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Re: pattern rules and pattern-specific-variables problem

From: Boris Kolpackov
Subject: Re: pattern rules and pattern-specific-variables problem
Date: Tue, 23 Aug 2005 19:13:28 +0200
User-agent: Mutt/1.5.6+20040907i


Paul D. Smith <address@hidden> writes:

>   bk> The idea is quite simple. Right now make will "apply" all matching
>   bk> pattern-specific variables in the order of definition. Proposed
>   bk> change will apply them in a different order: from the most generic
>   bk> to the most specialized.
> Hm.  Unless we can pre-sort the patterns by, say, the length of the
> pattern string _before_ expansion (in our example "foo%bar" is 7 chars,
> which is longer than "f%bar" at 5 chars, so f%bar would be matched first
> and foo%bar would be matched second) and have it always do the right
> thing, there doesn't seem to be any efficient way to manage this.

I believe you are right, pre-sorting pattern rules and pattern-specific
variables to be longest-first should do the trick.

> Offhand I can't think of an instance where sorting by length would give
> the wrong answer, but I haven't had my tea yet this morning :-).

It's actually quite easy to prove formally ;-).

>   bk> We can leave the old behavior by default and allow makefile
>   bk> writers to turn on the new behavior via MAKEFLAGS:
>   bk> MAKEFLAGS += --enable-pattern-specialization
> Yes... as you know, I just hate to add these kinds of flags to modify
> basic behavior though: every extra option increases the potential
> testing axes exponentially.

I agree knobs are evil but sometimes there is just no choice.


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