Don't apply @Sendable to enum cases in pattern matching

Author: DougGregor

lib/Sema/ConstraintSystem.cpp

@@ -1751,7 +1751,8 @@ FunctionType *ConstraintSystem::adjustFunctionTypeForConcurrency(
     if (auto *FD = dyn_cast<AbstractFunctionDecl>(decl)) {
       DC = FD->getDeclContext();
     } else if (auto EED = dyn_cast<EnumElementDecl>(decl)) {
-      if (EED->hasAssociatedValues()) {
+      if (EED->hasAssociatedValues() &&
+          !locator.endsWith<LocatorPathElt::PatternMatch>()) {
         DC = EED->getDeclContext();
       }
     }

test/Concurrency/sendable_methods.swift

@@ -279,3 +279,10 @@ func acceptSendableFunc<T, U>(_: @Sendable (T) -> U) { }
 acceptSendableFunc(InferredSendableE.c)
 acceptSendableFunc(GenericE<Int>.b)
 acceptSendableFunc(GenericE<NonSendable>.b)
+
+// Make sure pattern matching isn't affected by @Sendable on cases.
+func testPatternMatch(ge: [GenericE<Int>]) {
+  if case .b(let a) = ge.first {
+    _ = a
+  }
+}