[CSDiagnostics] Attach missing member diagnostic to a pattern/statement

If missing member is found in e.g. case statement or a pattern,
let's attach diagnostic directly to it.

Author: xedin

lib/Sema/CSDiagnostics.h

@@ -1188,6 +1188,12 @@ class MissingMemberFailure : public InvalidMemberRefFailure {
       : InvalidMemberRefFailure(solution, baseType, memberName, locator) {}
 
   SourceLoc getLoc() const override {
+    auto *locator = getLocator();
+
+    if (locator->findLast<LocatorPathElt::SyntacticElement>()) {
+      return constraints::getLoc(getAnchor());
+    }
+
     // Diagnostic should point to the member instead of its base expression.
     return constraints::getLoc(getRawAnchor());
   }

test/expr/closure/multi_statement.swift

@@ -350,3 +350,18 @@ func test_no_crash_with_circular_ref_due_to_error() {
     return 0
   }
 }
+
+func test_diagnosing_on_missing_member_in_case() {
+  enum E {
+    case one
+  }
+
+  func test(_: (E) -> Void) {}
+
+  test {
+    switch $0 {
+    case .one: break
+    case .unknown: break // expected-error {{type 'E' has no member 'unknown'}}
+    }
+  }
+}