Let module lookups ignore access control

…at least for declarations in the current module. We continue to pretend that inaccessible declarations in other modules do not exist.

include/swift/AST/LookupKinds.h

@@ -41,7 +41,8 @@ enum NLOptions : unsigned {
 
   /// Don't check access when doing lookup into a type.
   ///
-  /// This option is not valid when performing lookup into a module.
+  /// When performing lookup into a module, this option only applies to
+  /// declarations in the same module the lookup is coming from.
   NL_IgnoreAccessControl = 1 << 3,
 
   /// This lookup should only return type declarations.

lib/AST/ModuleNameLookup.cpp

@@ -165,6 +165,11 @@ void ModuleNameLookup<LookupStrategy>::lookupInModule(
         if (resolutionKind == ResolutionKind::MacrosOnly && !isa<MacroDecl>(VD))
           return true;
         if (respectAccessControl &&
+            // NL_IgnoreAccessControl applies only to the current module.
+            !((options & NL_IgnoreAccessControl) &&
+                moduleScopeContext &&
+                moduleScopeContext->getParentModule() ==
+                    VD->getDeclContext()->getParentModule()) &&
             !VD->isAccessibleFrom(moduleScopeContext, false,
                                   includeUsableFromInline))
           return true;

test/NameLookup/Inputs/accessibility_other.swift

@@ -2,7 +2,7 @@ import has_accessibility
 
 public let a = 0 // expected-note * {{did you mean 'a'?}}
 internal let b = 0 // expected-note * {{did you mean 'b'?}}
-private let c = 0
+private let c = 0 // expected-note {{'c' declared here}}
 
 extension Foo {
   public static func a() {}

test/NameLookup/accessibility.swift

@@ -26,7 +26,7 @@ markUsed(has_accessibility.z) // expected-error {{module 'has_accessibility' has
 
 markUsed(accessibility.a)
 markUsed(accessibility.b)
-markUsed(accessibility.c) // expected-error {{module 'accessibility' has no member named 'c'}}
+markUsed(accessibility.c) // expected-error {{'c' is inaccessible due to 'private' protection level}}
 
 markUsed(x)
 markUsed(y) // expected-error {{cannot find 'y' in scope}}