1 # $NetBSD: varmod-ifelse.mk,v 1.8 2020/12/10 16:47:42 rillig Exp $
3 # Tests for the ${cond:?then:else} variable modifier, which evaluates either
4 # the then-expression or the else-expression, depending on the condition.
6 # The modifier was added on 1998-04-01.
8 # Until 2015-10-11, the modifier always evaluated both the "then" and the
11 # TODO: Implementation
13 # The variable name of the expression is expanded and then taken as the
14 # condition. In this case it becomes:
16 # variable expression == "variable expression"
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:
22 # ${:Uvariable expression} == "literal"
24 # Evaluating the variable name lazily would require additional code in
25 # Var_Parse and ParseVarname, it would be more useful and predictable
27 .if ${${:Uvariable expression} == "literal":?bad:bad}
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
37 COND:= ${${UNDEF} == "":?bad-assign:bad-assign}
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}
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
53 .if ${1:?then:else:Q} != "then"
56 .if ${0:?then:else:Q} != "else:Q"
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"
66 .if ${1 == == 2:?yes:no} != ""
72 # If the "Bad conditional expression" appears in a quoted string literal, the
73 # error message "Malformed conditional" is not printed, leaving only the "Bad
74 # conditional expression".
76 # XXX: The left-hand side is enclosed in quotes. This results in Var_Parse
77 # being called without VARE_UNDEFERR being set. When ApplyModifier_IfElse
78 # returns AMR_CLEANUP as result, Var_Parse returns varUndefined since the
79 # value of the variable expression is still undefined. CondParser_String is
80 # then supposed to do proper error handling, but since varUndefined is local
81 # to var.c, it cannot distinguish this return value from an ordinary empty
82 # string. The left-hand side of the comparison is therefore just an empty
83 # string, which is obviously equal to the empty string on the right-hand side.
85 # XXX: The debug log for -dc shows a comparison between 1.0 and 0.0. The
86 # condition should be detected as being malformed before any comparison is
87 # done since there is no well-formed comparison in the condition at all.
89 .if "${1 == == 2:?yes:no}" != ""
92 . warning Oops, the parse error should have been propagated.
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.
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 SubstVarLong.
109 .if ${ ${:U\$}{VAR} == value :?ok:bad} != "ok"