[flutter_tools] Unhandled ProcessException when xcodebuild is missing or exits with code 72 during build macos #191176

Summary

In Flutter 3.47.0 telemetry, an unhandled ProcessException when invoking xcodebuild emerged as a top crash signature.

When running flutter build macos on a machine where Xcode is not installed, incomplete (e.g. Command Line Tools only), or misconfigured, flutter_tools crashes with an unhandled ProcessException instead of providing a graceful ToolExit error message.

Telemetry Profile

• Release: Flutter 3.47.0 (Top 10 crasher)
• Signature: ProcessException at RunResult.throwException at package:flutter_tools/src/base/process.dart-bd2448f2

Error Output

ProcessException: Process exited abnormally with exit code 72:
xcrun: error: unable to find utility "xcodebuild", not a developer tool or in PATH
  Command: /usr/bin/arch -arm64e xcrun xcodebuild -clonedSourcePackagesDirPath ... -skipPackageUpdates -skipPackagePluginValidation -skipPackageSignatureValidation -list -project Runner.xcodeproj

Stack Trace

#0      RunResult.throwException (package:flutter_tools/src/base/process.dart:153:5)
#1      _DefaultProcessUtils.run (package:flutter_tools/src/base/process.dart:379:19)
<asynchronous suspension>
#2      XcodeProjectInterpreter.getInfo (package:flutter_tools/src/ios/xcodeproj.dart:423:25)
<asynchronous suspension>
#3      buildMacOS (package:flutter_tools/src/macos/build_macos.dart:149:40)
<asynchronous suspension>
#4      BuildMacosCommand.runCommand (package:flutter_tools/src/commands/build_macos.dart:61:5)

Root Cause

1. buildMacOS in packages/flutter_tools/lib/src/macos/build_macos.dart lacked pre-flight toolchain validation (globals.xcodeProjectInterpreter?.isInstalled != true) before querying Xcode project information.
2. In XcodeProjectInterpreter.getInfo (packages/flutter_tools/lib/src/ios/xcodeproj.dart), xcodebuild -list is executed with throwOnError: true while only allowing exit codes 66 and 74. When xcrun returns exit code 72 (unable to find utility "xcodebuild"), _processUtils.run throws an uncaught ProcessException.
3. buildMacOS improperly used non-null assertions on projectInfo! when resolving build schemes.

Proposed Fix

• Add pre-flight Xcode toolchain check in buildMacOS to exit early with globals.userMessages.xcodeMissing.
• Wrap XcodeProjectInterpreter.getInfo in a try ... on ProcessException block to convert unexpected process failures to user-friendly ToolExit messages.
• Add safe null checks on projectInfo in buildMacOS.