fix libc++ crash

Author: cor3ntin

clang/include/clang/Sema/SemaConcept.h

@@ -131,23 +131,24 @@ struct NormalizedConstraint {
     return *this;
   }
 
-  CompoundConstraintKind getCompoundKind() const {
-    assert(!isAtomic() && "getCompoundKind called on atomic constraint.");
-    return Constraint.get<CompoundConstraint>().getInt();
-  }
-
   bool isAtomic() const { return Constraint.is<AtomicConstraint *>(); }
   bool isFoldExpanded() const {
     return Constraint.is<FoldExpandedConstraint *>();
   }
+  bool isCompound() const { return Constraint.is<CompoundConstraint *>(); }
+
+  CompoundConstraintKind getCompoundKind() const {
+    assert(isCompound() && "getCompoundKind on a non-compound constraint..");
+    return Constraint.get<CompoundConstraint>().getInt();
+  }
 
   NormalizedConstraint &getLHS() const {
-    assert(!isAtomic() && "getLHS called on atomic constraint.");
+    assert(isCompound() && "getLHS called on a non-compound constraint.");
     return Constraint.get<CompoundConstraint>().getPointer()->first;
   }
 
   NormalizedConstraint &getRHS() const {
-    assert(!isAtomic() && "getRHS called on atomic constraint.");
+    assert(isCompound() && "getRHS called on a non-compound constraint.");
     return Constraint.get<CompoundConstraint>().getPointer()->second;
   }
 

clang/lib/Sema/SemaConcept.cpp

@@ -1397,13 +1397,22 @@ substituteParameterMappings(Sema &S, NormalizedConstraint &N,
                             ConceptDecl *Concept,
                             const MultiLevelTemplateArgumentList &MLTAL,
                             const ASTTemplateArgumentListInfo *ArgsAsWritten) {
-  if (!N.isAtomic()) {
+
+  if (N.isCompound()) {
     if (substituteParameterMappings(S, N.getLHS(), Concept, MLTAL,
                                     ArgsAsWritten))
       return true;
     return substituteParameterMappings(S, N.getRHS(), Concept, MLTAL,
                                        ArgsAsWritten);
   }
+
+  if (N.isFoldExpanded()) {
+    Sema::ArgumentPackSubstitutionIndexRAII _(S, -1);
+    return substituteParameterMappings(
+        S, N.getFoldExpandedConstraint()->Constraint, Concept, MLTAL,
+        ArgsAsWritten);
+  }
+
   TemplateParameterList *TemplateParams = Concept->getTemplateParameters();
 
   AtomicConstraint &Atomic = *N.getAtomicConstraint();