[Qt-interest] qmake and DEPENDPATH subtlety

[Michael Ost]

Hi,

I've been stymied for a long time as to why some #includes are scanned 
in qmake and some are not. It's led me to paranoid and lengthy "rebuild 
project" sessions which have undermined my confidence in qmake / Qt Creator.

Then, thankfully!, I came across DEPENDPATH and that has helped immensely.

But there is a subtle detail that I didn't see documented that others 
might find helpful: if you use directories in your #include statements, 
DEPENDPATH should be the prefix to insert (like INCLUDEPATH works) 
instead of the directory itself.

This makes sense in retrospect, but it wasn't clear at first.

So, for others challenged like me, here are two project files --- the 
first fails to add test2.h as a dependency of test.cpp because 
DEPENDPATH gives the directory, not the prefix. And the second works 
because DEPENDPATH is changed to the prefix.

Ex 1 FAILS -

a/BAD.pro:
   TARGET = test
   TEMPLATE = lib
   INCLUDEPATH += ../b
   # Fails, becuase this is test2.h's directory not the prefix
   DEPENDPATH += ../b/c
   SOURCES += ../b/test.cpp
   HEADERS += ../b/c/test.h ../b/c/test2.h

a/GOOD.pro:
   TARGET = test
   TEMPLATE = lib
   INCLUDEPATH += ../b
   # Works, becuase this is the prefix
   DEPENDPATH += ../b
   SOURCES += ../b/test.cpp
   HEADERS += ../b/c/test.h ../b/c/test2.h

b/test.cpp:
   #include "c/test.h"

b/c/test.h:
   #include "c/test2.h"

b/c/test2.h:
   (empty)

Note that for both projects, "test.h" is found, presumably because it is 
in the CPP file. This seems to only impact headers that include headers.

Anyway, I hope this saves some other Qt programmer some headaches!

- Michael Ost