tests/printenv.py

files: speed up `hg files` when no flags change display

It's not the first time I see slowness from this command slow down
tools built on top of hg.

The majority of the time is spent merely printing the result before
this change, which is clearly not how it should be (especially since
the computation of the result also looks slow).

Running `hg files` in mozilla-central:

parent revision: 1,260s
this commit: 0,683s
this commit without batching ui.write: 0,931s
this commit replacing the body of the loop with `pass`: 0,566s

This looks like a prime candidate for a rust fast path, but until
then, it seems reasonable to optimize the python.

Differential Revision: https://phab.mercurial-scm.org/D8586

#!/usr/bin/env python
#
# simple script to be used in hooks
#
# put something like this in the repo .hg/hgrc:
#
#     [hooks]
#     changegroup = python "$TESTDIR/printenv.py" <hookname> [exit] [output]
#
#   - <hookname> is a mandatory argument (e.g. "changegroup")
#   - [exit] is the exit code of the hook (default: 0)
#   - [output] is the name of the output file (default: use sys.stdout)
#              the file will be opened in append mode.
#
from __future__ import absolute_import
import argparse
import os
import sys

try:
    import msvcrt

    msvcrt.setmode(sys.stdin.fileno(), os.O_BINARY)
    msvcrt.setmode(sys.stdout.fileno(), os.O_BINARY)
    msvcrt.setmode(sys.stderr.fileno(), os.O_BINARY)
except ImportError:
    pass

parser = argparse.ArgumentParser()
parser.add_argument("name", help="the hook name, used for display")
parser.add_argument(
    "exitcode",
    nargs="?",
    default=0,
    type=int,
    help="the exit code for the hook",
)
parser.add_argument(
    "out", nargs="?", default=None, help="where to write the output"
)
parser.add_argument(
    "--line",
    action="store_true",
    help="print environment variables one per line instead of on a single line",
)
args = parser.parse_args()

if args.out is None:
    out = sys.stdout
    out = getattr(out, "buffer", out)
else:
    out = open(args.out, "ab")

# variables with empty values may not exist on all platforms, filter
# them now for portability sake.
env = [(k, v) for k, v in os.environ.items() if k.startswith("HG_") and v]
env.sort()

out.write(b"%s hook: " % args.name.encode('ascii'))
if os.name == 'nt':
    filter = lambda x: x.replace('\\', '/')
else:
    filter = lambda x: x

vars = [
    b"%s=%s" % (k.encode('ascii'), filter(v).encode('ascii')) for k, v in env
]

# Print variables on out
if not args.line:
    out.write(b" ".join(vars))
else:
    for var in vars:
        out.write(var)
        out.write(b"\n")

out.write(b"\n")
out.close()

sys.exit(args.exitcode)