t4018-diff-funcname: test syntax of builtin xfuncname patterns

Signed-off-by: Brandon Casey <casey@nrlssc.navy.mil>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t4018-diff-funcname.sh

@@ -32,7 +32,18 @@ EOF
 
 sed 's/beer\\/beer,\\/' < Beer.java > Beer-correct.java
 
+builtin_patterns="bibtex java pascal ruby tex"
+for p in $builtin_patterns
+do
+	test_expect_success "builtin $p pattern compiles" '
+		echo "*.java diff=$p" > .gitattributes &&
+		! ( git diff --no-index Beer.java Beer-correct.java 2>&1 |
+			grep "fatal" > /dev/null )
+	'
+done
+
 test_expect_success 'default behaviour' '
+	rm -f .gitattributes &&
 	git diff --no-index Beer.java Beer-correct.java |
 	grep "^@@.*@@ public class Beer"
 '