[dart2js] Ensure JavaScriptFunction gets emitted for allowInterop

Change-Id: I320653a46da31cfb626c41a3a2307b1d1626173a
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/280205
Reviewed-by: Stephen Adams <sra@google.com>
Commit-Queue: Joshua Litt <joshualitt@google.com>

Author: joshualitt

pkg/compiler/lib/src/js_emitter/interceptor_stub_generator.dart

@@ -74,6 +74,8 @@ class InterceptorStubGenerator {
         condition = js('(typeof receiver) == "string"');
       } else if (cls == _commonElements.jsNullClass) {
         condition = js('receiver == null');
+      } else if (cls == _commonElements.jsJavaScriptFunctionClass) {
+        condition = js('(typeof receiver) == "function"');
       } else {
         throw 'internal error';
       }
@@ -89,6 +91,7 @@ class InterceptorStubGenerator {
     bool hasString = false;
     bool hasNative = false;
     bool anyNativeClasses = _nativeCodegenEnqueuer.hasInstantiatedNativeClasses;
+    bool hasJavaScriptFunction = false;
 
     for (ClassEntity cls in classes) {
       if (cls == _commonElements.jsArrayClass ||
@@ -108,6 +111,8 @@ class InterceptorStubGenerator {
         hasNumber = true;
       else if (cls == _commonElements.jsStringClass)
         hasString = true;
+      else if (cls == _commonElements.jsJavaScriptFunctionClass)
+        hasJavaScriptFunction = true;
       else {
         // The set of classes includes classes mixed-in to interceptor classes
         // and user extensions of native classes.
@@ -180,6 +185,14 @@ class InterceptorStubGenerator {
       statements.add(buildInterceptorCheck(_commonElements.jsArrayClass));
     }
 
+    // If a program `hasNative` then we will insert a check for
+    // `JavaScriptFunction` in the `hasNative` block of the interceptor logic.
+    // Otherwise, we have to insert a specific check for `JavScriptFunction.
+    if (hasJavaScriptFunction && !hasNative) {
+      statements.add(
+          buildInterceptorCheck(_commonElements.jsJavaScriptFunctionClass));
+    }
+
     if (hasNative) {
       statements.add(js.statement(r'''{
           if (typeof receiver != "object") {

pkg/compiler/lib/src/js_emitter/program_builder/program_builder.dart

@@ -251,7 +251,9 @@ class ProgramBuilder {
         _nativeCodegenEnqueuer.hasInstantiatedNativeClasses ||
             _nativeData.isAllowInteropUsed;
 
-    assert(!needsNativeSupport || nativeClasses.isNotEmpty);
+    assert(!needsNativeSupport ||
+        nativeClasses.isNotEmpty ||
+        _nativeData.isAllowInteropUsed);
 
     List<js.TokenFinalizer> finalizers = [_task.metadataCollector];
     if (_namer is js.TokenFinalizer) {

pkg/compiler/lib/src/native/enqueue.dart

@@ -92,6 +92,7 @@ abstract class NativeEnqueuer {
             type == _commonElements.stringType ||
             type == _commonElements.nullType ||
             type == _commonElements.boolType ||
+            type == _commonElements.jsJavaScriptFunctionType ||
             _dartTypes.isSubtype(type,
                 _elementEnvironment.getRawType(_commonElements.jsArrayClass))) {
           registerInstantiation(type);