submodule: implement a config API for lookup of .gitmodules values

In a superproject some commands need to interact with submodules. They
need to query values from the .gitmodules file either from the worktree
of from certain revisions. At the moment this is quite hard since a
caller would need to read the .gitmodules file from the history and then
parse the values. We want to provide an API for this so we have one
place to get values from .gitmodules from any revision (including the
worktree).

The API is realized as a cache which allows us to lazily read
.gitmodules configurations by commit into a runtime cache which can then
be used to easily lookup values from it. Currently only the values for
path or name are stored but it can be extended for any value needed.

It is expected that .gitmodules files do not change often between
commits. Thats why we lookup the .gitmodules sha1 from a commit and then
either lookup an already parsed configuration or parse and cache an
unknown one for each sha1. The cache is lazily build on demand for each
requested commit.

This cache can be used for all purposes which need knowledge about
submodule configurations. Example use cases are:

 * Recursive submodule checkout needs to lookup a submodule name from
   its path when a submodule first appears. This needs be done before
   this configuration exists in the worktree.

 * The implementation of submodule support for 'git archive' needs to
   lookup the submodule name to generate the archive when given a
   revision that is not checked out.

 * 'git fetch' when given the --recurse-submodules=on-demand option (or
   configuration) needs to lookup submodule names by path from the
   database rather than reading from the worktree. For new submodule it
   needs to lookup the name from its path to allow cloning new
   submodules into the .git folder so they can be checked out without
   any network interaction when the user does a checkout of that
   revision.

Signed-off-by: Heiko Voigt <hvoigt@hvoigt.net>
Signed-off-by: Stefan Beller <sbeller@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 443 insertions, 0 deletions

