[CSDiag] Don't increase candidate curry level if base is ignored

lib/Sema/CalleeCandidateInfo.cpp

@@ -717,7 +717,16 @@ void CalleeCandidateInfo::collectCalleeCandidates(Expr *fn,
   if (auto UDE = dyn_cast<UnresolvedDotExpr>(fn)) {
     declName = UDE->getName().getBaseName().userFacingName();
     uncurryLevel = 1;
-
+
+    // If base is a module or metatype, this is just a simple
+    // reference so its curry level should be 0.
+    if (auto *DRE = dyn_cast<DeclRefExpr>(UDE->getBase())) {
+      if (auto baseType = DRE->getType())
+        uncurryLevel =
+            (baseType->is<ModuleType>() || baseType->is<AnyMetatypeType>()) ? 0
+                                                                            : 1;
+    }
+
     // If we actually resolved the member to use, return it.
     auto loc = CS.getConstraintLocator(UDE, ConstraintLocator::Member);
     if (auto *member = CS.findResolvedMemberRef(loc)) {

test/Constraints/rdar45242032.swift

@@ -0,0 +1,22 @@
+// RUN: %target-typecheck-verify-swift -module-name M
+
+protocol P {
+  var v: String { get }
+}
+
+func foo(bar: [P], baz: [P]) {
+// expected-note@-1 {{'foo(bar:baz:)' declared here}}
+}
+
+struct S {
+  static func bar(fiz: [P], baz: [P]) {}
+// expected-note@-1 {{'bar(fiz:baz:)' declared here}}
+}
+
+do {
+  let _ = M.foo(bar & // expected-error {{missing argument for parameter 'bar' in call}}
+} // expected-error {{expected expression after operator}}
+
+do {
+  let _ = S.bar(fiz & // expected-error {{missing argument for parameter 'fiz' in call}}
+} // expected-error {{expected expression after operator}}