[PATCH] Fix build: don't recompile all C++ every time

[Lubomir I. Ivanov]

On 4 October 2013 19:54, Thiago Macieira <thiago at macieira.org> wrote:
> This was caused by the %.o: %.cpp rule depending on "uicables". Since
> it's a phony target, the file never exists, so make will always try to
> rebuild it. Regardless of whether anything got run because of that,
> the target will then be "newer" than the .o file that was being
> considered. Therefore, make thought it had to recompile again.
>
> Fix it by skipping the intermediate, phony target and telling make
> that the C++ objects depend directly on the header files.
>
> Signed-off-by: Thiago Macieira <thiago at macieira.org>
> ---
>  Rules.mk | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/Rules.mk b/Rules.mk
> index 30e2e21..ce1ba59 100644
> --- a/Rules.mk
> +++ b/Rules.mk
> @@ -185,7 +185,7 @@ MOCFLAGS = $(filter -I%, $(CXXFLAGS) $(EXTRA_FLAGS)) $(filter -D%, $(CXXFLAGS) $
>         @mkdir -p .dep/$(@D)
>         $(COMPILE_PREFIX)$(CC) $(CFLAGS) $(EXTRA_FLAGS) -MD -MF .dep/$@.dep -c -o $@ $<
>
> -%.o: %.cpp uicables
> +%.o: %.cpp $(UIC_HEADERS)
>         @$(PRETTYECHO) '    CXX' $<
>         @mkdir -p .dep/$(@D)
>         $(COMPILE_PREFIX)$(CXX) $(CXXFLAGS) $(EXTRA_FLAGS) -I.uic -Iqt-ui -MD -MF .dep/$@.dep -c -o $@ $<
> --
> 1.7.11.7
>
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this patch broke it for me after a 'make confclean'.

g++ -Wall -g     -c -o qthelper.o qthelper.cpp
In file included from qthelper.cpp:1:0:
qthelper.h:4:21: fatal error: QMultiMap: No such file or directory

^ looks like the includes are strangely gone from the command line?

attached patch fixes it for me - adds $(UIC_HEADERS) in the $(TARGET) rule.

BTW, i've noticed that the qt-ui/ui_*.h * files do not recompile on
*.ui changes because they are in a sub-folder (vpath?), but if a
create a new .ui file and put it in ./ it does trigger a UIC recompile
and CXX recompile that follows. one problem here is that a single .ui
file change recompiles the whole CXX stack, because the %.o: %.cpp
rule is fed with all UIC headers, but i'm not sure this can be easily
avoided.

lubomir
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