simulator manager

.bazelrc

@@ -32,7 +32,13 @@ build:clang --host_cxxopt="-fvisibility=hidden"
 
 # iOS setup
 build:ios --ios_multi_cpus=sim_arm64
-build:ios --@rules_apple//apple/build_settings:ios_simulator_device="iPhone 16 Pro"
+# The simulator device is not pinned here: which device profiles exist depends on
+# the installed Xcode's iOS runtime, so any value checked in goes stale. Set it in
+# .bazelrc.user, e.g.
+#
+#     build:ios --@rules_apple//apple/build_settings:ios_simulator_device="iPhone 17"
+#
+# `xcrun simctl list devicetypes` lists what is available locally.
 
 # Platform-specific options for each supported platform.
 build:remote_linux_x64 --extra_execution_platforms=//platform/linux_x64

MODULE.bazel

@@ -129,6 +129,29 @@ use_repo(maven, "maven")
 bazel_dep(name = "rules_kotlin", version = "2.3.20")
 bazel_dep(name = "rules_perl", version = "1.1.1")
 bazel_dep(name = "rules_swift", version = "4.0.0-rc2")
+
+# Swift Package Manager deps, used by //tools/simulator_manager.
+bazel_dep(name = "rules_swift_package_manager", version = "1.22.0")
+
+swift_deps = use_extension(
+    "@rules_swift_package_manager//:extensions.bzl",
+    "swift_deps",
+)
+swift_deps.from_package(
+    declare_swift_deps_info = True,
+    resolved = "//tools/simulator_manager:Package.resolved",
+    swift = "//tools/simulator_manager:Package.swift",
+)
+use_repo(
+    swift_deps,
+    "swift_deps_info",
+    "swift_package",
+    "swiftpkg_shellout",
+    "swiftpkg_swift_argument_parser",
+    "swiftpkg_swift_nio",
+    "swiftpkg_swift_nio_extras",
+)
+
 bazel_dep(name = "rules_nodejs", version = "6.7.4")
 bazel_dep(name = "aspect_rules_ts", version = "3.8.10")
 bazel_dep(name = "aspect_bazel_lib", version = "2.22.5")

ios/BUILD

@@ -1,7 +1,34 @@
 load("@bazel_skylib//rules:build_test.bzl", "build_test")
 load("@rules_apple//apple:ios.bzl", "ios_application", "ios_ui_test", "ios_unit_test")
+load(
+    "@rules_apple//apple/testing/default_runner:ios_xctestrun_runner.bzl",
+    "ios_xctestrun_runner",
+)
 load("@rules_swift//swift:swift.bzl", "swift_library")
 
