On Sun, Mar 12, 2017 at 09:01:49AM -0400, Jeff King wrote: > On Sat, Mar 11, 2017 at 10:28:18PM +0000, brian m. carlson wrote: > > > Many developers use functionality in their editors that allows for quick > > syntax checks, including warning about questionable constructs. This > > functionality allows rapid development with fewer errors. However, such > > functionality generally does not allow the specification of > > project-specific defines or command-line options. > > > > Since the SHA1_HEADER include is not defined in such a case, developers > > see spurious errors when using these tools. Furthermore, while using a > > macro as the argument to #include is permitted by C11, it isn't > > permitted by C89 and C99, and there are known implementations which > > reject it. > > > > Instead of using SHA1_HEADER, create a hash.h header and use #if > > and #elif to select the desired header. Have the Makefile pass an > > appropriate option to help the header select the right implementation to > > use. > > This has bit me once or twice in the past[1], too, so I'm happy to see > somebody tackling it. > > Your solution does mean that your tool, whatever it is, that runs > without the same CFLAGS as the Makefile may get a _different_ sha1 > implementation, though. That's probably good enough for some purposes > but perhaps not for others.
Yeah, my goal was basically to pass -fsyntax-only, not to produce useful
object files. My patch does basically require that the user have
OpenSSL installed, but I do, so it doesn't matter.
I considered after the fact that I might just do something like:
#ifdef SHA1_HEADER
#include SHA1_HEADER
#else
#include "block-sha1/sha1.h"
#endif
That would be the smallest change, but probably not the best.
> The "most correct" solution, I think, would be to stop using "-D" flags
> in favor of actually generating hash.h. Something like the patch
> below[2] (though I think it there are some rough edges with the
> dependencies).
I agree that's a better solution. I was concerned about avoiding ending
up rebuilding everything when we regenerated the file, but it looks like
you've avoided that with cmp.
> Of course the sha1 header is just one of many such defines. It's the one
> that is most visible because the result is syntactically valid without
> it, but anything you compile without the Makefile's CFLAGS may be subtly
> different than what the Makefile would produce. So arguably the Makefile
> should be writing out a build-options.h with all of the values, and that
> should get pulled in by git-compat-util.h.
>
> I don't know if we want to go down that rabbit hole or not. I offer it
> merely as an alternative. I'm OK with your patch as-is if you don't want
> to dump any more time into it.
I'll take this patch for now and fix it up with the comment I mentioned
below. If someone wants to improve the situation down the line, then
they can pick that up.
I assume I can apply your sign-off to the resulting patch?
> -Peff
>
> [1] I think I hit the problem when trying to debug some internal part of
> git and writing a one-off "foo.c" that calls the code I want. You
> can't compile it with "gcc foo.c".
>
> [2] Here's what a patch for the generated-header might look like:
>
> diff --git a/Makefile b/Makefile
> index 9f0eae428..0d65d50e9 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -690,6 +690,7 @@ XDIFF_LIB = xdiff/lib.a
> VCSSVN_LIB = vcs-svn/lib.a
>
> GENERATED_H += common-cmds.h
> +GENERATED_H += hash.h
>
> LIB_H = $(shell $(FIND) . \
> -name .git -prune -o \
> @@ -1639,8 +1640,7 @@ PERLLIB_EXTRA_SQ = $(subst ','\'',$(PERLLIB_EXTRA))
> # from the dependency list, that would make each entry appear twice.
> LIBS = $(filter-out %.o, $(GITLIBS)) $(EXTLIBS)
>
> -BASIC_CFLAGS += -DSHA1_HEADER='$(SHA1_HEADER_SQ)' \
> - $(COMPAT_CFLAGS)
> +BASIC_CFLAGS += $(COMPAT_CFLAGS)
> LIB_OBJS += $(COMPAT_OBJS)
>
> # Quote for C
> @@ -1781,7 +1781,7 @@ git$X: git.o GIT-LDFLAGS $(BUILTIN_OBJS) $(GITLIBS)
> $(QUIET_LINK)$(CC) $(ALL_CFLAGS) -o $@ $(ALL_LDFLAGS) \
> $(filter %.o,$^) $(LIBS)
>
> -help.sp help.s help.o: common-cmds.h
> +help.sp help.s help.o: common-cmds.h hash.h
>
> builtin/help.sp builtin/help.s builtin/help.o: common-cmds.h GIT-PREFIX
> builtin/help.sp builtin/help.s builtin/help.o: EXTRA_CPPFLAGS = \
> @@ -1805,6 +1805,10 @@ common-cmds.h: generate-cmdlist.sh command-list.txt
> common-cmds.h: $(wildcard Documentation/git-*.txt)
> $(QUIET_GEN)$(SHELL_PATH) ./generate-cmdlist.sh command-list.txt >$@+
> && mv $@+ $@
>
> +hash.h:
> + $(QUIET_GEN)echo '#include $(SHA1_HEADER)' >$@+ && \
> + { cmp $@+ $@ >/dev/null 2>/dev/null || mv $@+ $@; }
I think here we'd want to also "rm -f $@+", so that we don't leave an
extra file behind if we're up-to-date (which is the common case), much
like we do for GIT-BUILD-OPTIONS.
--
brian m. carlson / brian with sandals: Houston, Texas, US
+1 832 623 2791 | https://www.crustytoothpaste.net/~bmc | My opinion only
OpenPGP: https://keybase.io/bk2204
signature.asc
Description: PGP signature
