py3: add "b" prefix to string literals related to module policy

String literals without explicit prefix in __init__.py and policy.py
are treated as unicode object on Python3, because these modules are
loaded before setup of our specific code transformation (the later
module is imported at the beginning of __init__.py).

BTW, "modulepolicy" in __init__.py is initialized by "policy.policy".

This causes issues below;

  - checking "policy" value in other modules causes unintentional result

    For example, "b'py' not in (u'c', u'py')" returns True
    unintentionally on Python3.

  - writing "policy" out fails at conversion from unicode to bytes

    62939e0148f1 fixed this issue for default code path, but "policy"
    can be overridden by HGMODULEPOLICY environment variable (it should
    be rare case for developer using Python3, though).

This patch does:

  - add "b" prefix to all string literals, which are related to module
    policy, in modules above.

  - check existence of HGMODULEPOLICY, and overwrite "policy" only if
    it exists

    For simplicity, this patch omits checking "supports_bytes_environ",
    switching os.environ/os.environb, and so on (Yuya agreed this in
    personal talking)

mercurial/__init__.py

@@ -68,7 +68,7 b' class hgimporter(object):'
                 # indicates the type of module. So just assume what we found
                 # is OK (even though it could be a pure Python module).
             except ImportError:
-                if modulepolicy == 'c':
+                if modulepolicy == b'c':
                     raise
                 zl = ziploader('mercurial', 'pure')
                 mod = zl.load_module(name)
@@ -106,7 +106,7 b' class hgimporter(object):'
                                   'version should exist' % name)
 
         except ImportError:
-            if modulepolicy == 'c':
+            if modulepolicy == b'c':
                 raise
 
             # Could not load the C extension and pure Python is allowed. So

mercurial/policy.py

@@ -19,9 +19,9 b' import sys'
 #    py - only load pure Python modules
 #
 # By default, require the C extensions for performance reasons.
-policy = 'c'
-policynoc = ('cffi', 'cffi-allow', 'py')
-policynocffi = ('c', 'py')
+policy = b'c'
+policynoc = (b'cffi', b'cffi-allow', b'py')
+policynocffi = (b'c', b'py')
 
 try:
     from . import __modulepolicy__
@@ -42,4 +42,8 b' if sys.version_info[0] >= 3:'
     policy = b'py'
 
 # Environment variable can always force settings.
-policy = os.environ.get('HGMODULEPOLICY', policy)
+if sys.version_info[0] >= 3:
+    if 'HGMODULEPOLICY' in os.environ:
+        policy = os.environ['HGMODULEPOLICY'].encode('utf-8')
+else:
+    policy = os.environ.get('HGMODULEPOLICY', policy)

tests/test-check-code.t

@@ -27,8 +27,14 b' New errors are not allowed. Warnings are'
    use encoding.environ instead (py3)
   Skipping mercurial/httpclient/__init__.py it has no-che?k-code (glob)
   Skipping mercurial/httpclient/_readers.py it has no-che?k-code (glob)
-  mercurial/policy.py:45:
-   > policy = os.environ.get('HGMODULEPOLICY', policy)
+  mercurial/policy.py:46:
+   >     if 'HGMODULEPOLICY' in os.environ:
+   use encoding.environ instead (py3)
+  mercurial/policy.py:47:
+   >         policy = os.environ['HGMODULEPOLICY'].encode('utf-8')
+   use encoding.environ instead (py3)
+  mercurial/policy.py:49:
+   >     policy = os.environ.get('HGMODULEPOLICY', policy)
    use encoding.environ instead (py3)
   Skipping mercurial/statprof.py it has no-che?k-code (glob)
   [1]

tests/test-check-py3-commands.t

@@ -23,3 +23,10 b' The full traceback is hidden to have a s'
   $ $PYTHON3 `which hg` version | tail -1
   *** failed to import extension babar from imaginary_elephant: *: 'imaginary_elephant' (glob)
   warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+
+Test bytes-ness of policy.policy with HGMODULEPOLICY
+
+  $ HGMODULEPOLICY=py
+  $ export HGMODULEPOLICY
+  $ $PYTHON3 `which hg` debuginstall 2>&1 2>&1 | tail -1
+  no problems detected