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# $NetBSD: counter-append.mk,v 1.5 2021/04/04 10:13:09 rillig Exp $
#
# Demonstrates how to let make count the number of times a variable
# is actually accessed, using the ::+= variable modifier.
#
# This works since 2020-09-23. Before that, the counter ended up at having
# 6 words, even though the NEXT variable was only accessed 3 times.
# The cause for this surprising behavior was that the ::= variable modifiers
# returned an error marker instead of a simple empty string.
RELEVANT= yes (load-time part) # just to filter the output
COUNTER= # zero
NEXT= ${COUNTER::+=a}${COUNTER:[#]}
# This variable is first set to empty and then expanded.
# See parse.c, function Parse_Var, keyword "!Var_Exists".
A:= ${NEXT}
B:= ${NEXT}
C:= ${NEXT}
RELEVANT= no
all:
@: ${RELEVANT::=yes (run-time part)}
@echo A=${A:Q} B=${B:Q} C=${C:Q} COUNTER=${COUNTER:[#]:Q}
@: ${RELEVANT::=no}
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