hook: move stdio redirection to context manager

The old code was checking stdio redirection in a loop.
This didn't make sense. The pattern is better expressed
as a context manager IMO, so this commit refactors it
to be one.

Differential Revision: https://phab.mercurial-scm.org/D8338

mercurial/hook.py

@@ -1,326 +1,336
 # hook.py - hook support for mercurial
 #
 # Copyright 2007 Matt Mackall <[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
 
+import contextlib
 import os
 import sys
 
 from .i18n import _
 from .pycompat import getattr
 from . import (
     demandimport,
     encoding,
     error,
     extensions,
     pycompat,
     util,
 )
 from .utils import (
     procutil,
     resourceutil,
     stringutil,
 )
 
 
 def pythonhook(ui, repo, htype, hname, funcname, args, throw):
     '''call python hook. hook is callable object, looked up as
     name in python module. if callable returns "true", hook
     fails, else passes. if hook raises exception, treated as
     hook failure. exception propagates if throw is "true".
 
     reason for "true" meaning "hook failed" is so that
     unmodified commands (e.g. mercurial.commands.update) can
     be run as hooks without wrappers to convert return values.'''
 
     if callable(funcname):
         obj = funcname
         funcname = pycompat.sysbytes(obj.__module__ + "." + obj.__name__)
     else:
         d = funcname.rfind(b'.')
         if d == -1:
             raise error.HookLoadError(
                 _(b'%s hook is invalid: "%s" not in a module')
                 % (hname, funcname)
             )
         modname = funcname[:d]
         oldpaths = sys.path
         if resourceutil.mainfrozen():
             # binary installs require sys.path manipulation
             modpath, modfile = os.path.split(modname)
             if modpath and modfile:
                 sys.path = sys.path[:] + [modpath]
                 modname = modfile
         with demandimport.deactivated():
             try:
                 obj = __import__(pycompat.sysstr(modname))
             except (ImportError, SyntaxError):
                 e1 = sys.exc_info()
                 try:
                     # extensions are loaded with hgext_ prefix
                     obj = __import__("hgext_%s" % pycompat.sysstr(modname))
                 except (ImportError, SyntaxError):
                     e2 = sys.exc_info()
                     if ui.tracebackflag:
                         ui.warn(
                             _(
                                 b'exception from first failed import '
                                 b'attempt:\n'
                             )
                         )
                     ui.traceback(e1)
                     if ui.tracebackflag:
                         ui.warn(
                             _(
                                 b'exception from second failed import '
                                 b'attempt:\n'
                             )
                         )
                     ui.traceback(e2)
 
                     if not ui.tracebackflag:
                         tracebackhint = _(
                             b'run with --traceback for stack trace'
                         )
                     else:
                         tracebackhint = None
                     raise error.HookLoadError(
                         _(b'%s hook is invalid: import of "%s" failed')
                         % (hname, modname),
                         hint=tracebackhint,
                     )
         sys.path = oldpaths
         try:
             for p in funcname.split(b'.')[1:]:
                 obj = getattr(obj, p)
         except AttributeError:
             raise error.HookLoadError(
                 _(b'%s hook is invalid: "%s" is not defined')
                 % (hname, funcname)
             )
         if not callable(obj):
             raise error.HookLoadError(
                 _(b'%s hook is invalid: "%s" is not callable')
                 % (hname, funcname)
             )
 
     ui.note(_(b"calling hook %s: %s\n") % (hname, funcname))
     starttime = util.timer()
 
