1# $NetBSD: varmod-ifelse.mk,v 1.21 2023/02/18 18:23:58 rillig Exp $
2#
3# Tests for the ${cond:?then:else} variable modifier, which evaluates either
4# the then-expression or the else-expression, depending on the condition.
5#
6# The modifier was added on 1998-04-01.
7#
8# Until 2015-10-11, the modifier always evaluated both the "then" and the
9# "else" expressions.
10
11# TODO: Implementation
12
13# The variable name of the expression is expanded and then taken as the
14# condition.  In the below example it becomes:
15#
16#	variable expression == "literal"
17#
18# This confuses the parser, which expects an operator instead of the bare
19# word "expression".  If the name were expanded lazily, everything would be
20# fine since the condition would be:
21#
22#	${:Uvariable expression} == "literal"
23#
24# Evaluating the variable name lazily would require additional code in
25# Var_Parse and ParseVarname, it would be more useful and predictable
26# though.
27.if ${${:Uvariable expression} == "literal":?bad:bad}
28.  error
29.else
30.  error
31.endif
32
33# In a variable assignment, undefined variables are not an error.
34# Because of the early expansion, the whole condition evaluates to
35# ' == ""' though, which cannot be parsed because the left-hand side looks
36# empty.
37COND:=	${${UNDEF} == "":?bad-assign:bad-assign}
38
39# In a condition, undefined variables generate a "Malformed conditional"
40# error.  That error message is wrong though.  In lint mode, the correct
41# "Undefined variable" error message is generated.
42# The difference to the ':=' variable assignment is the additional
43# "Malformed conditional" error message.
44.if ${${UNDEF} == "":?bad-cond:bad-cond}
45.  error
46.else
47.  error
48.endif
49
50# When the :? is parsed, it is greedy.  The else branch spans all the
51# text, up until the closing character '}', even if the text looks like
52# another modifier.
53.if ${1:?then:else:Q} != "then"
54.  error
55.endif
56.if ${0:?then:else:Q} != "else:Q"
57.  error
58.endif
59
60# This line generates 2 error messages.  The first comes from evaluating the
61# malformed conditional "1 == == 2", which is reported as "Bad conditional
62# expression" by ApplyModifier_IfElse.  The variable expression containing that
63# conditional therefore returns a parse error from Var_Parse, and this parse
64# error propagates to CondEvalExpression, where the "Malformed conditional"
65# comes from.
66.if ${1 == == 2:?yes:no} != ""
67.  error
68.else
69.  error
70.endif
71
72# If the "Bad conditional expression" appears in a quoted string literal, the
73# error message "Malformed conditional" is not printed, leaving only the "Bad
74# conditional expression".
75#
76# XXX: The left-hand side is enclosed in quotes.  This results in Var_Parse
77# being called without VARE_UNDEFERR.  When ApplyModifier_IfElse
78# returns AMR_CLEANUP as result, Var_Parse returns varUndefined since the
79# value of the variable expression is still undefined.  CondParser_String is
80# then supposed to do proper error handling, but since varUndefined is local
81# to var.c, it cannot distinguish this return value from an ordinary empty
82# string.  The left-hand side of the comparison is therefore just an empty
83# string, which is obviously equal to the empty string on the right-hand side.
84#
85# XXX: The debug log for -dc shows a comparison between 1.0 and 0.0.  The
86# condition should be detected as being malformed before any comparison is
87# done since there is no well-formed comparison in the condition at all.
88.MAKEFLAGS: -dc
89.if "${1 == == 2:?yes:no}" != ""
90.  error
91.else
92.  warning Oops, the parse error should have been propagated.
93.endif
94.MAKEFLAGS: -d0
95
96# As of 2020-12-10, the variable "name" is first expanded, and the result of
97# this expansion is then taken as the condition.  To force the variable
98# expression in the condition to be evaluated at exactly the right point,
99# the '$' of the intended '${VAR}' escapes from the parser in form of the
100# expression ${:U\$}.  Because of this escaping, the variable "name" and thus
101# the condition ends up as "${VAR} == value", just as intended.
