[m-rev.] diff: fix hlc header file dependencies

[Fergus Henderson]

On 08-Aug-2001, Simon Taylor <stayl at cs.mu.OZ.AU> wrote:
> On 08-Aug-2001, Fergus Henderson <fjh at cs.mu.OZ.AU> wrote:
> > On 08-Aug-2001, Simon Taylor <stayl at cs.mu.OZ.AU> wrote:
> > > 
> > > compiler/modules.m:
> > > 	Fix another bug in the `.c_date' file change.
> > > 	The `.h' file for high-level C code grades should depend
> > > 	on the `.c' file for the module, not the `.c_date' file.
> > 
> > Why?
> > 
> > (No doubt your change is correct, but I'd like to understand it better.)
> 
> I'm not sure why the old rule caused compilation errors
> (the compiler was attempting to create the `.o' file for a module
> before all of the `.h' files for imported modules had been created),

It's generally a good idea to understand why a bug is happening before
trying to fix it.

> Even if it hadn't caused errors, it would cause unnecessary
> C compilations.

How so?

> By the way, do we need to add a datestamp file for the `.h' files
> with high-level C code to avoid unnecessarily recreating the `.o'
> files for importing moules when a module is recompiled but the
> header file is unchanged?

I don't think so.  mlds_to_c uses `update_interface' to create the header file,
so the date stamp on the header file won't be changed unless the header file
has changed.  Make may attempt to remake the `.h' file but the rule for
that is already an empty rule.

-- 
Fergus Henderson <fjh at cs.mu.oz.au>  |  "I have always known that the pursuit
The University of Melbourne         |  of excellence is a lethal habit"
WWW: <http://www.cs.mu.oz.au/~fjh>  |     -- the last words of T. S. Garp.
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