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[Clang][Backport] Demote mixed enumeration arithmetic error to a warning #131853

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[Clang][Backport] Demote mixed enumeration arithmetic error to a warning #131853

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[Clang][Backport] Demote mixed enumeration arithmetic error to a warn…
cor3ntin Mar 18, 2025
00c10b7
fix build
cor3ntin Mar 18, 2025
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3 changes: 3 additions & 0 deletions clang/docs/ReleaseNotes.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -299,6 +299,9 @@ C++ Language Changes
- The builtin type alias ``__builtin_common_type`` has been added to improve the
performance of ``std::common_type``.

- In C++26 mode, arithmetic conversion errors between mixed enumeration types can
be disabled with ``-Wno-enum-enum-conversion`` (#GH92340).

C++2c Feature Support
^^^^^^^^^^^^^^^^^^^^^

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6 changes: 5 additions & 1 deletion clang/include/clang/Basic/DiagnosticSemaKinds.td
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Expand Up @@ -7567,9 +7567,13 @@ def warn_arith_conv_mixed_enum_types_cxx20 : Warning<
"%sub{select_arith_conv_kind}0 "
"different enumeration types%diff{ ($ and $)|}1,2 is deprecated">,
InGroup<DeprecatedEnumEnumConversion>;
def err_conv_mixed_enum_types_cxx26 : Error<

def err_conv_mixed_enum_types: Error <
"invalid %sub{select_arith_conv_kind}0 "
"different enumeration types%diff{ ($ and $)|}1,2">;
def warn_conv_mixed_enum_types_cxx26 : Warning <
err_conv_mixed_enum_types.Summary>,
InGroup<EnumEnumConversion>, DefaultError;
Comment on lines +7570 to +7576
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@tstellar tstellar Mar 18, 2025

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I think this may be an ABI break if it changes enum values in the generated header.

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@cor3ntin cor3ntin Mar 18, 2025

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How do you usually deal with that?

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@tstellar tstellar Mar 18, 2025

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We usually just don't take these kinds of packages, but there may be a way to name the new option so that it ends up at the end of the enum list.

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@AaronBallman AaronBallman Mar 19, 2025

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I don't know of a reliable way to ensure the diagnostic is at the end of the list. I think putting it at the end of DiagnosticSemaKinds.td will suffice (we allocate diagnostic IDs in blocks based on the .td file they're in). However, I'm not certain that's a guarantee.

Perhaps we don't backport this?


def warn_arith_conv_mixed_anon_enum_types : Warning<
warn_arith_conv_mixed_enum_types.Summary>,
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4 changes: 2 additions & 2 deletions clang/lib/Sema/SemaExpr.cpp
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Expand Up @@ -1518,8 +1518,8 @@ static void checkEnumArithmeticConversions(Sema &S, Expr *LHS, Expr *RHS,
unsigned DiagID;
// In C++ 26, usual arithmetic conversions between 2 different enum types
// are ill-formed.
if (S.getLangOpts().CPlusPlus26)
DiagID = diag::err_conv_mixed_enum_types_cxx26;
if (getLangOpts().CPlusPlus26)
DiagID = diag::warn_conv_mixed_enum_types_cxx26;
else if (!L->castAs<EnumType>()->getDecl()->hasNameForLinkage() ||
!R->castAs<EnumType>()->getDecl()->hasNameForLinkage()) {
// If either enumeration type is unnamed, it's less likely that the
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5 changes: 3 additions & 2 deletions clang/test/SemaCXX/cxx2c-enum-compare.cpp
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@@ -1,9 +1,10 @@
// RUN: %clang_cc1 %s -std=c++2c -fsyntax-only -verify -triple %itanium_abi_triple
// RUN: %clang_cc1 %s -std=c++2c -fsyntax-only -verify=both,expected
// RUN: %clang_cc1 %s -std=c++2c -fsyntax-only -verify=both -Wno-enum-enum-conversion

enum E1 { e };
enum E2 { f };
void test() {
int b = e <= 3.7; // expected-error {{invalid comparison of enumeration type 'E1' with floating-point type 'double'}}
int b = e <= 3.7; // both-error {{invalid comparison of enumeration type 'E1' with floating-point type 'double'}}
int k = f - e; // expected-error {{invalid arithmetic between different enumeration types ('E2' and 'E1')}}
int x = 1 ? e : f; // expected-error {{invalid conditional expression between different enumeration types ('E1' and 'E2')}}
}
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