Add a button to open in android studio.

build.zig

@@ -257,6 +257,19 @@ pub fn build(b: *std.Build) void {
     });
     test_step.dependOn(&b.addRunArtifact(store_tests).step);
 
+    // Only the path rule is tested: finding and running a launcher is the
+    // machine's business, and the rule is what keeps the page from opening a
+    // file outside the review.
+    const studio_tests = b.addTest(.{
+        .root_module = b.createModule(.{
+            .root_source_file = b.path("src/review/studio.zig"),
+            .target = target,
+            .optimize = optimize,
+            .link_libc = true,
+        }),
+    });
+    test_step.dependOn(&b.addRunArtifact(studio_tests).step);
+
     // The mute rules are their own root. Whether a tab is silent at this instant,
     // and what its row menu says about that, is arithmetic on a deadline — and
     // it is the half of notifications that can be wrong without anyone noticing,

src/review/Server.zig

@@ -34,6 +34,7 @@ const Store = @import("Store.zig");
 const assets = @import("assets.zig");
 const git = @import("git.zig");
 const model = @import("model.zig");
+const studio = @import("studio.zig");
 
 const Server = @This();
 
@@ -687,6 +688,10 @@ fn handleApi(
     if (std.mem.eql(u8, path, "file")) {
         return self.handleFile(a, request, repo, query);
     }
+    if (std.mem.eql(u8, path, "studio/open")) {
+        if (method != .POST) return notFound(request);
+        return self.handleOpenInStudio(a, request, repo);
+    }
     if (std.mem.eql(u8, path, "comments")) {
         return switch (method) {
             .GET => writeJson(a, request, .ok, try store.list(a)),
@@ -738,6 +743,10 @@ fn handleRepo(
         .drafts = store.countByStatus(.draft),
         .openComments = store.countByStatus(.submitted),
         .context = tab.ctx,
+        // Whether the file headers should offer to open a file in Android
+        // Studio. Asked on every load rather than once, so installing it while
+        // the app runs is enough for the next reload to pick it up.
+        .studio = studio.find(a, self.io) != null,
     });
 }
 
@@ -918,6 +927,60 @@ fn handleFile(
     });
 }
 
+/// Open one of the review's files in Android Studio, at a line when given one.
+///
+/// The path is the diff's, relative to the work-tree root, and has to stay
+/// inside it; see `studio.isInside`. A file the diff deletes, or one reviewed in
+/// a commit that the work tree has since dropped, is a 404 rather than an IDE
+/// opening onto nothing.
+fn handleOpenInStudio(
+    self: *Server,
+    a: std.mem.Allocator,
+    request: *std.http.Server.Request,
+    repo: git.Repo,
+) !void {
+    const raw = try readBody(a, request) orelse return writeError(
+        a,
+        request,
+        .bad_request,
+        "path is required",
+    );
+    const body = std.json.parseFromSliceLeaky(
+        struct { path: []const u8 = "", line: ?u32 = null },
+        a,
+        raw,
+        .{ .ignore_unknown_fields = true },
+    ) catch return writeError(a, request, .bad_request, "expected {\"path\": \"...\", \"line\": n}");
+    if (!studio.isInside(body.path)) return writeError(
+        a,
+        request,
+        .bad_request,
+        "path must be relative to the repository and stay inside it",
+    );
+
+    const file = try std.fs.path.join(a, &.{ repo.path, body.path });
+    std.Io.Dir.accessAbsolute(self.io, file, .{}) catch return writeError(
+        a,
+        request,
+        .not_found,
+        "that file isn't in the work tree",
+    );
+    const launcher = studio.find(a, self.io) orelse return writeError(
+        a,
+        request,
+        .not_found,
+        "Android Studio wasn't found — put its studio launcher on PATH",
+    );
+
+    studio.open(a, self.io, launcher, repo.path, file, body.line) catch return writeError(
+        a,
+        request,
+        .internal_server_error,
+        "Android Studio could not be started",
+    );
+    return request.respond("", .{ .status = .no_content });
+}
+
 fn handleCreateComment(
     self: *Server,
     a: std.mem.Allocator,

