[PATCH] c++: Fix pasto in structured binding diagnostics [PR94571]

[Jakub Jelinek via Gcc-patches]

Hi!

This snippet has been copied from the non-structured binding declaration
parsing later in the function, and while for non-structured bindings
it can be followed by comma or semicolon, structured bindings may be
only followed by semicolon.

Fixed thusly, bootstrapped/regtested on x86_64-linux and i686-linux,
ok for trunk?

Or, do we want to have a different message for the case when there is
a comma (and keep this corrected one only if there is something else)
that would explain better what is the bug (or add a fix-it hint)?
Marek said in the PR that clang++ reports
error: decomposition declaration must be the only declaration in its group

There is another thing Marek noted (though, something for different spot),
that diagnostic for auto x(1), [e,f] = test2; could also use a clearer
wording like the above (or a fix-it hint), but the question is if we should
assume [ after , as a structured binding or if we should do some tentative
parsing first to figure out if it looks like a structured binding.

2020-04-15  Jakub Jelinek  <ja...@redhat.com>

        PR c++/94571
        * parser.c (cp_parser_simple_declaration): Fix up a pasto in
        diagnostics.

        * g++.dg/cpp1z/decomp51.C: New test.

--- gcc/cp/parser.c.jj  2020-04-08 11:59:23.772460767 +0200
+++ gcc/cp/parser.c     2020-04-14 10:15:54.824034781 +0200
@@ -13675,7 +13675,7 @@ cp_parser_simple_declaration (cp_parser*
            if ((decl != error_mark_node
                 && DECL_INITIAL (decl) != error_mark_node)
                || cp_parser_uncommitted_to_tentative_parse_p (parser))
-             cp_parser_error (parser, "expected %<,%> or %<;%>");
+             cp_parser_error (parser, "expected %<;%>");
            /* Skip tokens until we reach the end of the statement.  */
            cp_parser_skip_to_end_of_statement (parser);
            /* If the next token is now a `;', consume it.  */
--- gcc/testsuite/g++.dg/cpp1z/decomp51.C.jj    2020-04-14 10:18:58.318313777 
+0200
+++ gcc/testsuite/g++.dg/cpp1z/decomp51.C       2020-04-14 10:19:31.347823985 
+0200
@@ -0,0 +1,16 @@
+// PR c++/94571
+// { dg-do compile { target c++17 } }
+
+void
+foo ()
+{
+  int e[2], f[2];
+  auto [a,b] = e, [c,d] = f;   // { dg-error "expected ';' before ',' token" }
+}
+
+void
+bar ()
+{
+  int e[2];
+  auto [a, b] = e );           // { dg-error "expected ';' before '\\\)' 
token" }
+}

        Jakub