typing: add type hints to the `charencode` module

Since this module is dynamically imported from either `mercurial.pure` or
`mercurial.cext`, these hints aren't detected in `mercurial.encoding`, and need
to be imported directly there during the type-checking phase.  This keeps the
runtime selection via the policy config in place, but allows pytype to see these
as functions with proper signatures instead of just `Any`.  We don't attempt to
import the `mercurial.cext` version yet because there's no types stubs for that
module, but this will get the ball rolling.

I thought this would spill over into other modules from there, but the only two
*.pyi files that changed were for `encoding` and `charencode`.  Applying this to
other dynamically selected modules will clean some things up in other files, so
this is a start.  I had originally redefined the functions in the type-checking
block (like some of the `os.path` aliasing in `mercurial.util`), but this is
better because we won't have another duplication of the definitions that may get
out of date.

mercurial/encoding.py

@@ -40,6 +40,16 b' asciiupper = charencode.asciiupper'
 
 unichr = chr
 
+if typing.TYPE_CHECKING:
+    # TODO: make a stub file for .cext.charencode, and import here
+    from .pure.charencode import (
+        asciilower,
+        asciiupper,
+        isasciistr,
+        jsonescapeu8fast as _jsonescapeu8fast,
+    )
+
+
 # These unicode characters are ignored by HFS+ (Apple Technote 1150,
 # "Unicode Subtleties"), so we need to ignore them in some places for
 # sanity.
@@ -524,7 +534,7 b' class normcasespecs:'
     other = 0
 
 
-def jsonescape(s: Any, paranoid: Any = False) -> Any:
+def jsonescape(s: bytes, paranoid: bool = False) -> bytes:
     """returns a string suitable for JSON
 
     JSON is problematic for us because it doesn't support non-Unicode

mercurial/pure/charencode.py

@@ -11,7 +11,7 b' import array'
 from .. import pycompat
 
 
-def isasciistr(s):
+def isasciistr(s: bytes) -> bool:
     try:
         s.decode('ascii')
         return True
@@ -19,7 +19,7 b' def isasciistr(s):'
         return False
 
 
-def asciilower(s):
+def asciilower(s: bytes) -> bytes:
     """convert a string to lowercase if ASCII
 
     Raises UnicodeDecodeError if non-ASCII characters are found."""
@@ -27,7 +27,7 b' def asciilower(s):'
     return s.lower()
 
 
-def asciiupper(s):
+def asciiupper(s: bytes) -> bytes:
     """convert a string to uppercase if ASCII
 
     Raises UnicodeDecodeError if non-ASCII characters are found."""
@@ -52,7 +52,7 b' def asciiupper(s):'
 _jsonmap.extend(pycompat.bytechr(x) for x in range(128, 256))
 
 
-def jsonescapeu8fast(u8chars, paranoid):
+def jsonescapeu8fast(u8chars: bytes, paranoid: bool) -> bytes:
     """Convert a UTF-8 byte string to JSON-escaped form (fast path)
 
     Raises ValueError if non-ASCII characters have to be escaped.
@@ -70,7 +70,7 b' def jsonescapeu8fast(u8chars, paranoid):'
 _utf8strict = r'surrogatepass'
 
 
-def jsonescapeu8fallback(u8chars, paranoid):
+def jsonescapeu8fallback(u8chars: bytes, paranoid: bool) -> bytes:
     """Convert a UTF-8 byte string to JSON-escaped form (slow path)
 
     Escapes all non-ASCII characters no matter if paranoid is False.