836923 - Many of the NS_* nsresult constants don't work in C

Status: NEW

(Core :: XPCOM, defect)

Description

[Jeff Walden [:Waldo]]

In C the various constants like NS_OK and such are created by #defines.  Some of them are purely created from numeric constants.  Others look like this:

#define NS_ERROR_DOM_NO_MODIFICATION_ALLOWED_ERR   ((nsresult)(FAILURE(7)))

But it so happens that FAILURE is #define'd just before the list of error #defines, then #undef'd right after.  This is fine for all the non-C cases that put the error values into enum initializers or global consts, thereby using the definition of FAILURE at that point.  But the C case won't be, because use of NS_ERROR_DOM_NO_MODIFICATION_ALLOWED_ERR and so on will expand FAILURE based on its definition *at that point*.  So using this in a C file is going to have it expand into a call to a non-existent FAILURE function, and things will crash and burn.

There are two possible fixes here: make the C #defines work (not easy, given how the list of C #defines is generated), or switch all our C code that needs nsresult to C++.  I'd argue for the latter (there really isn't much) so we have fewer language quirks to think about, but then again I hope never to touch this again, so it's not *my* time that would be wasted making C work.  :-)