view tests/test-rebuildstate.t @ 44118:f81c17ec303c

hgdemandimport: apply lazy module loading to sys.meta_path finders

Python's `sys.meta_path` finders are the primary objects whose job it
is to find a module at import time. When `import` is called, Python
iterates objects in this list and calls `o.find_spec(...)` to find
a `ModuleSpec` (or None if the module couldn't be found by that
finder). If no meta path finder can find a module, import fails.

One of the default meta path finders is `PathFinder`. Its job is to
import modules from the filesystem and is probably the most important
importer. This finder looks at `sys.path` and `sys.path_hooks` to do
its job.

The `ModuleSpec` returned by `MetaPathImporter.find_spec()` has a
`loader` attribute, which defines the concrete module loader to use.
`sys.path_hooks` is a hook point for teaching `PathFinder` to
instantiate custom loader types.

Previously, we injected a custom `sys.path_hook` that told `PathFinder`
to wrap the default loaders with a loader that creates a module object
that is lazy.

This approach worked. But its main limitation was that it only applied
to the `PathFinder` meta path importer. There are other meta path
importers that are registered. And in the case of PyOxidizer loading
modules from memory, `PathFinder` doesn't come into play since
PyOxidizer's own meta path importer was handling all imports.

This commit changes our approach to lazy module loading by proxying
all meta path importers. Specifically, we overload the `find_spec()`
method to swap in a wrapped loader on the `ModuleSpec` before it
is returned. The end result of this is all meta path importers should
be lazy.

As much as I would have loved to utilize .__class__ manipulation to
achieve this, some meta path importers are implemented in C/Rust
in such a way that they cannot be monkeypatched. This is why we
use __getattribute__ to define a proxy.

Also, this change could theoretically open us up to regressions in
meta path importers whose loader is creating module objects which
can't be monkeypatched. But I'm not aware of any of these in the
wild. So I think we'll be safe.

According to hyperfine, this change yields a decent startup time win of
5-6ms:

```
Benchmark #1: ~/.pyenv/versions/3.6.10/bin/python ./hg version
  Time (mean ± σ):      86.8 ms ±   0.5 ms    [User: 78.0 ms, System: 8.7 ms]
  Range (min … max):    86.0 ms …  89.1 ms    50 runs

  Time (mean ± σ):      81.1 ms ±   2.7 ms    [User: 74.5 ms, System: 6.5 ms]
  Range (min … max):    77.8 ms …  90.5 ms    50 runs

Benchmark #2: ~/.pyenv/versions/3.7.6/bin/python ./hg version
  Time (mean ± σ):      78.9 ms ±   0.6 ms    [User: 70.2 ms, System: 8.7 ms]
  Range (min … max):    78.1 ms …  81.2 ms    50 runs

  Time (mean ± σ):      73.4 ms ±   0.6 ms    [User: 65.3 ms, System: 8.0 ms]
  Range (min … max):    72.4 ms …  75.7 ms    50 runs

Benchmark #3: ~/.pyenv/versions/3.8.1/bin/python ./hg version
  Time (mean ± σ):      78.1 ms ±   0.6 ms    [User: 70.2 ms, System: 7.9 ms]
  Range (min … max):    77.4 ms …  80.9 ms    50 runs

  Time (mean ± σ):      72.1 ms ±   0.4 ms    [User: 64.4 ms, System: 7.6 ms]
  Range (min … max):    71.4 ms …  74.1 ms    50 runs
```

Differential Revision: https://phab.mercurial-scm.org/D7954

  $ cat > adddrop.py <<EOF
  > from mercurial import registrar
  > cmdtable = {}
  > command = registrar.command(cmdtable)
  > @command(b'debugadddrop',
  >   [(b'', b'drop', False, b'drop file from dirstate', b'FILE'),
  >    (b'', b'normal-lookup', False, b'add file to dirstate', b'FILE')],
  >     b'hg debugadddrop')
  > def debugadddrop(ui, repo, *pats, **opts):
  >   '''Add or drop unnamed arguments to or from the dirstate'''
  >   drop = opts.get('drop')
  >   nl = opts.get('normal_lookup')
  >   if nl and drop:
  >       raise error.Abort('drop and normal-lookup are mutually exclusive')
  >   wlock = repo.wlock()
  >   try:
  >     for file in pats:
  >       if opts.get('normal_lookup'):
  >         repo.dirstate.normallookup(file)
  >       else:
  >         repo.dirstate.drop(file)
  > 
  >     repo.dirstate.write(repo.currenttransaction())
  >   finally:
  >     wlock.release()
  > EOF

  $ echo "[extensions]" >> $HGRCPATH
  $ echo "debugadddrop=`pwd`/adddrop.py" >> $HGRCPATH

basic test for hg debugrebuildstate

  $ hg init repo
  $ cd repo

  $ touch foo bar
  $ hg ci -Am 'add foo bar'
  adding bar
  adding foo

  $ touch baz
  $ hg add baz
  $ hg rm bar

  $ hg debugrebuildstate

state dump after

  $ hg debugstate --no-dates | sort
  n   0         -1 unset               bar
  n   0         -1 unset               foo

  $ hg debugadddrop --normal-lookup file1 file2
  $ hg debugadddrop --drop bar
  $ hg debugadddrop --drop
  $ hg debugstate --no-dates
  n   0         -1 unset               file1
  n   0         -1 unset               file2
  n   0         -1 unset               foo
  $ hg debugrebuildstate

status

  $ hg st -A
  ! bar
  ? baz
  C foo

Test debugdirstate --minimal where a file is not in parent manifest
but in the dirstate
  $ touch foo bar qux
  $ hg add qux
  $ hg remove bar
  $ hg status -A
  A qux
  R bar
  ? baz
  C foo
  $ hg debugadddrop --normal-lookup baz
  $ hg debugdirstate --no-dates
  r   0          0 * bar (glob)
  n   0         -1 * baz (glob)
  n 644          0 * foo (glob)
  a   0         -1 * qux (glob)
  $ hg debugrebuilddirstate --minimal
  $ hg debugdirstate --no-dates
  r   0          0 * bar (glob)
  n 644          0 * foo (glob)
  a   0         -1 * qux (glob)
  $ hg status -A
  A qux
  R bar
  ? baz
  C foo

Test debugdirstate --minimal where file is in the parent manifest but not the
dirstate
  $ hg manifest
  bar
  foo
  $ hg status -A
  A qux
  R bar
  ? baz
  C foo
  $ hg debugdirstate --no-dates
  r   0          0 * bar (glob)
  n 644          0 * foo (glob)
  a   0         -1 * qux (glob)
  $ hg debugadddrop --drop foo
  $ hg debugdirstate --no-dates
  r   0          0 * bar (glob)
  a   0         -1 * qux (glob)
  $ hg debugrebuilddirstate --minimal
  $ hg debugdirstate --no-dates
  r   0          0 * bar (glob)
  n   0         -1 * foo (glob)
  a   0         -1 * qux (glob)
  $ hg status -A
  A qux
  R bar
  ? baz
  C foo