test("closing the diff viewer returns to the route it opened from", async () =>
   }
 })
 
+test("branch diff source requests branch VCS diff", async () => {
+  const calls: Parameters<TuiPluginApi["client"]["vcs"]["diff"]>[0][] = []
+  const current: TuiRouteCurrent = { name: "diff", params: { mode: "branch" } }
+  let renderDiff: TuiRouteDefinition["render"] | undefined
+  await mkdir(Global.Path.state, { recursive: true })
+  await Bun.write(path.join(Global.Path.state, "kv.json"), "{}")
+
+  function Harness() {
+    const renderer = useRenderer()
+    const keymap = createDefaultOpenTuiKeymap(renderer)
+    const base = createTuiPluginApi({
+      keymap,
+      client: {
+        vcs: {
+          diff: async (parameters: Parameters<TuiPluginApi["client"]["vcs"]["diff"]>[0]) => {
+            calls.push(parameters)
+            return { data: [] }
+          },
+        },
+        session: { diff: async () => ({ data: [] }) },
+      } as unknown as TuiPluginApi["client"],
+    })
+    const api = {
+      ...base,
+      route: {
+        register(routes) {
+          renderDiff = routes.find((route) => route.name === "diff")?.render
+          return () => {}
+        },
+        navigate() {},
+        get current() {
+          return current
+        },
+      },
+    } satisfies TuiPluginApi
+
+    void diffViewerPlugin.tui(api, undefined, pluginMeta)
+
+    return (
+      <OpencodeKeymapProvider keymap={keymap}>
+        <TuiConfigProvider config={createTuiResolvedConfig()}>
+          <KVProvider>
+            <ThemeProvider mode="dark">
+              {renderDiff?.({ params: "params" in current ? current.params : undefined })}
+            </ThemeProvider>
+          </KVProvider>
+        </TuiConfigProvider>
+      </OpencodeKeymapProvider>
+    )
+  }
+
+  const app = await testRender(() => <Harness />, { width: 80, height: 20 })
+  try {
+    await waitForCall(app, calls)
+    expect(calls[0]).toEqual({ mode: "branch", context: 12 })
+  } finally {
+    app.renderer.destroy()
+  }
+})
+
 async function waitForCommand(
   app: Awaited<ReturnType<typeof testRender>>,
   commands: Map<string, unknown>,
@@ -97,6 +157,14 @@ async function waitForCommand(
   }
 }
 
+async function waitForCall(app: Awaited<ReturnType<typeof testRender>>, calls: unknown[]) {
+  for (let attempt = 0; attempt < 10; attempt++) {
+    await app.renderOnce()
+    if (calls.length > 0) return
+    await new Promise((resolve) => setTimeout(resolve, 25))
+  }
+}
+
 const pluginMeta = {
   id: "diff-viewer",
   source: "internal",