102#
103# This hack does not work for variables from .for loops since these are
104# expanded at parse time to their corresponding ${:Uvalue} expressions.
105# Making the '$' of the '${VAR}' expression indirect hides this expression
106# from the parser of the .for loop body.  See ForLoop_SubstVarLong.
107.MAKEFLAGS: -dc
108VAR=	value
109.if ${ ${:U\$}{VAR} == value:?ok:bad} != "ok"
110.  error
111.endif
112.MAKEFLAGS: -d0
113
114# On 2021-04-19, when building external/bsd/tmux with HAVE_LLVM=yes and
115# HAVE_GCC=no, the following conditional generated this error message:
116#
117#	make: Bad conditional expression 'string == "literal" && no >= 10'
118#	    in 'string == "literal" && no >= 10?yes:no'
119#
120# Despite the error message (which was not clearly marked with "error:"),
121# the build continued, for historical reasons, see main_Exit.
122#
123# The tricky detail here is that the condition that looks so obvious in the
124# form written in the makefile becomes tricky when it is actually evaluated.
125# This is because the condition is written in the place of the variable name
126# of the expression, and in an expression, the variable name is always
127# expanded first, before even looking at the modifiers.  This happens for the
128# modifier ':?' as well, so when CondEvalExpression gets to see the
129# expression, it already looks like this:
130#
131#	string == "literal" && no >= 10
132#
133# When parsing such an expression, the parser used to be strict.  It first
134# evaluated the left-hand side of the operator '&&' and then started parsing
135# the right-hand side 'no >= 10'.  The word 'no' is obviously a string
136# literal, not enclosed in quotes, which is OK, even on the left-hand side of
137# the comparison operator, but only because this is a condition in the
138# modifier ':?'.  In an ordinary directive '.if', this would be a parse error.
139# For strings, only the comparison operators '==' and '!=' are defined,
140# therefore parsing stopped at the '>', producing the 'Bad conditional
141# expression'.
142#
143# Ideally, the conditional expression would not be expanded before parsing
144# it.  This would allow to write the conditions exactly as seen below.  That
145# change has a high chance of breaking _some_ existing code and would need
146# to be thoroughly tested.
147#
148# Since cond.c 1.262 from 2021-04-20, make reports a more specific error
149# message in situations like these, pointing directly to the specific problem
150# instead of just saying that the whole condition is bad.
151STRING=		string
152NUMBER=		no		# not really a number
153.info ${${STRING} == "literal" && ${NUMBER} >= 10:?yes:no}.
154.info ${${STRING} == "literal" || ${NUMBER} >= 10:?yes:no}.
155
156# The following situation occasionally occurs with MKINET6 or similar
157# variables.
158NUMBER=		# empty, not really a number either
159.info ${${STRING} == "literal" && ${NUMBER} >= 10:?yes:no}.
160.info ${${STRING} == "literal" || ${NUMBER} >= 10:?yes:no}.
161
162# CondParser_LeafToken handles [0-9-+] specially, treating them as a number.
163PLUS=		+
164ASTERISK=	*
165EMPTY=		# empty
166# "true" since "+" is not the empty string.
167.info ${${PLUS}		:?true:false}
168# "false" since the variable named "*" is not defined.
169.info ${${ASTERISK}	:?true:false}
170# syntax error since the condition is completely blank.
171.info ${${EMPTY}	:?true:false}
172
173
174# Since the condition of the '?:' modifier is expanded before being parsed and
175# evaluated, it is common practice to enclose expressions in quotes, to avoid
176# producing syntactically invalid conditions such as ' == value'.  This only
177# works if the expanded values neither contain quotes nor backslashes.  For
178# strings containing quotes or backslashes, the '?:' modifier should not be
179# used.
