Repository: make head read-only and introduce set_head()

Following from the previous commits, make 'head' read-only and provide a
method to update head while providing a message.

The checkout() codepath which switches branches has been updated to
provide a reflog entry which mimics git's.

Author: carlosmn

pygit2/decl.h

@@ -30,6 +30,13 @@ typedef struct git_strarray {
 
 typedef int64_t git_off_t;
 
+typedef enum {
+	GIT_REF_INVALID = 0,
+	GIT_REF_OID = 1,
+	GIT_REF_SYMBOLIC = 2,
+	GIT_REF_LISTALL = 3,
+} git_ref_t;
+
 typedef enum {
 	GIT_OK = 0,
 	GIT_ERROR = -1,
@@ -450,6 +457,9 @@ int git_repository_init_ext(
 	const char *repo_path,
 	git_repository_init_options *opts);
 
+int git_repository_set_head(git_repository *repo, const char *refname, const git_signature *signature, const char *log_message);
+int git_repository_set_head_detached(git_repository *repo, const git_oid *commitish, const git_signature *signature, const char *log_message);
+
 /*
  * git_index
  */

pygit2/repository.py

@@ -274,7 +274,57 @@ def checkout(self, refname=None, **kwargs):
         oid = reference.resolve().target
         treeish = self[oid]
         self.checkout_tree(treeish, **kwargs)
-        self.head = refname
+        head = self.lookup_reference('HEAD')
+        if head.type == C.GIT_REF_SYMBOLIC:
+            from_ = self.head.shorthand
+        else:
+            from_ = head.target.hex
+
+        try:
+            signature = self.default_signature
+        except:
+            signature = None
+
+        reflog_text = "checkout: moving from %s to %s" % (from_, reference)
+        self.set_head(refname, signature, reflog_text)
+
+    #
+    # Setting HEAD
+    #
+    def set_head(self, target, signature=None, message=None):
+        """Set HEAD to point to the given target
+
+        Arguments:
+
+        target
+            The new target for HEAD. Can be a string or Oid (to detach)
+
+        signature
+            Signature to use for the reflog. If not provided, the repository's
+            default will be used
+
+        message
+            Message to use for the reflog
+        """
+
+        sig_ptr = ffi.new('git_signature **')
+        if signature:
+            ffi.buffer(sig_ptr)[:] = signature._pointer[:]
+
+        message_ptr = ffi.NULL
+        if message_ptr:
+            message_ptr = to_bytes(message)
+
+        if isinstance(target, Oid):
+            oid = ffi.new('git_oid *')
+            ffi.buffer(oid)[:] = target.raw[:]
+            err = C.git_repository_set_head_detached(self._repo, oid, sig_ptr[0], message_ptr)
+            check_error(err)
+            return
+
+        # if it's a string, then it's a reference name
+        err = C.git_repository_set_head(self._repo, to_bytes(target), sig_ptr[0], message_ptr)
+        check_error(err)
 
     #
     # Diff

src/repository.c

@@ -178,38 +178,6 @@ Repository_head__get__(Repository *self)
     return wrap_reference(head, self);
 }
 
-int
-Repository_head__set__(Repository *self, PyObject *py_val)
-{
-    int err;
-    if (PyObject_TypeCheck(py_val, &OidType)) {
-        git_oid oid;
-        py_oid_to_git_oid(py_val, &oid);
-        err = git_repository_set_head_detached(self->repo, &oid, NULL, NULL);
-        if (err < 0) {
-            Error_set(err);
-            return -1;
-        }
-    } else {
-        const char *refname;
-        PyObject *trefname;
-
-        refname = py_str_borrow_c_str(&trefname, py_val, NULL);
-        if (refname == NULL)
-            return -1;
-
-        err = git_repository_set_head(self->repo, refname, NULL, NULL);
-        Py_DECREF(trefname);
-        if (err < 0) {
-            Error_set_str(err, refname);
-            return -1;
-        }
-    }
-
-    return 0;
-}
-
-
 PyDoc_STRVAR(Repository_head_is_detached__doc__,
   "A repository's HEAD is detached when it points directly to a commit\n"
   "instead of a branch.");
@@ -1514,7 +1482,7 @@ PyMethodDef Repository_methods[] = {
 
 PyGetSetDef Repository_getseters[] = {
     GETTER(Repository, path),
-    GETSET(Repository, head),
+    GETTER(Repository, head),
     GETTER(Repository, head_is_detached),
     GETTER(Repository, head_is_unborn),
     GETTER(Repository, is_empty),

test/test_repository.py

@@ -76,10 +76,10 @@ def test_head(self):
 
     def test_set_head(self):
         # Test setting a detatched HEAD.
-        self.repo.head = Oid(hex=PARENT_SHA)
+        self.repo.set_head(Oid(hex=PARENT_SHA))
         self.assertEqual(self.repo.head.target.hex, PARENT_SHA)
         # And test setting a normal HEAD.
-        self.repo.head = "refs/heads/master"
+        self.repo.set_head("refs/heads/master")
         self.assertEqual(self.repo.head.name, "refs/heads/master")
         self.assertEqual(self.repo.head.target.hex, HEAD_SHA)