69 lines
2.0 KiB
Makefile
69 lines
2.0 KiB
Makefile
# $NetBSD: varmod-undefined.mk,v 1.8 2022/08/06 21:26:05 rillig Exp $
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#
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# Tests for the :U variable modifier, which returns the given string
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# if the variable is undefined.
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#
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# See also:
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# directive-for.mk
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# varmod-defined.mk
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# The pattern ${:Uword} is heavily used when expanding .for loops.
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#
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# This is how an expanded .for loop looks like.
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# .for word in one
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# . if ${word} != one
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.if ${:Uone} != one
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# . error ${word}
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. error ${:Uone}
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# . endif
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.endif
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# .endfor
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# The variable expressions in the text of the :U modifier may be arbitrarily
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# nested.
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.if ${:U${:Unested}${${${:Udeeply}}}} != nested
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. error
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.endif
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# The nested variable expressions may contain braces, and these braces don't
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# need to match pairwise. In the following example, the :S modifier uses '{'
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# as delimiter, which confuses both editors and humans because the opening
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# and closing braces don't match anymore. It's syntactically valid though.
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# For more similar examples, see varmod-subst.mk, mod-subst-delimiter.
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.if ${:U${:Uvalue:S{a{X{}} != vXlue
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. error
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.endif
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# The escaping rules for the :U modifier (left-hand side) and condition
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# string literals (right-hand side) are completely different.
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#
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# In the :U modifier, the backslash only escapes very few characters, all
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# other backslashes are retained.
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#
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# In condition string literals, the backslash always escapes the following
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# character, no matter whether it would be necessary or not.
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#
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# In both contexts, \n is an escaped letter n, not a newline; that's what
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# the .newline variable is for.
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#
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# Whitespace at the edges is preserved, on both sides of the comparison.
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#
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.if ${:U \: \} \$ \\ \a \b \n } != " : } \$ \\ \\a \\b \\n "
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. error
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.endif
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# Even after the :U modifier has been applied, the expression still remembers
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# that it originated from an undefined variable, and the :U modifier can
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# be used to overwrite the value of the expression.
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#
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.if ${UNDEF:Uvalue:S,a,X,} != "vXlue"
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. error
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.elif ${UNDEF:Uvalue:S,a,X,:Uwas undefined} != "was undefined"
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. error
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.endif
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all:
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@:;
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