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

[Noam Postavsky]

On Sat, 13 Apr 2019 at 10:06, Alan Mackenzie <address@hidden> wrote:

> > > > I just now timed it, and './configure' took 29 real-time seconds

> > > For the record, the slowness of `configure' irritates me, too.
>
> > For the record, I use the --cache-file option, and `configure' runs in
> > 2 real-time seconds. I use separate cache files per configuration, it
> > works pretty well.
>
> I tried that out yesterday, and indeed it takes about 2 seconds.  :-)
>
> But it's not clear how ./configure -C works.  What gets cached,

The macros used in configure.ac control what is cached.

> and how
> does configure know when something needs determining again rather than
> just copying a result from the cache?

The cache is not invalidated automatically, so you need to delete it
after upgrading devel libraries or compiler.

>  Presumably one needs to be
> prepared to delete the cache file when moving the top level directory to
> a different environment, and things like that.

Definitely can't take the cache file to a different machine.

> Is ./configure -C documented at all?

Not from the perspective of a user running ./configure as far as I
know, but see (autoconf.info) Caching Results.
https://www.gnu.org/software/autoconf/manual/autoconf-2.69/html_node/Caching-Results.html