remote: introduce set_instance_url

Users may want to override the URL on a particular instance of a remote,
instead of updating the configuration.  Previously, users could use a
callback to do this, but this is not particularly idiomatic.

include/git2/remote.h

@@ -212,18 +212,20 @@ GIT_EXTERN(const char *) git_remote_name(const git_remote *remote);
  * Get the remote's url
  *
  * If url.*.insteadOf has been configured for this URL, it will
- * return the modified URL.
+ * return the modified URL.  If `git_remote_set_instance_pushurl`
+ * has been called for this remote, then that URL will be returned.
  *
  * @param remote the remote
  * @return a pointer to the url
  */
 GIT_EXTERN(const char *) git_remote_url(const git_remote *remote);
 
 /**
- * Get the remote's url for pushing
+ * Get the remote's url for pushing.
  *
  * If url.*.pushInsteadOf has been configured for this URL, it
- * will return the modified URL.
+ * will return the modified URL.  If `git_remote_set_instance_pushurl`
+ * has been called for this remote, then that URL will be returned.
  *
  * @param remote the remote
  * @return a pointer to the url or NULL if no special url for pushing is set
@@ -257,6 +259,26 @@ GIT_EXTERN(int) git_remote_set_url(git_repository *repo, const char *remote, con
  */
 GIT_EXTERN(int) git_remote_set_pushurl(git_repository *repo, const char *remote, const char* url);
 
+/**
+ * Set the url for this particular url instance.  The URL in the
+ * configuration will be ignored, and will not be changed.
+ *
+ * @param remote the remote's name
+ * @param url the url to set
+ * @return 0 or an error value
+ */
+GIT_EXTERN(int) git_remote_set_instance_url(git_remote *remote, const char *url);
+
+/**
+ * Set the push url for this particular url instance.  The URL in the
+ * configuration will be ignored, and will not be changed.
+ *
+ * @param remote the remote's name
+ * @param url the url to set
+ * @return 0 or an error value
+ */
+GIT_EXTERN(int) git_remote_set_instance_pushurl(git_remote *remote, const char *url);
+
 /**
  * Add a fetch refspec to the remote's configuration
  *

src/remote.c

@@ -600,6 +600,22 @@ const char *git_remote_url(const git_remote *remote)
 	return remote->url;
 }
 
+int git_remote_set_instance_url(git_remote *remote, const char *url)
+{
+	char *tmp;
+
+	GIT_ASSERT_ARG(remote);
+	GIT_ASSERT_ARG(url);
+
+	if ((tmp = git__strdup(url)) == NULL)
+		return -1;
+
+	git__free(remote->url);
+	remote->url = tmp;
+
+	return 0;
+}
+
 static int set_url(git_repository *repo, const char *remote, const char *pattern, const char *url)
 {
 	git_config *cfg;
@@ -645,6 +661,22 @@ const char *git_remote_pushurl(const git_remote *remote)
 	return remote->pushurl;
 }
 
+int git_remote_set_instance_pushurl(git_remote *remote, const char *url)
+{
+	char *tmp;
+
+	GIT_ASSERT_ARG(remote);
+	GIT_ASSERT_ARG(url);
+
+	if ((tmp = git__strdup(url)) == NULL)
+		return -1;
+
+	git__free(remote->pushurl);
+	remote->pushurl = tmp;
+
+	return 0;
+}
+
 int git_remote_set_pushurl(git_repository *repo, const char *remote, const char* url)
 {
 	return set_url(repo, remote, CONFIG_PUSHURL_FMT, url);

tests/network/remote/remotes.c

@@ -121,6 +121,51 @@ void test_network_remote_remotes__urlresolve_passthrough(void)
 	git_buf_dispose(&url);
 }
 
+void test_network_remote_remotes__instance_url(void)
+{
+	git_buf url = GIT_BUF_INIT;
+	const char *orig_url = "git://github.com/libgit2/libgit2";
+
+	cl_assert_equal_s(git_remote_name(_remote), "test");
+	cl_assert_equal_s(git_remote_url(_remote), orig_url);
+
+	cl_git_pass(git_remote__urlfordirection(&url, _remote, GIT_DIRECTION_FETCH, NULL));
+	cl_assert_equal_s(url.ptr, orig_url);
+	git_buf_clear(&url);
+
+	cl_git_pass(git_remote__urlfordirection(&url, _remote, GIT_DIRECTION_PUSH, NULL));
+	cl_assert_equal_s(url.ptr, orig_url);
+	git_buf_clear(&url);
+
+	/* Setting the instance url updates the fetch and push URLs */
+	git_remote_set_instance_url(_remote, "https://github.com/new/remote/url");
+	cl_assert_equal_s(git_remote_url(_remote), "https://github.com/new/remote/url");
+	cl_assert_equal_p(git_remote_pushurl(_remote), NULL);
+
+	cl_git_pass(git_remote__urlfordirection(&url, _remote, GIT_DIRECTION_FETCH, NULL));
+	cl_assert_equal_s(url.ptr, "https://github.com/new/remote/url");
+	git_buf_clear(&url);
+
+	cl_git_pass(git_remote__urlfordirection(&url, _remote, GIT_DIRECTION_PUSH, NULL));
+	cl_assert_equal_s(url.ptr, "https://github.com/new/remote/url");
+	git_buf_clear(&url);
+
+	/* Setting the instance push url updates only the push URL */
+	git_remote_set_instance_pushurl(_remote, "https://github.com/new/push/url");
+	cl_assert_equal_s(git_remote_url(_remote), "https://github.com/new/remote/url");
+	cl_assert_equal_s(git_remote_pushurl(_remote), "https://github.com/new/push/url");
+
+	cl_git_pass(git_remote__urlfordirection(&url, _remote, GIT_DIRECTION_FETCH, NULL));
+	cl_assert_equal_s(url.ptr, "https://github.com/new/remote/url");
+	git_buf_clear(&url);
+
+	cl_git_pass(git_remote__urlfordirection(&url, _remote, GIT_DIRECTION_PUSH, NULL));
+	cl_assert_equal_s(url.ptr, "https://github.com/new/push/url");
+	git_buf_clear(&url);
+
+	git_buf_dispose(&url);
+}
+
 void test_network_remote_remotes__pushurl(void)
 {
 	const char *name = git_remote_name(_remote);