1 files changed, 55 insertions, 0 deletions
diff --git a/unit-tests/varmod-undefined.mk b/unit-tests/varmod-undefined.mk
new file mode 100644
index 000000000000..9ed35a8406fe
--- /dev/null
+++ b/unit-tests/varmod-undefined.mk
@@ -0,0 +1,55 @@
+# $NetBSD: varmod-undefined.mk,v 1.3 2020/08/23 20:49:33 rillig Exp $
+#
+# Tests for the :U variable modifier, which returns the given string
+# if the variable is undefined.
+#
+# The pattern ${:Uword} is heavily used when expanding .for loops.
+
+# This is how an expanded .for loop looks like.
+# .for word in one
+# .  if ${word} != one
+# .    error ${word}
+# .  endif
+# .endfor
+
+.if ${:Uone} != one
+.  error ${:Uone}
+.endif
+
+# The variable expressions in the text of the :U modifier may be arbitrarily
+# nested.
+
+.if ${:U${:Unested}${${${:Udeeply}}}} != nested
+.error
+.endif
+
+# The nested variable expressions may contain braces, and these braces don't
+# need to match pairwise.  In the following example, the :S modifier uses '{'
+# as delimiter, which confuses both editors and humans because the opening
+# and # closing braces don't match anymore.  It's syntactically valid though.
+# For more similar examples, see varmod-subst.mk, mod-subst-delimiter.
+
+.if ${:U${:Uvalue:S{a{X{}} != vXlue
+.error
+.endif
+
+# The escaping rules for the :U modifier (left-hand side) and condition
+# string literals (right-hand side) are completely different.
+#
+# In the :U modifier, the backslash only escapes very few characters, all
+# other backslashes are retained.
+#
+# In condition string literals, the backslash always escapes the following
+# character, no matter whether it would be necessary or not.
+#
+# In both contexts, \n is an escaped letter n, not a newline; that's what
+# the .newline variable is for.
+#
+# Whitespace at the edges is preserved, on both sides of the comparison.
+
+.if ${:U \: \} \$ \\ \a \b \n } != " : } \$ \\ \\a \\b \\n "
+.error
+.endif
+
+all:
+	@:;