Added support for loading Python at runtime (supports both Python 3 and 2) (#20674)

* Added new PythonLibrary struct to load Python library and symbols dynamically at runtime

- This adds support for both Python 3 and 2 with the same codebase.
- You can force a version of Python with the PYTHON_VERSION environment variable, a Python library path with PYTHON_LIBRARY and enable logging with PYTHON_LOADER_LOGGING.
- The implementation comes from the PythonKit Swift package (https://github.com/pvieito/PythonKit) removing the Foundation dependency.

* Style and structure changes

* Adding support for setting a Python version on-process

* Default minor version to nil

* Cleaned private method

* Update CMakeLists adding new files and removing CPython module

* Force setting an non-nil value type for Linux

* Redefined Python symbols to avoid libSyntax bug (SR-9316)

* Update tests

* `init(owning:)` should retain, while `init(borrowing:)` should not.

* Use loaded symbol values instead of their addresses as the type argument to `isType(_:type:)`.

* Make loaded symbols `let`s since they are themselves the address we need

* Minor clean-up.

- `()` -> `Void`.

- Drop parentheses at the result position from single-result function signatures.

- Replace !(==) with != in `isType(_:type:)`.

* Delete `_Py_TrueStructb`

* Fix ParsableInterface tests

Author: pvieito

stdlib/public/CMakeLists.txt

@@ -59,9 +59,7 @@ if(SWIFT_BUILD_STDLIB)
 endif()
 
 # SWIFT_ENABLE_TENSORFLOW
-find_package(PythonLibs 2.7 EXACT)
-if(SWIFT_BUILD_STDLIB AND PYTHONLIBS_FOUND)
-  add_subdirectory(CPython)
+if(SWIFT_BUILD_STDLIB)
   add_subdirectory(Python)
 endif()
 

stdlib/public/CPython/CMakeLists.txt

@@ -14,9 +14,6 @@
 #
 #===----------------------------------------------------------------------===#
 
-find_package(PythonLibs 2.7 EXACT REQUIRED)
-message(STATUS "Building Python.")
-
 set(SWIFT_PYTHON_EXISTS TRUE PARENT_SCOPE)
 
 set(SWIFT_SDK_OVERLAY_LIBRARY_BUILD_TYPES)
@@ -29,9 +26,10 @@ endif()
 
 add_swift_target_library(swiftPython ${SWIFT_SDK_OVERLAY_LIBRARY_BUILD_TYPES} IS_SDK_OVERLAY
   Python.swift
+  PythonLibrary.swift
+  PythonLibrary+Symbols.swift
   NumpyConversion.swift
 
-  DEPENDS cpython_modulemap
   TARGET_SDKS OSX CYGWIN FREEBSD LINUX HAIKU
   SWIFT_MODULE_DEPENDS_IOS Darwin
   SWIFT_MODULE_DEPENDS_OSX Darwin
@@ -42,5 +40,4 @@ add_swift_target_library(swiftPython ${SWIFT_SDK_OVERLAY_LIBRARY_BUILD_TYPES} IS
   SWIFT_MODULE_DEPENDS_CYGWIN Glibc
   SWIFT_MODULE_DEPENDS_HAIKU Glibc
   SWIFT_COMPILE_FLAGS "${SWIFT_RUNTIME_SWIFT_COMPILE_FLAGS}"
-  PRIVATE_LINK_LIBRARIES "${PYTHON_LIBRARIES}"
   LINK_FLAGS "${SWIFT_RUNTIME_SWIFT_LINK_FLAGS}")

stdlib/public/CPython/module.modulemap

@@ -2,7 +2,7 @@
 //
 // This source file is part of the Swift.org open source project
 //
-// Copyright (c) 2014 - 2017 Apple Inc. and the Swift project authors
+// Copyright (c) 2014 - 2018 Apple Inc. and the Swift project authors
 // Licensed under Apache License v2.0 with Runtime Library Exception
 //
 // See https://swift.org/LICENSE.txt for license information