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      1 # $NetBSD: varmod-loop-delete.mk,v 1.7 2024/08/29 20:20:36 rillig Exp $
      2 #
      3 # Tests for the variable modifier ':@', which as a side effect allows to
      4 # delete an arbitrary variable.
      5 
      6 # A side effect of the modifier ':@' is that the loop variable is created as
      7 # an actual variable in the current evaluation scope (Command/Global/target),
      8 # and at the end of the loop, this variable is deleted.  Since var.c 1.204
      9 # from 2016-02-18 and before var.c 1.963 from 2021-12-05, a variable could be
     10 # deleted while it was in use, leading to a use-after-free bug.
     11 #
     12 # See Var_Parse, comment 'the value of the variable must not change'.
     13 
     14 # Set up the variable that deletes itself when it is evaluated.
     15 VAR=	${:U:@VAR@@} rest of the value
     16 
     17 # In an assignment, the scope is 'Global'.  Since the variable 'VAR' is
     18 # defined in the global scope, it deletes itself.
     19 # expect+1: Cannot delete variable "VAR" while it is used
     20 EVAL:=	${VAR}
     21 .if ${EVAL} != " rest of the value"
     22 .  error
     23 .endif
     24 
     25 VAR=	${:U:@VAR@@} rest of the value
     26 all: .PHONY
     27 	# In the command that is associated with a target, the scope is the
     28 	# one from the target.  That scope only contains a few variables like
     29 	# '.TARGET', '.ALLSRC', '.IMPSRC'.  Make does not expect that these
     30 	# variables get modified from the outside.
     31 	#
     32 	# There is no variable named 'VAR' in the local scope, so nothing
     33 	# happens.
     34 	: $@: '${VAR}'
     35