Allow :: as an alias for . in imports

This is a first cut at how imports ought to adopt module selectors.

Author: beccadax

lib/Parse/ParseDecl.cpp

@@ -6582,7 +6582,9 @@ ParserResult<ImportDecl> Parser::parseDeclImport(ParseDeclOptions Flags,
           .fixItRemove(Tok.getLoc());
         return nullptr;
     }
-    HasNext = consumeIf(tok::period);
+    HasNext = consumeIf(tok::period) ||
+        (Context.LangOpts.hasFeature(Feature::ModuleSelector) &&
+         consumeIf(tok::colon_colon));
   } while (HasNext);
 
   if (Tok.is(tok::code_complete)) {

test/NameLookup/module_selector.swift

@@ -1,12 +1,15 @@
-// RUN: %target-typecheck-verify-swift -module-name main -I %S/Inputs -enable-experimental-feature ModuleSelector
+// RUN: %target-typecheck-verify-swift -sdk %clang-importer-sdk -module-name main -I %S/Inputs -enable-experimental-feature ModuleSelector
 
 // Make sure the lack of the experimental flag disables the feature:
-// RUN: not %target-typecheck-verify-swift -module-name main -I %S/Inputs 2>/dev/null
+// RUN: not %target-typecheck-verify-swift -sdk %clang-importer-sdk -module-name main -I %S/Inputs 2>/dev/null
 
 // REQUIRES: swift_feature_ModuleSelector
 
 import ModuleSelectorTestingKit
 
+import ctypes::bits   // FIXME: ban using :: with submodules?
+import struct ModuleSelectorTestingKit::A
+
 let magnitude: Never = fatalError()
 
 // Test correct code using `A`