clone: add clone.<url>.defaultObjectFilter config

Add a new configuration option that lets users specify a default
partial clone filter per URL pattern.  When cloning a repository
whose URL matches a configured pattern, git-clone automatically
applies the filter, equivalent to passing --filter on the command
line.

    [clone "https://github.com/"]
        defaultObjectFilter = blob:limit=5m

    [clone "https://internal.corp.com/large-project/"]
        defaultObjectFilter = blob:none

URL matching uses the existing urlmatch_config_entry() infrastructure,
following the same rules as http.<url>.* — you can match a domain,
a namespace path, or a specific project, and the most specific match
wins.

The config only affects the initial clone.  Once the clone completes,
the filter is recorded in remote.<name>.partialCloneFilter, so
subsequent fetches inherit it automatically.  An explicit --filter
flag on the command line takes precedence.

Only the URL-qualified form (clone.<url>.defaultObjectFilter) is
honored; a bare clone.defaultObjectFilter without a URL subsection
is ignored.

Signed-off-by: Alan Braithwaite <alan@braithwaite.dev>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: abraithwaite

Documentation/config/clone.adoc

@@ -21,3 +21,29 @@ endif::[]
 	If a partial clone filter is provided (see `--filter` in
 	linkgit:git-rev-list[1]) and `--recurse-submodules` is used, also apply
 	the filter to submodules.
+
+`clone.<url>.defaultObjectFilter`::
+	When set to a filter spec string (e.g., `blob:limit=1m`,
+	`blob:none`, `tree:0`), linkgit:git-clone[1] will automatically
+	use `--filter=<value>` when the clone URL matches `<url>`.
+	Objects matching the filter are excluded from the initial
+	transfer and lazily fetched on demand (e.g., during checkout).
+	Subsequent fetches inherit the filter via the per-remote config
+	that is written during the clone.
++
+The URL matching follows the same rules as `http.<url>.*` (see
+linkgit:git-config[1]).  The most specific URL match wins.  You can
+match a complete domain, a namespace, or a specific project:
++
+----
+[clone "https://github.com/"]
+    defaultObjectFilter = blob:limit=5m
+
+[clone "https://internal.corp.com/large-project/"]
+    defaultObjectFilter = blob:none
+----
++
+An explicit `--filter` option on the command line takes precedence
+over this config.  Only affects the initial clone; it has no effect
+on later fetches into an existing repository.  If the server does
+not support object filtering, the setting is silently ignored.

builtin/clone.c

@@ -44,6 +44,7 @@
 #include "path.h"
 #include "pkt-line.h"
 #include "list-objects-filter-options.h"
+#include "urlmatch.h"
 #include "hook.h"
 #include "bundle.h"
 #include "bundle-uri.h"
@@ -759,6 +760,65 @@ static int git_clone_config(const char *k, const char *v,
 	return git_default_config(k, v, ctx, cb);
 }
 
+struct clone_filter_data {
+	char *default_object_filter;
+};
+
+static int clone_filter_collect(const char *var, const char *value,
+				const struct config_context *ctx UNUSED,
+				void *cb)
+{
+	struct clone_filter_data *data = cb;
+
+	if (!strcmp(var, "clone.defaultobjectfilter")) {
+		free(data->default_object_filter);
+		data->default_object_filter = xstrdup(value);
+	}
+	return 0;
+}
+
+/*
+ * Look up clone.<url>.defaultObjectFilter using the urlmatch
+ * infrastructure.  Only URL-qualified forms are supported; a bare
+ * clone.defaultObjectFilter (without a URL) is ignored.
+ */
+static char *get_default_object_filter(const char *url)
+{
+	struct urlmatch_config config = URLMATCH_CONFIG_INIT;
+	struct clone_filter_data data = { 0 };
+	struct string_list_item *item;
+	char *normalized_url;
+
+	config.section = "clone";
+	config.key = "defaultobjectfilter";
+	config.collect_fn = clone_filter_collect;
+	config.cascade_fn = git_clone_config;
+	config.cb = &data;
+
+	normalized_url = url_normalize(url, &config.url);
+
+	repo_config(the_repository, urlmatch_config_entry, &config);
+	free(normalized_url);
+
+	/*
+	 * Reject the bare form clone.defaultObjectFilter (no URL
+	 * subsection).  urlmatch stores the best match in vars with
+	 * hostmatch_len == 0 for non-URL-qualified entries; discard
+	 * the result if that is what we got.
+	 */
+	item = string_list_lookup(&config.vars, "defaultobjectfilter");
+	if (item) {
+		const struct urlmatch_item *m = item->util;
+		if (!m->hostmatch_len && !m->pathmatch_len) {
+			FREE_AND_NULL(data.default_object_filter);
+		}
+	}
+
+	urlmatch_config_release(&config);
+
+	return data.default_object_filter;
+}
+
 static int write_one_config(const char *key, const char *value,
 			    const struct config_context *ctx,
 			    void *data)
@@ -1059,6 +1119,14 @@ int cmd_clone(int argc,
 	} else
 		die(_("repository '%s' does not exist"), repo_name);
 
