Re: Extending default suffix rules.

[Ralf Wildenhues]

* Remco Bras wrote on Sun, Mar 02, 2008 at 03:39:57PM CET:
> Op Sunday 02 March 2008 15:20:42 schreef Ralf Wildenhues:
> > Your rule is dangerous.  If the user interrupts make at the time the
> > convertors.sh script has run but the backup hasn't been restored yet,
> > the source will be wrong, and the next time you may have duplicate
> > function definitions (or whatnot else the sed script then does given
> > the wrong input file).
> >
> Fortunately, the sed script only fires on things matching the patterns
> convertors(type); or convertors(type,display_name_of_type);, not on the 
> expansion (which is a pair of normal C99 function definitions). If it did, 
> the same issues would arise if the gcc couldn't compile the generated file. 

But the interruption could also happen during the execution of
  cp $<{.backup,}

In that case, your innocent user will have an incomplete file and may
see weird errors later.  For maximum safety, any conversion scripts or
copies should first copy to a temporary file (inside the build tree)
and then mv atomically to the output file.  That way, even SIGQUIT
(CTRL-\) will not leave partial files (upon SIGINT, make will remove the
target file of the rule that is currently executed).

BTW, the {...,} is a bash extension and not POSIX compatible.

> I do like the option of using a different suffix, since it alerts any 
> contributor that whatever is in there may, in certain areas, not be standard 
> C. Also, it isolates any non-portability in the pre-processing process, 
> allowing the C that is generated to be compiled portably. Avoiding any 
> possible issues of macros that generate expansions that could be invocations 
> of themselves is a side benefit, but welcome.

I forgot earlier about the issue with distribution.  For the generated
stuff, you should either use nodist_foo_SOURCES and also
  CLEANFILES = $(nodist_foo_SOURCES)

or your rules should be prepared to know that the output is in the
source tree (mostly that means you don't have to do anything, at least
not with what you showed so far).

Cheers,
Ralf