+# Leases each test its own simulator from //tools/simulator_manager, so
+# concurrent actions on one worker never share a device.
+ios_xctestrun_runner(
+    name = "ios_leased_simulator_runner",
+    clean_up_simulator_action = "//tools/simulator_manager:release_simulator",
+    create_simulator_action = "//tools/simulator_manager:lease_simulator",
+    random = False,
+    # reuse_simulator doubles as the exclusivity toggle for the lease: opting out
+    # of reuse means no other test shares this device.
+    reuse_simulator = False,
+)
+
+# Non-exclusive leases: concurrent tests may share one simulator. Sharing is
+# opportunistic, not bounded — a request only joins a device that is already
+# active, so tests dispatched simultaneously can still each get their own.
+ios_xctestrun_runner(
+    name = "ios_shared_simulator_runner",
+    clean_up_simulator_action = "//tools/simulator_manager:release_simulator",
+    create_simulator_action = "//tools/simulator_manager:lease_simulator",
+    random = False,
+    reuse_simulator = True,
+)
+
 swift_library(
     name = "HelloAppLibrary",
     srcs = ["HelloApp.swift"],
@@ -49,7 +76,102 @@ swift_library(
 ios_ui_test(
     name = "HelloAppUITest",
     minimum_os_version = "26.0",
-    runner = "@rules_apple//apple/testing/default_runner:ios_xctestrun_ordered_runner",
+    runner = ":ios_leased_simulator_runner",
     test_host = ":HelloApp",
     deps = [":HelloAppUITestLib"],
+    exec_properties = {
+        "sandboxAllowed": "False",
+    },
+)
+
+swift_library(
+    name = "HelloConcurrentTestLib",
+    testonly = True,
+    srcs = ["HelloConcurrentTest.swift"],
+    module_name = "HelloConcurrentTest",
+)
+
+# Exercises concurrent leasing: run with --runs_per_test to get several
+# simultaneous leases from one target. Unlike HelloAppUITest this has no test
+# host, so it takes rules_apple's `simctl spawn` path rather than `xcodebuild`.
+#
+#     bazel test --config=ios --runs_per_test=3 //ios:HelloConcurrentTest
+#
+# Each run's log reports its simulator UDID; no two concurrent runs should match.
+# Manual because it is sensitive to how much memory the host has — see the
+# simulator_manager README.
+ios_unit_test(
+    name = "HelloConcurrentTest",
+    minimum_os_version = "26.0",
+    runner = ":ios_leased_simulator_runner",
+    tags = ["manual"],
+    timeout = "long",
+    deps = [":HelloConcurrentTestLib"],
+)
+
+# Same source, but leasing non-exclusively: several concurrent runs should
+# collapse onto fewer devices. Measured on a 16 GiB worker, 8 runs shared 2
+# simulators.
+ios_unit_test(
+    name = "HelloSharedSimulatorTest",
+    minimum_os_version = "26.0",
+    runner = ":ios_shared_simulator_runner",
+    tags = ["manual"],
+    timeout = "long",
+    deps = [":HelloConcurrentTestLib"],
+)
+
+swift_library(
+    name = "HelloDyingHostTestLib",
+    testonly = True,
+    srcs = ["HelloDyingHostTest.swift"],
+    module_name = "HelloDyingHostTest",
+)
+
+# Kills its own test host to check whether that alone produces the
+# "doesn't have a simulator leased" warning. Hosted, so the lease is held by the
+# rules_apple runner script rather than the test host -- see the test source.
+#
+#     bazel test --config=ios --config=opal --config=remote_macos_arm64 \
+#       --test_env=SIMULATOR_MANAGER_DEATH_MODE=signal //ios:HelloDyingHostTest
+ios_unit_test(
+    name = "HelloDyingHostTest",
+    minimum_os_version = "26.0",
+    runner = ":ios_leased_simulator_runner",
+    tags = ["manual"],
+    test_host = ":HelloApp",
+    deps = [":HelloDyingHostTestLib"],
+    exec_properties = {
+        "sandboxAllowed": "False",
+    },
+)
+
+swift_library(
+    name = "HelloHostedSnapshotTestLib",
+    testonly = True,
+    srcs = ["HelloHostedSnapshotTest.swift"],
+    module_name = "HelloHostedSnapshotTest",
 )
+
+# Hosted so rules_apple drives it with `xcodebuild -destination id=`, and leasing
+# exclusively so each concurrent action gets its own device.
+# Run with a high --runs_per_test to put more concurrent actions on a worker than it has
+# simulators:
+#
+#     bazel test --config=ios --config=opal --config=remote_macos_arm64 \
+#       --runs_per_test=8 //ios:HelloHostedSnapshotTest
+#
+# Manual for the same reason as HelloConcurrentTest: sensitive to worker memory.
+ios_unit_test(
+    name = "HelloHostedSnapshotTest",
+    minimum_os_version = "26.0",
+    runner = ":ios_leased_simulator_runner",
+    tags = ["manual"],
+    test_host = ":HelloApp",
+    timeout = "long",
+    deps = [":HelloHostedSnapshotTestLib"],
+    exec_properties = {
+        "sandboxAllowed": "False",
+    },
+)
+

ios/HelloConcurrentTest.swift

@@ -0,0 +1,17 @@
+import XCTest
+
+/// Checks that concurrent tests each lease their own simulator.
+///
+/// Unlike HelloAppConcurrentUITest this has no test host, so rules_apple runs it
+/// via `simctl spawn` rather than `xcodebuild`.
+///
+/// Several targets share this source; each logs its UDID, and no two should
+/// match. The sleep holds the lease long enough for the runs to actually overlap.
+class HelloConcurrentTest: XCTestCase {
+    func testHoldsItsOwnSimulator() {
+        let udid = ProcessInfo.processInfo.environment["SIMULATOR_UDID"] ?? "unknown"
+        print("CONCURRENT_UNIT_TEST_SIMULATOR_UDID=\(udid)")
+        XCTAssertEqual(1 + 1, 2)
+        Thread.sleep(forTimeInterval: 20)
+    }
+}

