[Sema][SVE] Don't allow sizeless types to be caught

[rsandifo-arm]

Summary

The same rules for throwing and catching incomplete types also apply
to sizeless types. This patch enforces that for try-catch statements.
It also makes sure that we use "sizeless type" rather "incomplete type"
in the associated message. (Both are correct, but "sizeless type" is
more specific and hopefully more user-friendly.)

[rsandifo-arm]

Allow pointers to sizeless types to be caught.

[efriedma]

LGTM

clang/include/clang/Basic/DiagnosticSemaKinds.td

def warn_deprecated_volatile_structured_binding : Warning<
   "volatile qualifier in structured binding declaration is deprecated">,
   InGroup<DeprecatedVolatile>;
 
 def err_catch_incomplete_ptr : Error<
   "cannot catch pointer to incomplete type %0">;
 def err_catch_incomplete_ref : Error<
   "cannot catch reference to incomplete type %0">;
 def err_catch_incomplete : Error<"cannot catch incomplete type %0">;
+def err_catch_sizeless : Error<
+  "cannot catch %select{|reference to }0sizeless type %1">;
 def err_catch_rvalue_ref : Error<"cannot catch exceptions by rvalue reference">;
 def err_catch_variably_modified : Error<
   "cannot catch variably modified type %0">;
 def err_qualified_catch_declarator : Error<
   "exception declarator cannot be qualified">;
 def err_early_catch_all : Error<"catch-all handler must come last">;
 def err_bad_memptr_rhs : Error<
   "right hand operand to %0 has non-pointer-to-member type %1">;

clang/lib/Sema/SemaDeclCXX.cpp

if (const PointerType *Ptr = BaseType->getAs<PointerType>()) {
     BaseType = Ref->getPointeeType();
     Mode = 2;
     DK = diag::err_catch_incomplete_ref;
   }
   if (!Invalid && (Mode == 0 || !BaseType->isVoidType()) &&
       !BaseType->isDependentType() && RequireCompleteType(Loc, BaseType, DK))
     Invalid = true;
 
+  if (!Invalid && Mode != 1 && BaseType->isSizelessType()) {
+    Diag(Loc, diag::err_catch_sizeless) << (Mode == 2 ? 1 : 0) << BaseType;
+    Invalid = true;
+  }
+
   if (!Invalid && !ExDeclType->isDependentType() &&
       RequireNonAbstractType(Loc, ExDeclType,
                              diag::err_abstract_type_in_decl,
                              AbstractVariableType))
     Invalid = true;
 
   // Only the non-fragile NeXT runtime currently supports C++ catches
   // of ObjC types, and no runtime supports catching ObjC types by value.

clang/test/SemaCXX/sizeless-1.cpp

#endif
   local_int8 = static_cast<svint8_t>(local_int16);  // expected-error {{static_cast from 'svint16_t' (aka '__SVInt16_t') to 'svint8_t' (aka '__SVInt8_t') is not allowed}}
   local_int8 = static_cast<svint8_t>(0);            // expected-error {{static_cast from 'int' to 'svint8_t' (aka '__SVInt8_t') is not allowed}}
   local_int16 = static_cast<svint16_t>(local_int8); // expected-error {{static_cast from 'svint8_t' (aka '__SVInt8_t') to 'svint16_t' (aka '__SVInt16_t') is not allowed}}
   sel = static_cast<int>(local_int8);               // expected-error {{static_cast from 'svint8_t' (aka '__SVInt8_t') to 'int' is not allowed}}
 
   throw local_int8; // expected-error {{cannot throw object of sizeless type 'svint8_t'}}
   throw global_int8_ptr;
 
+  try {
+  } catch (int) {
+  }
+  try {
+  } catch (svint8_t) { // expected-error {{cannot catch sizeless type 'svint8_t'}}
+  }
+  try {
+  } catch (svint8_t *) {
+  }
+  try {
+  } catch (svint8_t &) { // expected-error {{cannot catch reference to sizeless type 'svint8_t'}}
+  }
+
   local_int8.~__SVInt8_t(); // expected-error {{object expression of non-scalar type 'svint8_t' (aka '__SVInt8_t') cannot be used in a pseudo-destructor expression}}
 
   (void)svint8_t();
 
   local_int8 = svint8_t();
   local_int8 = svint16_t(); // expected-error {{assigning to 'svint8_t' (aka '__SVInt8_t') from incompatible type 'svint16_t'}}
 
   s_template<int> st_int;