diff --git a/submodule-config.c b/submodule-config.c
new file mode 100644
index 0000000..ea82edb
--- /dev/null
+++ b/submodule-config.c
@@ -0,0 +1,443 @@
+#include "cache.h"
+#include "submodule-config.h"
+#include "submodule.h"
+#include "strbuf.h"
+
+/*
+ * submodule cache lookup structure
+ * There is one shared set of 'struct submodule' entries which can be
+ * looked up by their sha1 blob id of the .gitmodule file and either
+ * using path or name as key.
+ * for_path stores submodule entries with path as key
+ * for_name stores submodule entries with name as key
+ */
+struct submodule_cache {
+	struct hashmap for_path;
+	struct hashmap for_name;
+};
+
+/*
+ * thin wrapper struct needed to insert 'struct submodule' entries to
+ * the hashmap
+ */
+struct submodule_entry {
+	struct hashmap_entry ent;
+	struct submodule *config;
+};
+
+enum lookup_type {
+	lookup_name,
+	lookup_path
+};
+
+static struct submodule_cache cache;
+static int is_cache_init;
+
+static int config_path_cmp(const struct submodule_entry *a,
+			   const struct submodule_entry *b,
+			   const void *unused)
+{
+	return strcmp(a->config->path, b->config->path) ||
+	       hashcmp(a->config->gitmodules_sha1, b->config->gitmodules_sha1);
+}
+
+static int config_name_cmp(const struct submodule_entry *a,
+			   const struct submodule_entry *b,
+			   const void *unused)
+{
+	return strcmp(a->config->name, b->config->name) ||
+	       hashcmp(a->config->gitmodules_sha1, b->config->gitmodules_sha1);
+}
+
+static void cache_init(struct submodule_cache *cache)
+{
+	hashmap_init(&cache->for_path, (hashmap_cmp_fn) config_path_cmp, 0);
+	hashmap_init(&cache->for_name, (hashmap_cmp_fn) config_name_cmp, 0);
+}
+
+static void free_one_config(struct submodule_entry *entry)
+{
+	free((void *) entry->config->path);
+	free((void *) entry->config->name);
+	free(entry->config);
+}
+
+static void cache_free(struct submodule_cache *cache)
+{
+	struct hashmap_iter iter;
+	struct submodule_entry *entry;
+
+	/*
+	 * We iterate over the name hash here to be symmetric with the
+	 * allocation of struct submodule entries. Each is allocated by
+	 * their .gitmodule blob sha1 and submodule name.
+	 */
+	hashmap_iter_init(&cache->for_name, &iter);
+	while ((entry = hashmap_iter_next(&iter)))
+		free_one_config(entry);
+
+	hashmap_free(&cache->for_path, 1);
+	hashmap_free(&cache->for_name, 1);
+}
+
+static unsigned int hash_sha1_string(const unsigned char *sha1,
+				     const char *string)
+{
+	return memhash(sha1, 20) + strhash(string);
+}
+
+static void cache_put_path(struct submodule_cache *cache,
+			   struct submodule *submodule)
+{
+	unsigned int hash = hash_sha1_string(submodule->gitmodules_sha1,
+					     submodule->path);
+	struct submodule_entry *e = xmalloc(sizeof(*e));
+	hashmap_entry_init(e, hash);
+	e->config = submodule;
+	hashmap_put(&cache->for_path, e);
+}
+
+static void cache_remove_path(struct submodule_cache *cache,
+			      struct submodule *submodule)
+{
+	unsigned int hash = hash_sha1_string(submodule->gitmodules_sha1,
+					     submodule->path);
+	struct submodule_entry e;
+	struct submodule_entry *removed;
+	hashmap_entry_init(&e, hash);
+	e.config = submodule;
+	removed = hashmap_remove(&cache->for_path, &e, NULL);
+	free(removed);
+}
+
+static void cache_add(struct submodule_cache *cache,
+		      struct submodule *submodule)
+{
+	unsigned int hash = hash_sha1_string(submodule->gitmodules_sha1,
+					     submodule->name);
+	struct submodule_entry *e = xmalloc(sizeof(*e));
+	hashmap_entry_init(e, hash);
+	e->config = submodule;
+	hashmap_add(&cache->for_name, e);
+}
+
+static const struct submodule *cache_lookup_path(struct submodule_cache *cache,
+		const unsigned char *gitmodules_sha1, const char *path)
+{
+	struct submodule_entry *entry;
+	unsigned int hash = hash_sha1_string(gitmodules_sha1, path);
+	struct submodule_entry key;
+	struct submodule key_config;
+
+	hashcpy(key_config.gitmodules_sha1, gitmodules_sha1);
+	key_config.path = path;
+
+	hashmap_entry_init(&key, hash);
+	key.config = &key_config;
+
