Re: About ./configure --cache-file (WAS: CHECK_STRUCTS/dmpstruct.h mechanism is broken.)

[Noam Postavsky]

On Sat, 13 Apr 2019 at 23:26, Daniel Colascione <address@hidden> wrote:
>
> On 4/13/19 7:44 PM, Paul Eggert wrote:
> > Noam Postavsky wrote:
> >> The cache is not invalidated automatically, so you need to delete it
> >> after upgrading devel libraries or compiler.
> >
> > ... or if you configure with different flags, or if you edit
> > configure.ac or if you do a bunch of other things. For the kind of work
> > I do, the cache is way more trouble than it's worth.

In practice, I've found the only problematic flag was
--with-x-toolkit, building with gtk caused a couple of tests to act
differently. Other than that, I even share cache files across Emacs
versions, the differences between configure.ac don't seem to be a
problem. Of course I expect it's different if you're editing
configure.ac and it's in an inconsistent state.

> I also
> wonder CC="ccache gcc" might help even for the case of a
> frequently-changed configure.ac.

It wouldn't help for the ./configure step itself, ccache doesn't cache
output of linking. Running ./configure does trigger a rebuild of all
of Emacs' C files, so ccache definitely helps for that.

https://ccache.dev/manual/latest.html:
autoconf compile/link Uncachable compilation or linking by an autoconf test.