remote: add function to create detached remotes

Right now it is only possible to create remotes from a repository. While
this is probably the most common use-case, there are commands which make
sense even without a repository, e.g. the equivalence of `git
ls-remote`. Add a new function `git_remote_create_detached`, which
simply accepts a URL.

AUTHORS

@@ -22,6 +22,7 @@ Dmitry Kakurin
 Dmitry Kovega
 Emeric Fermas
 Emmanuel Rodriguez
+Eric Myhre
 Florian Forster
 Holger Weiss
 Ingmar Vanhassel

CHANGELOG.md

@@ -138,6 +138,10 @@ v0.25
   `git_merge_driver_source_file_options()` added as accessors to
   `git_merge_driver_source`.
 
+* `git_remote_create_unattached()` creates a remote that is not associated
+  to any repository (and does not apply configuration like 'insteadof' rules).
+  This is mostly useful for e.g. emulating `git ls-remote` behavior.
+
 ### API removals
 
 * `git_blob_create_fromchunks()` has been removed in favour of

include/git2/remote.h

@@ -76,6 +76,24 @@ GIT_EXTERN(int) git_remote_create_anonymous(
 		const char *url);
 
 /**
+ * Create a remote without a connected local repo
+ *
+ * Create a remote with the given url in-memory. You can use this when
+ * you have a URL instead of a remote's name.
+ *
+ * Contrasted with git_remote_create_anonymous, a detached remote
+ * will not consider any repo configuration values (such as insteadof url
+ * substitutions).
+ *
+ * @param out pointer to the new remote objects
+ * @param url the remote repository's URL
+ * @return 0 or an error code
+ */
+GIT_EXTERN(int) git_remote_create_detached(
+		git_remote **out,
+		const char *url);
+
+/**
  * Get the information for a particular remote
  *
  * The name will be checked for validity.

src/remote.c

@@ -197,10 +197,10 @@ static int create_internal(git_remote **out, git_repository *repo, const char *n
 	git_buf var = GIT_BUF_INIT;
 	int error = -1;
 
-	/* name is optional */
-	assert(out && repo && url);
+	/* repo, name, and fetch are optional */
+	assert(out && url);
 
-	if ((error = git_repository_config_snapshot(&config_ro, repo)) < 0)
+	if (repo && (error = git_repository_config_snapshot(&config_ro, repo)) < 0)
 		return error;
 
 	remote = git__calloc(1, sizeof(git_remote));
@@ -212,7 +212,11 @@ static int create_internal(git_remote **out, git_repository *repo, const char *n
 		(error = canonicalize_url(&canonical_url, url)) < 0)
 		goto on_error;
 
-	remote->url = apply_insteadof(config_ro, canonical_url.ptr, GIT_DIRECTION_FETCH);
+	if (repo) {
+		remote->url = apply_insteadof(config_ro, canonical_url.ptr, GIT_DIRECTION_FETCH);
+	} else {
+		remote->url = git__strdup(canonical_url.ptr);
+	}
 	GITERR_CHECK_ALLOC(remote->url);
 
 	if (name != NULL) {
@@ -222,8 +226,9 @@ static int create_internal(git_remote **out, git_repository *repo, const char *n
 		if ((error = git_buf_printf(&var, CONFIG_URL_FMT, name)) < 0)
 			goto on_error;
 
-		if ((error = git_repository_config__weakptr(&config_rw, repo)) < 0 ||
-			(error = git_config_set_string(config_rw, var.ptr, canonical_url.ptr)) < 0)
+		if (repo &&
+			((error = git_repository_config__weakptr(&config_rw, repo)) < 0 ||
+			(error = git_config_set_string(config_rw, var.ptr, canonical_url.ptr)) < 0))
 			goto on_error;
 	}
 
@@ -235,7 +240,7 @@ static int create_internal(git_remote **out, git_repository *repo, const char *n
 		if (name && (error = write_add_refspec(repo, name, fetch, true)) < 0)
 			goto on_error;
 
-		if ((error = lookup_remote_prune_config(remote, config_ro, name)) < 0)
+		if (repo && (error = lookup_remote_prune_config(remote, config_ro, name)) < 0)
 			goto on_error;
 
 		/* Move the data over to where the matching functions can find them */
@@ -330,6 +335,11 @@ int git_remote_create_anonymous(git_remote **out, git_repository *repo, const ch
 	return create_internal(out, repo, NULL, url, NULL);
 }
 
+int git_remote_create_detached(git_remote **out, const char *url)
+{
+	return create_internal(out, NULL, NULL, url, NULL);
+}
+
 int git_remote_dup(git_remote **dest, git_remote *source)
 {
 	size_t i;