Compilation error due to overloaded method with unavailable parameter type

[Alex Buckley]

During overload resolution, Assertions::assertThat(BufferedImage) is a 
potentially applicable method so a compiler must test whether your 
actual argument's type is compatible with BufferedImage. Implementing 
that test almost certainly involves loading BufferedImage. 
Unfortunately, BufferedImage is not visible at compile time, because 
your module does not read any module exporting java.awt.image (unless 
your module explicitly 'requires java.desktop' as you found).

If the fest-assert module uses someone else's type (BufferedImage) in 
its exported API, then it should say 'requires public java.desktop'. 
Then, your module which 'requires fest-assert' will end up reading 
java.desktop. (Of course, java.desktop may not be observable in the 
first place, either because it doesn't physically exist or because 
-limitmods has been used. Then, the fest-assert module will rightly fail 
to resolve, and so will your module.)

I believe fest-assert is an automatic module, and we don't want 
automatic modules dragging in every module in the JDK by default. 
Automatic modules only read modules already in the module graph. Alan's 
suggestion to run with -addmods java.desktop will put java.desktop into 
the module graph.

Alex

On 5/31/2016 10:27 AM, Gunnar Morling wrote:
> Hi,
>
> I'm trying to compile some code with Jigsaw / Build 120 which is using the
> FEST Assert library [1]. For that purpose I copied that library to my
> module directory and added a dependency to my module-info.java.
>
> One class of FEST Assert I'm using, Assertions, contains several overloaded
> assertThat() methods, one of them [2]
> expecting java.awt.image.BufferedImage as a parameter. My code does *not*
> invoke that overloaded variant though, but rather the one taking List<?> as
> a parameter.
>
> Still I'm getting the following error:
>
>     class file for java.awt.image.BufferedImage not found
>
> I can make the error go away by adding "requires java.desktop" to
> module-info.java. But that seems not right, given I'm not using
> BufferedImage in my module at all.
>
> Is this a bug in Jigsaw? Or do I actually need that requires clause in
> order for overload resolution to work correctly?
>
> Thanks,
>
> --Gunnar
>
> [1] https://github.com/alexruiz/fest-assert-1.x
> [2]
> https://github.com/alexruiz/fest-assert-1.x/blob/1.4/src/main/java/org/fest/assertions/Assertions.java#L85
>