On Thu, Nov 09, 2023 at 07:07:03PM -0500, Jason Merrill wrote: > On 11/9/23 14:58, Marek Polacek wrote: > > Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk? > > > > -- >8 -- > > Here we are wrongly parsing > > > > int y(auto(42)); > > > > which uses the C++23 cast-to-prvalue feature, and initializes y to 42. > > However, we were treating the auto as an implicit template parameter. > > > > Fixing the auto{42} case is easy, but when auto is followed by a (, > > I found the fix to be much more involved. For instance, we cannot > > use cp_parser_expression, because that can give hard errors. It's > > also necessary to disambiguate 'auto(i)' as 'auto i', not a cast. > > auto(), auto(int), auto(f)(int), auto(*), auto(i[]), auto(...), etc. > > are all function declarations. We have to look at more than one > > token to decide. > > Yeah, this is a most vexing parse problem. The code is synthesizing > template parameters before we've resolved whether the auto is a > decl-specifier or not. > > > In this fix, I'm (ab)using cp_parser_declarator, with member_p=false > > so that it doesn't commit. But it handles even more complicated > > cases as > > > > int fn (auto (*const **&f)(int) -> char); > > But it doesn't seem to handle the extremely vexing > > struct A { > A(int,int); > }; > > int main() > { > int a; > A b(auto(a), 42); > }
Argh. This test should indeed be accepted and is currently rejected, but it's a different problem: 'b' is at block scope and you can't have a template there. But when I put it into a namespace scope, it shows that my patch doesn't work correctly. I've added auto-fncast14.C for the latter and opened c++/112482 for the block-scope problem. > I think we need to stop synthesizing immediately when we see RID_AUTO, and > instead go back after we successfully parse a declaration and synthesize for > any autos we saw along the way. :/ That seems very complicated :(. I had a different idea though; how about the following patch? The idea is that if we see that parsing the parameter-declaration-list didn't work, we undo what synthesize_ did, and let cp_parser_initializer parse "(auto(42))", which should succeed. I checked that after cp_finish_decl y is initialized to 42. Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk? -- >8 -- Here we are wrongly parsing int y(auto(42)); which uses the C++23 cast-to-prvalue feature, and initializes y to 42. However, we were treating the auto as an implicit template parameter. Fixing the auto{42} case is easy, but when auto is followed by a (, I found the fix to be much more involved. For instance, we cannot use cp_parser_expression, because that can give hard errors. It's also necessary to disambiguate 'auto(i)' as 'auto i', not a cast. auto(), auto(int), auto(f)(int), auto(*), auto(i[]), auto(...), etc. are all function declarations. This patch rectifies that by undoing the implicit function template modification. In the test above, we should notice that the parameter list is ill-formed, and since we've synthesized an implicit template parameter, we undo it by calling abort_fully_implicit_template. Then, we'll parse the "(auto(42))" as an initializer. PR c++/112410 gcc/cp/ChangeLog: * parser.cc (cp_parser_simple_type_specifier): Disambiguate between a variable and function declaration with auto. (cp_parser_parameter_declaration_clause): Maybe call abort_fully_implicit_template if it turned out the parameter list was ill-formed. gcc/testsuite/ChangeLog: * g++.dg/cpp23/auto-fncast13.C: New test. * g++.dg/cpp23/auto-fncast14.C: New test. --- gcc/cp/parser.cc | 27 +++++++++- gcc/testsuite/g++.dg/cpp23/auto-fncast13.C | 61 ++++++++++++++++++++++ gcc/testsuite/g++.dg/cpp23/auto-fncast14.C | 9 ++++ 3 files changed, 96 insertions(+), 1 deletion(-) create mode 100644 gcc/testsuite/g++.dg/cpp23/auto-fncast13.C create mode 100644 gcc/testsuite/g++.dg/cpp23/auto-fncast14.C diff --git a/gcc/cp/parser.cc b/gcc/cp/parser.cc index 5116bcb78f6..947351b09b8 100644 --- a/gcc/cp/parser.cc +++ b/gcc/cp/parser.cc @@ -19991,6 +19991,8 @@ cp_parser_simple_type_specifier (cp_parser* parser, /* The 'auto' might be the placeholder return type for a function decl with trailing return type. */ bool have_trailing_return_fn_decl = false; + /* Or it might be auto(x) or auto {x}. */ + bool decay_copy = false; cp_parser_parse_tentatively (parser); cp_lexer_consume_token (parser->lexer); @@ -20008,6 +20010,11 @@ cp_parser_simple_type_specifier (cp_parser* parser, /*consume_paren*/true); continue; } + else if (cp_lexer_next_token_is (parser->lexer, CPP_OPEN_BRACE)) + { + decay_copy = true; + break; + } if (cp_lexer_next_token_is (parser->lexer, CPP_DEREF)) { @@ -20019,6 +20026,11 @@ cp_parser_simple_type_specifier (cp_parser* parser, } cp_parser_abort_tentative_parse (parser); + if (decay_copy) + { + type = error_mark_node; + break; + } if (have_trailing_return_fn_decl) { type = make_auto (); @@ -24973,7 +24985,20 @@ cp_parser_parameter_declaration_clause (cp_parser* parser, parameter-declaration-list, then the entire parameter-declaration-clause is erroneous. */ if (parameters == error_mark_node) - return NULL_TREE; + { + /* For code like + int x(auto(42)); + A a(auto(i), 42); + we have synthesized an implicit template parameter and marked + what we thought was a function as an implicit function template. + But now, having seen the whole parameter list, we know it's not + a function declaration, so undo that. */ + if (parser->fully_implicit_function_template_p + /* Don't do this for the inner (). */ + && parser->default_arg_ok_p) + abort_fully_implicit_template (parser); + return NULL_TREE; + } /* Peek at the next token. */ token = cp_lexer_peek_token (parser->lexer); diff --git a/gcc/testsuite/g++.dg/cpp23/auto-fncast13.C b/gcc/testsuite/g++.dg/cpp23/auto-fncast13.C new file mode 100644 index 00000000000..1bceffb70cf --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp23/auto-fncast13.C @@ -0,0 +1,61 @@ +// PR c++/112410 +// { dg-do compile { target c++23 } } + +int f1 (auto(int) -> char); +int f2 (auto x); +int f3 (auto); +int f4 (auto(i)); + +int v1 (auto(42)); +int v2 (auto{42}); +int e1 (auto{i}); // { dg-error "not declared" } +int i; +int v3 (auto{i}); +int v4 (auto(i + 1)); +int v5 (auto(+i)); +int v6 (auto(i = 4)); + +int f5 (auto(i)); +int f6 (auto()); +int f7 (auto(int)); +int f8 (auto(f)(int)); +int f9 (auto(...) -> char); +// FIXME: ICEs (PR c++/89867) +//int f10 (auto(__attribute__((unused)) i)); +int f11 (auto((i))); +int f12 (auto(i[])); +int f13 (auto(*i)); +int f14 (auto(*)); + +int e2 (auto{}); // { dg-error "invalid use of .auto." } +int e3 (auto(i, i)); // { dg-error "invalid use of .auto." } + +char bar (int); +char baz (); +char qux (...); + +void +g (int i) +{ + f1 (bar); + f2 (42); + f3 (42); + f4 (42); + f5 (42); + f6 (baz); + f7 (bar); + f8 (bar); + f9 (qux); +// f10 (42); + f11 (42); + f12 (&i); + f13 (&i); + f14 (&i); + + v1 = 1; + v2 = 2; + v3 = 3; + v4 = 4; + v5 = 5; + v6 = 6; +} diff --git a/gcc/testsuite/g++.dg/cpp23/auto-fncast14.C b/gcc/testsuite/g++.dg/cpp23/auto-fncast14.C new file mode 100644 index 00000000000..9e7a06c87d5 --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp23/auto-fncast14.C @@ -0,0 +1,9 @@ +// PR c++/112410 +// { dg-do compile { target c++23 } } + +struct A { + A(int,int); +}; + +int a; +A b1(auto(a), 42); base-commit: e0c1476d5d7c450b1b16a40364cea4e91237ea93 -- 2.41.0