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

[Alan Mackenzie]

Hello, Paul.

On Sat, Apr 13, 2019 at 19:44:50 -0700, 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.

Are you sure?  I just tried it out.  My first run,
    ./configure -C --with-gif=no --with-tiff=no --with-gpm=no
, took ~2.3 seconds.  I built Emacs, and GPM was indeed not built in.

Then I did
    ./configure -C --with-gif=no --with-tiff=no --with-gpm
, which again took ~2.3s, built Emacs, and GPM was then present and
working.

So it seems that ./configure -C can cope with at least some flags being
changed between runs.  Which are these "different flags" which don't
work when you change them whilst using the -C cache?

-- 
Alan Mackenzie (Nuremberg, Germany).