[lawrencecchen]

Summary

Takes back #33023: its -XCTest argv check in CmuxNextTestRunLoopGuard.c is replaced by a stricter gate (the guard installs only in swiftpm-testing-helper), which covers the same xctest leg and also the whole-package swift test XCTest phase that starts xctest <bundle> with no -XCTest (SwiftPM release/6.3 SwiftTestCommand.swift lines 402, 1008-1014); nothing of #33023's behavior is lost.

Update after the feat merge (head 11884af). #33023 (e512575, merged 05:17Z) fixed the same fault on feat in a different way: the guard skips the hold when argv has -XCTest. In the merge conflict I kept one gate: the guard installs nothing unless the process is swiftpm-testing-helper. That covers #33023's case and every other host (an Xcode test host, xctest without -XCTest), and runs_xctest_leg is removed. This PR now adds (1) the stricter gate and (2) the regression test #33023 does not have. At the new base the regression test also passes, because its child xctest has -XCTest in its argv. The red results below are against the old base 362be7b7d362, before #33023.

Base red on feat-cmux-next (STATUS 8187): CmuxNext Swift test steps pass every Swift Testing test, then the XCTest phase of swift test (xctest -XCTest '' …/CmuxNextPackageTests.xctest) hangs for about 10 minutes and ends with "unexpected signal code 6". Seen on aws-m4pro-1, -3, -4, -6, -9 and on Blacksmith macOS 26.

Cause, from the stack of the hung xctest (aws-m4pro-6, feat 305434be55a1, step 3bd61ca1):

_XCTestMain -> -[XCTestDriver _runTests] -> -[XCTFuture value]
  -> +[XCTWaiter _synchronouslyWaitForTimeInterval:] -> CFRunLoopRun -> __CFRunLoopDoBlocks
  -> __cmux_next_test_runloop_guard_install_block_invoke -> guard_hold_the_main_loop -> CFRunLoopRun

The run-loop guard in Tests/Support/CmuxNextTestExitTrace (#25861) queues a block on the main run loop that never returns. That is correct only in swiftpm-testing-helper, whose main is swift_task_asyncMainDrainQueue. xctest loads the same bundle. When XCTest's start-up work is not done at once, XCTest turns the main run loop to wait for it. The guard's block runs in that turn and keeps the main thread, so XCTest never runs its suite. The host-dependent part is only how slow XCTest start-up is. On some hosts a Contacts store lookup in xctest fails for 22 s first: those are the CoreData 134020 / NSXPCConnection lines. On aws-m4pro-1 the same hang came with no CoreData line. No cmux code uses Contacts, AddressBook or CoreData. The CoreData lines are a symptom of a slow start-up, not the abort.

Fix: the guard installs nothing (no observer, no source, no block) in a process that is not swiftpm-testing-helper. In the helper, it works the same as before. Its own regression test (TestProcessExitTests.aStopOfTheOutermostRunLoopDoesNotEndTheTestRun) is unchanged.

Testing

Regression test XCTestPhaseTests.anXCTestWaitInTheXCTestPhaseReturns (red commit 980a603, before the fix): it runs a child xctest of this same bundle with an XCTest probe that waits on an expectation, the same way XCTest's start-up waits. It needs the probe to pass and xctest to exit 0 within 120 s. On the base, the guard keeps the child's main thread on every host, so the test does not depend on a slow start-up.

Focused command (fleet): cmux-ci run --class light --script scripts/ci/package-test-lane.sh --arg suite --arg Packages/macOS/CmuxNext --arg XCTestPhaseTests --arg EmptyLabelMeasureTests --ref SHA --target-worker WORKER

Red: fix/base-red-xctest-red-proof at 69e5a3b7c330 (base 362be7b7d362 plus the head's XCTestPhaseTests.swift, without the one test that calls the new C function; never merge). Green: PR head bc800c77fbe0.

commit	worker	step	XCTestPhaseTests	EmptyLabelMeasureTests	step exit
red 69e5a3b	aws-m4pro-6	7afcf04e	failed after 120.3 s (child xctest killed at the limit; its only output is the guard's "holding the main run loop open" line); then xctest signal 6, 787 s	xctest signal 6 after 2/2 Swift Testing passed, 659 s	1
red 69e5a3b	aws-m4pro-8	7a5152c2	failed after 121.7 s, same three issues	CoreData XPC lines, then failed, 660 s	1
green bc800c7	aws-m4pro-6	fb48cb94	2/2 passed (the XCTest wait returns in 0.15 s); XCTest phase "Executed 0 tests", exit 0; 11 s	2/2 passed; XCTest phase exit 0	0
green bc800c7	aws-m4pro-8	1cfd2401	2/2 passed; XCTest phase exit 0; 11 s	2/2 passed; XCTest phase exit 0; 3 s	0

aws-m4pro-6 failed on the base before (steps 3554f3fe, 3bd61ca1), and it fails at the red commit and passes at the head.

Observed / Not run

Observed: the hung xctest stack above (step 3bd61ca1, from the lane watchdog with a 240 s limit); the four steps in the table; scripts/cmux-next/prepush-gate.py on each push: no new violations. The base passed on aws-m4pro-7 and -9 in some runs (steps 7048809b, 65f92591): the base red needs a slow XCTest start-up, but the new test is red at the red commit on every host, because the probe's own wait(for:) turns the run loop.

