Adding stdlib resync script

Adding a quick script to keep the pieces of the standard library in sync
between the new stdlib build and the old one.

Author: etcwilde

.gitignore

@@ -78,3 +78,17 @@ SortedCFDatabase.def
 htmlcov
 .coverage
 /benchmark/scripts/Benchmark_Driverc
+
+#==============================================================================#
+# Ignore copied Swift Stdlib files while migrating stdlib
+#==============================================================================#
+Runtimes/**/*.swift
+Runtimes/**/*.h
+Runtimes/**/*.cpp
+Runtimes/**/*.c
+Runtimes/**/*.m
+Runtimes/**/*.mm
+Runtimes/**/*.def
+Runtimes/**/*.gyb
+Runtimes/**/*.apinotes
+Runtimes/**/*.yaml

Runtimes/Readme.md

@@ -2,6 +2,24 @@
 
 This directory contains the pieces of the Swift runtime libraries.
 
+## Development
+
+While we're bringing up the new standard library build, please do not commit the
+standard library source files. Use the `Resync.cmake` file to copy the files as
+needed.
+
+```sh
+$ cmake -P Resync.cmake
+```
+
+> [!IMPORTANT]
+> Re-run this script after updating your Swift checkout to ensure that you are
+> building the latest standard library sources.
+
+Once the migration is completed, we will be deleting this script. It
+is a temporary workaround to avoid trying to keep multiple sets of files in
+sync.
+
 ## Layering
 
 ```

Runtimes/Resync.cmake

@@ -0,0 +1,70 @@
+# This CMake script keeps the files in the new standard library build in sync
+# with the existing standard library.
+
+# TODO: Once the migration is completed, we can delete this file
+
+cmake_minimum_required(VERSION 3.21)
+
+# Where the standard library lives today
+set(StdlibSources "${CMAKE_CURRENT_LIST_DIR}/../stdlib")
+
+message(STATUS "Source dir: ${StdlibSources}")
+
+# Copy the files under the "name" directory in the standard library into the new
+# location under Runtimes
+function(copy_library_sources name from_prefix to_prefix)
+  message(STATUS "${name}[${StdlibSources}/${from_prefix}/${name}] -> ${to_prefix}/${name} ")
+
+  file(GLOB_RECURSE filenames
+    FOLLOW_SYMLINKS
+    LIST_DIRECTORIES FALSE
+    RELATIVE "${StdlibSources}/${from_prefix}"
+    "${StdlibSources}/${from_prefix}/${name}/*.swift"
+    "${StdlibSources}/${from_prefix}/${name}/*.h"
+    "${StdlibSources}/${from_prefix}/${name}/*.cpp"
+    "${StdlibSources}/${from_prefix}/${name}/*.c"
+    "${StdlibSources}/${from_prefix}/${name}/*.mm"
+    "${StdlibSources}/${from_prefix}/${name}/*.m"
+    "${StdlibSources}/${from_prefix}/${name}/*.def"
+    "${StdlibSources}/${from_prefix}/${name}/*.gyb"
+    "${StdlibSources}/${from_prefix}/${name}/*.apinotes"
+    "${StdlibSources}/${from_prefix}/${name}/*.yaml")
+
+  foreach(file ${filenames})
+    # Get and create the directory
+    get_filename_component(dirname ${file} DIRECTORY)
+    file(MAKE_DIRECTORY "${to_prefix}/${dirname}")
+    file(COPY_FILE
+      "${StdlibSources}/${from_prefix}/${file}"         # From
+      "${CMAKE_CURRENT_LIST_DIR}/${to_prefix}/${file}"  # To
+      RESULT _output
+      ONLY_IF_DIFFERENT)
+    if(_output)
+      message(SEND_ERROR
+        "Copy ${from_prefix}/${file} -> ${to_prefix}/${file} Failed: ${_output}")
+    endif()
+  endforeach()
+endfunction()
+
+# Directories in the existing standard library that make up the Core project
+
+# Copy shared core headers
+copy_library_sources(include "" "Core")
+
+set(CoreLibs
+  LLVMSupport)
+
+  # Add these as we get them building
+  # core
+  # Concurrency
+  # SwiftOnoneSUpport
+  # CommandLineSupport
+  # Demangling
+  # runtime)
+
+foreach(library ${CoreLibs})
+  copy_library_sources(${library} "public" "Core")
+endforeach()
+
+# TODO: Add source directories for the platform overlays, supplemental
+# libraries, and test support libraries.