180PRIMES=	2 3 5 7 11
181.if ${1 2 3 4 5:L:@n@$n:${ ("${PRIMES:M$n}" != "") :?prime:not_prime}@} != \
182  "1:not_prime 2:prime 3:prime 4:not_prime 5:prime"
183.  error
184.endif
185
186# When parsing the modifier ':?', there are 3 possible cases:
187#
188#	1. The whole expression is only parsed.
189#	2. The expression is parsed and the 'then' branch is evaluated.
190#	3. The expression is parsed and the 'else' branch is evaluated.
191#
192# In all of these cases, the expression must be parsed in the same way,
193# especially when one of the branches contains unbalanced '{}' braces.
194#
195# At 2020-01-01, the expressions from the 'then' and 'else' branches were
196# parsed differently, depending on whether the branch was taken or not.  When
197# the branch was taken, the parser recognized that in the modifier ':S,}},,',
198# the '}}' were ordinary characters.  When the branch was not taken, the
199# parser only counted balanced '{' and '}', ignoring any escaping or other
200# changes in the interpretation.
201#
202# In var.c 1.285 from 2020-07-20, the parsing of the expressions changed so
203# that in both cases the expression is parsed in the same way, taking the
204# unbalanced braces in the ':S' modifiers into account.  This change was not
205# on purpose, the commit message mentioned 'has the same effect', which was a
206# wrong assumption.
207#
208# In var.c 1.323 from 2020-07-26, the unintended fix from var.c 1.285 was
209# reverted, still not knowing about the difference between regular parsing and
210# balanced-mode parsing.
211#
212# In var.c 1.1028 from 2022-08-08, there was another attempt at fixing this
213# inconsistency in parsing, but since that broke parsing of the modifier ':@',
214# it was reverted in var.c 1.1029 from 2022-08-23.
215#
216# In var.c 1.1047 from 2023-02-18, the inconsistency in parsing was finally
217# fixed.  The modifier ':@' now parses the body in balanced mode, while
218# everywhere else the modifier parts have their subexpressions parsed in the
219# same way, no matter whether they are evaluated or not.
220#
221# The modifiers ':@' and ':?' are similar in that they conceptually contain
222# text to be evaluated later or conditionally, still they parse that text
223# differently.  The crucial difference is that the body of the modifier ':@'
224# is always parsed using balanced mode.  The modifier ':?', on the other hand,
225# must parse both of its branches in the same way, no matter whether they are
226# evaluated or not.  Since balanced mode and standard mode are incompatible,
227# it's impossible to use balanced mode in the modifier ':?'.
228.MAKEFLAGS: -dc
229.if 0 && ${1:?${:Uthen0:S,}},,}:${:Uelse0:S,}},,}} != "not evaluated"
230# At 2020-01-07, the expression evaluated to 'then0,,}}', even though it was
231# irrelevant as the '0' had already been evaluated to 'false'.
232.  error
233.endif
234.if 1 && ${0:?${:Uthen1:S,}},,}:${:Uelse1:S,}},,}} != "else1"
235.  error
236.endif
237.if 2 && ${1:?${:Uthen2:S,}},,}:${:Uelse2:S,}},,}} != "then2"
238# At 2020-01-07, the whole expression evaluated to 'then2,,}}' instead of the
239# expected 'then2'.  The 'then' branch of the ':?' modifier was parsed
240# normally, parsing and evaluating the ':S' modifier, thereby treating the
241# '}}' as ordinary characters and resulting in 'then2'.  The 'else' branch was
242# parsed in balanced mode, ignoring that the inner '}}' were ordinary
243# characters.  The '}}' were thus interpreted as the end of the 'else' branch
244# and the whole expression.  This left the trailing ',,}}', which together
245# with the 'then2' formed the result 'then2,,}}'.
246.  error
247.endif
248.MAKEFLAGS: -d0
249