[Bug c++/67810] New: Non-expression recognized as fold expression

[Bug c++/67810] New: Non-expression recognized as fold expression

[Casey at Carter dot net]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67810

            Bug ID: 67810
           Summary: Non-expression recognized as fold expression
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: Casey at Carter dot net
  Target Milestone: ---

r228351 fails to compile this correct program:

template <class...>
constexpr bool Test = true;

template <typename...Ts, bool = (Test<Ts&&...>)>
void f();

with error:

~/gcc6-r228351/bin/g++ -std=c++14 -c foo.cpp 
foo.cpp:4:41: warning: fold-expressions only available with -std=c++1z or
-std=gnu++1z
 template <typename...Ts, bool = (Test<Ts&&...>)>
                                         ^
foo.cpp:4:47: error: expected binary operator before ‘)’ token
 template <typename...Ts, bool = (Test<Ts&&...>)>
                                               ^
foo.cpp:5:1: error: expected primary-expression before ‘void’
 void f();
 ^
foo.cpp:5:1: error: expected ‘>’ before ‘void’
foo.cpp:5:9: error: expected unqualified-id before ‘;’ token
 void f();
         ^
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From: "matt at godbolt dot org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug middle-end/67809] Empty pointer-chasing loops aren't optimized out
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https://gcc.gnu.org/bugzilla/show_bug.cgi?idg809

Matt Godbolt <matt at godbolt dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |matt at godbolt dot org

--- Comment #1 from Matt Godbolt <matt at godbolt dot org> ---
A colleague has pointed out this of course is not a "do nothing" if the list is
circular. IANALL but I wonder if clang/icc take advantage of some kind of
"infinite loop is undefined behaviour" here that GCC doesn't.

[Bug c++/67810] Non-expression recognized as fold expression

[Casey at Carter dot net]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67810

Casey Carter <Casey at Carter dot net> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |Casey at Carter dot net,
                   |                            |jason at gcc dot gnu.org

--- Comment #1 from Casey Carter <Casey at Carter dot net> ---
Presumably this bug was introduced by the implementation of fold expressions in
r227883. CCing Jason.

[Bug c++/67810] Non-expression recognized as fold expression

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67810

Jason Merrill <jason at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|                            |2015-10-06
           Assignee|unassigned at gcc dot gnu.org      |jason at gcc dot gnu.org
     Ever confirmed|0                           |1

[Bug c++/67810] Non-expression recognized as fold expression

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67810

--- Comment #2 from Jason Merrill <jason at gcc dot gnu.org> ---
Author: jason
Date: Wed Oct  7 01:46:54 2015
New Revision: 228556

URL: https://gcc.gnu.org/viewcvs?rev=228556&root=gcc&view=rev
Log:
        PR c++/67810
        * parser.c (cp_parser_fold_expr_p): Remove.
        (is_binary_op): New.
        (cp_parser_fold_expression): Take LHS as parameter.
        (cp_parser_primary_expression): Call it after parsing an expression.
        (cp_parser_binary_expression, cp_parser_assignment_operator_opt)
        (cp_parser_expression): Ignore an operator followed by '...'.
        (is_binary_op): New.
        * pt.c (tsubst_unary_left_fold, tsubst_binary_left_fold)
        (tsubst_unary_right_fold, tsubst_binary_right_fold): Handle errors.

Added:
    trunk/gcc/testsuite/g++.dg/cpp1y/var-templ45.C
    trunk/gcc/testsuite/g++.dg/cpp1z/fold6.C
Modified:
    trunk/gcc/cp/ChangeLog
    trunk/gcc/cp/parser.c
    trunk/gcc/cp/pt.c
    trunk/gcc/testsuite/g++.dg/cpp1z/fold2.C

[Bug c++/67810] Non-expression recognized as fold expression

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67810

Jason Merrill <jason at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|---                         |FIXED
   Target Milestone|---                         |6.0

--- Comment #3 from Jason Merrill <jason at gcc dot gnu.org> ---
Fixed.