================
@@ -3058,6 +3058,133 @@ void Sema::NoteAllFoundTemplates(TemplateName Name) {
}
}
+static QualType commonTypeImpl(Sema &S, TemplateName BaseTemplate,
+ SourceLocation TemplateLoc,
+ ArrayRef<TemplateArgument> Ts) {
+ auto lookUpCommonType = [&](TemplateArgument T1,
+ TemplateArgument T2) -> QualType {
+ // Don't bother looking for other specializations if both types are
+ // builtins - users aren't allowed to specialize for them
+ if (T1.getAsType()->isBuiltinType() && T2.getAsType()->isBuiltinType())
+ return commonTypeImpl(S, BaseTemplate, TemplateLoc, {T1, T2});
+
+ TemplateArgumentListInfo Args;
+ Args.addArgument(TemplateArgumentLoc(
+ T1, S.Context.getTrivialTypeSourceInfo(T1.getAsType())));
+ Args.addArgument(TemplateArgumentLoc(
+ T2, S.Context.getTrivialTypeSourceInfo(T2.getAsType())));
+ QualType BaseTemplateInst =
+ S.CheckTemplateIdType(BaseTemplate, TemplateLoc, Args);
+ if (S.RequireCompleteType(TemplateLoc, BaseTemplateInst,
+ diag::err_incomplete_type))
+ return QualType();
+ return S.getTypeMember(BaseTemplateInst, "type");
+ };
+
+ // Note A: For the common_type trait applied to a template parameter pack T
of
+ // types, the member type shall be either defined or not present as follows:
+ switch (Ts.size()) {
+
+ // If sizeof...(T) is zero, there shall be no member type.
+ case 0:
+ return QualType();
+
+ // If sizeof...(T) is one, let T0 denote the sole type constituting the
+ // pack T. The member typedef-name type shall denote the same type, if any,
as
+ // common_type_t<T0, T0>; otherwise there shall be no member type.
+ case 1:
+ return lookUpCommonType(Ts[0], Ts[0]);
+
+ // If sizeof...(T) is two, let the first and second types constituting T be
+ // denoted by T1 and T2, respectively, and let D1 and D2 denote the same
types
+ // as decay_t<T1> and decay_t<T2>, respectively.
+ case 2: {
+ QualType T1 = Ts[0].getAsType();
+ QualType T2 = Ts[1].getAsType();
+ QualType D1 = S.BuiltinDecay(T1, {});
+ QualType D2 = S.BuiltinDecay(T2, {});
+
+ // If is_same_v<T1, D1> is false or is_same_v<T2, D2> is false, let C
denote
+ // the same type, if any, as common_type_t<D1, D2>.
+ if (!S.Context.hasSameType(T1, D1) || !S.Context.hasSameType(T2, D2))
+ return lookUpCommonType(D1, D2);
+
+ // Otherwise, if decay_t<decltype(false ? declval<D1>() : declval<D2>())>
+ // denotes a valid type, let C denote that type.
+ {
+ auto CheckConditionalOperands = [&](bool ConstRefQual) -> QualType {
+ EnterExpressionEvaluationContext UnevaluatedContext(
+ S, Sema::ExpressionEvaluationContext::Unevaluated);
+ Sema::SFINAETrap SFINAE(S, /*AccessCheckingSFINAE=*/true);
+ Sema::ContextRAII TUContext(S, S.Context.getTranslationUnitDecl());
+
+ // false
+ OpaqueValueExpr CondExpr(SourceLocation(), S.Context.BoolTy,
+ VK_PRValue);
+ ExprResult Cond = &CondExpr;
+
+ auto EVK = ConstRefQual ? VK_LValue : VK_PRValue;
+ if (ConstRefQual) {
+ D1.addConst();
+ D2.addConst();
+ }
+
+ // declval<D1>()
+ OpaqueValueExpr LHSExpr(TemplateLoc, D1, EVK);
+ ExprResult LHS = &LHSExpr;
+
+ // declval<D2>()
+ OpaqueValueExpr RHSExpr(TemplateLoc, D2, EVK);
+ ExprResult RHS = &RHSExpr;
+
+ ExprValueKind VK = VK_PRValue;
+ ExprObjectKind OK = OK_Ordinary;
+
+ // decltype(false ? declval<D1>() : declval<D2>())
+ QualType Result =
+ S.CheckConditionalOperands(Cond, LHS, RHS, VK, OK, TemplateLoc);
----------------
cor3ntin wrote:
So, I think we can call `CXXCheckConditionalOperands` here.
But the question I have is, should we factor out the part of
`CXXCheckConditionalOperands` that deals with types directly and use that?
One one hand, doing surgery to `CXXCheckConditionalOperands` requires care and
might be a tad difficult, on the other hand the whole danse we are doing here
is a bit convoluted
https://github.com/llvm/llvm-project/pull/99473
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