Re: make: ignore stale .depend

[christos%zoulas.com@localhost (Christos Zoulas)]

On Nov 26,  2:16pm, sjg%crufty.net@localhost ("Simon J. Gerraty") wrote:
-- Subject: Re: make: ignore stale .depend

| >Well, I am trying to understand what's going on here and how things are
| >supposed to work. I run make build, and after rb.h was renamed to rbtree.h
| >I get warnings about rb.h not found in /usr/src/lib/librump. Each time
| >I type make dependall in that directory, the dependencies are not being
| 
| This is a problem with bsd.dep.mk;
| .depend exists, and appears to be newer than ${__DPSRCS.d}, 
| so 'make depend' or 'make dependall' will not update it.
| Similarly, the .d.c suffix rule won't help since the .c file hasn't changed.
| 
| By itself, my patch won't help that - autodep.mk or equivalent is what
| you need for that, ie, the .d files are produced as a consequence of
| compiling the .o rather than as a separate step.  I've been using this
| model successfully for 10 years or so.
| 
| Also, the case that my patch (even with autodep.mk) is particularly
| useful for is reachover builds.  For .h's the worst case is that files
| get needlessly recompiled.  However (as the test case I quoted shows),
| if a .c file which is being compiled via reachover is moved, the build
| fails, and cannot proceed unless you remove the .depend file.
| 
| With is patch, a moved .c file is no more hassle than a moved .h,
| and with autodep.mk (or equivalent), .depend gets updated and you never
| have to worry about it again.  autodep.mk can't help if the compile
| fails.
| 
| >I understand, but I want to find a solution that does not cause make to
| >look for things in unexpected places.
| 
| Agreed.  For .c files (or more generally files which are sources)
| I don't think this will.  Consider the case where where a makefile does
| a reachover build and the dist directory changes.  The makefile will
| have been edited to have a new .PATH: to find the new srcs, so 
| it "just works".
| 
| The only case I can see getting screwed, is when a .h (more generally
| something which is not fed to a compiler directly) is moved. For this
| case, autodep.mk is all you really need, and searching for the file via
| .PATH could possibly find a file which is not the right one, so make
| could reach a bad decision - thinking target is up-to-date.
| 
| This case is dealt with automatically by meta mode, because regardless
| of what the mtimes say, meta_oodate() will note that a file that was
| used no longer exists and immediate flag out-of-date.
| 
| That notion - considering the target out-of-date immediately if there
| are stale .depend entries could easily be added to non-meta mode, and
| would solve the above.
| 
| Note that even without that, if the .h changed name, the .c file should
| have been changed, and would need recompiling anyway and autodep.mk will
| ensure the right things happen next time.
| 
| I'll have a dig to see if there is any clue in the GNode, by the time
| Dir_MTime() is called which could avoid identify the .h vs .c case
| (the later being the only one that really matters - s/.[ch]/language of 
choice/)
| 
| Bottom line though, this patch is mainly useful if you are already
| solving the case you mention - eg. via autodep.mk
| Note: that meta mode does this even better, the next rev of my mk-files
| tgz should include the basic bits needed.

Ok. Let's give it a try and we see if it improves things. 

christos