1 files changed, 64 insertions, 21 deletions
diff --git a/unit-tests/comment.mk b/unit-tests/comment.mk
index 7dd7dbbe28b5..1cdcfcdd86ba 100644
--- a/unit-tests/comment.mk
+++ b/unit-tests/comment.mk
@@ -1,31 +1,74 @@
-# This is a comment
-.if ${MACHINE_ARCH} == something
-FOO=bar
-.endif
-
-#\
-	Multiline comment
+# $NetBSD: comment.mk,v 1.2 2020/09/07 19:17:36 rillig Exp $
+#
+# Demonstrate how comments are written in makefiles.
 
-BAR=# defined
-FOOBAR= # defined 
+# This is a comment.
 
-# This is an escaped comment \
-that keeps going until the end of this line
+#\
+This is a multiline comment.
 
-# Another escaped comment \
+# Another multiline comment \
 that \
 goes \
-on
+on and on.
+
+ # Comments can be indented, but that is rather unusual.
+
+	# Comments can be indented with a tab.
+	# These are not shell commands, they are just makefile comments.
+
+.if 1			# There can be comments after conditions.
+.endif			# And after the closing directive.
+
+VAR=			# This comment makes the variable value empty.
+.if ${VAR} != ""
+.  error
+.endif
+
+# The comment does not need to start at the beginning of a word (as in the
+# shell), it can start anywhere.
+VAR=# defined but empty
+
+# The space before the comment is always trimmed.
+VAR=	value
+.if ${VAR} != "value"
+.  error
+.endif
 
 # This is NOT an escaped comment due to the double backslashes \\
-all: hi foo bar
-	@echo comment testing done
+VAR=	not part of the comment
+.if ${VAR} != "not part of the comment"
+.  error
+.endif
 
-hi:
-	@echo comment testing start
+# To escape a comment sign, precede it with a backslash.
+VAR=	\#		# Both in the assignment.
+.if ${VAR} != "\#"	# And in the comparison.
+.  error
+.endif
+
+# Since 2012-03-24 the variable modifier :[#] does not need to be escaped.
+# To keep the parsing code simple, any "[#" does not start a comment, even
+# outside of a variable expression.
+WORDS=	${VAR:[#]} [#
+.if ${WORDS} != "1 [#"
+.  error
+.endif
 
-foo:
-	@echo this is $@
+# An odd number of comment signs makes a line continuation, \\\
+no matter if it is 3 or 5 \\\\\
+or 9 backslashes. \\\\\\\\\
+This is the last line of the comment.
+VAR=	no comment anymore
+.if ${VAR} != "no comment anymore"
+.  error
+.endif
 
-bar:
-	@echo This is how a comment looks: '# comment'
+all:
+# In the commands associated with a target, the '#' does not start a makefile
+# comment.  The '#' is just passed to the shell, like any ordinary character.
+	echo This is a shell comment: # comment
+# If the '#' were to start a makefile comment, the following shell command
+# would have unbalanced quotes.
+	echo This is not a shell comment: '# comment'
+	@echo A shell comment can#not start in the middle of a word.