https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97573
--- Comment #2 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Marek Polacek <mpola...@gcc.gnu.org>: https://gcc.gnu.org/g:455ade18462e5076065b1970e21c622239797392 commit r11-4502-g455ade18462e5076065b1970e21c622239797392 Author: Marek Polacek <pola...@redhat.com> Date: Tue Oct 27 11:16:50 2020 -0400 c++: Deprecate arithmetic convs on different enums [PR97573] I noticed that C++20 P1120R0 deprecated certain arithmetic conversions as outlined in [depr.arith.conv.enum], but we don't warn about them. In particular, "If one operand is of enumeration type and the other operand is of a different enumeration type or a floating-point type, this behavior is deprecated." These will likely become ill-formed in C++23, so we should warn by default in C++20. To this effect, this patch adds two new warnings (like clang++): -Wdeprecated-enum-enum-conversion and -Wdeprecated-enum-float-conversion. They are enabled by default in C++20. In older dialects, to enable these warnings you can now use -Wenum-conversion which I made available in C++ too. Note that unlike C, in C++ it is not enabled by -Wextra, because that breaks bootstrap. We already warn about comparisons of two different enumeration types via -Wenum-compare, the rest is handled in this patch: we're performing the usual arithmetic conversions in these contexts: - an arithmetic operation, - a bitwise operation, - a comparison, - a conditional operator, - a compound assign operator. Using the spaceship operator as enum <=> real_type is ill-formed but we don't reject it yet. We should also address [depr.array.comp] too, but it's not handled in this patch. gcc/c-family/ChangeLog: PR c++/97573 * c-opts.c (c_common_post_options): In C++20, turn on -Wdeprecated-enum-enum-conversion and -Wdeprecated-enum-float-conversion. * c.opt (Wdeprecated-enum-enum-conversion, Wdeprecated-enum-float-conversion): New options. (Wenum-conversion): Allow for C++ too. gcc/cp/ChangeLog: PR c++/97573 * call.c (build_conditional_expr_1): Warn about the deprecated enum/real type conversion in C++20. Also warn about a non-enumerated and enumerated type in ?: when -Wenum-conversion is on. * typeck.c (do_warn_enum_conversions): New function. (cp_build_binary_op): Call it. gcc/ChangeLog: PR c++/97573 * doc/invoke.texi: Document -Wdeprecated-enum-enum-conversion and -Wdeprecated-enum-float-conversion. -Wenum-conversion is no longer C/ObjC only. gcc/testsuite/ChangeLog: PR c++/97573 * g++.dg/cpp0x/linkage2.C: Add dg-warning. * g++.dg/parse/attr3.C: Likewise. * g++.dg/cpp2a/enum-conv1.C: New test. * g++.dg/cpp2a/enum-conv2.C: New test. * g++.dg/cpp2a/enum-conv3.C: New test.
