[Macros] Update executable plugin test to use the python running 'lit'

Also, update 'mock_plugin.py' to support python2

rdar://105870339

Author: rintaro

test/Macros/macro_plugin_basic.swift

@@ -1,11 +1,10 @@
-// REQUIRES: rdar105870339
 // REQUIRES: OS=macosx
 
 // RUN: %empty-directory(%t)
 // RUN: split-file %s %t
 
-// RUN: sed -i '' -e 's#UTILS_DIR#%utils#' %t/plugin
-// RUN: sed -i '' -e 's#TEMP_DIR#%t#' %t/plugin
+// RUN: sed -i '' -e 's#PYTHON_EXEC_PATH#%{python}#' %t/plugin
+// RUN: sed -i '' -e 's#UTILS_DIR_PATH#%utils#' %t/plugin
 // RUN: chmod +x %t/plugin
 
 // RUN: %swift-target-frontend -typecheck -verify -swift-version 5 -enable-experimental-feature Macros -load-plugin-executable %t/plugin#TestPlugin %t/test.swift
@@ -21,9 +20,9 @@ func test() {
 }
 
 //--- plugin
-#!/usr/bin/env python3
+#!PYTHON_EXEC_PATH
 import sys
-sys.path.append('UTILS_DIR')
+sys.path.append('UTILS_DIR_PATH')
 
 import mock_plugin
 

utils/mock_plugin.py

@@ -98,14 +98,21 @@ def handle_request(req):
 
 
 def main():
+    if sys.version_info >= (3, 0):
+        stdin = sys.stdin.buffer
+        stdout = sys.stdout.buffer
+    else:
+        stdin = sys.stdin
+        stdout = sys.stdout
+
     # Message handling loop.
     while True:
         # Read request
-        request_header = sys.stdin.buffer.read(8)
+        request_header = stdin.read(8)
         if len(request_header) < 8:
             break
         request_size = struct.unpack('<Q', request_header)[0]
-        request_data = sys.stdin.buffer.read(request_size)
+        request_data = stdin.read(request_size)
         if len(request_data) != request_size:
             break
         request_object = json.loads(request_data)
@@ -118,9 +125,9 @@ def main():
         response_data = response_json.encode('utf-8')
         response_size = len(response_data)
         response_header = struct.pack('<Q', response_size)
-        sys.stdout.buffer.write(response_header)
-        sys.stdout.buffer.write(response_data)
-        sys.stdout.buffer.flush()
+        stdout.write(response_header)
+        stdout.write(response_data)
+        stdout.flush()
 
 
 if __name__ == '__main__':