Fix funny types used in attribute value representation

It was bothering me a lot that I abused small integer values
casted to (void *) to represent non string values in
gitattributes.  This corrects it by making the type of attribute
values (const char *), and using the address of a few statically
allocated character buffer to denote true/false.  Unset attributes
are represented as having NULLs as their values.

Added in-header documentation to explain how git_checkattr()
routine should be called.

Signed-off-by: Junio C Hamano <junkio@cox.net>

1 files changed, 15 insertions, 7 deletions

diff --git a/attr.h b/attr.h
index 8ec2d3d35..f1c2038b0 100644
--- a/attr.h
+++ b/attr.h
@@ -4,21 +4,29 @@
 /* An attribute is a pointer to this opaque structure */
 struct git_attr;
 
+/*
+ * Given a string, return the gitattribute object that
+ * corresponds to it.
+ */
 struct git_attr *git_attr(const char *, int);
 
 /* Internal use */
-#define ATTR__TRUE	((void *) 1)
-#define ATTR__FALSE	((void *) 0)
-#define ATTR__UNSET	((void *) -1)
+extern const char git_attr__true[];
+extern const char git_attr__false[];
 
 /* For public to check git_attr_check results */
-#define ATTR_TRUE(v) ((v) == ATTR__TRUE)
-#define ATTR_FALSE(v) ((v) == ATTR__FALSE)
-#define ATTR_UNSET(v) ((v) == ATTR__UNSET)
+#define ATTR_TRUE(v) ((v) == git_attr__true)
+#define ATTR_FALSE(v) ((v) == git_attr__false)
+#define ATTR_UNSET(v) ((v) == NULL)
 
+/*
+ * Send one or more git_attr_check to git_checkattr(), and
+ * each 'value' member tells what its value is.
+ * Unset one is returned as NULL.
+ */
 struct git_attr_check {
 	struct git_attr *attr;
-	void *value;
+	const char *value;
 };
 
 int git_checkattr(const char *path, int, struct git_attr_check *);