Add /clear autocompletion and improve help

Regards https://github.com/profanity-im/profanity/issues/855

https://github.com/profanity-im/profanity/pull/874 brought us the
`/clear` command. The author of that patch couldn't follow up with the
review boothj5 did.

So the autocompletion and updated help was missing.
This commit adds it.

src/command/cmd_ac.c

@@ -106,6 +106,7 @@ static char* _tray_autocomplete(ProfWin *window, const char *const input, gboole
 static char* _presence_autocomplete(ProfWin *window, const char *const input, gboolean previous);
 static char* _rooms_autocomplete(ProfWin *window, const char *const input, gboolean previous);
 static char* _statusbar_autocomplete(ProfWin *window, const char *const input, gboolean previous);
+static char* _clear_autocomplete(ProfWin *window, const char *const input, gboolean previous);
 
 static char* _script_autocomplete_func(const char *const prefix, gboolean previous);
 
@@ -217,6 +218,7 @@ static Autocomplete statusbar_self_ac;
 static Autocomplete statusbar_chat_ac;
 static Autocomplete statusbar_room_ac;
 static Autocomplete statusbar_show_ac;
+static Autocomplete clear_ac;
 
 void
 cmd_ac_init(void)
@@ -807,6 +809,9 @@ cmd_ac_init(void)
     autocomplete_add(blocked_ac, "add");
     autocomplete_add(blocked_ac, "remove");
 
+    clear_ac = autocomplete_new();
+    autocomplete_add(clear_ac, "persist_history");
+
     tray_ac = autocomplete_new();
     autocomplete_add(tray_ac, "on");
     autocomplete_add(tray_ac, "off");
@@ -1151,6 +1156,7 @@ cmd_ac_reset(ProfWin *window)
     autocomplete_reset(statusbar_chat_ac);
     autocomplete_reset(statusbar_room_ac);
     autocomplete_reset(statusbar_show_ac);
+    autocomplete_reset(clear_ac);
 
     autocomplete_reset(script_ac);
     if (script_show_ac) {
@@ -1288,6 +1294,7 @@ cmd_ac_uninit(void)
     autocomplete_free(statusbar_chat_ac);
     autocomplete_free(statusbar_room_ac);
     autocomplete_free(statusbar_show_ac);
+    autocomplete_free(clear_ac);
 }
 
 static void
@@ -1540,6 +1547,7 @@ _cmd_ac_complete_params(ProfWin *window, const char *const input, gboolean previ
     g_hash_table_insert(ac_funcs, "/presence",      _presence_autocomplete);
     g_hash_table_insert(ac_funcs, "/rooms",         _rooms_autocomplete);
     g_hash_table_insert(ac_funcs, "/statusbar",     _statusbar_autocomplete);
+    g_hash_table_insert(ac_funcs, "/clear",         _clear_autocomplete);
 
     int len = strlen(input);
     char parsed[len+1];
@@ -3415,3 +3423,21 @@ _statusbar_autocomplete(ProfWin *window, const char *const input, gboolean previ
 
     return NULL;
 }
+
+static char*
+_clear_autocomplete(ProfWin *window, const char *const input, gboolean previous)
+{
+    char *result = NULL;
+
+    result = autocomplete_param_with_ac(input, "/clear", clear_ac, TRUE, previous);
+    if (result) {
+        return result;
+    }
+
+    result = autocomplete_param_with_func(input, "/clear persist_history", prefs_autocomplete_boolean_choice, previous);
+    if (result) {
+        return result;
+    }
+
+    return NULL;
+}

src/command/cmd_defs.c

@@ -1107,17 +1107,23 @@ static struct cmd_t command_defs[] =
     },
 
     { "/clear",
-        parse_args, 0, 0, NULL,
+        parse_args, 0, 2, NULL,
         CMD_NOSUBFUNCS
         CMD_MAINFUNC(cmd_clear)
         CMD_TAGS(
             CMD_TAG_UI)
         CMD_SYN(
-            "/clear")
+            "/clear",
+            "/clear persist_history <on|off>")
         CMD_DESC(
-            "Clear the current window.")
-        CMD_NOARGS
-        CMD_NOEXAMPLES
+            "Clear the current window. "
+            "If you set persist_history you can still access the history by pressing PAGE UP.")
+        CMD_ARGS(
+            { "persist_history on|off", "Whether or not to clear the screen persistently"})
+        CMD_EXAMPLES(
+            "/clear",
+            "/clear persist_history",
+            "/clear persist_history on")
     },
 
     { "/quit",

src/command/cmd_funcs.c

@@ -5047,7 +5047,29 @@ cmd_tiny(ProfWin *window, const char *const command, gchar **args)
 gboolean
 cmd_clear(ProfWin *window, const char *const command, gchar **args)
 {
-    win_clear(window);
+    if (args[0] == NULL) {
+        win_clear(window);
+        return TRUE;
+    } else {
+        if ((g_strcmp0(args[0], "persist_history") == 0) ) {
+
+            if (args[1] != NULL) {
+                if ((g_strcmp0(args[1], "on") == 0) || (g_strcmp0(args[1], "off") == 0)) {
+                    _cmd_set_boolean_preference(args[1], command, "Persistant history", PREF_CLEAR_PERSIST_HISTORY);
+                    return TRUE;
+                }
+            } else {
+                if (prefs_get_boolean(PREF_CLEAR_PERSIST_HISTORY)) {
+                    win_println(window, THEME_DEFAULT, '!', "  Persistantly clear screen  : ON");
+                } else {
+                    win_println(window, THEME_DEFAULT, '!', "  Persistantly clear screen  : OFF");
+                }
+                return TRUE;
+            }
+        }
+    }
+    cons_bad_cmd_usage(command);
+
     return TRUE;
 }