[clang] [clang] Turn -Wenum-constexpr-conversion into a hard error (PR #67170)

[via cfe-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

<details>
<summary>Changes</summary>

Casting an int into an enum is undefined behavior if the int is outside of the range of the enum. UB is not allowed in constant expressions, therefore the compiler must produce a hard error in that case.

However, until now, the compiler produced a warning that could be suppressed. It should instead be a hard error, since the program is ill-formed in that case, as per the C++ Standard.

This patch turns the warning into an error. Additionally, references to the old warning are removed since they are now meaningless.

Fixes #<!-- -->59036

---
Full diff: https://github.com/llvm/llvm-project/pull/67170.diff


5 Files Affected:

- (modified) clang/docs/ReleaseNotes.rst (+3) 
- (modified) clang/include/clang/Basic/DiagnosticASTKinds.td (+3-2) 
- (modified) clang/lib/AST/ExprConstant.cpp (+2-2) 
- (modified) openmp/cmake/HandleOpenMPOptions.cmake (-1) 
- (modified) openmp/cmake/config-ix.cmake (-1) 


``````````diff
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 477a40630f11097..1792a2c22261d63 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -67,6 +67,9 @@ C++ Specific Potentially Breaking Changes
   (`#49884 <https://github.com/llvm/llvm-project/issues/49884>`_), and
   (`#61273 <https://github.com/llvm/llvm-project/issues/61273>`_)
 
+- The downgradable error ``--Wenum-constexpr-conversion`` has been upgraded
+  into a hard error, to comply with the C++ Standard.
+
 ABI Changes in This Version
 ---------------------------
 - Following the SystemV ABI for x86-64, ``__int128`` arguments will no longer
diff --git a/clang/include/clang/Basic/DiagnosticASTKinds.td b/clang/include/clang/Basic/DiagnosticASTKinds.td
index d2656310e79c9b8..58fbfef18e303ce 100644
--- a/clang/include/clang/Basic/DiagnosticASTKinds.td
+++ b/clang/include/clang/Basic/DiagnosticASTKinds.td
@@ -403,9 +403,10 @@ def warn_integer_constant_overflow : Warning<
 def warn_fixedpoint_constant_overflow : Warning<
   "overflow in expression; result is %0 with type %1">,
   InGroup<DiagGroup<"fixed-point-overflow">>;
-def warn_constexpr_unscoped_enum_out_of_range : Warning<
+
+def err_constexpr_unscoped_enum_out_of_range : Error<
   "integer value %0 is outside the valid range of values [%1, %2] for the "
-  "enumeration type %3">, DefaultError, InGroup<DiagGroup<"enum-constexpr-conversion">>;
+  "enumeration type %3">;
 
 // This is a temporary diagnostic, and shall be removed once our
 // implementation is complete, and like the preceding constexpr notes belongs
diff --git a/clang/lib/AST/ExprConstant.cpp b/clang/lib/AST/ExprConstant.cpp
index fea06b97259fe31..82d659aab28c7d0 100644
--- a/clang/lib/AST/ExprConstant.cpp
+++ b/clang/lib/AST/ExprConstant.cpp
@@ -13843,13 +13843,13 @@ bool IntExprEvaluator::VisitCastExpr(const CastExpr *E) {
             (Max.slt(Result.getInt().getSExtValue()) ||
              Min.sgt(Result.getInt().getSExtValue())))
           Info.Ctx.getDiagnostics().Report(
-              E->getExprLoc(), diag::warn_constexpr_unscoped_enum_out_of_range)
+              E->getExprLoc(), diag::err_constexpr_unscoped_enum_out_of_range)
               << llvm::toString(Result.getInt(), 10) << Min.getSExtValue()
               << Max.getSExtValue() << ED;
         else if (!ED->getNumNegativeBits() && ConstexprVar &&
                  Max.ult(Result.getInt().getZExtValue()))
           Info.Ctx.getDiagnostics().Report(
-              E->getExprLoc(), diag::warn_constexpr_unscoped_enum_out_of_range)
+              E->getExprLoc(), diag::err_constexpr_unscoped_enum_out_of_range)
               << llvm::toString(Result.getInt(), 10) << Min.getZExtValue()
               << Max.getZExtValue() << ED;
       }
diff --git a/openmp/cmake/HandleOpenMPOptions.cmake b/openmp/cmake/HandleOpenMPOptions.cmake
index 4d6782a6f0cbe87..81b3d560acf6d8c 100644
--- a/openmp/cmake/HandleOpenMPOptions.cmake
+++ b/openmp/cmake/HandleOpenMPOptions.cmake
@@ -31,7 +31,6 @@ append_if(OPENMP_HAVE_WSIGN_COMPARE_FLAG "-Wsign-compare" CMAKE_C_FLAGS CMAKE_CX
 # printed. Therefore, check for whether the compiler supports options in the
 # form -W<foo>, and if supported, add the corresponding -Wno-<foo> option.
 
-append_if(OPENMP_HAVE_WENUM_CONSTEXPR_CONVERSION_FLAG "-Wno-enum-constexpr-conversion" CMAKE_C_FLAGS CMAKE_CXX_FLAGS)
 append_if(OPENMP_HAVE_WEXTRA_FLAG "-Wno-extra" CMAKE_C_FLAGS CMAKE_CXX_FLAGS)
 append_if(OPENMP_HAVE_WPEDANTIC_FLAG "-Wno-pedantic" CMAKE_C_FLAGS CMAKE_CXX_FLAGS)
 append_if(OPENMP_HAVE_WMAYBE_UNINITIALIZED_FLAG "-Wno-maybe-uninitialized" CMAKE_C_FLAGS CMAKE_CXX_FLAGS)
diff --git a/openmp/cmake/config-ix.cmake b/openmp/cmake/config-ix.cmake
index 49e374286ac78cf..37fa4e85f3b27d1 100644
--- a/openmp/cmake/config-ix.cmake
+++ b/openmp/cmake/config-ix.cmake
@@ -32,7 +32,6 @@ check_cxx_compiler_flag(-Wsign-compare OPENMP_HAVE_WSIGN_COMPARE_FLAG)
 # printed. Therefore, check for whether the compiler supports options in the
 # form -W<foo>, and if supported, add the corresponding -Wno-<foo> option.
 
-check_cxx_compiler_flag(-Wenum-constexpr-conversion OPENMP_HAVE_WENUM_CONSTEXPR_CONVERSION_FLAG)
 check_cxx_compiler_flag(-Wextra OPENMP_HAVE_WEXTRA_FLAG)
 check_cxx_compiler_flag(-Wpedantic OPENMP_HAVE_WPEDANTIC_FLAG)
 check_cxx_compiler_flag(-Wmaybe-uninitialized OPENMP_HAVE_WMAYBE_UNINITIALIZED_FLAG)

``````````

</details>


https://github.com/llvm/llvm-project/pull/67170