appending target-specific variables: make 3.79 bug or feature?

[William F. Dowling]

Hi,

I have come across a difference between gnu make 3.78 and 3.79 that
may be a bug, and is certainly an incompatibility.  Consider this
Makefile:

foo : a += b
foo : a += c
foo :
        @echo $(a)

In 3.78 and earlier, the output of make is 'b c'; in 3.79 it is 'c'.
As I have quite a few Makefiles that rely on the former behavior, I
wonder
1) is the new behavior considered a bug or a feature?
2) if the latter, is there a workaround by which I can emulate the
   former behavior?

Thanks for your help -- GNU make is an amazing tool and I really
appreciate the huge amount of work that the contributers have done.

Thanks,

Will


-- 
William F. Dowling
Institute for Scientific Information
215-386-0100 x-1156