src/review/studio.zig

@@ -0,0 +1,165 @@
+//! Opening a file under review in Android Studio.
+//!
+//! Done through the IDE's own command-line launcher, `studio --line N <file>`,
+//! because that is the entry point that knows about windows. With Studio already
+//! running, the launcher does not start a second copy: it hands the file to the
+//! running instance and exits, and the instance opens it in the window of the
+//! project that contains it — the checkout's own window, not whichever one was
+//! focused last. With nothing running, the launcher *is* Studio starting up, and
+//! it opens the project the file belongs to.
+//!
+//! That second case is why the launcher is not simply a child of the app. A
+//! Studio started from here would land in playpen's own systemd scope, where it
+//! running out of memory would take the app down with it — the failure
+//! `scope.zig` exists to prevent for shells. So it goes into a scope of its own,
+//! and is detached from the request that started it, which must not sit waiting
+//! for an IDE to quit.
+
+const std = @import("std");
+
+/// Launcher names worth finding on PATH: JetBrains Toolbox's shim when its
+/// scripts directory is on PATH, what distro and snap packages install, and the
+/// script a plain tarball ships with.
+const path_names = [_][]const u8{ "studio", "android-studio", "studio.sh" };
+
+/// Where launchers live when nothing put them on PATH, under `$HOME`. Toolbox
+/// writes its shim here whether or not the directory is on PATH, which on a
+/// desktop session started from a launcher it usually is not.
+const home_paths = [_][]const u8{
+    ".local/share/JetBrains/Toolbox/scripts/studio",
+    "android-studio/bin/studio",
+    "android-studio/bin/studio.sh",
+};
+
+/// Where a tarball, a snap or a Flatpak leaves it system-wide.
+const system_paths = [_][]const u8{
+    "/opt/android-studio/bin/studio",
+    "/opt/android-studio/bin/studio.sh",
+    "/usr/local/android-studio/bin/studio.sh",
+    "/snap/bin/android-studio",
+    "/var/lib/flatpak/exports/bin/com.google.AndroidStudio",
+};
+
+/// The Android Studio launcher on this machine, or null if there is none where
+/// one is normally installed. Looked up afresh each time — a handful of
+/// `access` calls — so installing Studio while the app runs is enough.
+pub fn find(a: std.mem.Allocator, io: std.Io) ?[]const u8 {
+    if (std.c.getenv("PATH")) |raw| {
+        var dirs = std.mem.tokenizeScalar(u8, std.mem.span(raw), ':');
+        while (dirs.next()) |dir| {
+            if (!std.fs.path.isAbsolute(dir)) continue;
+            for (path_names) |name| {
+                const candidate = std.fs.path.join(a, &.{ dir, name }) catch return null;
+                if (executable(io, candidate)) return candidate;
+            }
+        }
+    }
+    if (std.c.getenv("HOME")) |raw| {
+        const home = std.mem.span(raw);
+        if (std.fs.path.isAbsolute(home)) for (home_paths) |rel| {
+            const candidate = std.fs.path.join(a, &.{ home, rel }) catch return null;
+            if (executable(io, candidate)) return candidate;
+        };
+    }
+    for (system_paths) |candidate| {
+        if (executable(io, candidate)) return candidate;
+    }
+    return null;
+}
+
+fn executable(io: std.Io, path: []const u8) bool {
+    std.Io.Dir.accessAbsolute(io, path, .{ .execute = true }) catch return false;
+    return true;
+}
+
+/// Whether `path` names something inside the directory it is relative to: not
+/// absolute, and never stepping up out of it. Paths here come from the page, and
+/// a request to show a file under review is no reason to hand an IDE any file
+/// on disk.
+pub fn isInside(path: []const u8) bool {
+    if (path.len == 0 or std.fs.path.isAbsolute(path)) return false;
