[Bug c++/106774] New: warning about comparison to true/false

["f.heckenbach@fh-soft.de" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106774

            Bug ID: 106774
           Summary: warning about comparison to true/false
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: f.heckenbach@fh-soft.de
  Target Milestone: ---

gcc has "-Wbool-compare" to warn about boolean expression compared with an
integer value different from true/false. This warning is enabled by -Wall.

However, a warning for comparisons with true and false may also be useful. The
former is redundant, the latter can be replaced with "!".

Actually, this warning may also be given when comparing a non-Boolean integral
expression with true or false. The former is not redundant, but may often not
be what's intended (if so, one should compare with 1). The latter is equivalent
to comparing with 0, but still strange style. And comparing non-integral (e.g.
floating-point) expressions with Boolean literals is certainly warning-worthy
(though it may be caught by "-Wfloat-equal" as well).

To sum up, a new warning about comparing any expression with true/false
literals. 

Maybe something like "-Wbool-compare=2" (which would not be enabled by -Wall, I
guess; maybe by -Wextra, but even if it must be given manually, I'd find it
useful).