Re: Allow setting variable using += without prior =

[Akim Demaille]

>>> "Simon" == Simon Josefsson <address@hidden> writes:

 > Please enlighten me if there is some obvious problem doing that, as
 > I can't see it.

I was the one to introduce this limitation, and here is the
rationale.

It was at a time where cleaning the distinction between user and
Automake variables was much needed.  This also implied that precise
rules had to be defined as to how ownership transfered.  Because I
know how painful it is to ensure backward compatibility of bad
decisions, I became very afraid of the possible case where Automake
1.x would not define FOO, and then Automake 1.y would.

A user's FOO += foo would then have a completely different result,
most probably not the one expected.  If you first FOO =, then again
the result is more predictable.

Note that using += on an Automake variable is usually much safer,
since that variable is not likely to have its semantics change.