This patch adds support for search-terms to 'notmuch search-tags'. If
no search-term is provided then the command returns a list of all tags
from the database.

If the user provides one or more search-terms as arguments then the
command collects tags from matching messages only.

This could be used by functions in the Emacs mode to further limit the
list of tags offered for completion. For example, functions that remove
tags from message(s) could offer only tags present in the message(s).

Signed-off-by: Jan Janak <jan@ryngle.com>
---
 notmuch-search-tags.c |   55 ++++++++++++++++++++++++++++++++++++------------
 notmuch.c             |   13 +++++++----
 2 files changed, 49 insertions(+), 19 deletions(-)

diff --git a/notmuch-search-tags.c b/notmuch-search-tags.c
index 1201165..7a1305e 100644
--- a/notmuch-search-tags.c
+++ b/notmuch-search-tags.c
@@ -21,34 +21,31 @@
 
 #include "notmuch-client.h"
 
-static int
-list_all_tags (notmuch_database_t* db)
+static void
+print_tags (notmuch_tags_t *tags)
 {
-    notmuch_tags_t* tags;
-    const char* t;
+    const char *t;
 
-    if ((tags = notmuch_database_get_all_tags (db)) == NULL) {
-	fprintf (stderr, "Error while obtaining tags from the database.\n");
-	return 1;
-    }
-
-    while((t = notmuch_tags_get (tags))) {
+    while ((t = notmuch_tags_get (tags))) {
 	printf ("%s\n", t);
 	notmuch_tags_advance (tags);
     }
-
-    notmuch_tags_destroy (tags);
-    return 0;
 }
 
 int
 notmuch_search_tags_command (void *ctx, int argc, char *argv[])
 {
+    notmuch_messages_t *msgs;
+    notmuch_tags_t *tags;
     notmuch_config_t *config;
     notmuch_database_t *db;
+    notmuch_query_t *query;
+    char *query_str;
 
+    tags = NULL;
     config = NULL;
     db = NULL;
+    query = NULL;
 
     if ((config = notmuch_config_open (ctx, NULL, NULL)) == NULL) {
 	goto error;
@@ -60,12 +57,42 @@ notmuch_search_tags_command (void *ctx, int argc, char *argv[])
 	goto error;
     }
 
-    if (list_all_tags (db) != 0) goto error;
+    if (argc > 0) {
+	if ((query_str = query_string_from_args (ctx, argc, argv)) == NULL) {
+	    fprintf (stderr, "Out of memory.\n");
+	    goto error;
+	}
+
+	if (*query_str == '\0') {
+	    fprintf (stderr, "Error: Invalid search string.\n");
+	    goto error;
+	}
+
+	if ((query = notmuch_query_create (db, query_str)) == NULL) {
+	    fprintf (stderr, "Out of memory\n");
+	    goto error;
+	}
+
+
+	msgs = notmuch_query_search_messages (query);
+	if ((tags = notmuch_messages_collect_tags (msgs)) == NULL) goto error;
+    } else {
+	if ((tags = notmuch_database_get_all_tags (db)) == NULL) {
+	    fprintf (stderr, "Error while getting tags from the database.\n");
+	    goto error;
+	}
+    }
+
+    print_tags (tags);
 
+    notmuch_tags_destroy (tags);
+    if (query) notmuch_query_destroy (query);
     notmuch_database_close (db);
     return 0;
 
 error:
+    if (tags) notmuch_tags_destroy (tags);
+    if (query) notmuch_query_destroy (query);
     if (db) notmuch_database_close (db);
     return 1;
 }
diff --git a/notmuch.c b/notmuch.c
index c57bb5c..5b0284c 100644
--- a/notmuch.c
+++ b/notmuch.c
@@ -255,11 +255,14 @@ command_t commands[] = {
       "\t\t\"notmuch restore\" command provides you a way to import\n"
       "\t\tall of your tags (or labels as sup calls them)." },
     { "search-tags", notmuch_search_tags_command,
-      NULL,
-      "List all tags found in the database.",
-      "\t\tThis command returns an alphabetically sorted list of all tags\n"
-      "\t\tthat are present in the database. In other words, the resulting\n"
-      "\t\tlist is a collection of all tags from all messages." },
+      "[<search-terms> [...] ]",
+      "\t\tList all tags found in the database or matching messages.",
+      "\t\tRun this command without any search-term(s) to obtain a list\n"
+      "\t\tof all tags found in the database. If you provide one or more\n"
+      "\t\tsearch-terms as argument(s) then the resulting list will\n"
+      "\t\tcontain tags only from messages that match the search-term(s).\n"
+      "\n"
+      "\t\tIn both cases the list will be alphabetically sorted." },
     { "help", notmuch_help_command,
       "[<command>]",
       "\t\tThis message, or more detailed help for the named command.",
-- 
1.6.3.3