[clang] [clang] Implement CWG3135 - constexpr structured bindings with prvalues from tuples (PR #191880)

[Matthias Wippich via cfe-commits]

================
@@ -1361,25 +1361,28 @@ static bool checkTupleLikeDecomposition(Sema &S,
       return true;
     Expr *Init = E.get();
 
-    //   Given the type T designated by std::tuple_element<i - 1, E>::type,
+    //   Given the type T designated by std::tuple_element<i - 1, E>::type
     QualType T = getTupleLikeElementType(S, Loc, I, DecompType);
     if (T.isNull())
       return true;
 
-    //   each vi is a variable of type "reference to T" initialized with the
-    //   initializer, where the reference is an lvalue reference if the
-    //   initializer is an lvalue and an rvalue reference otherwise
-    QualType RefType =
-        S.BuildReferenceType(T, E.get()->isLValue(), Loc, B->getDeclName());
-    if (RefType.isNull())
+    // C++26 [dcl.struct.bind]p7:
+    //   and the type Ui, defined as Ti if the initializer is a prvalue,
+    //   as "lvalue reference to Ti" if the initializer is an lvalue,
+    //   or as "rvalue reference to Ti" otherwise
+    // "defined as Ti if the initializer is a prvalue" was introduced by CWG3135
+    QualType U = E.get()->isPRValue() && S.getLangOpts().CPlusPlus26
+                     ? T
----------------
Tsche wrote:

okay, treating as DR

https://github.com/llvm/llvm-project/pull/191880