[VM/Runtime] - Fix for issue #42421

Set global null safety flag based on the snapshot instead of trying to
detect it per isolate (was causing issues with the vm isolate loading).
Should fix #42421

Bug:42421
Change-Id: I9143560b76fedcb991e96522cbf5d820fde99f7f
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/151866
Reviewed-by: Alexander Markov <[email protected]>
Commit-Queue: Siva Annamalai <[email protected]>

Author: a-siva

runtime/vm/clustered_snapshot.cc

@@ -6713,6 +6713,21 @@ char* SnapshotHeaderReader::InitializeGlobalVMFlagsFromSnapshot(
 #undef CHECK_FLAG
 #undef SET_FLAG
 
+#if defined(DART_PRECOMPILED_RUNTIME)
+    if (FLAG_null_safety == kNullSafetyOptionUnspecified) {
+      if (strncmp(cursor, "null-safety", end - cursor) == 0) {
+        FLAG_null_safety = kNullSafetyOptionStrong;
+        cursor = end;
+        continue;
+      }
+      if (strncmp(cursor, "no-null-safety", end - cursor) == 0) {
+        FLAG_null_safety = kNullSafetyOptionWeak;
+        cursor = end;
+        continue;
+      }
+    }
+#endif  // defined(DART_PRECOMPILED_RUNTIME)
+
     cursor = end;
   }
 

runtime/vm/dart.cc

@@ -753,12 +753,13 @@ bool Dart::DetectNullSafety(const char* script_uri,
                             intptr_t kernel_buffer_size,
                             const char* package_config,
                             const char* original_working_directory) {
+#if !defined(DART_PRECOMPILED_RUNTIME)
   // Before creating the isolate we first determine the null safety mode
   // in which the isolate needs to run based on one of these factors :
   // - if loading from source, based on opt-in status of the source
   // - if loading from a kernel file, based on the mode used when
   //   generating the kernel file
-  // - if loading from an appJIT or AOT snapshot, based on the mode used
+  // - if loading from an appJIT, based on the mode used
   //   when generating the snapshot.
   ASSERT(FLAG_null_safety == kNullSafetyOptionUnspecified);
 
@@ -772,7 +773,6 @@ bool Dart::DetectNullSafety(const char* script_uri,
     }
   }
 
-#if !defined(DART_PRECOMPILED_RUNTIME)
   // If kernel_buffer is specified, it could be a self contained
   // kernel file or the kernel file of the application,
   // figure out the null safety mode by sniffing the kernel file.
@@ -791,8 +791,10 @@ bool Dart::DetectNullSafety(const char* script_uri,
     return KernelIsolate::DetectNullSafety(script_uri, package_config,
                                            original_working_directory);
   }
-#endif  // !defined(DART_PRECOMPILED_RUNTIME)
   return false;
+#else
+  UNREACHABLE();
+#endif  // !defined(DART_PRECOMPILED_RUNTIME)
 }
 
 #if defined(DART_PRECOMPILED_RUNTIME)

runtime/vm/dart_api_impl.cc

@@ -6032,6 +6032,10 @@ DART_EXPORT bool Dart_DetectNullSafety(const char* script_uri,
                                        const uint8_t* snapshot_instructions,
                                        const uint8_t* kernel_buffer,
                                        intptr_t kernel_buffer_size) {
+#if defined(DART_PRECOMPILED_RUNTIME)
+  ASSERT(FLAG_null_safety != kNullSafetyOptionUnspecified);
+  return (FLAG_null_safety == kNullSafetyOptionStrong);
+#else
   bool null_safety;
   if (FLAG_null_safety == kNullSafetyOptionUnspecified) {
     null_safety = Dart::DetectNullSafety(
@@ -6041,6 +6045,7 @@ DART_EXPORT bool Dart_DetectNullSafety(const char* script_uri,
     null_safety = (FLAG_null_safety == kNullSafetyOptionStrong);
   }
   return null_safety;
+#endif  // defined(DART_PRECOMPILED_RUNTIME)
 }
 
 // --- Service support ---