Make JS function out of JS object when casting to JSFunctor interface

jso/impl/src/main/java/org/teavm/jso/impl/JSClassProcessor.java

@@ -61,6 +61,7 @@ import org.teavm.model.TextLocation;
 import org.teavm.model.ValueType;
 import org.teavm.model.Variable;
 import org.teavm.model.instructions.AssignInstruction;
+import org.teavm.model.instructions.CastInstruction;
 import org.teavm.model.instructions.ExitInstruction;
 import org.teavm.model.instructions.InvocationType;
 import org.teavm.model.instructions.InvokeInstruction;
@@ -252,25 +253,55 @@ class JSClassProcessor {
         for (int i = 0; i < program.basicBlockCount(); ++i) {
             BasicBlock block = program.basicBlockAt(i);
             for (Instruction insn : block) {
-                if (!(insn instanceof InvokeInstruction)) {
+                if (insn instanceof CastInstruction) {
-                    continue;
+                    replacement.clear();
-                }
+                    CallLocation callLocation = new CallLocation(methodToProcess.getReference(), insn.getLocation());
-                InvokeInstruction invoke = (InvokeInstruction) insn;
+                    if (processCast((CastInstruction) insn, callLocation)) {
+                        insn.insertNextAll(replacement);
+                        insn.delete();
+                    }
+                } else if (insn instanceof InvokeInstruction) {
+                    InvokeInstruction invoke = (InvokeInstruction) insn;
 
-                MethodReader method = getMethod(invoke.getMethod());
+                    MethodReader method = getMethod(invoke.getMethod());
-                if (method == null) {
+                    if (method == null) {
-                    continue;
+                        continue;
-                }
+                    }
-                CallLocation callLocation = new CallLocation(methodToProcess.getReference(), insn.getLocation());
+                    CallLocation callLocation = new CallLocation(methodToProcess.getReference(), insn.getLocation());
-                replacement.clear();
+                    replacement.clear();
-                if (processInvocation(method, callLocation, invoke, methodToProcess)) {
+                    if (processInvocation(method, callLocation, invoke, methodToProcess)) {
-                    insn.insertNextAll(replacement);
+                        insn.insertNextAll(replacement);
-                    insn.delete();
+                        insn.delete();
+                    }
                 }
             }
         }
     }
 
+    private boolean processCast(CastInstruction cast, CallLocation location) {
+        if (!(cast.getTargetType() instanceof ValueType.Object)) {
+            return false;
+        }
+
+        String targetClassName = ((ValueType.Object) cast.getTargetType()).getClassName();
+        if (!typeHelper.isJavaScriptClass(targetClassName)) {
+            return false;
+        }
+        ClassReader targetClass = classSource.get(targetClassName);
+        if (targetClass.getAnnotations().get(JSFunctor.class.getName()) == null) {
+            return false;
+        }
+
+        Variable result = marshaller.unwrapFunctor(location, cast.getValue(), targetClass);
+        AssignInstruction assign = new AssignInstruction();
+        assign.setLocation(location.getSourceLocation());
+        assign.setAssignee(result);
+        assign.setReceiver(cast.getReceiver());
+        replacement.add(assign);
+
+        return true;
+    }
+
     private boolean processInvocation(MethodReader method, CallLocation callLocation, InvokeInstruction invoke,
             MethodHolder methodToProcess) {
         if (method.getAnnotations().get(JSBody.class.getName()) != null) {

jso/impl/src/main/java/org/teavm/jso/impl/JSNativeGenerator.java

@@ -76,8 +76,8 @@ public class JSNativeGenerator implements Injector, DependencyPlugin, Generator
         String thisName = context.getParameterName(1);
         String methodName = context.getParameterName(2);
 
-        writer.append("if").ws().append("(").append(thisName).ws().append("===").ws().append("null)").ws()
+        writer.append("if").ws().append("(typeof ").append(thisName).ws().append("!==").ws().append("\"function\")")
-                .append("return null;").softNewLine();
+                .ws().append("return ").append(thisName).append(";").softNewLine();
         writer.append("var result").ws().append("=").ws().append("{};").softNewLine();
         writer.append("result[").append(methodName).append("]").ws().append("=").ws().append(thisName)
                 .append(";").softNewLine();

jso/impl/src/main/java/org/teavm/jso/impl/JSValueMarshaller.java

@@ -462,7 +462,7 @@ class JSValueMarshaller {
         return result;
     }
 
-    private Variable unwrapFunctor(CallLocation location, Variable var, ClassReader type) {
+    Variable unwrapFunctor(CallLocation location, Variable var, ClassReader type) {
         if (!isProperFunctor(type)) {
             diagnostics.error(location, "Wrong functor: {{c0}}", type.getName());
             return var;

tests/src/test/java/org/teavm/jso/test/FunctorTest.java

@@ -83,6 +83,12 @@ public class FunctorTest {
         assertEquals("q,w", function.foo("q", "w"));
     }
 
+    @Test
+    public void castToFunctor() {
+        JSBiFunction f = getBiFunctionAsObject().cast();
+        assertEquals(23042, f.foo(23, 42));
+    }
+
     @JSBody(params = { "f", "a", "b" }, script = "return '(' + f(a, b) + ')';")
     private static native String testMethod(JSBiFunction f, int a, int b);
 
@@ -95,6 +101,12 @@ public class FunctorTest {
             + "};")
     private static native JSBiFunction getBiFunction();
 
+    @JSBody(script = ""
+            + "return function(a, b) {"
+            + "return a * 1000 + b;"
+            + "};")
+    private static native JSObject getBiFunctionAsObject();
+
     @JSBody(script = ""
             + "return function(a, b) {"
             + "return a + ',' + b;"