Not run: the whole-package swift test (the broad pass); Blacksmith macOS. I did not find what in xctest does the Contacts store lookup (a system framework; no cmux code uses Contacts, AddressBook or CoreData). With the fix, that lookup can only make the XCTest phase slower; it cannot hold it.

Changelog

none

Proof

No capture: test-support code only; nothing in the app changes.

[github-actions]

cmux status _{(one comment, edited in place; each line is updated by the job that owns it)}

Review 11884af: HQ feed card · gallery before/after runs · checks

App of this head (app.zip, kept 1 day)

gh workflow run reload-build.yml -R manaflow-ai/cmux --ref feat-cmux-next -f tag=pr33013 -f ref=fix/base-red-xctest-contacts -f platform=macos -f backend_mode=local

web and size checks: green

Shipped in:

• cmux NEXT nightly 1.0.0-nightly.4160373381601 (d485585f77)
• cmux NEXT nightly 1.0.0-nightly.4160614853601 (0e8eb9bf99)

[blacksmith-sh]

Found 1 test failure on Blacksmith runners:

Failure

Test	View Logs
build_only must be a conjunctive exclusion on the helper, signing, and publication jobs , and must not gate the unsigned app build/ build_only must be a conjunctive exclusion on the helper, signing, and publication jobs , and must not gate the unsigned app build	View Logs

^{Need help on this PR? Tag @codesmith-bot with what you need.}

[lawrencecchen]

Non-green checks at bc800c7, classified: all are base findings in files this PR does not touch.

• cmux-next checks: (1) check-no-process-scan red on cmux-tui/crates/cmux-tui/src/link/machine_update/apply.rs (2 process-scan lines, baseline 1); (2) check-fixture-host-names red on webviews/src/agent-session/acpmux/HarnessStatusCard.gallery.tsx:50.
• defaults-snapshot: check-menu-actions.py red on Packages/macOS/CmuxNext/Sources/CmuxNextTabs/Playground/TabBarPlaygroundNewTabControl.swift.
  This PR changes only Packages/macOS/CmuxNext/Tests/** and one comment in Packages/macOS/CmuxNext/Package.swift.

[lawrencecchen]

Review (independent subagent): SHIP at bc800c7

• Correctness first. The guard now installs only in swiftpm-testing-helper, which swift test uses for Swift Testing on macOS. The direct lane (run-swift-testing-suites.sh, then run_swift_test_bundle.py) and exit-test children use the same helper. Listing runs still return early. No lane runs CmuxNext tests in xcodebuild or in an Xcode test host. xctest has no swift_task_asyncMainDrainQueue exit, so it does not need the guard.
• The guard's own regression test (TestProcessExitTests.aStopOfTheOutermostRunLoopDoesNotEndTheTestRun, including its CMUX_NEXT_TEST_RUNLOOP_GUARD=0 red proof) runs in the helper and works as before.
• Earlier HOLD (03c6725) fixed: the child is now xcrun --find xctest run directly, with SWIFT_TESTING_ENABLED=0, as SwiftPM starts that phase. The header and Package.swift comments are up to date. The test types are nonisolated (the target defaults to the main actor).
• Red proof 69e5a3b is base 362be7b plus the head's test without the new C function. It failed at 120 s on aws-m4pro-6 (7afcf04e) and aws-m4pro-8 (7a5152c2). The lane's own XCTest phase got signal 6 after about 660 s, which is the original base red.
• Green bc800c7 passed on aws-m4pro-6 (fb48cb94) and aws-m4pro-8 (1cfd2401). Both XCTest phases exit 0 and both steps exit 0.
• prepush-gate: no new violations.
• Not shown: the probe inside a whole-package swift test XCTest phase. The child test covers it under the same environment.

[lawrencecchen]

Review (independent subagent): SHIP at 11884af

• The merge of origin/feat-cmux-next (parent 9c84f8f) is correct and complete. Against feat, the diff changes only the 4 PR files. No conflict marker is left. runs_xctest_leg from test(next): the run loop guard never holds the XCTest leg's main loop (signal-6 abort on some fleet Macs) #33023 has no reference left. getprogname/strcmp have their includes. CmuxNextTestExitTrace.c and CmuxNextTestWindowCensus.c include crt_externs.h themselves.
• Removing the argv -XCTest gate loses no case. The name gate (swiftpm-testing-helper only) covers every case the argv gate covers. It also covers an Xcode test host, and xctest when it starts without -XCTest. This is probably the XCTest phase of an unfiltered whole-package swift test; I did not check SwiftPM's source.
• The guard still works in the helper. In fleet step f0ef00e0 (aws-m4pro-6, at this head, exit 0), TestProcessExitTests.aStopOfTheOutermostRunLoopDoesNotEndTheTestRun passed, with restarts 1-3. Both XCTestPhaseTests passed, EmptyLabelMeasureTests passed, and each XCTest leg ended at once.
• Honest note: at the current base (with test(next): the run loop guard never holds the XCTest leg's main loop (signal-6 abort on some fleet Macs) #33023), the child xctest in anXCTestWaitInTheXCTestPhaseReturns has -XCTest in its argv, so that test also passes at the base. It was red at the old base 362be7b (before test(next): the run loop guard never holds the XCTest leg's main loop (signal-6 abort on some fleet Macs) #33023). Now it protects against a regression. Optional follow-up: also start the child with no -XCTest, to get a red at the current base.