check-py3-compat: manually format and print warnings

The warnings mechanism may print to stderr on Python 3. Independent buffering
of stdout and stderr can lead to warnings output not being printed properly.

This commit traps warnings when executing individual files and prints
warnings to stdout so output is deterministic.

Differential Revision: https://phab.mercurial-scm.org/D5845

contrib/check-py3-compat.py

@@ -1,96 +1,102 b''
 #!/usr/bin/env python
 #
 # check-py3-compat - check Python 3 compatibility of Mercurial files
 #
 # Copyright 2015 Gregory Szorc <[e-mail]>
 #
 # This software may be used and distributed according to the terms of the
 # GNU General Public License version 2 or any later version.
 
 from __future__ import absolute_import, print_function
 
 import ast
 import importlib
 import os
 import sys
 import traceback
+import warnings
 
 def check_compat_py2(f):
     """Check Python 3 compatibility for a file with Python 2"""
     with open(f, 'rb') as fh:
         content = fh.read()
     root = ast.parse(content)
 
     # Ignore empty files.
     if not root.body:
         return
 
     futures = set()
     haveprint = False
     for node in ast.walk(root):
         if isinstance(node, ast.ImportFrom):
             if node.module == '__future__':
                 futures |= set(n.name for n in node.names)
         elif isinstance(node, ast.Print):
             haveprint = True
 
     if 'absolute_import' not in futures:
         print('%s not using absolute_import' % f)
     if haveprint and 'print_function' not in futures:
         print('%s requires print_function' % f)
 
 def check_compat_py3(f):
     """Check Python 3 compatibility of a file with Python 3."""
     with open(f, 'rb') as fh:
         content = fh.read()
 
     try:
         ast.parse(content, filename=f)
     except SyntaxError as e:
         print('%s: invalid syntax: %s' % (f, e))
         return
 
     # Try to import the module.
     # For now we only support modules in packages because figuring out module
     # paths for things not in a package can be confusing.
     if (f.startswith(('hgdemandimport/', 'hgext/', 'mercurial/'))
         and not f.endswith('__init__.py')):
         assert f.endswith('.py')
         name = f.replace('/', '.')[:-3]
         try:
             importlib.import_module(name)
         except Exception as e:
             exc_type, exc_value, tb = sys.exc_info()
             # We walk the stack and ignore frames from our custom importer,
             # import mechanisms, and stdlib modules. This kinda/sorta
             # emulates CPython behavior in import.c while also attempting
             # to pin blame on a Mercurial file.
             for frame in reversed(traceback.extract_tb(tb)):
                 if frame.name == '_call_with_frames_removed':
                     continue
                 if 'importlib' in frame.filename:
                     continue
                 if 'mercurial/__init__.py' in frame.filename:
                     continue
                 if frame.filename.startswith(sys.prefix):
                     continue
                 break
 
             if frame.filename:
                 filename = os.path.basename(frame.filename)
                 print('%s: error importing: <%s> %s (error at %s:%d)' % (
                       f, type(e).__name__, e, filename, frame.lineno))
             else:
                 print('%s: error importing module: <%s> %s (line %d)' % (
                       f, type(e).__name__, e, frame.lineno))
 
 if __name__ == '__main__':
     if sys.version_info[0] == 2:
         fn = check_compat_py2
     else:
         fn = check_compat_py3
 
     for f in sys.argv[1:]:
-        fn(f)
+        with warnings.catch_warnings(record=True) as warns:
+            fn(f)
+
+        for w in warns:
+            print(warnings.formatwarning(w.message, w.category,
+                                         w.filename, w.lineno).rstrip())
 
     sys.exit(0)