[Sema][SR-720] Fallback to ExprPattern if enum element not found for UnresolvedDotExpr

lib/Sema/TypeCheckPattern.cpp

@@ -454,6 +454,8 @@ class ResolvePattern : public ASTVisitor<ResolvePattern,
     EnumElementDecl *referencedElement
       = lookupEnumMemberElement(TC, DC, ty, ude->getName().getBaseName(),
                                 ude->getLoc());
+    if (!referencedElement)
+      return nullptr;
 
     // Build a TypeRepr from the head of the full path.
     // FIXME: Compound names.

test/ClangModules/enum-with-target.swift

@@ -14,7 +14,7 @@ let calendarUnitsDep: CalendarUnitDeprecated = [.eraCalendarUnitDeprecated, .yea
 // rdar://problem/21081557
 func pokeRawValue(_ random: SomeRandomEnum) {
   switch (random) {
-  case SomeRandomEnum.RawValue // expected-error{{enum case 'RawValue' not found in type 'SomeRandomEnum'}}
+  case SomeRandomEnum.RawValue // expected-error{{expression pattern of type 'RawValue.Type' (aka 'Int.Type') cannot match values of type 'SomeRandomEnum'}}
     // expected-error@-1{{expected ':' after 'case'}}
   }
 }

test/Parse/switch.swift

@@ -279,3 +279,30 @@ func f0(values: [Whatever]) { // expected-note {{did you mean 'values'?}}
         break
     }
 }
+
+// sr-720
+enum Whichever {
+  case Thing
+  static let title = "title"
+  static let alias: Whichever = .Thing
+}
+func f1(x: String, y: Whichever) {
+  switch x {
+    case Whichever.title: // Ok. Don't emit diagnostics for static member of enum.
+        break
+    case Whichever.buzz: // expected-error {{type 'Whichever' has no member 'buzz'}}
+        break
+    case Whichever.alias: // expected-error {{expression pattern of type 'Whichever' cannot match values of type 'String'}}
+        break
+    default:
+      break
+  }
+  switch y {
+    case Whichever.Thing: // Ok.
+        break
+    case Whichever.alias: // Ok. Don't emit diagnostics for static member of enum.
+        break
+    case Whichever.title: // expected-error {{expression pattern of type 'String' cannot match values of type 'Whichever'}}
+        break
+  }
+}