Auto populate runtime source directory

This patch causes the convenient flow to automatically populate the
sources into the new runtime directory layout. This is run at build-time
so that it repopulates on each build. Since the resync script uses
`COPY_IF_DIFFERENT`, only files that change in the main source directory
are copied over, so incremental builds should still work.

Fixed a small bug in the resync script to ensure that it creates the
subdirectories in the right places.

CMakeLists.txt

@@ -1583,6 +1583,11 @@ endif()
 # New standard library build
 option(SWIFT_ENABLE_NEW_RUNTIME_BUILD "Build Swift runtimes with new build system" OFF)
 if(SWIFT_ENABLE_NEW_RUNTIME_BUILD)
+
+  add_custom_target(PopulateRuntimeSourceDir
+    COMMAND "${CMAKE_COMMAND}" -P "${CMAKE_CURRENT_SOURCE_DIR}/Runtimes/Resync.cmake"
+    COMMENT "Copying sources into new runtime build")
+
   foreach(sdk ${SWIFT_SDKS})
     foreach(arch ${SWIFT_SDK_${sdk}_ARCHITECTURES})
       # Provide a mechanism to skip building one of these runtimes
@@ -1599,6 +1604,8 @@ if(SWIFT_ENABLE_NEW_RUNTIME_BUILD)
         # TODO: Add this once we're ready to start swapping out the libraries
         #       for testing
         # INSTALL_DIR "${CMAKE_BINARY_DIR}/"
+
+        DEPENDS PopulateRuntimeSourceDir
         CMAKE_ARGS
           -DCMAKE_INSTALL_LIBDIR:FILEPATH=lib/swift/${SWIFT_SDK_${sdk}_LIB_SUBDIR}/${arch}
           # Compiler will see mismatched swift modules and fail initial checks
@@ -1616,8 +1623,4 @@ if(SWIFT_ENABLE_NEW_RUNTIME_BUILD)
       endif()
     endforeach()
   endforeach()
-
-  # Materialize sources in the new build
-  execute_process(COMMAND
-    "${CMAKE_COMMAND}" -P "${CMAKE_CURRENT_SOURCE_DIR}/Runtimes/Resync.cmake")
 endif()

Runtimes/Resync.cmake

@@ -15,6 +15,8 @@ message(STATUS "Source dir: ${StdlibSources}")
 function(copy_library_sources name from_prefix to_prefix)
   message(STATUS "${name}[${StdlibSources}/${from_prefix}/${name}] -> ${to_prefix}/${name} ")
 
+  set(full_to_prefix "${CMAKE_CURRENT_LIST_DIR}/${to_prefix}")
+
   file(GLOB_RECURSE filenames
     FOLLOW_SYMLINKS
     LIST_DIRECTORIES FALSE
@@ -36,15 +38,15 @@ function(copy_library_sources name from_prefix to_prefix)
   foreach(file ${filenames})
     # Get and create the directory
     get_filename_component(dirname ${file} DIRECTORY)
-    file(MAKE_DIRECTORY "${to_prefix}/${dirname}")
+    file(MAKE_DIRECTORY "${full_to_prefix}/${dirname}")
     file(COPY_FILE
       "${StdlibSources}/${from_prefix}/${file}"         # From
-      "${CMAKE_CURRENT_LIST_DIR}/${to_prefix}/${file}"  # To
+      "${full_to_prefix}/${file}"                       # To
       RESULT _output
       ONLY_IF_DIFFERENT)
     if(_output)
       message(SEND_ERROR
-        "Copy ${from_prefix}/${file} -> ${to_prefix}/${file} Failed: ${_output}")
+        "Copy ${from_prefix}/${file} -> ${full_to_prefix}/${file} Failed: ${_output}")
     endif()
   endforeach()
 endfunction()