[VM/Debugger] Fix bug where breakpoints set in compiled field initializers do not resolve immediately

TEST=verified that
pkg/vm_service/test/breakpoint_resolves_immediately_in_compiled_field_initializer_test.dart
fails without the changes in this CL and passes with them, verified that
none of the existing debugger tests got broken by this CL

Change-Id: I6acb5576a80e5d633b012c866fe90bf13d2c1ba6
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/369162
Commit-Queue: Derek Xu <derekx@google.com>
Reviewed-by: Alexander Aprelev <aam@google.com>

pkg/vm_service/test/breakpoint_resolves_immediately_in_compiled_field_initializer_test.dart

@@ -0,0 +1,65 @@
+// Copyright (c) 2024, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:developer' show debugger;
+
+import 'package:test/test.dart';
+import 'package:vm_service/vm_service.dart';
+
+import 'common/service_test_common.dart';
+import 'common/test_helper.dart';
+
+// AUTOGENERATED START
+//
+// Update these constants by running:
+//
+// dart pkg/vm_service/test/update_line_numbers.dart <test.dart>
+//
+const LINE_A = 28;
+const LINE_B = 34;
+// AUTOGENERATED END
+
+int getTwo() => 3;
+
+int getThree() => 3;
+
+class C {
+  static int x = getTwo() + getThree(); // LINE_A
+}
+
+Future<void> testeeMain() async {
+  final y = C.x;
+  print(y);
+  debugger(); // LINE_B
+}
+
+final tests = <IsolateTest>[
+  // Ensure that the main isolate has stopped at the [debugger] statement at the
+  // end of [testeeMain].
+  hasStoppedAtBreakpoint,
+  stoppedAtLine(LINE_B),
+  (VmService service, IsolateRef isolateRef) async {
+    final isolateId = isolateRef.id!;
+    final isolate = await service.getIsolate(isolateId);
+    final rootLib = await service.getObject(
+      isolateId,
+      isolate.rootLib!.id!,
+    ) as Library;
+    final scriptId = rootLib.scripts![0].id!;
+
+    // Add a breakpoint at the initializer of `C.x`.
+    final breakpoint = await service.addBreakpoint(isolateId, scriptId, LINE_A);
+    // It is guaranteed that the initializer of `C.x` has been compiled at this
+    // point, because `C.x` was already used to initialize `y`, so we ensure
+    // that the newly set breakpoint has been resolved immediately.
+    expect(breakpoint.resolved, true);
+  },
+];
+
+void main([args = const <String>[]]) => runIsolateTests(
+      args,
+      tests,
+      'breakpoint_resolves_immediately_in_compiled_field_initializer_test.dart',
+      testeeConcurrent: testeeMain,
+    );

runtime/vm/debugger.cc

@@ -2302,8 +2302,10 @@ void Debugger::FindCompiledFunctions(
         });
 
     Class& cls = Class::Handle(zone);
-    Function& function = Function::Handle(zone);
     Array& functions = Array::Handle(zone);
+    Function& function = Function::Handle(zone);
+    Array& fields = Array::Handle(zone);
+    Field& field = Field::Handle(zone);
 
     const ClassTable& class_table = *isolate_->group()->class_table();
     const intptr_t num_classes = class_table.NumCids();
@@ -2346,6 +2348,28 @@ void Debugger::FindCompiledFunctions(
             }
           }
         }
+        fields = cls.fields();
+        if (!fields.IsNull()) {
+          const intptr_t num_fields = fields.Length();
+          for (intptr_t pos = 0; pos < num_fields; pos++) {
+            field ^= fields.At(pos);
+            ASSERT(!field.IsNull());
+            if (field.Script() != script.ptr()) {
+              continue;
+            }
+            if (!field.has_nontrivial_initializer()) {
+              continue;
+            }
+            function = field.EnsureInitializerFunction();
+            ASSERT(!function.IsNull());
+            if (function.is_debuggable() && function.HasCode() &&
+                function.token_pos() == start_pos &&
+                function.end_token_pos() == end_pos &&
+                function.script() == script.ptr()) {
+              code_function_list->Add(function);
+            }
+          }
+        }
       }
     }
   }
@@ -2476,11 +2500,8 @@ bool Debugger::FindBestFit(const Script& script,
           }
         }
       }
-      // If none of the functions in the class contain token_pos, then we
-      // check if it falls within a function literal initializer of a field
-      // that has not been initialized yet. If the field (and hence the
-      // function literal initializer) has already been initialized, then
-      // it would have been found above in the object store as a closure.
+      // If none of the functions in the class contain token_pos, then we check
+      // if it falls within a function literal initializer of a field.
       fields = cls.fields();
       if (!fields.IsNull()) {
         const intptr_t num_fields = fields.Length();
@@ -2501,6 +2522,7 @@ bool Debugger::FindBestFit(const Script& script,
           end = field.end_token_pos();
           if (token_pos.IsWithin(start, end) ||
               start.IsWithin(token_pos, last_token_pos)) {
+            *best_fit = field.InitializerFunction();
             return true;
           }
         }