1 files changed, 31 insertions, 0 deletions
diff --git a/unit-tests/counter.mk b/unit-tests/counter.mk
new file mode 100644
index 0000000000000..23e7dcc0e8d29
--- /dev/null
+++ b/unit-tests/counter.mk
@@ -0,0 +1,31 @@
+# $NetBSD: counter.mk,v 1.1 2020/08/02 14:53:02 rillig Exp $
+#
+# Demonstrates that it is not easily possible to let make count
+# the number of times a variable is actually accessed.
+#
+# As of 2020-08-02, the counter ends up at having 4 words, even
+# though the NEXT variable is only accessed 3 times.  This is
+# surprising.
+#
+# A hint to this surprising behavior is that the variables don't
+# get fully expanded.  For example, A does not simply contain the
+# value "1" but an additional unexpanded ${COUNTER:...} before it.
+
+RELEVANT=	yes (load-time part)	# just to filter the output
+
+COUNTER=	# zero
+
+NEXT=		${COUNTER::=${COUNTER} a}${COUNTER:[#]}
+
+# This variable is first set to empty and then expanded.
+# See parse.c, function Parse_DoVar, 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}