[clang] [Clang][C++26] Implement "Ordering of constraints involving fold expressions (PR #98160)

[Aaron Ballman via cfe-commits]

================
@@ -1390,17 +1577,82 @@ NormalizedConstraint::fromConstraintExpr(Sema &S, 
NamedDecl *D, const Expr *E) {
       return std::nullopt;
 
     return New;
+  } else if (auto *FE = dyn_cast<const CXXFoldExpr>(E);
+             FE && S.getLangOpts().CPlusPlus26 &&
+             (FE->getOperator() == BinaryOperatorKind::BO_LAnd ||
+              FE->getOperator() == BinaryOperatorKind::BO_LOr)) {
+
+    FoldExpandedConstraint::FoldOperatorKind Kind =
+        FE->getOperator() == BinaryOperatorKind::BO_LAnd
+            ? FoldExpandedConstraint::FoldOperatorKind::FoAnd
+            : FoldExpandedConstraint::FoldOperatorKind::FoOr;
+
+    if (FE->getInit()) {
+      auto LHS = fromConstraintExpr(S, D, FE->getLHS());
+      auto RHS = fromConstraintExpr(S, D, FE->getRHS());
+      if (!LHS || !RHS)
+        return std::nullopt;
+
+      if (FE->isRightFold())
+        RHS = NormalizedConstraint{new (S.Context) FoldExpandedConstraint{
+            Kind, std::move(*RHS), FE->getPattern()}};
+      else
+        LHS = NormalizedConstraint{new (S.Context) FoldExpandedConstraint{
+            Kind, std::move(*LHS), FE->getPattern()}};
+
+      return NormalizedConstraint(
+          S.Context, std::move(*LHS), std::move(*RHS),
+          FE->getOperator() == BinaryOperatorKind::BO_LAnd ? CCK_Conjunction
+                                                           : CCK_Disjunction);
+    }
+    auto Sub = fromConstraintExpr(S, D, FE->getPattern());
+    return NormalizedConstraint{new (S.Context) FoldExpandedConstraint{
+        Kind, std::move(*Sub), FE->getPattern()}};
   }
+
   return NormalizedConstraint{new (S.Context) AtomicConstraint(S, E)};
 }
 
-using NormalForm =
-    llvm::SmallVector<llvm::SmallVector<AtomicConstraint *, 2>, 4>;
+/*static void CollectConstraintParams(const AtomicConstraint& C,
----------------
AaronBallman wrote:

Dead code?

https://github.com/llvm/llvm-project/pull/98160
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