     try:
         r = obj(ui=ui, repo=repo, hooktype=htype, **pycompat.strkwargs(args))
     except Exception as exc:
         if isinstance(exc, error.Abort):
             ui.warn(_(b'error: %s hook failed: %s\n') % (hname, exc.args[0]))
         else:
             ui.warn(
                 _(b'error: %s hook raised an exception: %s\n')
                 % (hname, stringutil.forcebytestr(exc))
             )
         if throw:
             raise
         if not ui.tracebackflag:
             ui.warn(_(b'(run with --traceback for stack trace)\n'))
         ui.traceback()
         return True, True
     finally:
         duration = util.timer() - starttime
         ui.log(
             b'pythonhook',
             b'pythonhook-%s: %s finished in %0.2f seconds\n',
             htype,
             funcname,
             duration,
         )
     if r:
         if throw:
             raise error.HookAbort(_(b'%s hook failed') % hname)
         ui.warn(_(b'warning: %s hook failed\n') % hname)
     return r, False
 
 
 def _exthook(ui, repo, htype, name, cmd, args, throw):
     starttime = util.timer()
     env = {}
 
     # make in-memory changes visible to external process
     if repo is not None:
         tr = repo.currenttransaction()
         repo.dirstate.write(tr)
         if tr and tr.writepending():
             env[b'HG_PENDING'] = repo.root
     env[b'HG_HOOKTYPE'] = htype
     env[b'HG_HOOKNAME'] = name
 
     for k, v in pycompat.iteritems(args):
         if callable(v):
             v = v()
         if isinstance(v, (dict, list)):
             v = stringutil.pprint(v)
         env[b'HG_' + k.upper()] = v
 
     if ui.configbool(b'hooks', b'tonative.%s' % name, False):
         oldcmd = cmd
         cmd = procutil.shelltonative(cmd, env)
         if cmd != oldcmd:
             ui.note(_(b'converting hook "%s" to native\n') % name)
 
     ui.note(_(b"running hook %s: %s\n") % (name, cmd))
 
     if repo:
         cwd = repo.root
     else:
         cwd = encoding.getcwd()
     r = ui.system(cmd, environ=env, cwd=cwd, blockedtag=b'exthook-%s' % (name,))
 
     duration = util.timer() - starttime
     ui.log(
         b'exthook',
         b'exthook-%s: %s finished in %0.2f seconds\n',
         name,
         cmd,
         duration,
     )
     if r:
         desc = procutil.explainexit(r)
         if throw:
             raise error.HookAbort(_(b'%s hook %s') % (name, desc))
         ui.warn(_(b'warning: %s hook %s\n') % (name, desc))
     return r
 
 
 # represent an untrusted hook command
 _fromuntrusted = object()
 
 
 def _allhooks(ui):
     """return a list of (hook-id, cmd) pairs sorted by priority"""
     hooks = _hookitems(ui)
     # Be careful in this section, propagating the real commands from untrusted
     # sources would create a security vulnerability, make sure anything altered
     # in that section uses "_fromuntrusted" as its command.
     untrustedhooks = _hookitems(ui, _untrusted=True)
     for name, value in untrustedhooks.items():
         trustedvalue = hooks.get(name, (None, None, name, _fromuntrusted))
         if value != trustedvalue:
             (lp, lo, lk, lv) = trustedvalue
             hooks[name] = (lp, lo, lk, _fromuntrusted)
     # (end of the security sensitive section)
     return [(k, v) for p, o, k, v in sorted(hooks.values())]
 
 
 def _hookitems(ui, _untrusted=False):
     """return all hooks items ready to be sorted"""
     hooks = {}
     for name, cmd in ui.configitems(b'hooks', untrusted=_untrusted):
         if name.startswith(b'priority.') or name.startswith(b'tonative.'):
             continue
 
         priority = ui.configint(b'hooks', b'priority.%s' % name, 0)
         hooks[name] = (-priority, len(hooks), name, cmd)
     return hooks
 
 
 _redirect = False
 
 
 def redirect(state):
     global _redirect
     _redirect = state
 
 
 def hashook(ui, htype):
     """return True if a hook is configured for 'htype'"""
     if not ui.callhooks:
         return False
     for hname, cmd in _allhooks(ui):
         if hname.split(b'.')[0] == htype and cmd:
             return True
     return False
 
 
 def hook(ui, repo, htype, throw=False, **args):
     if not ui.callhooks:
         return False
 
     hooks = []
     for hname, cmd in _allhooks(ui):
         if hname.split(b'.')[0] == htype and cmd:
             hooks.append((hname, cmd))
 
     res = runhooks(ui, repo, htype, hooks, throw=throw, **args)
     r = False
     for hname, cmd in hooks:
         r = res[hname][0] or r
     return r
 