+    if (std.mem.indexOfScalar(u8, path, 0) != null) return false;
+    var parts = std.mem.splitScalar(u8, path, '/');
+    while (parts.next()) |part| {
+        if (std.mem.eql(u8, part, "..")) return false;
+    }
+    return true;
+}
+
+/// Backgrounds the launcher and exits, so the request returns as soon as it has
+/// started rather than when Studio quits. The launcher's own output goes nowhere:
+/// it would otherwise hold the pipes `std.process.run` is reading open, and the
+/// run would last as long as the IDE does.
+///
+/// The scope is the same bargain `scope.zig` makes for shells, made with
+/// `systemd-run` because this side of the app has no D-Bus connection to make it
+/// with. Only tried when there is a session bus to ask; without one the launcher
+/// runs in the app's own cgroup, as anything did before scopes.
+const launch_script =
+    \\if [ -S "${XDG_RUNTIME_DIR:-/nonexistent}/bus" ] && command -v systemd-run >/dev/null 2>&1; then
+    \\  set -- systemd-run --user --scope --collect --quiet --slice=app.slice \
+    \\    --description="Android Studio (from playpen)" -p OOMPolicy=continue -- "$@"
+    \\fi
+    \\"$@" </dev/null >/dev/null 2>&1 &
+;
+
+/// Open `file`, an absolute path, in Android Studio at `line` (1-based) if one
+/// is given. Returns once the launcher has been started, not once it has opened
+/// anything: the launcher answers nothing back either way.
+pub fn open(
+    a: std.mem.Allocator,
+    io: std.Io,
+    launcher: []const u8,
+    cwd: []const u8,
+    file: []const u8,
+    line: ?u32,
+) !void {
+    var argv: std.ArrayListUnmanaged([]const u8) = .empty;
+    try argv.appendSlice(a, &.{ "sh", "-c", launch_script, "sh", launcher });
+    if (line) |n| try argv.appendSlice(a, &.{ "--line", try std.fmt.allocPrint(a, "{d}", .{n}) });
+    try argv.append(a, file);
+
+    // The server's `Io` hands children an empty environment, which suits git
+    // and would leave the launcher unable to find a display to open a window
+    // on, a session bus for the scope, or even the running instance it is
+    // meant to hand the file to — that is found through `$HOME`. So this one
+    // gets the app's own.
+    var env = try processEnviron().createMap(a);
+    const result = std.process.run(a, io, .{
+        .argv = argv.items,
+        .cwd = .{ .path = cwd },
+        .environ_map = &env,
+        .stdout_limit = .limited(4 * 1024),
+        .stderr_limit = .limited(4 * 1024),
+        .timeout = .{ .duration = .{ .raw = .fromSeconds(5), .clock = .awake } },
+    }) catch |err| {
+        std.log.warn("review: launching Android Studio: {s}", .{@errorName(err)});
+        return error.LaunchFailed;
+    };
+    switch (result.term) {
+        .exited => |code| if (code != 0) {
+            std.log.warn("review: launching Android Studio exited {d}: {s}", .{
+                code, std.mem.trim(u8, result.stderr, " \t\r\n"),
+            });
+            return error.LaunchFailed;
+        },
+        else => return error.LaunchFailed,
+    }
+}
+
+fn processEnviron() std.process.Environ {
+    var n: usize = 0;
+    while (std.c.environ[n] != null) : (n += 1) {}
+    return .{ .block = .{ .slice = std.c.environ[0..n :null] } };
+}
+
+test "isInside keeps paths within the work tree" {
+    try std.testing.expect(isInside("app/src/main/Foo.kt"));
+    try std.testing.expect(isInside("README.md"));
+    try std.testing.expect(isInside("a/..b/c"));
+    try std.testing.expect(!isInside(""));
+    try std.testing.expect(!isInside("/etc/passwd"));
+    try std.testing.expect(!isInside("../elsewhere"));
+    try std.testing.expect(!isInside("app/../../elsewhere"));
+    try std.testing.expect(!isInside("app/.."));
+}

