2.7.0 RC1 SDM not working when using java.util.List - Example attached

[Jan Thewes]

Hello guys,

we're currently running in problems related to the SDM in GWT 2.7. We've attached two examples.

JsListWrapperWorking is an example project where everything is working fine. It is CODE IDENTICAL to JsListWrapperNotWorking.

In the latter one we've moved the source for the two classes JsArrayListWrapper and JsArrayWrapper to another module.

No source code has been touched.

When starting SDM for JsListWrapperWorking everything is working fine.

When starting SDM for JsListWrapperNotWorking we get following exception:

[ERROR] Errors in 'file:~/JsListWrapperNotWorking/src/de/gad/list/client/JsListWrapperNotWorking.java'

[ERROR] Line 19: Referencing interface method 'java.util.List.size()': implemented by 'de.gad.list.client.myListImpl.JsArrayListWrapper'; references to instance methods in overlay types are illegal; use a stronger type or a Java trampoline method

If you need any further information I'll provide them as soon as possible!

Cheers,

Jan

[Thomas Broyer]

[+cc stalcup@]

This might be because of incremental compilation: when JsArrayListWrapper is in another module, that module is "precompiled", so the compiler knows about the type. When it's in the same module, because it's the module being compiled, it can be pruned (unused) and as consequence doesn't interfere with the JSNI checks.

The workaround would be to call a static method passing the List as argument, and call the size() method in that static method, in Java-land, outside of JSNI.

[John Stalcup]

I'm able to repro this both with -noincremental and -incremental, but only randomly (seems about 30% of the time).

Still looking into it.

[John Stalcup]

It's more like, 50% of the time.

Here's what's going on:

It's currently illegal to call foo.blah() in JSNI if the variable foo is either a JSO type or interface that is implemented by some JSO type.

The error you're seeing is JsniReferenceResolver enforcing this requirement, the weird part is that it should enforce it all the time but it's only enforcing it 50% of the time.

The reason this is occurring is that depending on the order that JDT processes types we may or may not yet have collected the knowledge to know that the java.util.List interface is used on a JSO before JsniReferenceResolver performns its check.

We need to move the correctness check to some later stage, late enough that "is JSO" checks will always be accurate.

In the 50% of compiles that are succeeding for you right now you're actually vulnerable to runtime errors because it's outputting code that attempts to call the "size()" function on the prototype of the "list" parameter (and that will fail if the instance that is passed in happens to be a JsArrayListWrapper).

[John Stalcup]

A "fix" for this is now committed. Which means this code snippet will now be rejected all the time.

To accomplish the same thing you need to execute the .size() function dispatch (or really any function dispatch on a List instance since you've used the List interface on a JSO type) inside of a *Java* not inside of a JSNI function. This is relatively straight forward if you make a static Java function that takes a List instance and calls size() on it, and you can call this static Java function inside of your JSNI.

[Jan Thewes]

Ok thanks so far.

Because the List.size() call is executed from GXT I don't have the possibility to change that call.

I've rewritten my JsArrayListWrapper and it's not a JSO any more.

So I'm good to go.

Cheers,

Jan