 
[e-mail]
+def redirect_stdio():
+    """Redirects stdout to stderr, if possible."""
+
+    oldstdout = -1
+    try:
+        if _redirect:
+            try:
+                stdoutno = procutil.stdout.fileno()
+                stderrno = procutil.stderr.fileno()
+                # temporarily redirect stdout to stderr, if possible
+                if stdoutno >= 0 and stderrno >= 0:
+                    procutil.stdout.flush()
+                    oldstdout = os.dup(stdoutno)
+                    os.dup2(stderrno, stdoutno)
+            except (OSError, AttributeError):
+                # files seem to be bogus, give up on redirecting (WSGI, etc)
+                pass
+
+        yield
+
+    finally:
+        # The stderr is fully buffered on Windows when connected to a pipe.
+        # A forcible flush is required to make small stderr data in the
+        # remote side available to the client immediately.
+        procutil.stderr.flush()
+
+        if _redirect and oldstdout >= 0:
+            procutil.stdout.flush()  # write hook output to stderr fd
+            os.dup2(oldstdout, stdoutno)
+            os.close(oldstdout)
+
+
 def runhooks(ui, repo, htype, hooks, throw=False, **args):
     args = pycompat.byteskwargs(args)
     res = {}
-    oldstdout = -1
 
-    try:
+    with redirect_stdio():
         for hname, cmd in hooks:
-            if oldstdout == -1 and _redirect:
-                try:
-                    stdoutno = procutil.stdout.fileno()
-                    stderrno = procutil.stderr.fileno()
-                    # temporarily redirect stdout to stderr, if possible
-                    if stdoutno >= 0 and stderrno >= 0:
-                        procutil.stdout.flush()
-                        oldstdout = os.dup(stdoutno)
-                        os.dup2(stderrno, stdoutno)
-                except (OSError, AttributeError):
-                    # files seem to be bogus, give up on redirecting (WSGI, etc)
-                    pass
-
             if cmd is _fromuntrusted:
                 if throw:
                     raise error.HookAbort(
                         _(b'untrusted hook %s not executed') % hname,
                         hint=_(b"see 'hg help config.trusted'"),
                     )
                 ui.warn(_(b'warning: untrusted hook %s not executed\n') % hname)
                 r = 1
                 raised = False
             elif callable(cmd):
                 r, raised = pythonhook(ui, repo, htype, hname, cmd, args, throw)
             elif cmd.startswith(b'python:'):
                 if cmd.count(b':') >= 2:
                     path, cmd = cmd[7:].rsplit(b':', 1)
                     path = util.expandpath(path)
                     if repo:
                         path = os.path.join(repo.root, path)
                     try:
                         mod = extensions.loadpath(path, b'hghook.%s' % hname)
                     except Exception:
                         ui.write(_(b"loading %s hook failed:\n") % hname)
                         raise
                     hookfn = getattr(mod, cmd)
                 else:
                     hookfn = cmd[7:].strip()
                 r, raised = pythonhook(
                     ui, repo, htype, hname, hookfn, args, throw
                 )
             else:
                 r = _exthook(ui, repo, htype, hname, cmd, args, throw)
                 raised = False
 
             res[hname] = r, raised
-    finally:
-        # The stderr is fully buffered on Windows when connected to a pipe.
-        # A forcible flush is required to make small stderr data in the
-        # remote side available to the client immediately.
-        procutil.stderr.flush()
-
-        if _redirect and oldstdout >= 0:
-            procutil.stdout.flush()  # write hook output to stderr fd
-            os.dup2(oldstdout, stdoutno)
-            os.close(oldstdout)
 
     return res