view tests/test-imports-checker.t @ 44950:f9734b2d59cc

py3: make stdout line-buffered if connected to a TTY

Status messages that are to be shown on the terminal should be written to the
file descriptor before anything further is done, to keep the user updated.

One common way to achieve this is to make stdout line-buffered if it is
connected to a TTY. This is done on Python 2 (except on Windows, where libc,
which the CPython 2 streams depend on, does not properly support this).

Python 3 rolls it own I/O streams. On Python 3, buffered binary streams can't be
set line-buffered. The previous code (added in 227ba1afcb65) incorrectly
assumed that on Python 3, pycompat.stdout (sys.stdout.buffer) is already
line-buffered. However the interpreter initializes it with a block-buffered
stream or an unbuffered stream (when the -u option or the PYTHONUNBUFFERED
environment variable is set), never with a line-buffered stream.

One example where the current behavior is unacceptable is when running
`hg pull https://www.mercurial-scm.org/repo/hg` on Python 3, where the line
"pulling from https://www.mercurial-scm.org/repo/hg" does not appear on the
terminal before the hg process blocks while waiting for the server.

Various approaches to fix this problem are possible, including:

1. Weaken the contract of procutil.stdout to not give any guarantees about
   buffering behavior. In this case, users of procutil.stdout need to be
   changed to do enough flushes. In particular,
  1. either ui must insert enough flushes for ui.write() and friends, or
  2. ui.write() and friends get split into flushing and fully buffered
     methods, or
  3. users of ui.write() and friends must flush explicitly.
2. Make stdout unbuffered.
3. Make stdout line-buffered. Since Python 3 does not natively support that for
   binary streams, we must implement it ourselves.

(2.) is problematic because using unbuffered I/O changes the performance
characteristics significantly compared to line-buffered (which is used on
Python 2) and this would be a regression.

(1.2.) and (1.3) are a substantial amount of work. It’s unclear whether the
added complexity would be justified, given that raw performance doesn’t matter
that much when writing to a terminal much faster than the user could read it.

(1.1.) pushes complexity into the ui class instead of separating the concern of
how stdout is buffered. Other users of procutil.stdout would still need to take
care of the flushes.

This patch implements (3.). The general performance considerations are very
similar to (1.1.). The extra method invocation and method forwarding add a
little more overhead if the class is used. In exchange, it doesn’t add overhead
if not used.


For the benchmarks, I compared the previous implementation (incorrect on Python
3), (1.1.), (3.) and (2.). The command was chosen so that the streams were
configured as if they were writing to a TTY, but actually write to a pager,
which is also the default:
HGRCPATH=/dev/null python3 ./hg --cwd ~/vcs/mozilla-central --time --pager yes --config pager.pager='cat > /dev/null' status --all

previous:
time: real 7.880 secs (user 7.290+0.050 sys 0.580+0.170)
time: real 7.830 secs (user 7.220+0.070 sys 0.590+0.140)
time: real 7.800 secs (user 7.210+0.050 sys 0.570+0.170)

(1.1.) using Yuya Nishihara’s patch:
time: real 9.860 secs (user 8.670+0.350 sys 1.160+0.830)
time: real 9.540 secs (user 8.430+0.370 sys 1.100+0.770)
time: real 9.830 secs (user 8.630+0.370 sys 1.180+0.840)

(3.) using this patch:
time: real 9.580 secs (user 8.480+0.350 sys 1.090+0.770)
time: real 9.670 secs (user 8.480+0.330 sys 1.170+0.860)
time: real 9.640 secs (user 8.500+0.350 sys 1.130+0.810)

(2.) using a previous patch by me:
time: real 10.480 secs (user 8.850+0.720 sys 1.590+1.500)
time: real 10.490 secs (user 8.750+0.750 sys 1.710+1.470)
time: real 10.240 secs (user 8.600+0.700 sys 1.590+1.510)


As expected, there’s no difference on Python 2, as exactly the same code paths
are used:

previous:
time: real 6.950 secs (user 5.870+0.330 sys 1.070+0.770)
time: real 7.040 secs (user 6.040+0.360 sys 0.980+0.750)
time: real 7.070 secs (user 5.950+0.360 sys 1.100+0.760)

this patch:
time: real 7.010 secs (user 5.900+0.390 sys 1.070+0.730)
time: real 7.000 secs (user 5.850+0.350 sys 1.120+0.760)
time: real 7.000 secs (user 5.790+0.380 sys 1.170+0.710)

#require test-repo

  $ . "$TESTDIR/helpers-testrepo.sh"
  $ testrepohgenv
  $ import_checker="$TESTDIR"/../contrib/import-checker.py

Run the doctests from the import checker, and make sure
it's working correctly.
  $ TERM=dumb
  $ export TERM
  $ "$PYTHON" -m doctest $import_checker

Run additional tests for the import checker

  $ mkdir testpackage
  $ touch testpackage/__init__.py

  $ cat > testpackage/multiple.py << EOF
  > from __future__ import absolute_import
  > import os, sys
  > EOF

