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Re: builddir vs. srcdir

From: Paul Pogonyshev
Subject: Re: builddir vs. srcdir
Date: Fri, 18 Mar 2005 21:34:15 +0200
User-agent: KMail/1.4.3

> Hello,
> On Sat, Mar 12, 2005 at 06:56:20PM +0200, Paul Pogonyshev wrote:
> > Everything seems to work just fine and as expected,
> your code, which is in whole cited below, doesn't actually know
> about the dependency
> foo.c foo.h: foo.list
> So if you change the .list file, the other files won't be rebuilt.
> This might be a dangerous bug.

It doesn't know about the dependency, but the files will be rebuilt
as a ``side-effect'' of the timestamp rule.  I actually just tried
this out.

> In general, stamps are always dangerous, so it's good to avoid them if
> possible.  I'd try something like this:
> [file `aux/list.make']
> SUFFIXES = .list
> .list.c: Makefile $(PARSE_LIST_COMMAND)
> .list.h: Makefile $(PARSE_LIST_COMMAND)
> PARSE_LIST_BUILD_RULE =                                               \
>       $(PARSE_LIST_COMMAND) $(PARSE_LIST_FLAGS)               \
>       `test -f '$<' || echo '$(srcdir)/'`$< $*.h $*.c &&      \
>       touch $*.h
> [usage]
> LIST_FILES = foo.list bar.list
> # Prevent problems with parallel make:
> foo.h: foo.c
> bar.h: bar.c
> noinst_LIBRARIES = libfoo.a
> libfoo_a_SOURCES = ... $(LIST_FILES)
> # This hint is needed only for included files; *.c files
> # are handled by normal target dependencies:
> include $(top_srcdir)/aux/list.make

Sorry, but I'll stick with my setup.  My parser depends on my lowest-
level library (`libutils') and almost the whole build-tree depends on
the generated files.  So, when I touched my `libutils' in any way, I
would get a full-blown rebuild of the project.  That's why I used `cmp'
and only replaced the `.[ch]' files with the newly generated if they
differed.  And so I need timestamps to avoid unecessary commands run
all the time (I want to see ``nothing to be done...'' when it is the

> Let me add some comments:
> 1) The maintainer of Automake said that $(LIST_FILES:.list=.h) is safe,
>    and I trust him.

Oh, great, that is what I was looking for!

> 2) nodist_libfoo_a_SOURCES was redundant, especially the .c files.
>    Automake knows how to transform .list to .o, and listing the
>    intermediate files again could cause problems.

With your setup, yes.  Not with mine, unfortunately.

> 3) I try to have the BUILT_SOURCES hist as small as possible, so when
>    the .c file is a prerequisite of the corresponding .o, there is no
>    need to pre-build it using BUILT_SOURCES.
> 4) With parallel make, the PARSE_LIST_COMMAND cnnot be run twice in
>    parallel, because of the "foo.c: foo.h" dependency.  So we are safe.

I need to add this rule in my setup too.

Anyway, even if I don't accept your advice this time, thank you for
the help.  :)


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