Re: toolchain/46750: make oddity expanding variables assigned to with +=

[David Holland <dholland-bugs%netbsd.org@localhost>]

The following reply was made to PR toolchain/46750; it has been noted by GNATS.

From: David Holland <dholland-bugs%netbsd.org@localhost>
To: gnats-bugs%NetBSD.org@localhost
Cc: 
Subject: Re: toolchain/46750: make oddity expanding variables assigned to
 with +=
Date: Mon, 30 Jul 2012 07:30:21 +0000

 On Sun, Jul 29, 2012 at 02:25:02PM +0000, Edgar Fu? wrote:
  >  > This is the way make works.
  >  Then either the first element (e.g. :[1]) should be empty or start with =
  >  a space.
 
 :[1] gives the first word; since words are delimited by whitespace,
 any leading whitespace is not part of the first word.
 
  >  You currently get different results from
  >  - asking for the whole value, which should be a space-separated list =
  >  (you get " foo bar")
  >  - asking explicitly for a space-separated list (you get "foo bar")
  >  - asking for the individual elements and space-joining them (you get =
  >  "foo bar")
  >  
  >  > Whitespace after =3D (or :=3D) can be removed, but whitespace
  >  > after +=3D must be kept - otherwise you can't build strings.
  >
  >  The manpage says (for all variants of assignments):
  >     Any white-space before the assigned value is removed=
 
 It is.
 
 What it's doing is inserting a space between the old value of the
 variable and the appended material. This is what it's supposed to do;
 otherwise, if you did
 
 FOO=bar
 FOO+=baz
 
 you'd get "barbaz" instead of "bar baz".
 
 The problem is that it's doing this even if the old value is the empty
 string, so you get a leading space. Relatedly, if you do
 
 FOO=foo
 FOO+=
 FOO+=
 FOO+=
 
 foo:
        echo /${FOO}/
 
 you get
 
 /foo   /
 
 which is also wrong.
 
 -- 
 David A. Holland
 dholland%netbsd.org@localhost