+	entry = hashmap_get(&cache->for_path, &key, NULL);
+	if (entry)
+		return entry->config;
+	return NULL;
+}
+
+static struct submodule *cache_lookup_name(struct submodule_cache *cache,
+		const unsigned char *gitmodules_sha1, const char *name)
+{
+	struct submodule_entry *entry;
+	unsigned int hash = hash_sha1_string(gitmodules_sha1, name);
+	struct submodule_entry key;
+	struct submodule key_config;
+
+	hashcpy(key_config.gitmodules_sha1, gitmodules_sha1);
+	key_config.name = name;
+
+	hashmap_entry_init(&key, hash);
+	key.config = &key_config;
+
+	entry = hashmap_get(&cache->for_name, &key, NULL);
+	if (entry)
+		return entry->config;
+	return NULL;
+}
+
+static int name_and_item_from_var(const char *var, struct strbuf *name,
+				  struct strbuf *item)
+{
+	const char *subsection, *key;
+	int subsection_len, parse;
+	parse = parse_config_key(var, "submodule", &subsection,
+			&subsection_len, &key);
+	if (parse < 0 || !subsection)
+		return 0;
+
+	strbuf_add(name, subsection, subsection_len);
+	strbuf_addstr(item, key);
+
+	return 1;
+}
+
+static struct submodule *lookup_or_create_by_name(struct submodule_cache *cache,
+		const unsigned char *gitmodules_sha1, const char *name)
+{
+	struct submodule *submodule;
+	struct strbuf name_buf = STRBUF_INIT;
+
+	submodule = cache_lookup_name(cache, gitmodules_sha1, name);
+	if (submodule)
+		return submodule;
+
+	submodule = xmalloc(sizeof(*submodule));
+
+	strbuf_addstr(&name_buf, name);
+	submodule->name = strbuf_detach(&name_buf, NULL);
+
+	submodule->path = NULL;
+	submodule->url = NULL;
+	submodule->fetch_recurse = RECURSE_SUBMODULES_NONE;
+	submodule->ignore = NULL;
+
+	hashcpy(submodule->gitmodules_sha1, gitmodules_sha1);
+
+	cache_add(cache, submodule);
+
+	return submodule;
+}
+
+static void warn_multiple_config(const unsigned char *commit_sha1,
+				 const char *name, const char *option)
+{
+	const char *commit_string = "WORKTREE";
+	if (commit_sha1)
+		commit_string = sha1_to_hex(commit_sha1);
+	warning("%s:.gitmodules, multiple configurations found for "
+			"'submodule.%s.%s'. Skipping second one!",
+			commit_string, name, option);
+}
+
+struct parse_config_parameter {
+	struct submodule_cache *cache;
+	const unsigned char *commit_sha1;
+	const unsigned char *gitmodules_sha1;
+	int overwrite;
+};
+
+static int parse_config(const char *var, const char *value, void *data)
+{
+	struct parse_config_parameter *me = data;
+	struct submodule *submodule;
+	struct strbuf name = STRBUF_INIT, item = STRBUF_INIT;
+	int ret = 0;
+
+	/* this also ensures that we only parse submodule entries */
+	if (!name_and_item_from_var(var, &name, &item))
+		return 0;
+
+	submodule = lookup_or_create_by_name(me->cache, me->gitmodules_sha1,
+			name.buf);
+
+	if (!strcmp(item.buf, "path")) {
+		struct strbuf path = STRBUF_INIT;
+		if (!value) {
+			ret = config_error_nonbool(var);
+			goto release_return;
+		}
+		if (!me->overwrite && submodule->path != NULL) {
+			warn_multiple_config(me->commit_sha1, submodule->name,
+					"path");
+			goto release_return;
+		}
+
+		if (submodule->path)
+			cache_remove_path(me->cache, submodule);
+		free((void *) submodule->path);
+		strbuf_addstr(&path, value);
+		submodule->path = strbuf_detach(&path, NULL);
+		cache_put_path(me->cache, submodule);
+	} else if (!strcmp(item.buf, "fetchrecursesubmodules")) {
+		if (!me->overwrite &&
+		    submodule->fetch_recurse != RECURSE_SUBMODULES_NONE) {
+			warn_multiple_config(me->commit_sha1, submodule->name,
+					"fetchrecursesubmodules");
+			goto release_return;
+		}
+
+		submodule->fetch_recurse = parse_fetch_recurse_submodules_arg(var, value);
+	} else if (!strcmp(item.buf, "ignore")) {
+		struct strbuf ignore = STRBUF_INIT;
+		if (!me->overwrite && submodule->ignore != NULL) {
+			warn_multiple_config(me->commit_sha1, submodule->name,
+					"ignore");
+			goto release_return;
+		}
+		if (!value) {
+			ret = config_error_nonbool(var);
+			goto release_return;
+		}
+		if (strcmp(value, "untracked") && strcmp(value, "dirty") &&
+		    strcmp(value, "all") && strcmp(value, "none")) {
