Shims generation improvement

- When return type is not directly supported and just a Dart_Handle,
  automatically create persistent handles
- Change `Dart_LoadLibrary` to `Dart_LookupLibrary`
- switch from iostream to cstdio, I have no idea why, but it doesn't
  work for me in emulators and it's not a big difference.

TEST=ci,manual
Change-Id: I9b6539c7f16e81af9e8a9ab3995d6040bac64a1d
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/429962
Reviewed-by: Tess Strickland <[email protected]>
Commit-Queue: Ivan Inozemtsev <[email protected]>

Author: iinozemtsev

pkg/vm/lib/embedder/shims.dart

@@ -23,6 +23,20 @@ void _convertDartTypeToC(
   }
 }
 
+String _getCReturnType(CoreTypes? coreTypes, DartType type) {
+  if (coreTypes == null) {
+    return 'Dart_Handle';
+  } else if (type is VoidType) {
+    return 'void';
+  } else if (type == coreTypes.intNonNullableRawType) {
+    return 'int64_t';
+  } else if (type == coreTypes.doubleNonNullableRawType) {
+    return 'double';
+  } else {
+    return 'Dart_Handle';
+  }
+}
+
 void _convertCValueToDart(
   StringBuffer buffer,
   CoreTypes coreTypes,
@@ -653,10 +667,18 @@ class EntryPointCallShim extends EntryPointFunctionShim {
 
   @override
   void _writeReturnBody(StringBuffer buffer) {
+    var isDartHandle = _getCReturnType(coreTypes, returnType) == 'Dart_Handle';
+
+    if (isDartHandle) {
+      buffer.write('Dart_NewPersistentHandle(');
+    }
     buffer.write('Dart_Invoke(');
     _writeTarget(buffer);
     buffer.write(', Dart_NewStringFromCString("$baseName"), ');
     _writeArgumentsListCountAndPointer(buffer);
     buffer.write(')');
+    if (isDartHandle) {
+      buffer.write(')');
+    }
   }
 }

pkg/vm/lib/embedder/writer.dart

@@ -58,7 +58,8 @@ class EntryPointShimWriter {
     definitions.write('''
 #include "${path.basename(_headerPath)}"
 
-#include <iostream>
+#include <cstdio>
+#include <cstdlib>
 #include <string>
 #include <string_view>
 #include <unordered_map>
@@ -68,9 +69,9 @@ namespace {
 
 Dart_Handle CheckError(Dart_Handle handle, std::string_view context = "") {
   if (Dart_IsError(handle)) {
-    std::cerr << "Error " << context << ": " << Dart_GetError(handle)
-              << std::endl;
-    std::exit(1);
+    std::string context_str(context);
+    fprintf(stderr, "Error %s: %s\\n", context_str.c_str(), Dart_GetError(handle));
+    exit(1);
   }
   return handle;
 }
@@ -79,8 +80,8 @@ int64_t IntFromHandle(Dart_Handle handle) {
   CheckError(handle, "IntFromHandle received an error");
 
   if (!Dart_IsInteger(handle)) {
-    std::cerr << "IntFromHandle handle is not an int" << std::endl;
-    std::exit(1);
+    fprintf(stderr, "IntFromHandle handle is not an int\\n");
+    exit(1);
   }
 
   int64_t result;
@@ -93,8 +94,8 @@ double DoubleFromHandle(Dart_Handle handle) {
   CheckError(handle, "DoubleFromHandle received an error");
 
   if (!Dart_IsDouble(handle)) {
-    std::cerr << "DoubleFromHandle handle is not an double" << std::endl;
-    std::exit(1);
+    fprintf(stderr, "DoubleFromHandle handle is not a double\\n");
+    exit(1);
   }
 
   double result;
@@ -119,7 +120,7 @@ class PackageState {
       definitions.write('Dart_RootLibrary()');
     } else {
       definitions.write(
-        'Dart_LoadLibrary(Dart_NewStringFromCString(kLibraryUri))',
+        'Dart_LookupLibrary(Dart_NewStringFromCString(kLibraryUri))',
       );
     }
     definitions.writeln(''';