Add builtin -q

Used to query for a builtin's existence, like `type -q` and `functions
-q` can be used to query for a things and a functions existence respectively.

doc_src/builtin.txt

@@ -2,7 +2,8 @@
 
 \subsection builtin-synopsis Synopsis
 \fish{synopsis}
-builtin BUILTINNAME [OPTIONS...]
+builtin [OPTIONS...] BUILTINNAME
+builtin --query BUILTINNAMES...
 \endfish
 
 \subsection builtin-description Description
@@ -12,6 +13,7 @@ builtin BUILTINNAME [OPTIONS...]
 The following parameters are available:
 
 - `-n` or `--names` List the names of all defined builtins
+- `-q` or `--query` tests if any of the specified builtins exists.
 
 
 \subsection builtin-example Example

src/builtin_builtin.cpp

@@ -17,10 +17,13 @@
 struct builtin_cmd_opts_t {
     bool print_help = false;
     bool list_names = false;
+    bool query = false;
 };
-static const wchar_t *const short_options = L":hn";
+static const wchar_t *const short_options = L":hnq";
 static const struct woption long_options[] = {
-    {L"help", no_argument, NULL, 'h'}, {L"names", no_argument, NULL, 'n'}, {NULL, 0, NULL, 0}};
+    {L"help", no_argument, NULL, 'h'}, {L"names", no_argument, NULL, 'n'},
+    {L"query", no_argument, NULL, 'q'},
+    {NULL, 0, NULL, 0}};
 
 static int parse_cmd_opts(builtin_cmd_opts_t &opts, int *optind, int argc, wchar_t **argv,
                           parser_t &parser, io_streams_t &streams) {
@@ -37,6 +40,10 @@ static int parse_cmd_opts(builtin_cmd_opts_t &opts, int *optind, int argc, wchar
                 opts.list_names = true;
                 break;
             }
+            case 'q': {
+                opts.query = true;
+                break;
+            }
             case ':': {
                 builtin_missing_argument(parser, streams, cmd, argv[w.woptind - 1]);
                 return STATUS_INVALID_ARGS;
@@ -73,6 +80,24 @@ int builtin_builtin(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
         return STATUS_CMD_OK;
     }
 
+    if (opts.query && opts.list_names) {
+        streams.err.append_format(BUILTIN_ERR_COMBO2, cmd,
+                                  _(L"--query and --names are mutually exclusive"));
+        return STATUS_INVALID_ARGS;
+    }
+
+    if (opts.query) {
+        wcstring_list_t names = builtin_get_names();
+        retval = STATUS_CMD_ERROR;
+        for (int i = optind; i < argc; i++) {
+            if (contains(names, argv[i])) {
+                retval = STATUS_CMD_OK;
+                break;
+            }
+        }
+        return retval;
+    }
+
     if (opts.list_names) {
         wcstring_list_t names = builtin_get_names();
         std::sort(names.begin(), names.end());

tests/test_builtinbuiltin.err

@@ -0,0 +1,2 @@
+builtin: Invalid combination of options,
+--query and --names are mutually exclusive

tests/test_builtinbuiltin.in

@@ -0,0 +1,7 @@
+# Tests for the "builtin" builtin/keyword.
+builtin -q string; and echo String exists
+builtin -q; and echo None exists
+builtin -q string echo banana; and echo Some of these exist
+builtin -nq string
+echo $status
+exit 0

tests/test_builtinbuiltin.out

@@ -0,0 +1,3 @@
+String exists
+Some of these exist
+2