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varmod-defined.mk revision 1.11 
      1 # $NetBSD: varmod-defined.mk,v 1.11 2021/04/11 13:35:56 rillig Exp $
      2 #
      3 # Tests for the :D variable modifier, which returns the given string
      4 # if the variable is defined.  It is closely related to the :U modifier.
      5 
      6 .MAKE.SAVE_DOLLARS=	yes
      7 
      8 DEF=	defined
      9 .undef UNDEF
     10 
     11 # Since DEF is defined, the value of the expression is "value", not
     12 # "defined".
     13 #
     14 .if ${DEF:Dvalue} != "value"
     15 .  error
     16 .endif
     17 
     18 # Since UNDEF is not defined, the "value" is ignored.  Instead of leaving the
     19 # expression undefined, it is set to "", exactly to allow the expression to
     20 # be used in .if conditions.  In this place, other undefined expressions
     21 # would generate an error message.
     22 # XXX: Ideally the error message would be "undefined variable", but as of
     23 # 2020-08-25 it is "Malformed conditional".
     24 #
     25 .if ${UNDEF:Dvalue} != ""
     26 .  error
     27 .endif
     28 
     29 # The modifier text may contain plain text as well as expressions.
     30 #
     31 .if ${DEF:D<${DEF}>} != "<defined>"
     32 .  error
     33 .endif
     34 
     35 # Special characters that would be interpreted differently can be escaped.
     36 # These are '}' (the closing character of the expression), ':', '$' and '\'.
     37 # Any other backslash sequences are preserved.
     38 #
     39 # The escaping rules for string literals in conditions are completely
     40 # different though. There, any character may be escaped using a backslash.
     41 #
     42 .if ${DEF:D \} \: \$ \\ \) \n } != " } : \$ \\ \\) \\n "
     43 .  error
     44 .endif
     45 
     46 # Like in several other places in variable expressions, when
     47 # ApplyModifier_Defined calls Var_Parse, double dollars lead to a parse
     48 # error that is silently ignored.  This makes all dollar signs disappear,
     49 # except for the last, which is a well-formed variable expression.
     50 #
     51 .if ${DEF:D$$$$$${DEF}} != "defined"
     52 .  error
     53 .endif
     54 
     55 # Any other text is written without any further escaping.  In contrast
     56 # to the :M modifier, parentheses and braces do not need to be nested.
     57 # Instead, the :D modifier is implemented sanely by parsing nested
     58 # expressions as such, without trying any shortcuts. See ApplyModifier_Match
     59 # for an inferior variant.
     60 #
     61 .if ${DEF:D!&((((} != "!&(((("
     62 .  error
     63 .endif
     64 
     65 # The :D modifier is often used in combination with the :U modifier.
     66 # It does not matter in which order the :D and :U modifiers appear.
     67 .if ${UNDEF:Dyes:Uno} != no
     68 .  error
     69 .endif
     70 .if ${UNDEF:Uno:Dyes} != no
     71 .  error
     72 .endif
     73 .if ${DEF:Dyes:Uno} != yes
     74 .  error
     75 .endif
     76 .if ${DEF:Uno:Dyes} != yes
     77 .  error
     78 .endif
     79 
     80 # Since the variable with the empty name is never defined, the :D modifier
     81 # can be used to add comments in the middle of an expression.  That
     82 # expression always evaluates to an empty string.
     83 .if ${:D This is a comment. } != ""
     84 .  error
     85 .endif
     86 
     87 # TODO: Add more tests for parsing the plain text part, to cover each branch
     88 # of ApplyModifier_Defined.
     89 
     90 # The :D and :U modifiers behave differently from the :@var@ modifier in
     91 # that they preserve dollars in a ':=' assignment.  This is because
     92 # ApplyModifier_Defined passes the emode unmodified to Var_Parse, unlike
     93 # ApplyModifier_Loop, which uses ParseModifierPart, which in turn removes
     94 # the keepDollar flag from emode.
     95 #
     96 # XXX: This inconsistency is documented nowhere.
     97 .MAKEFLAGS: -dv
     98 8_DOLLARS=	$$$$$$$$
     99 VAR:=		${8_DOLLARS}
    100 VAR:=		${VAR:D${8_DOLLARS}}
    101 VAR:=		${VAR:@var@${8_DOLLARS}@}
    102 .MAKEFLAGS: -d0
    103 
    104 all:
    105 	@:;
    106