[Clang] Implement P2864R2 Remove Deprecated Arithmetic Conversion on…

[cor3ntin]

… Enumerations

https://isocpp.org/files/papers/P2864R2.pdf

[llvmbot]

@llvm/pr-subscribers-clang

Author: cor3ntin (cor3ntin)

Changes

… Enumerations

https://isocpp.org/files/papers/P2864R2.pdf

---

Full diff: https://github.com/llvm/llvm-project/pull/73105.diff

5 Files Affected:

• (modified) clang/docs/ReleaseNotes.rst (+3)
• (modified) clang/include/clang/Basic/DiagnosticSemaKinds.td (+9)
• (modified) clang/lib/Sema/SemaExpr.cpp (+11-5)
• (added) clang/test/SemaCXX/cxx2c-enum-compare.cpp (+9)
• (modified) clang/www/cxx_status.html (+1-1)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 157afd9e8629152..1a330dccdce58a8 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -182,6 +182,9 @@ C++2c Feature Support
   This is applied to both C++ standard attributes, and other attributes supported by Clang.
   This completes the implementation of `P2361R6 Unevaluated Strings <https://wg21.link/P2361R6>`_
 
+- Implemented `P2864R2 Remove Deprecated Arithmetic Conversion on Enumerations From
+C++26 <https://wg21.link/P2864R2>`_.
+
 
 Resolutions to C++ Defect Reports
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
index 990692c06d7d3a8..7c9e5999d2c87fa 100644
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -7216,6 +7216,11 @@ def warn_arith_conv_enum_float_cxx20 : Warning<
   "%plural{2:with|4:from|:and}0 "
   "%select{enumeration|floating-point}1 type %3 is deprecated">,
   InGroup<DeprecatedEnumFloatConversion>;
+def err_arith_conv_enum_float_cxx26 : Error<
+  "invalid %sub{select_arith_conv_kind}0 "
+  "%select{floating-point|enumeration}1 type %2 "
+  "%plural{2:with|4:from|:and}0 "
+  "%select{enumeration|floating-point}1 type %3">;
 def warn_arith_conv_mixed_enum_types : Warning<
   "%sub{select_arith_conv_kind}0 "
   "different enumeration types%diff{ ($ and $)|}1,2">,
@@ -7224,6 +7229,10 @@ def warn_arith_conv_mixed_enum_types_cxx20 : Warning<
   "%sub{select_arith_conv_kind}0 "
   "different enumeration types%diff{ ($ and $)|}1,2 is deprecated">,
   InGroup<DeprecatedEnumEnumConversion>;
+def err_conv_mixed_enum_types_cxx26 : Error<
+  "invalid %sub{select_arith_conv_kind}0 "
+  "different enumeration types%diff{ ($ and $)|}1,2">;
+
 def warn_arith_conv_mixed_anon_enum_types : Warning<
   warn_arith_conv_mixed_enum_types.Summary>,
   InGroup<AnonEnumEnumConversion>, DefaultIgnore;
diff --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
index fc39d6149c1cc65..d1b2b8084b8ffea 100644
--- a/clang/lib/Sema/SemaExpr.cpp
+++ b/clang/lib/Sema/SemaExpr.cpp
@@ -1503,16 +1503,22 @@ static void checkEnumArithmeticConversions(Sema &S, Expr *LHS, Expr *RHS,
   bool IsCompAssign = ACK == Sema::ACK_CompAssign;
   if ((!IsCompAssign && LEnum && R->isFloatingType()) ||
       (REnum && L->isFloatingType())) {
-    S.Diag(Loc, S.getLangOpts().CPlusPlus20
+    S.Diag(Loc, S.getLangOpts().CPlusPlus26
+                    ? diag::err_arith_conv_enum_float_cxx26
+                : S.getLangOpts().CPlusPlus20
                     ? diag::warn_arith_conv_enum_float_cxx20
                     : diag::warn_arith_conv_enum_float)
-        << LHS->getSourceRange() << RHS->getSourceRange()
-        << (int)ACK << LEnum << L << R;
+        << LHS->getSourceRange() << RHS->getSourceRange() << (int)ACK << LEnum
+        << L << R;
   } else if (!IsCompAssign && LEnum && REnum &&
              !S.Context.hasSameUnqualifiedType(L, R)) {
     unsigned DiagID;
-    if (!L->castAs<EnumType>()->getDecl()->hasNameForLinkage() ||
-        !R->castAs<EnumType>()->getDecl()->hasNameForLinkage()) {
+    // 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;
+    else if (!L->castAs<EnumType>()->getDecl()->hasNameForLinkage() ||
+             !R->castAs<EnumType>()->getDecl()->hasNameForLinkage()) {
       // If either enumeration type is unnamed, it's less likely that the
       // user cares about this, but this situation is still deprecated in
       // C++2a. Use a different warning group.
diff --git a/clang/test/SemaCXX/cxx2c-enum-compare.cpp b/clang/test/SemaCXX/cxx2c-enum-compare.cpp
new file mode 100644
index 000000000000000..796136c774357bc
--- /dev/null
+++ b/clang/test/SemaCXX/cxx2c-enum-compare.cpp
@@ -0,0 +1,9 @@
+// RUN: %clang_cc1 %s -std=cxx2c -fsyntax-only -verify -triple %itanium_abi_triple
+
+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 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')}}
+}
diff --git a/clang/www/cxx_status.html b/clang/www/cxx_status.html
index 621439d0bae9666..9fb6b0cda4da50d 100755
--- a/clang/www/cxx_status.html
+++ b/clang/www/cxx_status.html
@@ -161,7 +161,7 @@ <h2 id="cxx26">C++2c implementation status</h2>
  <tr>
   <td>Remove Deprecated Arithmetic Conversion on Enumerations</td>
   <td><a href="https://wg21.link/P2864R2">P2864R2</a></td>
-  <td class="none" align="center">No</td>
+  <td class="unreleased" align="center">Clang 18</td>
  </tr>
 
 </table>

[AaronBallman]

LGTM -- I'm a bit worried about breaking working code, but the user has to explicitly opt into C++26 mode and so it's only slightly unreasonable for them to have to change their previously correct, working code because of this. I say we leave it as an error, but if users complain about this being too strict, we can relax it to be a warning that defaults to an error or just leave it deprecated and support it forever.

[AaronBallman]

Suggested change

	- Implemented `P2864R2 Remove Deprecated Arithmetic Conversion on Enumerations From
	C++26 <https://wg21.link/P2864R2>`_.
	- Implemented `P2864R2 Remove Deprecated Arithmetic Conversion on Enumerations From C++26 <https://wg21.link/P2864R2>`_.

This should fix the Sphinx build issues.

[dyung]

@cor3ntin Your commit seems to be causing 2 test failures in the clang-tools-extra tests, can you try to fix them or revert if you need time to investigate?

https://lab.llvm.org/buildbot/#/builders/139/builds/54467

[cor3ntin]

@PiotrZSL You beat me to it, thanks a lot!

[PiotrZSL]

Actually that is more like a quick fix, we can live with it. More proper way would be simply to split those tests into pre-c++20 and universal.