API functions returning Promises should not throw exceptions.

Source/bindings/core/v8/V8BindingMacros.h

Index: Source/bindings/core/v8/V8BindingMacros.h
diff --git a/Source/bindings/core/v8/V8BindingMacros.h b/Source/bindings/core/v8/V8BindingMacros.h
index 165d5b7b0144f1c7756a018f4110c2bc2a598063..2756f1d76c74f25a306b99ad4320e4c046461f32 100644
--- a/Source/bindings/core/v8/V8BindingMacros.h
+++ b/Source/bindings/core/v8/V8BindingMacros.h
@@ -70,6 +70,23 @@ namespace blink {
         }                                          \
     }
 
+#define TONATIVE_VOID_ASYNC_INTERNAL(var, value, info)                                          \
+    var = (value);                                                                              \
+    if (UNLIKELY(block.HasCaught())) {                                                          \
+        v8SetReturnValue(info, ScriptPromise::rejectRaw(info.GetIsolate(), block.Exception())); \
+        rethrow.cancel();                                                                       \

[Jens Widell, 2014/07/30 10:29:10]

Would it work to do block.Reset() here instead? I think that would be marginally
nicer, since the rethrower them remains a simple stateless modifier.

[yhirano, 2014/07/31 03:03:25]

Sadly, No.
When an exception is thrown and is caught by a v8::TryCatch block, the block has
to keep the exception object to swallow it.
Otherwise, the cancellation on the v8::TryCatch destructor doesn't take effect.
Hence we can't use Reset here.

[Jens Widell, 2014/07/31 08:29:09]

That is unfortunate, and sounds like a bug in TryCatch to me. If I understand
correctly, calling ReThrow() after Reset() "resurrects" the exception? If that's
the case, then what *does* Reset() do?

Another aspect to consider here is that V8RethrowTryCatchScope is used in many
generated functions, so adding a little bit of logic to it may lead to a
noticable increase in binary size. (Or may not, since it's all inlined.)

[yhirano, 2014/08/06 05:48:47]

I've just created a V8 patch. https://codereview.chromium.org/443853002/
If it is accepted, we will be able to replace |rethrow.cancel()| with
|block.ReThrow()|.

[yhirano, 2014/08/11 06:29:35]

Done.

+        return;                                                                                 \
+    }
+
+#define TONATIVE_VOID_ASYNC(type, var, value, info)     \
+    type var;                                           \
+    {                                                   \
+        v8::TryCatch block;                             \
+        V8RethrowTryCatchScope rethrow(block);          \

[Jens Widell, 2014/07/30 10:29:10]

Additionally, if we skip rethrow.cancel(), we could drop this rethrower, which
is entirely pointless (always cancelled.)

[yhirano, 2014/07/31 03:03:25]

I think we can't skip rethrow.cancel() at present.

[yhirano, 2014/08/11 06:29:35]

Done.

+        TONATIVE_VOID_ASYNC_INTERNAL(var, value, info); \
+    }
+
+
 #define TONATIVE_VOID_EXCEPTIONSTATE_INTERNAL(var, value, exceptionState) \
     var = (value);                                                        \
     if (UNLIKELY(block.HasCaught() || exceptionState.throwIfNeeded()))    \
@@ -93,6 +110,26 @@ namespace blink {
             return retVal;                                                        \
     }
 
+#define TONATIVE_VOID_EXCEPTIONSTATE_ASYNC_INTERNAL(scriptState, var, value, exceptionState, info) \
+    var = (value);                                                                                 \
+    if (UNLIKELY(block.HasCaught())) {                                                             \
+        v8SetReturnValue(info, ScriptPromise::rejectRaw(info.GetIsolate(), block.Exception()));    \
+        rethrow.cancel();                                                                          \
+        return;                                                                                    \
+    }                                                                                              \
+    if (UNLIKELY(exceptionState.hadException())) {                                                 \
+        v8SetReturnValue(info, exceptionState.reject(scriptState).v8Value());                      \
+        return;                                                                                    \
+    }
+
+#define TONATIVE_VOID_EXCEPTIONSTATE_ASYNC(scriptState, type, var, value, exceptionState, info) \
+    type var;                                                                                   \
+    {                                                                                           \
+        v8::TryCatch block;                                                                     \
+        V8RethrowTryCatchScope rethrow(block);                                                  \
+        TONATIVE_VOID_EXCEPTIONSTATE_INTERNAL(scriptState, var, value, exceptionState, info);   \
+    }
+
 // type is an instance of class template V8StringResource<>,
 // but Mode argument varies; using type (not Mode) for consistency
 // with other macros and ease of code generation
@@ -111,6 +148,22 @@ namespace blink {
     if (UNLIKELY(!var.prepare()))                  \
         return retVal;
 
+#define TOSTRING_VOID_ASYNC_INTERNAL(var, value, info)                                             \
+    var = (value);                                                                                 \
+    if (UNLIKELY(!var.prepare()))  {                                                               \
+        rethrow.cancel();                                                                          \
+        info.GetReturnValue().Set(ScriptPromise::rejectRaw(info.GetIsolate(), block.Exception())); \
+        return;                                                                                    \
+    }
+
+#define TOSTRING_VOID_ASYNC(type, var, value, info)           \
+    type var;                                                 \
+    {                                                         \
+        v8::TryCatch block;                                   \
+        V8RethrowTryCatchScope rethrow(block);                \
+        TOSTRING_VOID_ASYNC_INTERNAL(type, var, value, info); \
+    }
+
 } // namespace blink
 
 #endif // V8BindingMacros_h