[alsa-devel] [PATCH 1/2] ucm: Enable all warnings for automake C preprocessor

[Takashi Sakamoto]

Hi,

On Dec 27 2016 19:08, mengdong.lin at linux.intel.com wrote:
> From: Mengdong Lin <mengdong.lin at linux.intel.com>
>
> To display warnings for us to fix them, add '-Wall' to AM_CPPFLAGS.
>
> Signed-off-by: Mengdong Lin <mengdong.lin at linux.intel.com>
>
> diff --git a/src/ucm/Makefile.am b/src/ucm/Makefile.am
> index 9d66b24..79e57d2 100644
> --- a/src/ucm/Makefile.am
> +++ b/src/ucm/Makefile.am
> @@ -7,4 +7,4 @@ noinst_HEADERS = ucm_local.h
>  all: libucm.la
>
>
> -AM_CPPFLAGS=-I$(top_srcdir)/include
> +AM_CPPFLAGS=-I$(top_srcdir)/include -Wall

As long as I know, the '-Wall' option is for C/C++ compiler. Therefore, 
it's not necessarily correct to add the option to 'AM_CPPFLAGS' as 
options for preprocessor. In a manual of GNU Automake, there're some 
samples for this option; '-I' and '-D'[0]. Usage of 'AM_CFLAGS' might be 
better in this case.

...But this indication is a bit nitpicking and I'm not so strongly 
oppose this patch. I'll manage to describe the reason.

In a manual of GNU compiler collection, there're samples of implicit 
rules for C/C++ compilers:
  * $(CC) $(CPPFLAGS) $(CFLAGS) -c
  * $(CXX) $(CPPFLAGS) $(CXXFLAGS) -c

If the place of 'CPPFLAGS' is replaced with options in AM_CPPFLAGS, your 
patch has an effect for both of C code and C++ code. This is somehow 
expected for some developers, while it's also be obtrusive because of 
sub-effect to C++ code in our case.

Currently, alsa-lib includes no C++ codes, while this patch could bring 
the obtrusiveness for future when some C++ codes were added (i.e. by 
code refactoring). But the result were preferable by itself, I believe.

Well, if Makefile.am includes 'mumble_CFLAGS' lines, options in 
'AM_CFLAGS' is ignored to generate the 'mumble'. For example, a command 
to generate 'user_ctl_element_set' object in 'test' directory is this 
case (I wrote it[2]).

Currently I cannot judge which way is better... I'm sorry but could I 
request your opinion for this patch with the view of these specifications?

[0]: 
https://www.gnu.org/software/automake/manual/html_node/Program-Variables.html
[1]: 
https://www.gnu.org/software/make/manual/html_node/Catalogue-of-Rules.html#Catalogue-of-Rules
[2]: 
http://git.alsa-project.org/?p=alsa-lib.git;a=blob;f=test/Makefile.am;h=5f35159af2d64c12e5d394cff884765808d38e5b;hb=HEAD#l29


Regards

Takashi Sakamoto