+			warning("Invalid parameter '%s' for config option "
+					"'submodule.%s.ignore'", value, var);
+			goto release_return;
+		}
+
+		free((void *) submodule->ignore);
+		strbuf_addstr(&ignore, value);
+		submodule->ignore = strbuf_detach(&ignore, NULL);
+	} else if (!strcmp(item.buf, "url")) {
+		struct strbuf url = STRBUF_INIT;
+		if (!value) {
+			ret = config_error_nonbool(var);
+			goto release_return;
+		}
+		if (!me->overwrite && submodule->url != NULL) {
+			warn_multiple_config(me->commit_sha1, submodule->name,
+					"url");
+			goto release_return;
+		}
+
+		free((void *) submodule->url);
+		strbuf_addstr(&url, value);
+		submodule->url = strbuf_detach(&url, NULL);
+	}
+
+release_return:
+	strbuf_release(&name);
+	strbuf_release(&item);
+
+	return ret;
+}
+
+static int gitmodule_sha1_from_commit(const unsigned char *commit_sha1,
+				      unsigned char *gitmodules_sha1)
+{
+	struct strbuf rev = STRBUF_INIT;
+	int ret = 0;
+
+	if (is_null_sha1(commit_sha1)) {
+		hashcpy(gitmodules_sha1, null_sha1);
+		return 1;
+	}
+
+	strbuf_addf(&rev, "%s:.gitmodules", sha1_to_hex(commit_sha1));
+	if (get_sha1(rev.buf, gitmodules_sha1) >= 0)
+		ret = 1;
+
+	strbuf_release(&rev);
+	return ret;
+}
+
+/* This does a lookup of a submodule configuration by name or by path
+ * (key) with on-demand reading of the appropriate .gitmodules from
+ * revisions.
+ */
+static const struct submodule *config_from(struct submodule_cache *cache,
+		const unsigned char *commit_sha1, const char *key,
+		enum lookup_type lookup_type)
+{
+	struct strbuf rev = STRBUF_INIT;
+	unsigned long config_size;
+	char *config;
+	unsigned char sha1[20];
+	enum object_type type;
+	const struct submodule *submodule = NULL;
+	struct parse_config_parameter parameter;
+
+	/*
+	 * If any parameter except the cache is a NULL pointer just
+	 * return the first submodule. Can be used to check whether
+	 * there are any submodules parsed.
+	 */
+	if (!commit_sha1 || !key) {
+		struct hashmap_iter iter;
+		struct submodule_entry *entry;
+
+		hashmap_iter_init(&cache->for_name, &iter);
+		entry = hashmap_iter_next(&iter);
+		if (!entry)
+			return NULL;
+		return entry->config;
+	}
+
+	if (!gitmodule_sha1_from_commit(commit_sha1, sha1))
+		return NULL;
+
+	switch (lookup_type) {
+	case lookup_name:
+		submodule = cache_lookup_name(cache, sha1, key);
+		break;
+	case lookup_path:
+		submodule = cache_lookup_path(cache, sha1, key);
+		break;
+	}
+	if (submodule)
+		return submodule;
+
+	config = read_sha1_file(sha1, &type, &config_size);
+	if (!config)
+		return NULL;
+
+	if (type != OBJ_BLOB) {
+		free(config);
+		return NULL;
+	}
+
+	/* fill the submodule config into the cache */
+	parameter.cache = cache;
+	parameter.commit_sha1 = commit_sha1;
+	parameter.gitmodules_sha1 = sha1;
+	parameter.overwrite = 0;
+	git_config_from_buf(parse_config, rev.buf, config, config_size,
+			&parameter);
+	free(config);
+
+	switch (lookup_type) {
+	case lookup_name:
+		return cache_lookup_name(cache, sha1, key);
+	case lookup_path:
+		return cache_lookup_path(cache, sha1, key);
+	default:
+		return NULL;
+	}
+}
+
+static const struct submodule *config_from_path(struct submodule_cache *cache,
+		const unsigned char *commit_sha1, const char *path)
+{
+	return config_from(cache, commit_sha1, path, lookup_path);
+}
+
+static const struct submodule *config_from_name(struct submodule_cache *cache,
+		const unsigned char *commit_sha1, const char *name)
+{
+	return config_from(cache, commit_sha1, name, lookup_name);
+}
+
+static void ensure_cache_init(void)
+{
+	if (is_cache_init)
+		return;
+
+	cache_init(&cache);
+	is_cache_init = 1;
+}
+
+const struct submodule *submodule_from_name(const unsigned char *commit_sha1,
+		const char *name)
+{
+	ensure_cache_init();
+	return config_from_name(&cache, commit_sha1, name);
+}
+
+const struct submodule *submodule_from_path(const unsigned char *commit_sha1,
+		const char *path)
+{
+	ensure_cache_init();
+	return config_from_path(&cache, commit_sha1, path);
+}
+
+void submodule_free(void)
+{
+	cache_free(&cache);
+	is_cache_init = 0;
+}