Merge pull request #24590 from DougGregor/pattern-type-check-crash-5.1

[5.1] [Type checker] Fix a crash-on-invalid in pattern type checking.

Author: DougGregor

lib/Sema/TypeCheckPattern.cpp

@@ -1438,6 +1438,10 @@ bool TypeChecker::coercePatternToType(Pattern *&P, TypeResolution resolution,
           }
         }
       }
+
+      if (!elt)
+        return true;
+
       enumTy = type;
     } else {
       // Check if the explicitly-written enum type matches the type we're

validation-test/compiler_crashers_2_fixed/0194-rdar49731284.swift

@@ -0,0 +1,12 @@
+// RUN: not %target-swift-frontend -typecheck %s
+
+open class Foo {
+  open class func foo<T: Equatable>(value: T?, other: T?) {
+    switch (value, other) {
+    case (.some(let unwrappedValue &), .none): // the & here triggers it
+      fallthrough
+    default:
+      fatalError()
+    }
+  }
+}