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varmod-indirect.mk revision 1.1 
      1 # $NetBSD: varmod-indirect.mk,v 1.1 2020/12/01 22:16:36 rillig Exp $
      2 #
      3 # Tests for indirect variable modifiers, such as in ${VAR:${M_modifiers}}.
      4 # These can be used for very basic purposes like converting a string to either
      5 # uppercase or lowercase, as well as for fairly advanced modifiers that first
      6 # look like line noise and are hard to decipher.
      7 #
      8 # TODO: Since when are indirect modifiers supported?
      9 
     10 
     11 # The nested variable expression expands to "tu", and this is interpreted as
     12 # a variable modifier for the value "Upper", resulting in "UPPER".
     13 .if ${Upper:L:${:Utu}} != "UPPER"
     14 .  error
     15 .endif
     16 
     17 # The nested variable expression expands to "tl", and this is interpreted as
     18 # a variable modifier for the value "Lower", resulting in "lower".
     19 .if ${Lower:L:${:Utl}} != "lower"
     20 .  error
     21 .endif
     22 
     23 
     24 # The nested variable expression is ${1 != 1:?Z:tl}, consisting of the
     25 # condition "1 != 1", the then-branch "Z" and the else-branch "tl".  Since
     26 # the condition evaluates to false, the then-branch is ignored (it would
     27 # have been an unknown modifier anyway) and the ":tl" modifier is applied.
     28 .if ${Mixed:L:${1 != 1:?Z:tl}} != "mixed"
     29 .  error
     30 .endif
     31 
     32 
     33 # The indirect modifier can also replace an ':L' modifier, which allows for
     34 # brain twisters since by reading the expression alone, it is not possible
     35 # to say whether the variable name will be evaluated as a variable name or
     36 # as the immediate value of the expression.
     37 VAR=	value
     38 M_ExpandVar=	# an empty modifier
     39 M_VarAsValue=	L
     40 #
     41 .if ${VAR:${M_ExpandVar}} != "value"
     42 .  error
     43 .endif
     44 .if ${VAR:${M_VarAsValue}} != "VAR"
     45 .  error
     46 .endif
     47 
     48 # The indirect modifier M_ListToSkip, when applied to a list of patterns,
     49 # expands to a sequence of ':N' modifiers, each of which filters one of the
     50 # patterns.  This list of patterns can then be applied to another variable
     51 # to actually filter that variable.
     52 #
     53 M_ListToSkip=	@pat@N$${pat}@:ts:
     54 #
     55 # The dollar signs need to be doubled in the above modifier expression,
     56 # otherwise they would be expanded too early, that is, when parsing the
     57 # modifier itself.
     58 #
     59 # In the following example, M_NoPrimes expands to 'N2:N3:N5:N7:N1[1379]'.
     60 # The 'N' comes from the expression 'N${pat}', the separating colons come
     61 # from the modifier ':ts:'.
     62 #
     63 #.MAKEFLAGS: -dcv		# Uncomment this line to see the details
     64 #
     65 PRIMES=		2 3 5 7 1[1379]
     66 M_NoPrimes=	${PRIMES:${M_ListToSkip}}
     67 .if ${:U:range=20:${M_NoPrimes}} != "1 4 6 8 9 10 12 14 15 16 18 20"
     68 .  error
     69 .endif
     70 .MAKEFLAGS: -d0
     71 
     72 all:
     73