fix(build): turn off Xcode's Thread Performance Checker in the iOS scheme

[ndonkoHenri]

Fixes #5480

Problem

Apps built with flet build that use sqlite3 stop when run from Xcode on iOS 18 or later:

Assertion failed: (0), function isBulkReadStatement, file SQLiteDatabaseTracking.cpp, line 711.

The assert isn't in SQLite or Flet. It's in libRPAC.dylib, Xcode's Thread Performance Checker, which Xcode's Run injects into the app and, for iOS 18+ destinations, configures with its launch disk-write checks on (PERFC_ENABLE_AGPC_DISKWRITES_LAUNCH_CHECKS=1). On iOS the library wraps 19 sqlite3_* functions: the close wrapper stops tracking a connection before closing it, and the finalize wrapper asserts when a statement's connection isn't tracked. So any sqlite3_finalize() after a close aborts, although SQLite allows it. Even sqlite3_close() returning SQLITE_BUSY, with the connection still open, followed by sqlite3_finalize() aborts.

CPython (the same code in 3.12, 3.13 and 3.14) finalizes after closing when:

• a connection is garbage-collected instead of closed. Its statement cache references it, so the cycle collector frees it, and the abort lands at the next collection rather than where the connection went out of scope;
• with sqlite3.connect(...) is used, which commits but doesn't close;
• a connection is closed while a cursor still has unread rows.

An explicit close() finalizes statements first, which is why the snippet posted in the issue doesn't crash.

Nothing outside Xcode's Run loads the checker: flutter run/flet debug on a simulator, home-screen launches, TestFlight and the App Store are unaffected. Xcode turns these checks on only for iOS 18+ destinations, which is why downgrading the simulator runtime "fixed" it in the issue comments. With Xcode 26+, flet debug ios on a physical device launches through LLDB (Flutter's lldbDebugging, on by default) and only falls back to Xcode's Run if that fails.

Changes

• iOS build template Runner.xcscheme: the LaunchAction sets disablePerformanceAntipatternChecker = "YES", the setting behind the Thread Performance Checker checkbox in the scheme's Diagnostics tab. Only Xcode's Run uses it; builds and archives are unchanged. Anyone who wants the checker can turn it back on in the scheme editor.
• Changelog entry.

No docs change: flet build re-renders the template when the Flet version changes, so existing projects pick this up on upgrade.

Why not the alternatives

• PERFC_ENABLE_SQLITE_WRITE_STATEMENT_INSPECTION=0 in the scheme's environment: also fixes it (verified) and keeps the checker's other warnings, but it's an undocumented internal switch that Apple can rename.
• Linking SQLite statically into _sqlite3: the checker would no longer see the calls, but it adds app size and CVE upkeep for a debug-only problem.
• client/ios: doesn't embed Python, and the checker's warnings are useful to people working on the client natively, so it's unchanged.

Testing

Xcode 27.0 (27A266a), iOS 18.6 simulator (iPhone 16 Pro), Python 3.14.7, an app built with flet build ios-simulator and started with Xcode's Run action (driven over JXA, as flutter_tools does):

Scenario	Current scheme	With this change
Connection never closed	aborts	runs
with sqlite3.connect()	aborts	runs
close() with unread rows	aborts¹	runs

¹ Launched with the environment Xcode injects (simctl launch) rather than through Xcode itself.

• Current scheme: an LLDB breakpoint on __assert_rtn caught isBulkReadStatement (SQLiteDatabaseTracking.cpp, line 711), called from libRPAC's interposed_sqlite3_finalize, called from _sqlite3. The code from the issue runs even with the current scheme, since it closes explicitly.
• With this change: libRPAC isn't loaded, and the scheme's custom LLDB init file still loads, so debugging is unaffected.
• The attribute survives Flutter's scheme migrations (they insert customLLDBInitFile and enableGPUValidationMode as strings) and another flet build; Xcode doesn't rewrite it.
• A standalone C program reproduces the assert on the iOS 18.6, 26.3 and 26.5 simulator runtimes under the injected environment, and passes without the checker or with the SQLite inspection turned off.

Summary by Sourcery

Disable Xcode’s Thread Performance Checker in generated iOS schemes to prevent sqlite3-related crashes during Xcode launches.

Bug Fixes:

• Prevent iOS apps using sqlite3 from aborting when launched from Xcode on iOS 18 and later by disabling the incompatible Thread Performance Checker in generated Xcode schemes.

Chores:

• Document the iOS Xcode launch fix in the changelog.

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View logs

[Copilot]

Copilot review overview

🔵 Needs a closer look

The scheme setting needs an automated regression test before approval.

Review effort: Balanced
Findings: None

What changed in this PR

Disables Xcode’s Thread Performance Checker in generated iOS schemes to prevent SQLite assertion failures during Xcode launches.

Changes:

• Adds disablePerformanceAntipatternChecker = "YES" to the iOS LaunchAction.
• Documents the fix in the changelog.

File	Review
sdk/​python/​templates/​build/​{{cookiecutter.out_dir}}/​ios/​Runner.xcodeproj/​xcshareddata/​xcschemes/​Runner.xcscheme	Disables the checker; needs a template-contract regression test.
CHANGELOG.md	Records the fix; wording could be clearer.

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