[m-dev.] For review: fix an alt install dir annoyance

[Fergus Henderson]

OK, given your responses I'm happy for you to go ahead and commit this one.

On 09-Jan-2000, Warwick Harvey <wharvey at cs.monash.edu.au> wrote:
> Fergus wrote:
> > On 07-Jan-2000, Warwick Harvey <wharvey at cs.monash.edu.au> wrote:
> > > Added some extra dependencies to the generated `.d' files, so that local
> > > `.int', `.opt', etc. files shadow the installed versions properly (e.g. for
> > > when you're trying to build a new version of an already installed library).
> > ...
> > > (In theory, perhaps this change shouldn't be needed; however, Make has a
> > > habit of ignoring pattern rules whenever it feels like it.)
> > 
> > It would be better if we understood why those pattern rules
> > were being ignored (I'm not a big fan of "voodoo" programming ;-).
> 
> OK, here's what it does, all in accordance with the Make documentation:
> 
> It looks in the current directory, does not find the `.int' file.  So it 
> searches the path, and finds the one in the library directory.  It then 
> tries applying a bunch of pattern rules, and cannot figure out how to 
> rebuild the `.int' file in the library directory (since there is no 
> corresponding `.m' file in the library directory).  Since they were only 
> pattern rules, it figures the `.int' file didn't need to be rebuilt and does 
> nothing.  If instead we have explicit (non-pattern) dependencies, it decides 
> that there _is_ something wrong, and that the `.int' file needs to be 
> rebuilt.  It then tries to rebuild the `.int' file, but in the current 
> directory this time.  In the current directory, the `.m' file is found, and 
> the `.int' file is rebuilt correctly.
> 
> Based on the above, pattern rules of the form:
> 
> 	$(MERCURY_INT_DIR)/%.int : %.date
> 	        @:
> 
> (a la those in extras/clpr/Mmakefile) would also fix the problem --- but 
> only for the standard installation location.  I don't know whether or not 
> one could devise appropriate hackery to get it to include all extra 
> directories specified by the user, and I don't particularly want to try.
> 
> > > -# Be very careful about changing the following rules.
> > > -# The `@:' is a silent do-nothing command.
> > > -# It is used to force GNU Make to recheck the timestamp
> > > -# on the target file.  (It is a pity that GNU Make doesn't
> > > -# have a way of handling these sorts of rules in a nicer manner.)
> > 
> > That comment should remain;
> > if the places where `@:' is used are different,
> > then the comment should be moved, not deleted.
> 
> Yup, sorry, fixed:
> 
> --- save/compiler/modules.m     Sun Jan  9 23:09:11 2000
> +++ compiler/modules.m  Sun Jan  9 23:10:03 2000
> @@ -1689,6 +1689,15 @@
>                 module_name_to_file_name(ModuleName, ".date3", no,
>                                                         Date3FileName),
>  
> +               /*
> +               ** Be very careful about changing the following rules.
> +               ** The `@:' is a silent do-nothing command.
> +               ** It is used to force GNU Make to recheck the timestamp
> +               ** on the target file.  (It is a pity that GNU Make doesn't
> +               ** have a way of handling these sorts of rules in a nicer
> +               ** manner.)
> +               */
> +
>                 io__write_strings(DepStream, [
>                         "\n",
>                         Int0FileName, " : ", Date0FileName, "\n",
> 
> > Also, with this change in place, should the following
> > code from extras/clpr/Mmakefile be deleted?
> 
> It shouldn't hurt either way.  It could also be converted to try using the 
> builtin library installation support, but it works the way it is.
> 
> I'm currently playing with this stuff for clpz (my integer solver plugged 
> into clpr).  Once I've got it working satisfactorily, I'll be porting it to 
> clpr, and at that point it shouldn't be too hard to back-patch the Mmakefile 
> in the main branch.
> 
> Warwick
> 
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-- 
Fergus Henderson <fjh at cs.mu.oz.au>  |  "I have always known that the pursuit
WWW: <http://www.cs.mu.oz.au/~fjh>  |  of excellence is a lethal habit"
PGP: finger fjh at 128.250.37.3        |     -- the last words of T. S. Garp.
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