Re: [PATCH] Documentation/CodingGuidelines: improve header includes rules
- From
Christian Couder <chriscool@tuxfamily.org>
- Date
- Apr 16, 2009, 05:10 UTC
- Message-ID
- <200904160710.28473.chriscool@tuxfamily.org>
- In-Reply-To
- <20090415075819.GC23332@coredump.intra.peff.net>
Le mercredi 15 avril 2009, Jeff King a écrit :
Show 16 quoted lines
> On Tue, Apr 14, 2009 at 12:34:33AM +0200, Christian Couder wrote: > > - The third one means that for example if we have "revision.h" > > that includes "diff.h" and "commit.h", then it's ok to include > > "revision.h" in a C file, only if at least one feature from > > "revision.h" is actually used in the C file. > > > > It is not ok to include "revision.h" if features from "diff.h" > > and "commit.h" are used but no feature from "revision.h" is > > used. > > Why? I thought the guiding principle mentioned earlier was "don't waste > programmers' time figuring out what should and shouldn't be included". > > Sure, I would not expect somebody to include a header that is totally > unrelated, but it seems that most of the source files lazily include > cache.h just to get "everything".
The third rule is:
+ - After the first #include in a C file, only header files containing + features that are actually used in the C file should be included. + (This means that it is not ok to include an header file only + because this header file includes other header files with features + that are used in the C file.)
So this rule is only for #include after the first one, and "cache.h" should be the first one if it is included.
I added this rule because we need a little sanity too and it can be misleading to see an include of some feature when in fact no features from the include are used.
> Stripping unnecessary includes doesn't even speed up compilation, as our > Makefile overspecifies the header dependencies anyway.
Perhaps the dependencies will not be overspecified one day, and I think it should at least speed up a little bit compilation of the C file where unnecessary includes have been stripped. And anyway it looks simpler and does not mislead into thinking that some feature are used when they are not.
Best regards, Christian.