[Bug c++/25689] missed diagnostic about assignment used as truth value.

[Bug c++/25689] missed diagnostic about assignment used as truth value.

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=25689

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|2014-10-12 00:00:00         |2021-8-9
           Severity|minor                       |enhancement

[Bug c++/25689] missed diagnostic about assignment used as truth value.

[zhaoweiliew at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=25689

--- Comment #3 from Zhao Wei Liew <zhaoweiliew at gmail dot com> ---
Created attachment 52395
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=52395&action=edit
Test patch (seeking feedback)

Hi! I wrote a small patch to fix this issue, but I think that it has much room
for improvement, though I'm not very sure how. Could anyone take a look and
give me feedback on how I could improve the patch?

Here's an example code snippet. I've commented the expected and actual
diagnostic results beside the lines of code.

struct A {
  A& operator=(int);
  operator bool();
};

void f(A a, A b)
{
  if (a = 0); // GCC warns after patch (correct)
  if (a.operator=(0)) {} // GCC warns after patch (incorrect, but doesn't sound
like a major issue)
  if (a = b) {} // GCC does not warn before & after patch (incorrect)
}

Specifically, there are 2 issues:
1. GCC warns for `if (a.operator=(0))`
2. GCC does not warn for `if (a = b)` where the default copy/move assignment
operator is used.

Thanks!

[Bug c++/25689] missed diagnostic about assignment used as truth value.

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=25689

--- Comment #4 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jason Merrill <jason@gcc.gnu.org>:

https://gcc.gnu.org/g:654f6978cdc85a3970ff2c478d4df3e55cf4d3ab

commit r13-23-g654f6978cdc85a3970ff2c478d4df3e55cf4d3ab
Author: Zhao Wei Liew <zhaoweiliew@gmail.com>
Date:   Tue Feb 15 17:44:29 2022 +0800

    c++: Add diagnostic when operator= is used as truth cond [PR25689]

    When compiling the following code with g++ -Wparentheses, GCC does not
    warn on the if statement. For example, there is no warning for this code:

    struct A {
            A& operator=(int);
            operator bool();
    };

    void f(A a) {
            if (a = 0); // no warning
    }

    This is because a = 0 is a call to operator=, which GCC does not handle.

    This patch fixes this issue by handling calls to operator= when deciding
    to warn.

    Bootstrapped and regression tested on x86_64-pc-linux-gnu.

            PR c++/25689

    gcc/cp/ChangeLog:

            * call.cc (extract_call_expr): Return a NULL_TREE on failure
            instead of asserting.
            (build_new_method_call): Suppress -Wparentheses diagnostic for
            MODIFY_EXPR.
            * semantics.cc (is_assignment_op_expr_p): Add function to check
            if an expression is a call to an op= operator expression.
            (maybe_convert_cond): Handle the case of a op= operator expression
            for the -Wparentheses diagnostic.

    gcc/testsuite/ChangeLog:

            * g++.dg/warn/Wparentheses-31.C: New test.

    Signed-off-by: Zhao Wei Liew <zhaoweiliew@gmail.com>

[Bug c++/25689] missed diagnostic about assignment used as truth value.

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=25689

Patrick Palka <ppalka at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |ppalka at gcc dot gnu.org
             Status|NEW                         |RESOLVED
   Target Milestone|---                         |13.0
         Resolution|---                         |FIXED

--- Comment #5 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Fixed for GCC 13 I think?

[Bug c++/25689] New: missed diagnostic about assignment used as truth value.

[pluto at agmk dot net]

[ foo.cpp ]

struct Var {
    operator int() const;
    Var& operator = (int);
    bool operator == (int);
};
bool operator == (int, Var&);

void foo(Var var)
{
    if (var = 0);  // if (var.operator=(0))
}

[ foo.cpp.t03.gimple ]

void foo(Var) (var)
{
  bool retval.0;
  struct Var & D.1768;
  int D.1769;

  D.1768 = operator= (&var, 0);
  D.1769 = operator 1 (D.1768);
  retval.0 = D.1769 != 0;
}


-- 
           Summary: missed diagnostic about assignment used as truth value.
           Product: gcc
           Version: 4.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: pluto at agmk dot net
 GCC build triplet: i686-pld-linux
  GCC host triplet: i686-pld-linux
GCC target triplet: i686-pld-linux


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=25689

[Bug c++/25689] missed diagnostic about assignment used as truth value.

[pinskia at gcc dot gnu dot org]

------- Comment #1 from pinskia at gcc dot gnu dot org  2006-01-06 12:32 -------
Confirmed.


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Severity|normal                      |minor
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|0                           |1
           Keywords|                            |diagnostic
   Last reconfirmed|0000-00-00 00:00:00         |2006-01-06 12:32:23
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=25689