Add feature flag for module selector

# Conflicts:
#	test/NameLookup/module_selector.swift

Author: beccadax

include/swift/Basic/LangOptions.h

@@ -292,6 +292,9 @@ namespace swift {
     /// language modes.
     bool WarnConcurrency = false;
 
+    /// Enable experimental 'Module::name' syntax.
+    bool EnableExperimentalModuleSelector = false;
+
     /// Enable experimental #assert feature.
     bool EnableExperimentalStaticAssert = false;
 

include/swift/Option/FrontendOptions.td

@@ -427,6 +427,10 @@ def suppress_static_exclusivity_swap : Flag<["-"], "suppress-static-exclusivity-
 def enable_sil_opaque_values : Flag<["-"], "enable-sil-opaque-values">,
   HelpText<"Enable SIL Opaque Values">;
 
+def enable_experimental_module_selector :
+  Flag<["-"], "enable-experimental-module-selector">,
+  HelpText<"Enable experimental 'Module::name' syntax">;
+
 def enable_experimental_static_assert :
   Flag<["-"], "enable-experimental-static-assert">,
   HelpText<"Enable experimental #assert">;

lib/Frontend/CompilerInvocation.cpp

@@ -416,6 +416,9 @@ static bool ParseLangArgs(LangOptions &Opts, ArgList &Args,
   Opts.DiagnosticsEditorMode |= Args.hasArg(OPT_diagnostics_editor_mode,
                                             OPT_serialize_diagnostics_path);
 
+  Opts.EnableExperimentalModuleSelector |=
+    Args.hasArg(OPT_enable_experimental_module_selector);
+
   Opts.EnableExperimentalStaticAssert |=
     Args.hasArg(OPT_enable_experimental_static_assert);
 

test/NameLookup/module_selector.swift

@@ -0,0 +1 @@
+// RUN: %target-typecheck-verify-swift -enable-experimental-module-selector %s