+	if (!filter_options.choice) {
+		char *config_filter = get_default_object_filter(repo);
+		if (config_filter) {
+			parse_list_objects_filter(&filter_options, config_filter);
+			free(config_filter);
+		}
+	}
+
 	/* no need to be strict, transport_set_option() will validate it again */
 	if (option_depth && atoi(option_depth) < 1)
 		die(_("depth %s is not a positive number"), option_depth);

t/t5616-partial-clone.sh

@@ -723,6 +723,79 @@ test_expect_success 'after fetching descendants of non-promisor commits, gc work
 	git -C partial gc --prune=now
 '
 
+# Test clone.<url>.defaultObjectFilter config
+
+test_expect_success 'setup for clone.defaultObjectFilter tests' '
+	git init default-filter-src &&
+	echo "small" >default-filter-src/small.txt &&
+	dd if=/dev/zero of=default-filter-src/large.bin bs=1024 count=100 2>/dev/null &&
+	git -C default-filter-src add . &&
+	git -C default-filter-src commit -m "initial" &&
+
+	git clone --bare "file://$(pwd)/default-filter-src" default-filter-srv.bare &&
+	git -C default-filter-srv.bare config --local uploadpack.allowfilter 1 &&
+	git -C default-filter-srv.bare config --local uploadpack.allowanysha1inwant 1
+'
+
+test_expect_success 'clone with clone.<url>.defaultObjectFilter applies filter' '
+	SERVER_URL="file://$(pwd)/default-filter-srv.bare" &&
+	git -c "clone.$SERVER_URL.defaultObjectFilter=blob:limit=1k" clone \
+		"$SERVER_URL" default-filter-clone &&
+
+	test "$(git -C default-filter-clone config --local remote.origin.promisor)" = "true" &&
+	test "$(git -C default-filter-clone config --local remote.origin.partialclonefilter)" = "blob:limit=1024"
+'
+
+test_expect_success 'clone with --filter overrides clone.<url>.defaultObjectFilter' '
+	SERVER_URL="file://$(pwd)/default-filter-srv.bare" &&
+	git -c "clone.$SERVER_URL.defaultObjectFilter=blob:limit=1k" \
+		clone --filter=blob:none "$SERVER_URL" default-filter-override &&
+
+	test "$(git -C default-filter-override config --local remote.origin.partialclonefilter)" = "blob:none"
+'
+
+test_expect_success 'clone with clone.<url>.defaultObjectFilter=blob:none works' '
+	SERVER_URL="file://$(pwd)/default-filter-srv.bare" &&
+	git -c "clone.$SERVER_URL.defaultObjectFilter=blob:none" clone \
+		"$SERVER_URL" default-filter-blobnone &&
+
+	test "$(git -C default-filter-blobnone config --local remote.origin.promisor)" = "true" &&
+	test "$(git -C default-filter-blobnone config --local remote.origin.partialclonefilter)" = "blob:none"
+'
+
+test_expect_success 'clone.<url>.defaultObjectFilter with tree:0 works' '
+	SERVER_URL="file://$(pwd)/default-filter-srv.bare" &&
+	git -c "clone.$SERVER_URL.defaultObjectFilter=tree:0" clone \
+		"$SERVER_URL" default-filter-tree0 &&
+
+	test "$(git -C default-filter-tree0 config --local remote.origin.promisor)" = "true" &&
+	test "$(git -C default-filter-tree0 config --local remote.origin.partialclonefilter)" = "tree:0"
+'
+
+test_expect_success 'most specific URL match wins for clone.defaultObjectFilter' '
+	SERVER_URL="file://$(pwd)/default-filter-srv.bare" &&
+	git \
+		-c "clone.file://.defaultObjectFilter=blob:limit=1k" \
+		-c "clone.$SERVER_URL.defaultObjectFilter=blob:none" \
+		clone "$SERVER_URL" default-filter-url-specific &&
+
+	test "$(git -C default-filter-url-specific config --local remote.origin.partialclonefilter)" = "blob:none"
+'
+
+test_expect_success 'non-matching URL does not apply clone.defaultObjectFilter' '
+	git \
+		-c "clone.https://other.example.com/.defaultObjectFilter=blob:none" \
+		clone "file://$(pwd)/default-filter-srv.bare" default-filter-url-nomatch &&
+
+	test_must_fail git -C default-filter-url-nomatch config --local remote.origin.promisor
+'
+
+test_expect_success 'bare clone.defaultObjectFilter without URL is ignored' '
+	git -c clone.defaultObjectFilter=blob:none \
+		clone "file://$(pwd)/default-filter-srv.bare" default-filter-bare-key &&
+
+	test_must_fail git -C default-filter-bare-key config --local remote.origin.promisor
+'
 
 . "$TEST_DIRECTORY"/lib-httpd.sh
 start_httpd