web/src/App.tsx

@@ -629,6 +629,16 @@ export default function App() {
     setLocate({ file, seq: ++locateSeq.current });
   }, []);
 
+  // Success is Studio coming to the front, so only a failure needs saying here.
+  const openInStudio = useCallback(
+    (file: string, line?: number) => {
+      api
+        .openInStudio(file, line)
+        .catch((e) => flash(e instanceof Error ? e.message : String(e)));
+    },
+    [flash],
+  );
+
   const draftCount = useMemo(
     () => comments.filter((c) => c.status === 'draft').length,
     [comments],
@@ -963,6 +973,7 @@ export default function App() {
                 reveal={reveal}
                 onSetViewed={setFileViewed}
                 onLocate={locateFile}
+                onOpenInStudio={repo?.studio ? openInStudio : undefined}
                 onStartDraft={setDraft}
                 onCancelDraft={cancelDraft}
                 onSubmitDraft={submitDraft}

web/src/api.ts

@@ -202,6 +202,11 @@ export const api = {
   reopen: (id: string) => postJSON(`${apiBase}/comments/${id}/reopen`).then(json<Comment>),
 
   // Submits every draft in the review — the same set the rail shows.
+  // Hands the file to Android Studio's launcher, which opens it in the window of
+  // the project containing it. Resolves once the launcher has started, not once
+  // the file is on screen: nothing comes back from the IDE either way.
+  openInStudio: (path: string, line?: number) =>
+    postJSON(`${apiBase}/studio/open`, { path, line }).then(json<void>),
   submit: () => postJSON(`${apiBase}/review/submit`).then(json<{ submitted: number }>),
 
   // Deletes every comment, whatever its status. The reviewer's viewed marks are

web/src/components/DiffView.tsx

@@ -66,6 +66,9 @@ interface Props {
   onSetViewed: (file: string, viewed: boolean, source?: string) => void;
   // Reveals the file in the left rail's file list.
   onLocate: (file: string) => void;
+  // Opens the file in Android Studio at `line`. Absent when there's no Studio to
+  // open it in, which hides the button.
+  onOpenInStudio?: (file: string, line?: number) => void;
   onStartDraft: (d: DraftTarget) => void;
   onCancelDraft: () => void;
   onSubmitDraft: (body: string) => Promise<void>;
@@ -435,6 +438,7 @@ export function DiffView({
   reveal,
   onSetViewed,
   onLocate,
+  onOpenInStudio,
   onStartDraft,
   onCancelDraft,
   onSubmitDraft,
@@ -484,6 +488,7 @@ export function DiffView({
             bodyRef={bodyRef(path)}
             onSetViewed={onSetViewed}
             onLocate={onLocate}
+            onOpenInStudio={onOpenInStudio}
             onStartDraft={onStartDraft}
             onCancelDraft={onCancelDraft}
             onSubmitDraft={onSubmitDraft}
@@ -495,6 +500,21 @@ export function DiffView({
   );
 }
 
+// Where a file's first change sits in the work tree — the line to open it at. A
+// deletion has no line of its own on the new side, so it lands on the line that
+// now sits where the removed ones were.
+function firstChangedLine(hunks: HunkData[]): number | undefined {
+  const hunk = hunks[0];
+  if (!hunk) return undefined;
+  let next = hunk.newStart;
+  for (const change of hunk.changes) {
+    if (change.type === 'insert') return change.lineNumber;
+    if (change.type === 'delete') return Math.max(1, next);
+    next = change.newLineNumber + 1;
+  }
+  return Math.max(1, hunk.newStart);
+}
+
 function statusLabel(type: string): string {
   switch (type) {
     case 'add':
@@ -542,6 +562,7 @@ const FileView = memo(function FileView({
   bodyRef,
   onSetViewed,
   onLocate,
+  onOpenInStudio,
   onStartDraft,
   onCancelDraft,
   onSubmitDraft,
@@ -567,6 +588,7 @@ const FileView = memo(function FileView({
   bodyRef: (el: HTMLElement | null) => void;
   onSetViewed: Props['onSetViewed'];
   onLocate: Props['onLocate'];
+  onOpenInStudio: Props['onOpenInStudio'];
   onStartDraft: (d: DraftTarget) => void;
   onCancelDraft: () => void;
   onSubmitDraft: Props['onSubmitDraft'];
@@ -763,6 +785,21 @@ const FileView = memo(function FileView({
         >
           <Icon name="focus-center" />
         </button>
+        {onOpenInStudio && file.type !== 'delete' && (
+          <button
+            className="icon-btn"
+            onClick={() =>
+              onOpenInStudio(
+                path,
+                firstChangedLine(showingSince ? sinceHunks! : file.hunks),
+              )
+            }
+            title="Open in Android Studio"
+            aria-label="Open in Android Studio"
+          >
+            <Icon name="code" />
+          </button>
+        )}
         {file.type !== 'modify' && (
           <span className={`file-status file-status-${file.type}`}>
             {statusLabel(file.type)}

