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varname-dot-newline.mk revision 1.7 
      1 # $NetBSD: varname-dot-newline.mk,v 1.7 2024/06/15 22:06:31 rillig Exp $
      2 #
      3 # Tests for the special .newline variable, which contains a single newline
      4 # character (U+000A).
      5 
      6 
      7 # https://austingroupbugs.net/view.php?id=1549 proposes:
      8 # > After all macro expansion is complete, when an escaped <newline> is
      9 # > found in a command line in a makefile, the command line that is executed
     10 # > shall contain the <backslash>, the <newline>, and the next line, except
     11 # > that the first character of the next line shall not be included if it is
     12 # > a <tab>.
     13 #
     14 # The above quote assumes that each resulting <newline> character has a "next
     15 # line", but that's not how the .newline variable works.
     16 BACKSLASH_NEWLINE:=	\${.newline}
     17 
     18 
     19 # Check that .newline is read-only
     20 
     21 NEWLINE:=	${.newline}
     22 
     23 .if make(try-to-modify)
     24 # A '?=' assignment is fine.  This pattern can be used to provide the variable
     25 # to older or other variants of make that don't know that variable.
     26 .newline?=	fallback
     27 # expect+1: Cannot overwrite ".newline" as it is read-only
     28 .newline=	overwritten
     29 # expect+1: Cannot append to ".newline" as it is read-only
     30 .newline+=	appended
     31 # expect+1: Cannot delete ".newline" as it is read-only
     32 .undef .newline
     33 .endif
     34 
     35 .if ${.newline} != ${NEWLINE}
     36 .  error The .newline variable can be overwritten.  It should be read-only.
     37 .endif
     38 
     39 all:
     40 	@${MAKE} -f ${MAKEFILE} try-to-modify || true
     41 	@echo 'first${.newline}second'
     42 	@echo 'backslash newline: <${BACKSLASH_NEWLINE}>'
     43