[Bug c++/67910] Two autos in a single function confuses the type system

["guille at cal dot berkeley.edu" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67910

--- Comment #5 from Guille <guille at cal dot berkeley.edu> ---
(In reply to Marc Glisse from comment #4)
> This seems to be already fixed on trunk.

Just tested on most recent gcc version 5.2.1 20151006 (GCC) and it doesn't
compile:


t.c: In function ‘int main()’:
t.c:10:12: error: conversion from ‘B’ to non-scalar type ‘A’ requested
     A a = f(B());
            ^
t.c: In instantiation of ‘auto:1 f(auto:1) [with auto:1 = B]’:
t.c:10:16:   required from here
t.c:6:39: error: could not convert ‘A()’ from ‘A’ to ‘B’
 static auto f(auto b) -> A { return A(); }
                                       ^
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From: "msebor at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/67913] New: new expression with negative size not diagnosed
Date: Fri, 09 Oct 2015 21:32:00 -0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?idg913

            Bug ID: 67913
           Summary: new expression with negative size not diagnosed
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: msebor at gcc dot gnu.org
  Target Milestone: ---

A new expression is considered erroneous if the expression in its
noptr-new-declarator is of non-class type and its value before converting to
std::size_t is less than zero.  If the expression is a constant expression, the
program is ill-fomed.  The following program contains two such ill-formed
expressions is not diagnosed by GCC.

void* operator new[] (unsigned long, void *p) { return p; }

void foo (void)
{
    char c;
    new char [-1];
    new (&c) char [-1];
}

Clang issues the following warnings for it:

a.cpp:6:15: warning: array size is negative [-Wbad-array-new-length]
    new char [-1];
              ^~
a.cpp:7:20: warning: array size is negative [-Wbad-array-new-length]
    new (&c) char [-1];
                   ^~
2 warnings generated.