docs: list reserved keywords

doc_src/cmds/function.rst

@@ -68,6 +68,8 @@ By using one of the event handler switches, a function can be made to run automa
 
 - ``fish_cancel``, which is emitted when a commandline is cleared (used for terminal-shell integration).
 
+Functions may not be named the same as a reserved keyword. These are elements of fish syntax or builtin commands which are essential for the operations of the shell. Current reserved words are ``[``, ``_``, ``and``, ``argparse``, ``begin``, ``break``, ``builtin``, ``case``, ``command``, ``continue``, ``else``, ``end``, ``eval``, ``exec``, ``for``, ``function``, ``if``, ``not``, ``or``, ``read``, ``return``, ``set``, ``status``, ``string``, ``switch``, ``test``, ``time``, and ``while``.
+
 Example
 -------
 

src/parser_keywords.cpp

@@ -22,6 +22,7 @@ static const wcstring subcommand_keywords[]{L"command", L"builtin", L"while", L"
 static const string_set_t block_keywords = {L"for",      L"while",  L"if",
                                             L"function", L"switch", L"begin"};
 
+// Don't forget to add any new reserved keywords to the documentation
 static const wcstring reserved_keywords[] = {
     L"end",    L"case", L"else",   L"return", L"continue", L"break", L"argparse", L"read",
     L"string", L"set",  L"status", L"test",   L"[",        L"_",     L"eval"};