[interop] restructure Swift -> C++ interop tests

We will place tests that test the semantics and runtime of the generated
C++ code into Interop/SwiftToCxx. PrintCxx test directory will only be
used to test high level flow without concerning itself about the C++ semantics.

Author: hyp

test/Interop/SwiftToCxx/module/module-to-namespace.swift

@@ -0,0 +1,9 @@
+// RUN: %empty-directory(%t)
+// RUN: %target-swift-frontend(mock-sdk: %clang-importer-sdk) %s -typecheck -module-name Test -emit-cxx-header-path %t/empty.h
+// RUN: %FileCheck %s < %t/empty.h
+
+// RUN: %check-cxx-header-in-clang -std=c++14 %t/empty.h
+// RUN: %check-cxx-header-in-clang -std=c++17 %t/empty.h
+
+// CHECK-LABEL: namespace Test {
+// CHECK:       } // namespace Test

test/PrintAsCxx/empty.swift

@@ -2,8 +2,8 @@
 // RUN: %target-swift-frontend(mock-sdk: %clang-importer-sdk) %s -typecheck -emit-cxx-header-path %t/empty.h
 // RUN: %FileCheck %s < %t/empty.h
 
-// RUN: %check-in-clang++ -std=c++14 %t/empty.h
-// RUN: %check-in-clang++ -std=c++17 %t/empty.h
+// RUN: %check-cxx-header-in-clang -std=c++14 %t/empty.h
+// RUN: %check-cxx-header-in-clang -std=c++17 %t/empty.h
 
 // CHECK-NOT: @import Swift;
 // CHECK-NOT: IBSegueAction

test/PrintAsCxx/lit.local.cfg

@@ -4,8 +4,8 @@
 
 // RUN: %check-in-clang -std=c99 %t/empty.h
 // RUN: %check-in-clang -std=c11 %t/empty.h
-// RUN: %check-in-clang++ -std=c++98 %t/empty.h
-// RUN: %check-in-clang++ -std=c++14 %t/empty.h
+// RUN: %check-cxx-header-in-clang -x objective-c++-header -std=c++98 %t/empty.h
+// RUN: %check-cxx-header-in-clang -x objective-c++-header -std=c++14 %t/empty.h
 
 // RUN: %check-in-clang -std=c99 -fno-modules -Qunused-arguments %t/empty.h
 // RUN: not %check-in-clang -I %S/Inputs/clang-headers %t/empty.h 2>&1 | %FileCheck %s --check-prefix=CUSTOM-OBJC-PROLOGUE

test/PrintAsObjC/empty.swift

@@ -9,12 +9,3 @@ config.substitutions.insert(0, ('%check-in-clang',
   '-F %%clang-importer-sdk-path/frameworks '
   '-I %%clang-include-dir '
   '-isysroot %r/Inputs/clang-importer-sdk' % config.test_source_root) )
-
-config.substitutions.insert(0, ('%check-in-clang\+\+',
-  '%%clang++ -fsyntax-only -x objective-c++-header -fobjc-arc '
-  '-Weverything -Werror -Wno-unused-macros -Wno-incomplete-module '
-  '-Wno-auto-import -Wno-variadic-macros -Wno-c++98-compat-pedantic '
-  '-Wno-unused-command-line-argument ' # for -fmodules-cache-path
-  '-F %%clang-importer-sdk-path/frameworks '
-  '-I %%clang-include-dir '
-  '-isysroot %r/Inputs/clang-importer-sdk' % config.test_source_root) )

test/PrintAsObjC/lit.local.cfg

@@ -558,13 +558,39 @@ config.substitutions.append( ('%clang_apinotes',
                               "%r -cc1apinotes" %
                                 (config.clang)) )
 
+config.substitutions.append( ('%clangxx',
+                              "%r %s" %
+                                (config.clangxx, clang_mcp_opt)) )
+
 # This must come after all substitutions containing "%clang".
 # Note: %clang is the locally-built clang.
 # To get Xcode's clang, use %target-clang.
 config.substitutions.append( ('%clang',
                               "%r %s" %
                                 (config.clang, clang_mcp_opt)) )
 
+# Verifies that a C++ file can be compiled without warnings except for some exceptions.
+config.substitutions.insert(0, ('%check-cxx-header-in-clang',
+  '%%clangxx -fsyntax-only -x c++-header '
+  # Turn on all warnings and promote them to errors
+  '-Weverything -Werror '
+  # Don't warn about unused macros in our C++.
+  '-Wno-unused-macros '
+  # Don't warn about module imports used at #includes.
+  '-Wno-incomplete-module -Wno-auto-import '
+  # Don't warn about any variadic macros we might have.
+  '-Wno-variadic-macros '
+  # Don't warn about any C++98 compatibility issues.
+  '-Wno-c++98-compat-pedantic '
+  # Don't warn about poison system directories in the Linux system paths.
+  '-Wno-poison-system-directories '
+  # For -fmodules-cache-path, when modules are off.
+  '-Wno-unused-command-line-argument '
+  # Use standard header/framework search paths.
+  '-F %%clang-importer-sdk-path/frameworks '
+  '-I %%clang-include-dir '
+  '-isysroot %r/Inputs/clang-importer-sdk' % config.test_source_root) )
+
 ###
 
 def disallow(execName):