[bug #58734] gmake does not check for the existence of a file before complaining it is missing

[Jörg Schilling]

Follow-up Comment #5, bug #58734 (project make):

I forgot to mention, that this happens in parallel and in serial mode. So your
assumption is wrong.

Caching is not a bad thing if it helps to speed up things. I did not make
related tests and I am not going to doubt here because this would put effort
on the wrong target. 

I am also not going to add unneeded hidden files when there is already a file
that is created as a result of the command that has been run.

The main problem for this bug is that gmake does not implement the cache the
right way.

If you like to use caching the right way, you may do so whenever this caching
contains information that leads to the assumption that a target is up to
date.

The gmake command failed not because of caching in general but because of the
fact that gmake does not correct invalid cache content.

Please keep in mind that the current implementation of gmake causes gmake to
stop working with a wrong error message. If you run gmake again, it works
further on, up to the next similar problem while other make implementations
just continue to work with the first call.

This behavior of gmake is annoying and slows down the compilation.

It would be so easy just to re-check the time stamp of every cached file that
is believed to be out of date or missing. Time stamp checking is also faster
than re-running a command for a related rule.

A time stamp in "make" may have three values (the last one is a range):

- File dos not exist. This may become invalid if cached.

- Younger than any file. This will never become invalid for the lifetime of
make.

- A specific time stamp. This may become invalid and rechecking is faster than
running a command again. In special as only the time stamp of a single file
needs to be checked in such a case.

Just a note: I've seen commands that have been run twice as a result of not
verifying the third case in gmake.

BTW: some of the problems I have with gmake would go away if there was not an
unlucky combination of contradictory behavior.

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