[clang][diagnostics] Update note_constexpr_invalid_cast to use enum_select and adjust its uses (#130868)

Handles #123121

This patch updates `note_constexpr_invalid_cast` diagnostic to use
`enum_select` instead of `select,` improving readability and reducing
reliance on magic numbers in caller sites.

Author: ayokunle321

clang/include/clang/Basic/DiagnosticASTKinds.td

@@ -11,8 +11,9 @@ let Component = "AST" in {
 // Constant expression diagnostics. These (and their users) belong in Sema.
 def note_expr_divide_by_zero : Note<"division by zero">;
 def note_constexpr_invalid_cast : Note<
-  "%select{reinterpret_cast|dynamic_cast|%select{this conversion|cast that"
-  " performs the conversions of a reinterpret_cast}1|cast from %1}0"
+  "%enum_select<ConstexprInvalidCastKind>{%Reinterpret{reinterpret_cast}|%Dynamic{dynamic_cast}|"
+  "%ThisConversionOrReinterpret{%select{this conversion|cast that performs the conversions "
+  "of a reinterpret_cast}1}|%CastFrom{cast from %1}}0"
   " is not allowed in a constant expression"
   "%select{| in C++ standards before C++20||}0">;
 def note_constexpr_invalid_void_star_cast : Note<

clang/lib/AST/ByteCode/Interp.h

@@ -2369,12 +2369,14 @@ static inline bool PtrPtrCast(InterpState &S, CodePtr OpPC, bool SrcIsVoidPtr) {
     } else if (!S.getLangOpts().CPlusPlus26) {
       const SourceInfo &E = S.Current->getSource(OpPC);
       S.CCEDiag(E, diag::note_constexpr_invalid_cast)
-          << 3 << "'void *'" << S.Current->getRange(OpPC);
+          << diag::ConstexprInvalidCastKind::CastFrom << "'void *'"
+          << S.Current->getRange(OpPC);
     }
   } else {
     const SourceInfo &E = S.Current->getSource(OpPC);
     S.CCEDiag(E, diag::note_constexpr_invalid_cast)
-        << 2 << S.getLangOpts().CPlusPlus << S.Current->getRange(OpPC);
+        << diag::ConstexprInvalidCastKind::ThisConversionOrReinterpret
+        << S.getLangOpts().CPlusPlus << S.Current->getRange(OpPC);
   }
 
   return true;
@@ -2739,7 +2741,8 @@ inline bool GetIntPtr(InterpState &S, CodePtr OpPC, const Descriptor *Desc) {
 
   if (Desc)
     S.CCEDiag(S.Current->getSource(OpPC), diag::note_constexpr_invalid_cast)
-        << 2 << S.getLangOpts().CPlusPlus;
+        << diag::ConstexprInvalidCastKind::ThisConversionOrReinterpret
+        << S.getLangOpts().CPlusPlus;
 
   S.Stk.push<Pointer>(static_cast<uint64_t>(IntVal), Desc);
   return true;

clang/lib/AST/ExprConstant.cpp

@@ -8103,12 +8103,14 @@ class ExprEvaluatorBase
   }
 
   bool VisitCXXReinterpretCastExpr(const CXXReinterpretCastExpr *E) {
-    CCEDiag(E, diag::note_constexpr_invalid_cast) << 0;
+    CCEDiag(E, diag::note_constexpr_invalid_cast)
+        << diag::ConstexprInvalidCastKind::Reinterpret;
     return static_cast<Derived*>(this)->VisitCastExpr(E);
   }
   bool VisitCXXDynamicCastExpr(const CXXDynamicCastExpr *E) {
     if (!Info.Ctx.getLangOpts().CPlusPlus20)
-      CCEDiag(E, diag::note_constexpr_invalid_cast) << 1;
+      CCEDiag(E, diag::note_constexpr_invalid_cast)
+          << diag::ConstexprInvalidCastKind::Dynamic;
     return static_cast<Derived*>(this)->VisitCastExpr(E);
   }
   bool VisitBuiltinBitCastExpr(const BuiltinBitCastExpr *E) {
@@ -8833,7 +8835,8 @@ class LValueExprEvaluator
 
     case CK_LValueBitCast:
       this->CCEDiag(E, diag::note_constexpr_invalid_cast)
-          << 2 << Info.Ctx.getLangOpts().CPlusPlus;
+          << diag::ConstexprInvalidCastKind::ThisConversionOrReinterpret
+          << Info.Ctx.getLangOpts().CPlusPlus;
       if (!Visit(E->getSubExpr()))
         return false;
       Result.Designator.setInvalid();
@@ -9670,10 +9673,12 @@ bool PointerExprEvaluator::VisitCastExpr(const CastExpr *E) {
                 << E->getType()->getPointeeType();
           else
             CCEDiag(E, diag::note_constexpr_invalid_cast)
-                << 3 << SubExpr->getType();
+                << diag::ConstexprInvalidCastKind::CastFrom
+                << SubExpr->getType();
         } else
           CCEDiag(E, diag::note_constexpr_invalid_cast)
-              << 2 << Info.Ctx.getLangOpts().CPlusPlus;
+              << diag::ConstexprInvalidCastKind::ThisConversionOrReinterpret
+              << Info.Ctx.getLangOpts().CPlusPlus;
         Result.Designator.setInvalid();
       }
     }
@@ -9712,7 +9717,8 @@ bool PointerExprEvaluator::VisitCastExpr(const CastExpr *E) {
 
   case CK_IntegralToPointer: {
     CCEDiag(E, diag::note_constexpr_invalid_cast)
-        << 2 << Info.Ctx.getLangOpts().CPlusPlus;
+        << diag::ConstexprInvalidCastKind::ThisConversionOrReinterpret
+        << Info.Ctx.getLangOpts().CPlusPlus;
 
     APValue Value;
     if (!EvaluateIntegerOrLValue(SubExpr, Value, Info))
@@ -11177,7 +11183,8 @@ bool VectorExprEvaluator::VisitCastExpr(const CastExpr *E) {
       // Give up if the input isn't an int, float, or vector.  For example, we
       // reject "(v4i16)(intptr_t)&a".
       Info.FFDiag(E, diag::note_constexpr_invalid_cast)
-          << 2 << Info.Ctx.getLangOpts().CPlusPlus;
+          << diag::ConstexprInvalidCastKind::ThisConversionOrReinterpret
+          << Info.Ctx.getLangOpts().CPlusPlus;
       return false;
     }
 
@@ -15201,7 +15208,8 @@ bool IntExprEvaluator::VisitCastExpr(const CastExpr *E) {
 
   case CK_PointerToIntegral: {
     CCEDiag(E, diag::note_constexpr_invalid_cast)
-        << 2 << Info.Ctx.getLangOpts().CPlusPlus << E->getSourceRange();
+        << diag::ConstexprInvalidCastKind::ThisConversionOrReinterpret
+        << Info.Ctx.getLangOpts().CPlusPlus << E->getSourceRange();
 
     LValue LV;
     if (!EvaluatePointer(SubExpr, LV, Info))