1# $NetBSD: varmod-match-escape.mk,v 1.7 2021/04/03 11:08:40 rillig Exp $
2#
3# As of 2020-08-01, the :M and :N modifiers interpret backslashes differently,
4# depending on whether there was a variable expression somewhere before the
5# first backslash or not.  See ApplyModifier_Match, "copy = true".
6#
7# Apart from the different and possibly confusing debug output, there is no
8# difference in behavior.  When parsing the modifier text, only \{, \} and \:
9# are unescaped, and in the pattern matching these have the same meaning as
10# their plain variants '{', '}' and ':'.  In the pattern matching from
11# Str_Match, only \*, \? or \[ would make a noticeable difference.
12
13.MAKEFLAGS: -dcv
14
15SPECIALS=	\: : \\ * \*
16.if ${SPECIALS:M${:U}\:} != ${SPECIALS:M\:${:U}}
17.  warning unexpected
18.endif
19
20# And now both cases combined: A single modifier with both an escaped ':'
21# as well as a variable expression that expands to a ':'.
22#
23# XXX: As of 2020-11-01, when an escaped ':' occurs before the variable
24# expression, the whole modifier text is subject to unescaping '\:' to ':',
25# before the variable expression is expanded.  This means that the '\:' in
26# the variable expression is expanded as well, turning ${:U\:} into a simple
27# ${:U:}, which silently expands to an empty string, instead of generating
28# an error message.
29#
30# XXX: As of 2020-11-01, the modifier on the right-hand side of the
31# comparison is parsed differently though.  First, the variable expression
32# is parsed, resulting in ':' and needSubst=true.  After that, the escaped
33# ':' is seen, and this time, copy=true is not executed but stays copy=false.
34# Therefore the escaped ':' is kept as-is, and the final pattern becomes
35# ':\:'.
36#
37# If ApplyModifier_Match had used the same parsing algorithm as Var_Subst,
38# both patterns would end up as '::'.
39#
40VALUES=		: :: :\:
41.if ${VALUES:M\:${:U\:}} != ${VALUES:M${:U\:}\:}
42.  warning XXX: Oops
43.endif
44
45.MAKEFLAGS: -d0
46
47# XXX: As of 2020-11-01, unlike all other variable modifiers, a '$' in the
48# :M and :N modifiers is written as '$$', not as '\$'.  This is confusing,
49# undocumented and hopefully not used in practice.
50.if ${:U\$:M$$} != "\$"
51.  error
52.endif
53
54# XXX: As of 2020-11-01, unlike all other variable modifiers, '\$' is not
55# parsed as an escaped '$'.  Instead, ApplyModifier_Match first scans for
56# the ':' at the end of the modifier, which results in the pattern '\$'.
57# No unescaping takes place since the pattern neither contained '\:' nor
58# '\{' nor '\}'.  But the text is expanded, and a lonely '$' at the end
59# is silently discarded.  The resulting expanded pattern is thus '\', that
60# is a single backslash.
61.if ${:U\$:M\$} != ""
62.  error
63.endif
64
65# In lint mode, the case of a lonely '$' is covered with an error message.
66.MAKEFLAGS: -dL
67.if ${:U\$:M\$} != ""
68.  error
69.endif
70
71# The control flow of the pattern parser depends on the actual string that
72# is being matched.  There needs to be either a test that shows a difference
73# in behavior, or a proof that the behavior does not depend on the actual
74# string.
75#
76# TODO: Str_Match("a-z]", "[a-z]")
77# TODO: Str_Match("012", "[0-]]")
78# TODO: Str_Match("0]", "[0-]]")
79# TODO: Str_Match("1]", "[0-]]")
80# TODO: Str_Match("[", "[[]")
81# TODO: Str_Match("]", "[]")
82# TODO: Str_Match("]", "[[-]]")
83
84# In brackets, the backslash is just an ordinary character.
85# Outside brackets, it is an escape character for a few special characters.
86# TODO: Str_Match("\\", "[\\-]]")
87# TODO: Str_Match("-]", "[\\-]]")
88
89all:
90	@:;
91