[clang][NFC] Factor out VLA checks in type traits (#88646)

This is a follow-up to #88473 suggested by @cor3ntin in
#88473 (comment).

clang/lib/Sema/SemaExprCXX.cpp

@@ -5012,6 +5012,20 @@ Sema::PerformImplicitConversion(Expr *From, QualType ToType,
   return From;
 }
 
+/// Checks that type T is not a VLA.
+///
+/// @returns @c true if @p T is VLA and a diagnostic was emitted,
+/// @c false otherwise.
+static bool DiagnoseVLAInCXXTypeTrait(Sema &S, const TypeSourceInfo *T,
+                                      clang::tok::TokenKind TypeTraitID) {
+  if (!T->getType()->isVariableArrayType())
+    return false;
+
+  S.Diag(T->getTypeLoc().getBeginLoc(), diag::err_vla_unsupported)
+      << 1 << TypeTraitID;
+  return true;
+}
+
 /// Check the completeness of a type in a unary type trait.
 ///
 /// If the particular type trait requires a complete type, tries to complete
@@ -5188,7 +5202,9 @@ static bool HasNoThrowOperator(const RecordType *RT, OverloadedOperatorKind Op,
 }
 
 static bool EvaluateUnaryTypeTrait(Sema &Self, TypeTrait UTT,
-                                   SourceLocation KeyLoc, QualType T) {
+                                   SourceLocation KeyLoc,
+                                   TypeSourceInfo *TInfo) {
+  QualType T = TInfo->getType();
   assert(!T->isDependentType() && "Cannot evaluate traits of dependent type");
 
   ASTContext &C = Self.Context;
@@ -5205,21 +5221,13 @@ static bool EvaluateUnaryTypeTrait(Sema &Self, TypeTrait UTT,
   case UTT_IsArray:
     return T->isArrayType();
   case UTT_IsBoundedArray:
-    if (!T->isVariableArrayType()) {
-      return T->isArrayType() && !T->isIncompleteArrayType();
-    }
-
-    Self.Diag(KeyLoc, diag::err_vla_unsupported)
-        << 1 << tok::kw___is_bounded_array;
-    return false;
+    if (DiagnoseVLAInCXXTypeTrait(Self, TInfo, tok::kw___is_bounded_array))
+      return false;
+    return T->isArrayType() && !T->isIncompleteArrayType();
   case UTT_IsUnboundedArray:
-    if (!T->isVariableArrayType()) {
-      return T->isIncompleteArrayType();
-    }
-
-    Self.Diag(KeyLoc, diag::err_vla_unsupported)
-        << 1 << tok::kw___is_unbounded_array;
-    return false;
+    if (DiagnoseVLAInCXXTypeTrait(Self, TInfo, tok::kw___is_unbounded_array))
+      return false;
+    return T->isIncompleteArrayType();
   case UTT_IsPointer:
     return T->isAnyPointerType();
   case UTT_IsNullPointer:
@@ -5631,7 +5639,7 @@ static bool EvaluateBooleanTypeTrait(Sema &S, TypeTrait Kind,
     return false;
 
   if (Kind <= UTT_Last)
-    return EvaluateUnaryTypeTrait(S, Kind, KWLoc, Args[0]->getType());
+    return EvaluateUnaryTypeTrait(S, Kind, KWLoc, Args[0]);
 
   // Evaluate ReferenceBindsToTemporary and ReferenceConstructsFromTemporary
   // alongside the IsConstructible traits to avoid duplication.
@@ -6093,12 +6101,9 @@ static bool EvaluateBinaryTypeTrait(Sema &Self, TypeTrait BTT, const TypeSourceI
       Self.RequireCompleteType(Rhs->getTypeLoc().getBeginLoc(), RhsT,
                                diag::err_incomplete_type);
 
-    if (LhsT->isVariableArrayType())
-      Self.Diag(Lhs->getTypeLoc().getBeginLoc(), diag::err_vla_unsupported)
-          << 1 << tok::kw___is_layout_compatible;
-    if (RhsT->isVariableArrayType())
-      Self.Diag(Rhs->getTypeLoc().getBeginLoc(), diag::err_vla_unsupported)
-          << 1 << tok::kw___is_layout_compatible;
+    DiagnoseVLAInCXXTypeTrait(Self, Lhs, tok::kw___is_layout_compatible);
+    DiagnoseVLAInCXXTypeTrait(Self, Rhs, tok::kw___is_layout_compatible);
+
     return Self.IsLayoutCompatible(LhsT, RhsT);
   }
   case BTT_IsPointerInterconvertibleBaseOf: {
@@ -6108,12 +6113,10 @@ static bool EvaluateBinaryTypeTrait(Sema &Self, TypeTrait BTT, const TypeSourceI
                                diag::err_incomplete_type);
     }
 
-    if (LhsT->isVariableArrayType())
-      Self.Diag(Lhs->getTypeLoc().getBeginLoc(), diag::err_vla_unsupported)
-          << 1 << tok::kw___is_pointer_interconvertible_base_of;
-    if (RhsT->isVariableArrayType())
-      Self.Diag(Rhs->getTypeLoc().getBeginLoc(), diag::err_vla_unsupported)
-          << 1 << tok::kw___is_pointer_interconvertible_base_of;
+    DiagnoseVLAInCXXTypeTrait(Self, Lhs,
+                              tok::kw___is_pointer_interconvertible_base_of);
+    DiagnoseVLAInCXXTypeTrait(Self, Rhs,
+                              tok::kw___is_pointer_interconvertible_base_of);
 
     return Self.IsPointerInterconvertibleBaseOf(Lhs, Rhs);
   }