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# $NetBSD: varmod-ifelse.mk,v 1.5 2020/10/23 14:24:51 rillig Exp $
#
# Tests for the ${cond:?then:else} variable modifier, which evaluates either
# the then-expression or the else-expression, depending on the condition.
#
# The modifier was added on 1998-04-01.
#
# Until 2015-10-11, the modifier always evaluated both the "then" and the
# "else" expressions.
# TODO: Implementation
# The variable name of the expression is expanded and then taken as the
# condition. In this case it becomes:
#
# variable expression == "variable expression"
#
# This confuses the parser, which expects an operator instead of the bare
# word "expression". If the name were expanded lazily, everything would be
# fine since the condition would be:
#
# ${:Uvariable expression} == "literal"
#
# Evaluating the variable name lazily would require additional code in
# Var_Parse and ParseVarname, it would be more useful and predictable
# though.
.if ${${:Uvariable expression} == "literal":?bad:bad}
. error
.else
. error
.endif
# In a variable assignment, undefined variables are not an error.
# Because of the early expansion, the whole condition evaluates to
# ' == ""' though, which cannot be parsed because the left-hand side looks
# empty.
COND:= ${${UNDEF} == "":?bad-assign:bad-assign}
# In a condition, undefined variables generate a "Malformed conditional"
# error. That error message is wrong though. In lint mode, the correct
# "Undefined variable" error message is generated.
# The difference to the ':=' variable assignment is the additional
# "Malformed conditional" error message.
.if ${${UNDEF} == "":?bad-cond:bad-cond}
. error
.else
. error
.endif
# When the :? is parsed, it is greedy. The else branch spans all the
# text, up until the closing character '}', even if the text looks like
# another modifier.
.if ${1:?then:else:Q} != "then"
. error
.endif
.if ${0:?then:else:Q} != "else:Q"
. error
.endif
all:
@:;
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