611986 - nsWindow.cpp compilation failure on mingw after landing bug 586228

Status: RESOLVED FIXED

(Core :: Widget: Win32, defect)

Description

[Jacek Caban]

There are two problems:
- mingw doesn't like function to void* implicit casts as a function argument

- On win64 we loose precision here:
  int windowStatus =
   reinterpret_cast<int>(GetPropW(hWnd, kManageWindowInfoProperty));
It's an error instead of warning on mingw-w64. Casting to LONG_PTR instead of int fixes it (then the value is implicitly casted to int anyways).

I've also fixed a warning about passing NULL as an int argument.

Comment 1

[Jacek Caban]

Attachment: fix v1.0

Comment 2

[Vladimir Vukicevic [:vlad] [:vladv] (needinfo me, slow to respond)]

Comment on attachment 490380 [details] [diff] [review]
fix v1.0

>diff --git a/widget/src/windows/nsWindow.cpp b/widget/src/windows/nsWindow.cpp
>index cb5bd30..05035da 100644
>--- a/widget/src/windows/nsWindow.cpp
>+++ b/widget/src/windows/nsWindow.cpp
>@@ -1992,7 +1992,7 @@ GetWindowInfoHook(HWND hWnd, PWINDOWINFO pwi)
>     return FALSE;
>   }
>   int windowStatus = 
>-    reinterpret_cast<int>(GetPropW(hWnd, kManageWindowInfoProperty));
>+    reinterpret_cast<LONG_PTR>(GetPropW(hWnd, kManageWindowInfoProperty));

Erm, this doesn't make sense -- the assignment is to an int, how is reinterpret_cast<LONG_PTR> correct?

Comment 3

[Jacek Caban]

(In reply to comment #2)
> Erm, this doesn't make sense -- the assignment is to an int, how is
> reinterpret_cast<LONG_PTR> correct?

This way we have in fact two casts here. The first is done by reinterpret_cast. GetPropW returns HANDLE type, which is typedefed to void*. We do void* to int cast that loses precision and it's an error for GCC. Casting to LONG_PTR changes pointer to integer without losing precision.

The second cast is implicit from LONG_PTR to int. It loses precision, but its fine since both values are integers.

Comment 4

[Jacek Caban]

vlad, reading again, my explanation could be not clean enough.

No we have one cast:
reinterpret_cast from HANDLE (void*) to int  <-- invalid, losing precision

With my patch:
reinterpret_cast from HANDLE (void*) to LONG_PTR  <-- good, doesn't lose precision
implicit cast LONG_PTR to int   <-- good, it's valid for different int type casting

Comment 5

[Jacek Caban]

vlad, ping

Comment 6

[Jacek Caban]

Thanks for review, pushed:

http://hg.mozilla.org/mozilla-central/rev/e21c1c2813ad