remote: introduce remote.<name>.serverOption configuration

Currently, server options for Git protocol v2 can only be specified via
the command line option "--server-option" or "-o", which is inconvenient
when users want to specify a list of default options to send. Therefore,
we are introducing a new configuration to hold a list of default server
options, akin to the `push.pushOption` configuration for push options.

Initially, I named the new configuration `fetch.serverOption` to align
with `push.pushOption`. However, after discussing with Patrick, it was
renamed to `remote.<name>.serverOption` as suggested, because:

1. Server options are designed to be server-specific, making it more
   logical to use a per-remote configuration.
2. Using "fetch." prefixed configurations in git-clone or git-ls-remote
   seems out of place and inconsistent in design.

The parsing logic for `remote.<name>.serverOption` also relies on
`transport.c:parse_transport_option`, similar to `push.pushOption`, and
they follow the same priority design:

1. Server options set in lower-priority configuration files (e.g.,
   /etc/gitconfig or $HOME/.gitconfig) can be overridden or unset in
   more specific repository configurations using an empty string.
2. Command-line specified server options take precedence over those from
   the configuration.

Server options from configuration are stored to the corresponding
`remote.h:remote` as a new field `server_options`.  The field will be
utilized in the subsequent commit to help initialize the
`server_options` of `transport.h:transport`.

And documentation have been updated accordingly.

Helped-by: Patrick Steinhardt <[email protected]>
Helped-by: Junio C Hamano <[email protected]>
Reported-by: Liu Zhongbo <[email protected]>
Signed-off-by: Xing Xin <[email protected]>
Reviewed-by: Patrick Steinhardt <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: blanet

Documentation/config/remote.txt

@@ -96,3 +96,13 @@ remote.<name>.partialclonefilter::
 	Changing or clearing this value will only affect fetches for new commits.
 	To fetch associated objects for commits already present in the local object
 	database, use the `--refetch` option of linkgit:git-fetch[1].
+
+remote.<name>.serverOption::
+	The default set of server options used when fetching from this remote.
+	These server options can be overridden by the `--server-option=` command
+	line arguments.
++
+This is a multi-valued variable, and an empty value can be used in a higher
+priority configuration file (e.g. `.git/config` in a repository) to clear
+the values inherited from a lower priority configuration files (e.g.
+`$HOME/.gitconfig`).

remote.c

@@ -24,6 +24,7 @@
 #include "advice.h"
 #include "connect.h"
 #include "parse-options.h"
+#include "transport.h"
 
 enum map_direction { FROM_SRC, FROM_DST };
 
@@ -143,6 +144,7 @@ static struct remote *make_remote(struct remote_state *remote_state,
 	ret->name = xstrndup(name, len);
 	refspec_init(&ret->push, REFSPEC_PUSH);
 	refspec_init(&ret->fetch, REFSPEC_FETCH);
+	string_list_init_dup(&ret->server_options);
 
 	ALLOC_GROW(remote_state->remotes, remote_state->remotes_nr + 1,
 		   remote_state->remotes_alloc);
@@ -166,6 +168,7 @@ static void remote_clear(struct remote *remote)
 	free((char *)remote->uploadpack);
 	FREE_AND_NULL(remote->http_proxy);
 	FREE_AND_NULL(remote->http_proxy_authmethod);
+	string_list_clear(&remote->server_options, 0);
 }
 
 static void add_merge(struct branch *branch, const char *name)
@@ -508,6 +511,9 @@ static int handle_config(const char *key, const char *value,
 	} else if (!strcmp(subkey, "vcs")) {
 		FREE_AND_NULL(remote->foreign_vcs);
 		return git_config_string(&remote->foreign_vcs, key, value);
+	} else if (!strcmp(subkey, "serveroption")) {
+		return parse_transport_option(key, value,
+					      &remote->server_options);
 	}
 	return 0;
 }

remote.h

@@ -4,6 +4,7 @@
 #include "hash.h"
 #include "hashmap.h"
 #include "refspec.h"
+#include "string-list.h"
 #include "strvec.h"
 
 struct option;
@@ -104,6 +105,8 @@ struct remote {
 
 	/* The method used for authenticating against `http_proxy`. */
 	char *http_proxy_authmethod;
+
+	struct string_list server_options;
 };
 
 /**