Add ident filter

This adds the ident filter (that knows how to replace $Id$) and
tweaks the filter APIs and code so that git_filter_source objects
actually have the updated OID of the object being filtered when
it is a known value.

2 files changed, 13 insertions, 4 deletions

diff --git a/include/git2/filter.h b/include/git2/filter.h
index 8ef88d81b..649ed97cf 100644
--- a/include/git2/filter.h
+++ b/include/git2/filter.h
@@ -42,11 +42,13 @@ typedef enum {
  * file data.  Libgit2 includes one built in filter and it is possible to
  * write your own (see git2/sys/filter.h for information on that).
  *
- * The built in filter is:
+ * The two builtin filters are:
  *
  * * "crlf" which uses the complex rules with the "text", "eol", and
  *   "crlf" file attributes to decide how to convert between LF and CRLF
  *   line endings
+ * * "ident" which replaces "$Id$" in a blob with "$Id: <blob OID>$" upon
+ *   checkout and replaced "$Id: <anything>$" with "$Id$" on checkin.
  */
 typedef struct git_filter git_filter;
 
@@ -70,6 +72,7 @@ typedef struct git_filter_list git_filter_list;
  *
  * @param filters Output newly created git_filter_list (or NULL)
  * @param repo Repository object that contains `path`
+ * @param blob The blob to which the filter will be applied (if known)
  * @param path Relative path of the file to be filtered
  * @param mode Filtering direction (WT->ODB or ODB->WT)
  * @return 0 on success (which could still return NULL if no filters are
@@ -78,6 +81,7 @@ typedef struct git_filter_list git_filter_list;
 GIT_EXTERN(int) git_filter_list_load(
 	git_filter_list **filters,
 	git_repository *repo,
+	git_blob *blob, /* can be NULL */
 	const char *path,
 	git_filter_mode_t mode);
 
diff --git a/include/git2/sys/filter.h b/include/git2/sys/filter.h
index ca5738a53..c35fe55f6 100644
--- a/include/git2/sys/filter.h
+++ b/include/git2/sys/filter.h
@@ -26,7 +26,11 @@ GIT_BEGIN_DECL
  */
 GIT_EXTERN(git_filter *) git_filter_lookup(const char *name);
 
-#define GIT_FILTER_CRLF "crlf"
+#define GIT_FILTER_CRLF  "crlf"
+#define GIT_FILTER_IDENT "ident"
+
+#define GIT_FILTER_CRLF_PRIORITY 0
+#define GIT_FILTER_IDENT_PRIORITY 100
 
 /**
  * Create a new empty filter list
@@ -199,8 +203,9 @@ struct git_filter {
  * issued in order of `priority` on smudge (to workdir), and in reverse
  * order of `priority` on clean (to odb).
  *
- * One filter will be preregistered with libgit2:
- * - GIT_FILTER_CRLF with priority of 0.
+ * Two filters are preregistered with libgit2:
+ * - GIT_FILTER_CRLF with priority 0
+ * - GIT_FILTER_IDENT with priority 100
  *
  * Currently the filter registry is not thread safe, so any registering or
  * deregistering of filters must be done outside of any possible usage of