web/src/components/Icon.tsx

@@ -21,6 +21,7 @@ const PATHS = {
     'M.513 1.513A1.75 1.75 0 0 1 1.75 1h3.5c.55 0 1.07.26 1.4.7l.9 1.2a.25.25 0 0 0 .2.1H13a1 1 0 0 1 1 1v.5H2.75a.75.75 0 0 0 0 1.5h11.978a1 1 0 0 1 .994 1.117L15 13.25A1.75 1.75 0 0 1 13.25 15H1.75A1.75 1.75 0 0 1 0 13.25V2.75c0-.464.184-.91.513-1.237Z',
   'file-diff':
     'M1 1.75C1 .784 1.784 0 2.75 0h7.586c.464 0 .909.184 1.237.513l2.914 2.914c.329.328.513.773.513 1.237v9.586A1.75 1.75 0 0 1 13.25 16H2.75A1.75 1.75 0 0 1 1 14.25Zm1.75-.25a.25.25 0 0 0-.25.25v12.5c0 .138.112.25.25.25h10.5a.25.25 0 0 0 .25-.25V4.664a.25.25 0 0 0-.073-.177l-2.914-2.914a.25.25 0 0 0-.177-.073ZM8 3.25a.75.75 0 0 1 .75.75v1.5h1.5a.75.75 0 0 1 0 1.5h-1.5v1.5a.75.75 0 0 1-1.5 0V7h-1.5a.75.75 0 0 1 0-1.5h1.5V4A.75.75 0 0 1 8 3.25Zm-3 8a.75.75 0 0 1 .75-.75h4.5a.75.75 0 0 1 0 1.5h-4.5a.75.75 0 0 1-.75-.75Z',
+  code: 'm11.28 3.22 4.25 4.25a.75.75 0 0 1 0 1.06l-4.25 4.25a.749.749 0 0 1-1.275-.326.749.749 0 0 1 .215-.734L13.94 8l-3.72-3.72a.749.749 0 0 1 .326-1.275.749.749 0 0 1 .734.215Zm-6.56 0a.751.751 0 0 1 1.042.018.751.751 0 0 1 .018 1.042L2.06 8l3.72 3.72a.749.749 0 0 1-.326 1.275.749.749 0 0 1-.734-.215L.47 8.53a.75.75 0 0 1 0-1.06Z',
   copy: 'M0 6.75C0 5.784.784 5 1.75 5h1.5a.75.75 0 0 1 0 1.5h-1.5a.25.25 0 0 0-.25.25v7.5c0 .138.112.25.25.25h7.5a.25.25 0 0 0 .25-.25v-1.5a.75.75 0 0 1 1.5 0v1.5A1.75 1.75 0 0 1 9.25 16h-7.5A1.75 1.75 0 0 1 0 14.25ZM5 1.75C5 .784 5.784 0 6.75 0h7.5C15.216 0 16 .784 16 1.75v7.5A1.75 1.75 0 0 1 14.25 11h-7.5A1.75 1.75 0 0 1 5 9.25Zm1.75-.25a.25.25 0 0 0-.25.25v7.5c0 .138.112.25.25.25h7.5a.25.25 0 0 0 .25-.25v-7.5a.25.25 0 0 0-.25-.25Z',
   unfold:
     'm8.177.677 2.896 2.896a.25.25 0 0 1-.177.427H8.75v1.25a.75.75 0 0 1-1.5 0V4H5.104a.25.25 0 0 1-.177-.427L7.823.677a.25.25 0 0 1 .354 0ZM7.25 10.75a.75.75 0 0 1 1.5 0V12h2.146a.25.25 0 0 1 .177.427l-2.896 2.896a.25.25 0 0 1-.354 0l-2.896-2.896A.25.25 0 0 1 5.104 12H7.25v-1.25Zm-5-2a.75.75 0 0 0 0-1.5h-.5a.75.75 0 0 0 0 1.5h.5ZM6 8a.75.75 0 0 1-.75.75h-.5a.75.75 0 0 1 0-1.5h.5A.75.75 0 0 1 6 8Zm2.25.75a.75.75 0 0 0 0-1.5h-.5a.75.75 0 0 0 0 1.5h.5ZM12 8a.75.75 0 0 1-.75.75h-.5a.75.75 0 0 1 0-1.5h.5A.75.75 0 0 1 12 8Zm2.25.75a.75.75 0 0 0 0-1.5h-.5a.75.75 0 0 0 0 1.5h.5Z',

web/src/types.ts

@@ -96,6 +96,9 @@ export interface RepoState extends RepoInfo {
   // page publishes one. The browser is the source of truth for what's on screen;
   // this copy is what lets an agent review, and anchor comments to, the same diff.
   context?: DiffContext | null;
+  // Whether this machine has an Android Studio for the file headers to open
+  // files in (see api.openInStudio).
+  studio: boolean;
 }
 
 export interface DiffFile {