cond-func-empty.mk revision 1.3 
1# $NetBSD: cond-func-empty.mk,v 1.3 2020/09/03 17:13:42 rillig Exp $
2#
3# Tests for the empty() function in .if conditions, which tests a variable
4# expression for emptiness.
5#
6# Note that the argument in the parentheses is indeed a variable name,
7# optionally followed by variable modifiers.  This is like the defined()
8# function.
9#
10
11.undef UNDEF
12EMPTY=	# empty
13SPACE=	${:U }
14WORD=	word
15
16# An undefined variable is empty.
17.if !empty(UNDEF)
18.  error
19.endif
20
21# An undefined variable has the empty string as the value, and the :M
22# variable modifier does not change that.
23#
24.if !empty(UNDEF:M*)
25.  error
26.endif
27
28# The :S modifier replaces the empty value with an actual word, and
29# after that the expression is no longer empty.  Because the variable
30# was undefined in the first place, the expression has the flag VAR_JUNK
31# but not VAR_KEEP, therefore it is still considered undefined.
32#
33# XXX: This is hard to explain to someone who doesn't know these
34# implementation details.
35#
36.if !empty(UNDEF:S,^$,value,W)
37.  error
38.endif
39
40# The :U modifier modifies expressions based on undefined variables
41# (VAR_JUNK) by adding the VAR_KEEP flag, which marks the expression
42# as "being interesting enough to be further processed".
43#
44.if empty(UNDEF:S,^$,value,W:Ufallback)
45.  error
46.endif
47
48# And now to the surprising part.  Applying the following :S modifier to the
49# undefined variable makes it non-empty, but the marker VAR_JUNK is preserved
50# nevertheless.  The :U modifier that follows only looks at VAR_JUNK to decide
51# whether the variable is defined or not.  This kind of makes sense since the
52# :U modifier tests the _variable_, not the _expression_.
53#
54# But since the variable was undefined to begin with, the fallback value is
55# used in this expression.
56#
57.if ${UNDEF:S,^$,value,W:Ufallback} != "fallback"
58.  error
59.endif
60
61# The variable EMPTY is completely empty (0 characters).
62.if !empty(EMPTY)
63.  error
64.endif
65
66# The variable SPACE has a single space, which counts as being empty.
67.if !empty(SPACE)
68.  error
69.endif
70
71# The variable .newline has a single newline, which counts as being empty.
72.if !empty(.newline)
73.  error
74.endif
75
76# The empty variable named "" gets a fallback value of " ", which counts as
77# empty.
78#
79# Contrary to the other functions in conditionals, the trailing space is not
80# stripped off, as can be seen in the -dv debug log.  If the space had been
81# stripped, it wouldn't make a difference in this case.
82#
83.if !empty(:U )
84.  error
85.endif
86
87# Now the variable named " " gets a non-empty value, which demonstrates that
88# neither leading nor trailing spaces are trimmed in the argument of the
89# function.  If the spaces were trimmed, the variable name would be "" and
90# that variable is indeed undefined.  Since get_mpt_arg calls Var_Parse
91# without VARE_UNDEFERR, the value of the undefined variable is returned as
92# an empty string.
93${:U }=	space
94.if empty( )
95.  error
96.endif
97
98# The value of the following expression is " word", which is not empty.
99.if empty(:U word)
100.  error
101.endif
102
103# The :L modifier creates a variable expression that has the same value as
104# its name, which both are "VAR" in this case.  The value is therefore not
105# empty.
106.if empty(VAR:L)
107.  error
108.endif
109
110# The variable WORD has the value "word", which does not count as empty.
111.if empty(WORD)
112.  error
113.endif
114
115# The expression ${} for a variable with the empty name always evaluates
116# to an empty string (see Var_Parse, varNoError).
117.if !empty()
118.  error
119.endif
120
121all:
122	@:;
123