Make LLDB check a warning instead of a failure (#164828)

We added LLDB file in https://github.com/flutter/flutter/pull/164344.
This adjusts it so if the LLDB file is missing it gives a warning rather
than an error that fails the build.

## Pre-launch Checklist

- [x] I read the [Contributor Guide] and followed the process outlined
there for submitting PRs.
- [x] I read the [Tree Hygiene] wiki page, which explains my
responsibilities.
- [x] I read and followed the [Flutter Style Guide], including [Features
we expect every widget to implement].
- [x] I signed the [CLA].
- [x] I listed at least one issue that this PR fixes in the description
above.
- [x] I updated/added relevant documentation (doc comments with `///`).
- [x] I added new tests to check the change I am making, or this PR is
[test-exempt].
- [x] I followed the [breaking change policy] and added [Data Driven
Fixes] where supported.
- [x] All existing and new tests are passing.

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packages/flutter_tools/lib/src/build_system/targets/ios.dart

@@ -503,11 +503,13 @@ abstract class IosLLDBInit extends Target {
     // an error.
     final String? srcRoot = environment.defines[kSrcRoot];
     if (srcRoot == null) {
-      throw MissingDefineException(kSdkRoot, name);
+      environment.logger.printError('Failed to find $srcRoot');
+      return;
     }
     final Directory xcodeProjectDir = environment.fileSystem.directory(srcRoot);
     if (!xcodeProjectDir.existsSync()) {
-      throw Exception('Failed to find ${xcodeProjectDir.path}');
+      environment.logger.printError('Failed to find ${xcodeProjectDir.path}');
+      return;
     }
 
     bool anyLLDBInitFound = false;
@@ -522,14 +524,20 @@ abstract class IosLLDBInit extends Target {
     if (!anyLLDBInitFound) {
       final FlutterProject flutterProject = FlutterProject.fromDirectory(environment.projectDir);
       if (flutterProject.isModule) {
-        throwToolExit(
-          'Debugging Flutter on new iOS versions requires an LLDB Init File. To '
+        // We use print here to make sure Xcode adds the message to the build logs. See
+        // https://developer.apple.com/documentation/xcode/running-custom-scripts-during-a-build#Log-errors-and-warnings-from-your-script
+        // ignore: avoid_print
+        print(
+          'warning: Debugging Flutter on new iOS versions requires an LLDB Init File. To '
           'ensure debug mode works, please run "flutter build ios --config-only" '
           'in your Flutter project and follow the instructions to add the file.',
         );
       } else {
-        throwToolExit(
-          'Debugging Flutter on new iOS versions requires an LLDB Init File. To '
+        // We use print here to make sure Xcode adds the message to the build logs. See
+        // https://developer.apple.com/documentation/xcode/running-custom-scripts-during-a-build#Log-errors-and-warnings-from-your-script
+        // ignore: avoid_print
+        print(
+          'warning: Debugging Flutter on new iOS versions requires an LLDB Init File. To '
           'ensure debug mode works, please run "flutter build ios --config-only" '
           'in your Flutter project and automatically add the files.',
         );

packages/flutter_tools/test/general.shard/build_system/targets/ios_test.dart

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'dart:async';
+
 import 'package:file/memory.dart';
 import 'package:file_testing/file_testing.dart';
 import 'package:flutter_tools/src/artifacts.dart';
@@ -1155,7 +1157,7 @@ void main() {
 
   group('DebugIosLLDBInit', () {
     testUsingContext(
-      'throws error if missing LLDB Init File in all schemes',
+      'prints warning if missing LLDB Init File in all schemes',
       () async {
         const String projectPath = 'path/to/project';
         fileSystem.directory(projectPath).createSync(recursive: true);
@@ -1165,11 +1167,12 @@ void main() {
         environment.defines[kSrcRoot] = projectPath;
         environment.defines[kTargetDeviceOSVersion] = '18.4.1';
 
+        final StringBuffer buffer = await capturedConsolePrint(() async {
+          await const DebugIosLLDBInit().build(environment);
+        });
         expect(
-          const DebugIosLLDBInit().build(environment),
-          throwsToolExit(
-            message: 'Debugging Flutter on new iOS versions requires an LLDB Init File.',
-          ),
+          buffer.toString(),
+          contains('warning: Debugging Flutter on new iOS versions requires an LLDB Init File.'),
         );
       },
       overrides: <Type, Generator>{
@@ -1261,3 +1264,20 @@ class FakeXcodeProjectInterpreter extends Fake implements XcodeProjectInterprete
     return XcodeProjectInfo(<String>[], <String>[], schemes, BufferLogger.test());
   }
 }
+
+/// Capture console print events into a string buffer.
+Future<StringBuffer> capturedConsolePrint(Future<void> Function() body) async {
+  final StringBuffer buffer = StringBuffer();
+  await runZoned<Future<void>>(
+    () async {
+      // Service the event loop.
+      await body();
+    },
+    zoneSpecification: ZoneSpecification(
+      print: (Zone self, ZoneDelegate parent, Zone zone, String line) {
+        buffer.writeln(line);
+      },
+    ),
+  );
+  return buffer;
+}