Sema: Don't split up pack types in matchExistentialTypes()

Author: slavapestov

lib/Sema/CSSimplify.cpp

@@ -3880,19 +3880,6 @@ ConstraintSystem::matchExistentialTypes(Type type1, Type type2,
     return getTypeMatchFailure(locator);
   }
 
-  // ConformsTo constraints are generated when opening a generic
-  // signature with a RequirementKind::Conformance requirement, so
-  // we must handle pack types on the left by splitting up into
-  // smaller constraints.
-  if (auto *packType = type1->getAs<PackType>()) {
-    for (unsigned i = 0, e = packType->getNumElements(); i < e; ++i) {
-      addConstraint(kind, packType->getElementType(i), type2,
-                    locator.withPathElement(LocatorPathElt::PackElement(i)));
-    }
-
-    return getTypeMatchSuccess();
-  }
-
   TypeMatchOptions subflags = getDefaultDecompositionOptions(flags);
 
   // Handle existential metatypes.
@@ -8318,6 +8305,7 @@ ConstraintSystem::SolutionKind ConstraintSystem::simplifyConformsToConstraint(
                                  ConstraintKind kind,
                                  ConstraintLocatorBuilder locator,
                                  TypeMatchOptions flags) {
+
   if (auto proto = protocol->getAs<ProtocolType>()) {
     return simplifyConformsToConstraint(type, proto->getDecl(), kind,
                                         locator, flags);
@@ -8326,6 +8314,28 @@ ConstraintSystem::SolutionKind ConstraintSystem::simplifyConformsToConstraint(
   // Dig out the fixed type to which this type refers.
   type = getFixedTypeRecursive(type, flags, /*wantRValue=*/true);
 
+  // ConformsTo constraints are generated when opening a generic
+  // signature with a RequirementKind::Conformance requirement, so
+  // we must handle pack types on the left by splitting up into
+  // smaller constraints.
+  if (auto *packType = type->getAs<PackType>()) {
+    for (unsigned i = 0, e = packType->getNumElements(); i < e; ++i) {
+      auto eltType = packType->getElementType(i);
+      if (auto *packExpansionType = eltType->getAs<PackExpansionType>()) {
+        auto patternLoc =
+            locator.withPathElement(ConstraintLocator::PackExpansionPattern);
+        addConstraint(ConstraintKind::ConformsTo,
+                      packExpansionType->getPatternType(), protocol,
+                      patternLoc);
+      } else {
+        addConstraint(ConstraintKind::ConformsTo, eltType, protocol,
+                      locator.withPathElement(LocatorPathElt::PackElement(i)));
+      }
+    }
+
+    return SolutionKind::Solved;
+  }
+
   return matchExistentialTypes(type, protocol, kind, flags, locator);
 }