1 # $NetBSD: var-op-expand.mk,v 1.4 2020/11/08 14:00:52 rillig Exp $
3 # Tests for the := variable assignment operator, which expands its
8 # XXX: edge case: When a variable name refers to an undefined variable, the
9 # behavior differs between the '=' and the ':=' assignment operators.
10 # This bug exists since var.c 1.42 from 2000-05-11.
12 # The '=' operator expands the undefined variable to an empty string, thus
13 # assigning to VAR_ASSIGN_. In the name of variables to be set, it should
14 # really be forbidden to refer to undefined variables.
16 # The ':=' operator expands the variable name twice. In one of these
17 # expansions, the undefined variable expression is preserved (controlled by
18 # preserveUndefined in VarAssign_EvalSubst), in the other expansion it expands
19 # to an empty string. This way, 2 variables are created using a single
20 # variable assignment. It's magic. :-/
22 VAR_ASSIGN_${UNDEF}= undef value
23 VAR_SUBST_${UNDEF}:= undef value