  $ cat > testpackage/unsorted.py << EOF
  > from __future__ import absolute_import
  > import sys
  > import os
  > EOF

  $ cat > testpackage/stdafterlocal.py << EOF
  > from __future__ import absolute_import
  > from . import unsorted
  > import os
  > EOF

  $ cat > testpackage/requirerelative.py << EOF
  > from __future__ import absolute_import
  > import testpackage.unsorted
  > EOF

  $ cat > testpackage/importalias.py << EOF
  > from __future__ import absolute_import
  > import ui
  > EOF

  $ cat > testpackage/relativestdlib.py << EOF
  > from __future__ import absolute_import
  > from .. import os
  > EOF

  $ cat > testpackage/stdlibfrom.py << EOF
  > from __future__ import absolute_import
  > from collections import abc
  > EOF

  $ cat > testpackage/symbolimport.py << EOF
  > from __future__ import absolute_import
  > from .unsorted import foo
  > EOF

  $ cat > testpackage/latesymbolimport.py << EOF
  > from __future__ import absolute_import
  > from . import unsorted
  > from mercurial.node import hex
  > EOF

  $ cat > testpackage/multiplegroups.py << EOF
  > from __future__ import absolute_import
  > from . import unsorted
  > from . import more
  > EOF

  $ mkdir testpackage/subpackage
  $ cat > testpackage/subpackage/levelpriority.py << EOF
  > from __future__ import absolute_import
  > from . import foo
  > from .. import parent
  > EOF

  $ touch testpackage/subpackage/foo.py
  $ cat > testpackage/subpackage/__init__.py << EOF
  > from __future__ import absolute_import
  > from . import levelpriority  # should not cause cycle
  > EOF

  $ cat > testpackage/subpackage/localimport.py << EOF
  > from __future__ import absolute_import
  > from . import foo
  > def bar():
  >     # should not cause "higher-level import should come first"
  >     from .. import unsorted
  >     # but other errors should be detected
  >     from .. import more
  >     import testpackage.subpackage.levelpriority
  > EOF

  $ cat > testpackage/importmodulefromsub.py << EOF
  > from __future__ import absolute_import
  > from .subpackage import foo  # not a "direct symbol import"
  > EOF

  $ cat > testpackage/importsymbolfromsub.py << EOF
  > from __future__ import absolute_import
  > from .subpackage import foo, nonmodule
  > EOF

  $ cat > testpackage/sortedentries.py << EOF
  > from __future__ import absolute_import
  > from . import (
  >     foo,
  >     bar,
  > )
  > EOF

  $ cat > testpackage/importfromalias.py << EOF
  > from __future__ import absolute_import
  > from . import ui
  > EOF

  $ cat > testpackage/importfromrelative.py << EOF
  > from __future__ import absolute_import
  > from testpackage.unsorted import foo
  > EOF

  $ mkdir testpackage2
  $ touch testpackage2/__init__.py

  $ cat > testpackage2/latesymbolimport.py << EOF
  > from __future__ import absolute_import
  > from testpackage import unsorted
  > from mercurial.node import hex
  > EOF

# Shadowing a stdlib module to test "relative import of stdlib module" is
# allowed if the module is also being checked

  $ mkdir email
  $ touch email/__init__.py
  $ touch email/errors.py
  $ cat > email/utils.py << EOF
  > from __future__ import absolute_import
  > from . import errors
  > EOF

  $ "$PYTHON" "$import_checker" testpackage*/*.py testpackage/subpackage/*.py \
  >   email/*.py
  testpackage/importalias.py:2: ui module must be "as" aliased to uimod
  testpackage/importfromalias.py:2: ui from testpackage must be "as" aliased to uimod
  testpackage/importfromrelative.py:2: import should be relative: testpackage.unsorted
  testpackage/importfromrelative.py:2: direct symbol import foo from testpackage.unsorted
  testpackage/importsymbolfromsub.py:2: direct symbol import nonmodule from testpackage.subpackage
  testpackage/latesymbolimport.py:3: symbol import follows non-symbol import: mercurial.node
  testpackage/multiple.py:2: multiple imported names: os, sys
  testpackage/multiplegroups.py:3: multiple "from . import" statements
  testpackage/relativestdlib.py:2: relative import of stdlib module
  testpackage/requirerelative.py:2: import should be relative: testpackage.unsorted
  testpackage/sortedentries.py:2: imports from testpackage not lexically sorted: bar < foo
  testpackage/stdafterlocal.py:3: stdlib import "os" follows local import: testpackage
  testpackage/stdlibfrom.py:2: direct symbol import abc from collections
  testpackage/subpackage/levelpriority.py:3: higher-level import should come first: testpackage
  testpackage/subpackage/localimport.py:7: multiple "from .. import" statements
  testpackage/subpackage/localimport.py:8: import should be relative: testpackage.subpackage.levelpriority
  testpackage/symbolimport.py:2: direct symbol import foo from testpackage.unsorted
  testpackage/unsorted.py:3: imports not lexically sorted: os < sys
  testpackage2/latesymbolimport.py:3: symbol import follows non-symbol import: mercurial.node
  [1]