code: be robust to reference with invalid tags

Because we want to support $<a->b>$, we must accept -> in type tags,
and reject $<->$, as it is unfinished.
Reported by Ahcheong Lee.

* src/scan-code.l (yylex): Make sure "tag" does not end with -, since
-> does not close the tag.
* tests/input.at (Stray $ or @): Check this.

THANKS

@@ -4,8 +4,9 @@ it is today without the invaluable help of these people:
 Aaro Koskinen             [email protected]
 Аскар Сафин               [email protected]
 Adam Sampson              [email protected]
+Ahcheong Lee              [email protected]
 Airy Andre                [email protected]
-Akim Demaille             akim@lrde.epita.fr
+Akim Demaille             akim@gnu.org
 Albert Chin-A-Young       [email protected]
 Alexander Belopolsky      [email protected]
 Alexandre Duret-Lutz      [email protected]

src/scan-code.l

@@ -81,7 +81,7 @@ static bool untyped_var_seen;
    historically almost any character is allowed in a tag.  We disallow
    NUL and newline, as this simplifies our implementation.  We allow
    "->" as a means to dereference a pointer.  */
-tag      ([^\0\n>]|->)+
+tag      ([^\0\n>]|->)*[^-]
 
 /* Zero or more instances of backslash-newline.  Following GCC, allow
    white space between the backslash and the newline.  */

tests/input.at

@@ -2548,7 +2548,9 @@ AT_DATA_GRAMMAR([[input.y]],
 %printer        { $%; @%; } <*> exp TOK;
 %{ $ @ %} // Should not warn.
 %%
-exp: TOK        { $%; @%; $$ = $1; };
+exp: TOK        { $%; @%; $$ = $1; }
+   | 'a'        { $<->1; $$ = 1; }
+   | 'b'        { $<foo->bar>$; }
 %%
 $ @ // Should not warn.
 ]])
@@ -2562,6 +2564,7 @@ input.y:13.19: warning: stray '$' [-Wother]
 input.y:13.23: warning: stray '@' [-Wother]
 input.y:16.19: warning: stray '$' [-Wother]
 input.y:16.23: warning: stray '@' [-Wother]
+input.y:17.19: warning: stray '$' [-Wother]
 ]])
 
 AT_BISON_OPTION_POPDEFS