Hi,
I'm having a look at this very old parsing issue. We reject things like:
struct S { void operator () (); };
void foo ()
{
( S()() );
}
because the parenthesized S()() triggers an hard error from groktypename
as called at the end of cp_parser_type_id (called by
cp_parser_cast_expression), about a function returning a function. Of
course we have to parse it as an unary-expression.
I scratched my head for a while, but then I noticed that in
cp_parser_cast_expression, a bit later the cp_parser_type_id call at
issue, we are *already* using a cp_parser_tokens_start_cast_expression
which helps use figuring out whether the tokens following the outer ')'
make sense as a cast-expression. Using it a bit earlier to completely
avoid calling cp_parser_type_id in the cases at issue, appears to work
well, for a - negligeable in my opinion - additional computational cost.
Then, cp_parser_unary_expression is actually used. As part of that,
cp_parser_postfix_expression looks for a compound-literal, but not in
the robust way we are using elsewhere involving a
cp_parser_skip_to_closing_parenthesis, but just using tentative parsing
with cp_parser_type_id. Thus we are incurring again in the same issue.
Parsing the compound-literal in the same way used elesewhere - thus
looking for the '{' after the ')', solves the problem. In my personal
opinion, again, the computational cost shouldn't be too high, because if
we don't find '{' we completely avoid cp_parser_type_id.
Is this the kind of approach we want to pursue for this issue?
Tested x86_64-linux.
Thanks!
Paolo.
/////////////////////////////
Index: cp/parser.c
===================================================================
--- cp/parser.c (revision 204202)
+++ cp/parser.c (working copy)
@@ -5800,31 +5800,45 @@ cp_parser_postfix_expression (cp_parser *parser, b
&& cp_lexer_next_token_is (parser->lexer, CPP_OPEN_PAREN))
{
tree initializer = NULL_TREE;
- bool saved_in_type_id_in_expr_p;
+ bool compound_literal_p;
cp_parser_parse_tentatively (parser);
/* Consume the `('. */
cp_lexer_consume_token (parser->lexer);
- /* Parse the type. */
- saved_in_type_id_in_expr_p = parser->in_type_id_in_expr_p;
- parser->in_type_id_in_expr_p = true;
- type = cp_parser_type_id (parser);
- parser->in_type_id_in_expr_p = saved_in_type_id_in_expr_p;
- /* Look for the `)'. */
- cp_parser_require (parser, CPP_CLOSE_PAREN, RT_CLOSE_PAREN);
+
+ /* Avoid calling cp_parser_type_id pointlessly, see comment
+ in cp_parser_cast_expression about c++/29234. */
+ cp_lexer_save_tokens (parser->lexer);
+
+ compound_literal_p
+ = (cp_parser_skip_to_closing_parenthesis (parser, false, false,
+ /*consume_paren=*/true)
+ && cp_lexer_next_token_is (parser->lexer, CPP_OPEN_BRACE));
+
+ /* Roll back the tokens we skipped. */
+ cp_lexer_rollback_tokens (parser->lexer);
+
+ if (!compound_literal_p)
+ cp_parser_simulate_error (parser);
+ else
+ {
+ /* Parse the type. */
+ bool saved_in_type_id_in_expr_p = parser->in_type_id_in_expr_p;
+ parser->in_type_id_in_expr_p = true;
+ type = cp_parser_type_id (parser);
+ parser->in_type_id_in_expr_p = saved_in_type_id_in_expr_p;
+ /* Look for the `)'. */
+ cp_parser_require (parser, CPP_CLOSE_PAREN, RT_CLOSE_PAREN);
+ }
+
/* If things aren't going well, there's no need to
keep going. */
if (!cp_parser_error_occurred (parser))
{
- if (cp_lexer_next_token_is (parser->lexer, CPP_OPEN_BRACE))
- {
- bool non_constant_p;
- /* Parse the brace-enclosed initializer list. */
- initializer = cp_parser_braced_list (parser,
- &non_constant_p);
- }
- else
- cp_parser_simulate_error (parser);
+ bool non_constant_p;
+ /* Parse the brace-enclosed initializer list. */
+ initializer = cp_parser_braced_list (parser,
+ &non_constant_p);
}
/* If that worked, we're definitely looking at a
compound-literal expression. */
@@ -7559,7 +7573,9 @@ cp_parser_cast_expression (cp_parser *parser, bool
{
tree type = NULL_TREE;
tree expr = NULL_TREE;
+ bool skip_to_closing_ok_p;
bool compound_literal_p;
+ bool cast_expression_p;
const char *saved_message;
/* There's no way to know yet whether or not this is a cast.
@@ -7587,21 +7603,44 @@ cp_parser_cast_expression (cp_parser *parser, bool
if the token after the `)' is a `{'. If so, we are not
looking at a cast-expression.
+ Another tricky case is the following (c++/29234):
+
+ struct S { void operator () (); };
+
+ void foo ()
+ {
+ ( S()() );
+ }
+
+ where the parenthesized S()(), as a type-id would be parsed as a
+ function returning a function. Thus see if the tokens after the
+ outer `)' are starting a cast-expression.
+
Save tokens so that we can put them back. */
cp_lexer_save_tokens (parser->lexer);
- /* Skip tokens until the next token is a closing parenthesis.
- If we find the closing `)', and the next token is a `{', then
+
+ /* Skip tokens until the next token is a closing parenthesis. */
+ skip_to_closing_ok_p
+ = cp_parser_skip_to_closing_parenthesis (parser, false, false,
+ /*consume_paren=*/true);
+
+ /* If we find the closing `)', and the next token is a `{', then
we are looking at a compound-literal. */
compound_literal_p
- = (cp_parser_skip_to_closing_parenthesis (parser, false, false,
- /*consume_paren=*/true)
+ = (skip_to_closing_ok_p
&& cp_lexer_next_token_is (parser->lexer, CPP_OPEN_BRACE));
+
+ /* Alternately, we may be looking at a cast-expression. */
+ cast_expression_p
+ = (skip_to_closing_ok_p
+ && cp_parser_tokens_start_cast_expression (parser));
+
/* Roll back the tokens we skipped. */
cp_lexer_rollback_tokens (parser->lexer);
- /* If we were looking at a compound-literal, simulate an error
- so that the call to cp_parser_parse_definitely below will
- fail. */
- if (compound_literal_p)
+ /* If we were looking at a compound-literal or we can't possibly
+ be looking at a cast-expression, simulate an error so that the
+ call to cp_parser_parse_definitely below will fail. */
+ if (compound_literal_p || !cast_expression_p)
cp_parser_simulate_error (parser);
else
{
@@ -7620,8 +7659,7 @@ cp_parser_cast_expression (cp_parser *parser, bool
/* At this point this can only be either a cast or a
parenthesized ctor such as `(T ())' that looks like a cast to
function returning T. */
- if (!cp_parser_error_occurred (parser)
- && cp_parser_tokens_start_cast_expression (parser))
+ if (!cp_parser_error_occurred (parser))
{
cp_parser_parse_definitely (parser);
expr = cp_parser_cast_expression (parser,
Index: testsuite/g++.dg/parse/pr29234.C
===================================================================
--- testsuite/g++.dg/parse/pr29234.C (revision 0)
+++ testsuite/g++.dg/parse/pr29234.C (working copy)
@@ -0,0 +1,16 @@
+// PR c++/29234
+
+struct S { void operator()(); };
+
+void foo ()
+{
+ ( S()() );
+}
+
+struct C { void operator[](C); };
+
+void bar ()
+{
+ C x;
+ ( C()[x] );
+}