ios/HelloDyingHostTest.swift

@@ -0,0 +1,48 @@
+import Darwin
+import XCTest
+
+/// Kills its own test host mid-suite, to find out whether a dying test process is
+/// enough to produce a "PID N doesn't have a simulator leased" warning.
+///
+/// The warning means the daemon had no lease for the PID that tried to release
+/// one, which happens when the daemon already reclaimed the lease via its
+/// leaser-exit listener. The open question is *whose* death triggers that: the
+/// lease is keyed on the rules_apple runner script's PID
+/// (`XCTESTRUN_RUNNER_PID`), and that script outlives the test host, so killing
+/// the host may leave the lease untouched.
+///
+/// `SIMULATOR_MANAGER_DEATH_MODE` selects how to die.
+///
+///  * `signal` -- SIGKILL, matching "Test crashed with signal kill before
+///    establishing connection".
+///  * `exit` -- a zero exit, matching "The test runner exited with code 0 before
+///    establishing connection".
+///  * `runner` -- SIGKILL to the rules_apple runner script, i.e. the process that
+///    actually holds the lease. `signal` and `exit` only kill the test host,
+///    which the script outlives, so the script still releases its own live lease
+///    successfully. This mode targets the lease holder itself.
+///
+/// Unset means don't die, so the target is also a control.
+class HelloDyingHostTest: XCTestCase {
+    /// Named to sort before `testDies`: XCTest runs cases alphabetically, so this
+    /// establishes that the suite was really running before the host went away.
+    func testAaaRunsBeforeDying() {
+        let udid = ProcessInfo.processInfo.environment["SIMULATOR_UDID"] ?? "unknown"
+        print("DYING_HOST_SIMULATOR_UDID=\(udid)")
+        print("DYING_HOST_PID=\(getpid())")
+    }
+
+    func testDies() {
+        let mode = ProcessInfo.processInfo.environment["SIMULATOR_MANAGER_DEATH_MODE"] ?? ""
+        print("DYING_HOST_DEATH_MODE=\(mode)")
+
+        switch mode {
+        case "signal":
+            kill(getpid(), SIGKILL)
+        case "exit":
+            exit(0)
+        default:
+            break
+        }
+    }
+}

ios/HelloHostedSnapshotTest.swift

@@ -0,0 +1,56 @@
+import UIKit
+import XCTest
+
+/// The distinguishing features, versus HelloConcurrentTest:
+///
+///  * it has a test host, so rules_apple drives it with `xcodebuild` and a
+///    `-destination id=` rather than `simctl spawn`. `xcodebuild` installs the
+///    host onto the device, which is the step that reports `No matching device`
+///    when a device is removed underneath it.
+///  * it renders views, so it needs a booted UI stack rather than just a process
+///    to run in. A test host that dies mid-render produces the "Restarting after
+///    unexpected exit, crash, or test timeout" line.
+///
+/// Many small cases rather than one long sleep: the failures this is meant to
+/// provoke land between cases -- on install, or on a device pulled out from under
+/// a suite that is partway through -- so the suite needs many opportunities to be
+/// interrupted.
+class HelloHostedSnapshotTest: XCTestCase {
+    func testLogsItsDevice() {
+        let udid = ProcessInfo.processInfo.environment["SIMULATOR_UDID"] ?? "unknown"
+        print("HOSTED_SNAPSHOT_SIMULATOR_UDID=\(udid)")
+    }
+
+    /// Renders a view hierarchy repeatedly, approximating snapshot work: enough
+    /// UIKit and memory traffic per case to make contention on a shared device
+    /// observable, without asserting on images we would then have to record.
+    func testRendersRepeatedly() {
+        for iteration in 0 ..< 40 {
+            let view = UIView(frame: CGRect(x: 0, y: 0, width: 390, height: 844))
+            view.backgroundColor = iteration.isMultiple(of: 2) ? .systemBlue : .systemRed
+
+            let label = UILabel(frame: view.bounds.insetBy(dx: 20, dy: 20))
+            label.text = "iteration \(iteration)"
+            label.numberOfLines = 0
+            view.addSubview(label)
+
+            let renderer = UIGraphicsImageRenderer(bounds: view.bounds)
+            let image = renderer.image { context in
+                view.layer.render(in: context.cgContext)
+            }
+            XCTAssertGreaterThan(image.size.width, 0)
+        }
+    }
+
+    func testPresentsViewControllers() {
+        for _ in 0 ..< 10 {
+            let controller = UIViewController()
+            controller.view.backgroundColor = .white
+            let child = UIViewController()
+            controller.addChild(child)
+            controller.view.addSubview(child.view)
+            child.didMove(toParent: controller)
+            XCTAssertNotNil(controller.view)
+        }
+    }
+}