[llvm-branch-commits] [clang] [Clang] Demote mixed enumeration arithmetic error to a warning (#131811) (PR #139396)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: cor3ntin (cor3ntin)

<details>
<summary>Changes</summary>

In C++, defaulted to an error.

C++ removed these features but the removal negatively impacts users.

Fixes #<!-- -->92340

---
Full diff: https://github.com/llvm/llvm-project/pull/139396.diff


4 Files Affected:

- (modified) clang/include/clang/Basic/DiagnosticSemaKinds.td (+5-1) 
- (modified) clang/lib/Sema/SemaChecking.cpp (+15-1) 
- (modified) clang/lib/Sema/SemaExpr.cpp (+2-2) 
- (modified) clang/test/SemaCXX/cxx2c-enum-compare.cpp (+3-2) 


``````````diff
diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
index ec2a140e04d5b..6c93a46d8f36c 100644
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -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;
 
 def warn_arith_conv_mixed_anon_enum_types : Warning<
   warn_arith_conv_mixed_enum_types.Summary>,
diff --git a/clang/lib/Sema/SemaChecking.cpp b/clang/lib/Sema/SemaChecking.cpp
index e440f60526bb3..00f7f87838cf1 100644
--- a/clang/lib/Sema/SemaChecking.cpp
+++ b/clang/lib/Sema/SemaChecking.cpp
@@ -14688,7 +14688,21 @@ bool Sema::BuiltinVectorToScalarMath(CallExpr *TheCall) {
   return false;
 }
 
-bool Sema::BuiltinVectorMath(CallExpr *TheCall, QualType &Res, bool FPOnly) {
+static bool checkBuiltinVectorMathMixedEnums(Sema &S, Expr *LHS, Expr *RHS,
+                                             SourceLocation Loc) {
+  QualType L = LHS->getEnumCoercedType(S.Context),
+           R = RHS->getEnumCoercedType(S.Context);
+  if (L->isUnscopedEnumerationType() && R->isUnscopedEnumerationType() &&
+      !S.Context.hasSameUnqualifiedType(L, R)) {
+    return S.Diag(Loc, diag::err_conv_mixed_enum_types)
+           << LHS->getSourceRange() << RHS->getSourceRange()
+           << /*Arithmetic Between*/ 0 << L << R;
+  }
+  return false;
+}
+
+std::optional<QualType> Sema::BuiltinVectorMath(CallExpr *TheCall,
+                                                bool FPOnly) {
   if (checkArgCount(TheCall, 2))
     return true;
 
diff --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
index e253e3a17328f..eae7f1c3aa781 100644
--- a/clang/lib/Sema/SemaExpr.cpp
+++ b/clang/lib/Sema/SemaExpr.cpp
@@ -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
diff --git a/clang/test/SemaCXX/cxx2c-enum-compare.cpp b/clang/test/SemaCXX/cxx2c-enum-compare.cpp
index f47278a60725e..96fbd368b1696 100644
--- a/clang/test/SemaCXX/cxx2c-enum-compare.cpp
+++ b/clang/test/SemaCXX/cxx2c-enum-compare.cpp
@@ -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')}}
 }

``````````

</details>


https://github.com/llvm/llvm-project/pull/139396