fix: Add FileModifiedCallback

Used by the kernel during hot reloading to determine what to reload. When it's not set, hot reload takes a long time.

Prepare some methods for eventual environment setup.

src/dart_dll.cpp

@@ -8,6 +8,7 @@
 
 #include <bin/dartutils.h>
 #include <bin/dfe.h>
+#include <bin/file.h>
 #include <bin/gzip.h>
 #include <bin/loader.h>
 #include <bin/isolate_data.h>
@@ -30,6 +31,21 @@ extern const uint8_t* observatory_assets_archive;
 }  // namespace bin
 }  // namespace dart
 
+static bool FileModifiedCallback(const char* url, int64_t since) {
+  auto path = File::UriToPath(url);
+  if (path == nullptr) {
+    // If it isn't a file on local disk, we don't know if it has been
+    // modified.
+    return true;
+  }
+  int64_t data[File::kStatSize];
+  File::Stat(nullptr, path.get(), data);
+  if (data[File::kType] == File::kDoesNotExist) {
+    return true;
+  }
+  return data[File::kModifiedTime] > since;
+}
+
 Dart_Handle GetVMServiceAssetsArchiveCallback() {
   uint8_t* decompressed = NULL;
   intptr_t decompressed_len = 0;
@@ -161,6 +177,8 @@ bool DartDll_Initialize(const DartDllConfig& config) {
   std::cout << "Dart initialized, error was: "
             << (initError != nullptr ? initError : "null") << std::endl;
 
+  Dart_SetFileModifiedCallback(&FileModifiedCallback);
+
   return true;
 }
 

src/isolate_setup.cpp

@@ -69,6 +69,9 @@ Dart_Handle SetupCoreLibraries(Dart_Isolate isolate,
     }
   }
 
+  result = Dart_SetEnvironmentCallback(DartUtils::EnvironmentCallback);
+  if (Dart_IsError(result)) return result;
+
   // Setup the native resolver as the snapshot does not carry it.
   Builtin::SetNativeResolver(Builtin::kBuiltinLibrary);
   Builtin::SetNativeResolver(Builtin::kIOLibrary);
@@ -160,7 +163,11 @@ Dart_Isolate CreateVmServiceIsolate(const char* script_uri,
     return nullptr;
   }
 
-  // TODO -- Dart_SetEnvironmentCallback(DartUtils::EnvironmentCallback)
+  Dart_EnterIsolate(isolate);
+  Dart_EnterScope();
+  Dart_SetEnvironmentCallback(DartUtils::EnvironmentCallback);
+  Dart_ExitScope();
+  Dart_ExitIsolate();
 
   return isolate;
 }