Hello, * Allan Caffee wrote on Thu, Feb 26, 2009 at 02:49:16PM CET: > That is certainly one possibility. Unfortunately though that means that > in the Makefile.am files you _must_ use += since Automake will error out > if you assign more than one value to a variable (within the same > Automake conditional block).
Which is a good thing: two assignments are a potential error, and will often result in something undesirable. > But I was hoping for away that wouldn't > require the author of Makefile.am to change their syntax. I want to > "sneak" some additional files onto the clean list. This attitude can be fixed by changing the default approach: always write your Makefile.am files or snippets so they only append to variables. :-) That way, the only person needing to adjust is the one supplying the outer file (or you first include a snippet that initializes all needed variables to empty). > Modern Automake does support appending. But only appending to a > variable that has already been set. Yes. This is done primarily to be able to diagnose typos, e.g., foolish = foo1ish += bar (no pun intended, BTW), but also to provide more deterministic semantics in the presence of conditionals (I don't remember the details). Is it worth the hassle? It's certainly a trade-off: - more work due to required initializations of all variables, - OTOH typos in variables can have rather subtle implications, esp. if those variables are of the "magic automake" kind. I suppose a more sophisticated implementation would allow to let automake work in a mode that wouldn't error out on += for uninitialized variables (e.g., with a command line switch -Wno-var-append or so). > My understanding is that Automake > handles appending in a way very similar to that shown above, using temp > variables which depending on the Automake conditionals defined, may or > may not be empty. Yes, possibly. > This allows it to sidestep implementations of Make > which don't allow +=. Perhaps we could just drop the error about > appending to an undefined variable and treat it as setting the variable > if not already set. I don't know how this would effect the reporting of > "multiply defined" variables though. See above. > The real reason I think it would be nice to have this flexibility is for > macro authors to be able to add files to be cleaned up/distributed > without requiring the users to manually add anything to their setup. So > assuming anything I just said was actually correct, how difficult would > it be to safely allow this? I think thinking through the special cases that can come up with conditionals would be most of the work. If you want to contribute a patch, please read the HACKING file in the git tree. Cheers, Ralf
