1# $NetBSD: cond-late.mk,v 1.10 2025/06/30 21:44:39 rillig Exp $ 2# 3# Using the :? modifier, expressions can contain conditional 4# expressions that are evaluated late, at expansion time. 5# 6# Any expressions appearing in these conditions are expanded before parsing 7# the condition. This is different from conditions in .if directives, where 8# expressions are evaluated individually and only as far as necessary, see 9# cond-short.mk. 10# 11# Because of this, variables that are used in these lazy conditions 12# should not contain double-quotes, or the parser will probably fail. 13# 14# They should also not contain operators like == or <, since these are 15# actually interpreted as these operators. This is demonstrated below. 16# 17 18all: parse-time cond-literal 19 20parse-time: .PHONY 21 @${MAKE} -f ${MAKEFILE} do-parse-time || true 22 23COND.true= "yes" == "yes" 24COND.false= "yes" != "yes" 25 26.if make(do-parse-time) 27VAR= ${${UNDEF} != "no":?:} 28# expect+1: Bad condition 29. if empty(VAR:Mpattern) 30. endif 31.endif 32 33# If the order of evaluation were to change to first parse the condition 34# and then expand the variables, the output would change from the 35# current "yes no" to "yes yes", since both variables are non-empty. 36# expect: yes 37# expect: no 38cond-literal: 39 @echo ${ ${COND.true} :?yes:no} 40 @echo ${ ${COND.false} :?yes:no} 41