[CS] Walk into patterns when looking for closure referenced vars

Previously we would skip over ExprPatterns, but
we need to ensure that we walk them, as they may
have interesting variable references that the
closure needs to be connected to the type
variables for.

rdar://110617471

lib/Sema/CSGen.cpp

@@ -2949,10 +2949,6 @@ namespace {
         PreWalkAction walkToDeclPre(Decl *D) override {
           return Action::VisitChildrenIf(isa<PatternBindingDecl>(D));
         }
-
-        PreWalkResult<Pattern *> walkToPatternPre(Pattern *P) override {
-          return Action::SkipChildren(P);
-        }
       } collectVarRefs(CS);
 
       // Walk the capture list if this closure has one,  because it could

test/Constraints/rdar110617471.swift

@@ -0,0 +1,25 @@
+// RUN: %target-typecheck-verify-swift
+
+// rdar://110617471: Make sure we can type-check this.
+class C {
+  var prop = 0
+}
+
+func foo(_ fn: () -> Void) {}
+
+class D {
+  let c = C()
+
+  func bar() {
+    foo { [c] in
+      foo {
+        switch 0 {
+        case c.prop:
+          break
+        default:
+          break
+        }
+      }
+    }
+  }
+}