Allow forcing the creation or renaming of references

Add internal reference create and rename functions which take a force
parameter, telling them to overwrite an existing reference if it
exists.

These functions try to update the reference if it's of the same type
as the one it's going to be replaced by. Otherwise the old reference
becomes invalid.

Signed-off-by: Carlos Martín Nieto <cmn@elego.de>

include/git2/refs.h

@@ -69,6 +69,27 @@ GIT_EXTERN(int) git_reference_lookup(git_reference **reference_out, git_reposito
 GIT_EXTERN(int) git_reference_create_symbolic(git_reference **ref_out, git_repository *repo, const char *name, const char *target);
 
 /**
+ * Create a new symbolic reference, overwriting an existing one with
+ * the same name, if it exists.
+ *
+ * If the new reference isn't a symbolic one, any pointers to the old
+ * reference become invalid.
+ *
+ * The reference will be created in the repository and written
+ * to the disk.
+ *
+ * This reference is owned by the repository and shall not
+ * be free'd by the user.
+ *
+ * @param ref_out Pointer to the newly created reference
+ * @param repo Repository where that reference will live
+ * @param name The name of the reference
+ * @param target The target of the reference
+ * @return 0 on success; error code otherwise
+ */
+GIT_EXTERN(int) git_reference_create_symbolic_force(git_reference **ref_out, git_repository *repo, const char *name, const char *target);
+
+/**
  * Create a new object id reference.
  *
  * The reference will be created in the repository and written
@@ -86,6 +107,27 @@ GIT_EXTERN(int) git_reference_create_symbolic(git_reference **ref_out, git_repos
 GIT_EXTERN(int) git_reference_create_oid(git_reference **ref_out, git_repository *repo, const char *name, const git_oid *id);
 
 /**
+ * Create a new object id reference, overwriting an existing one with
+ * the same name, if it exists.
+ *
+ * If the new reference isn't a symbolic one, any pointers to the old
+ * reference become invalid.
+ *
+ * The reference will be created in the repository and written
+ * to the disk.
+ *
+ * This reference is owned by the repository and shall not
+ * be free'd by the user.
+ *
+ * @param ref_out Pointer to the newly created reference
+ * @param repo Repository where that reference will live
+ * @param name The name of the reference
+ * @param id The object id pointed to by the reference.
+ * @return 0 on success; error code otherwise
+ */
+GIT_EXTERN(int) git_reference_create_oid_force(git_reference **ref_out, git_repository *repo, const char *name, const git_oid *id);
+
+/**
  * Get the OID pointed to by a reference.
  * 
  * Only available if the reference is direct (i.e. not symbolic)
@@ -190,6 +232,20 @@ GIT_EXTERN(int) git_reference_set_oid(git_reference *ref, const git_oid *id);
 GIT_EXTERN(int) git_reference_rename(git_reference *ref, const char *new_name);
 
 /**
+ * Rename an existing reference, overwriting an existing one with the
+ * same name, if it exists.
+ *
+ * This method works for both direct and symbolic references.
+ * The new name will be checked for validity and may be
+ * modified into a normalized form.
+ *
+ * The refernece will be immediately renamed in-memory
+ * and on disk.
+ *
+ */
+GIT_EXTERN(int) git_reference_rename_force(git_reference *ref, const char *new_name);
+
+/**
  * Delete an existing reference
  *
  * This method works for both direct and symbolic references.