view tests/test-narrow-clone-no-ellipsis.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

  $ . "$TESTDIR/narrow-library.sh"

  $ hg init master
  $ cd master
  $ mkdir dir
  $ mkdir dir/src
  $ cd dir/src
  $ for x in `$TESTDIR/seq.py 20`; do echo $x > "f$x"; hg add "f$x"; hg commit -m "Commit src $x"; done
  $ cd ..
  $ mkdir tests
  $ cd tests
  $ for x in `$TESTDIR/seq.py 20`; do echo $x > "t$x"; hg add "t$x"; hg commit -m "Commit test $x"; done
  $ cd ../../..

narrow clone a file, f10

  $ hg clone --narrow ssh://user@dummy/master narrow --noupdate --include "dir/src/f10"
  requesting all changes
  adding changesets
  adding manifests
  adding file changes
  added 40 changesets with 1 changes to 1 files
  new changesets *:* (glob)
  $ cd narrow
  $ cat .hg/requires | grep -v generaldelta
  dotencode
  fncache
  narrowhg-experimental
  revlogv1
  sparserevlog
  store
  testonly-simplestore (reposimplestore !)

  $ hg tracked
  I path:dir/src/f10
  $ hg update
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ find * | sort
  dir
  dir/src
  dir/src/f10
  $ cat dir/src/f10
  10

  $ cd ..

narrow clone a directory, tests/, except tests/t19

  $ hg clone --narrow ssh://user@dummy/master narrowdir --noupdate --include "dir/tests/" --exclude "dir/tests/t19"
  requesting all changes
  adding changesets
  adding manifests
  adding file changes
  added 40 changesets with 19 changes to 19 files
  new changesets *:* (glob)
  $ cd narrowdir
  $ hg tracked
  I path:dir/tests
  X path:dir/tests/t19
  $ hg update
  19 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ find * | sort
  dir
  dir/tests
  dir/tests/t1
  dir/tests/t10
  dir/tests/t11
  dir/tests/t12
  dir/tests/t13
  dir/tests/t14
  dir/tests/t15
  dir/tests/t16
  dir/tests/t17
  dir/tests/t18
  dir/tests/t2
  dir/tests/t20
  dir/tests/t3
  dir/tests/t4
  dir/tests/t5
  dir/tests/t6
  dir/tests/t7
  dir/tests/t8
  dir/tests/t9

  $ cd ..

narrow clone everything but a directory (tests/)

  $ hg clone --narrow ssh://user@dummy/master narrowroot --noupdate --exclude "dir/tests"
  requesting all changes
  adding changesets
  adding manifests
  adding file changes
  added 40 changesets with 20 changes to 20 files
  new changesets *:* (glob)
  $ cd narrowroot
  $ hg tracked
  I path:.
  X path:dir/tests
  $ hg update
  20 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ find * | sort
  dir
  dir/src
  dir/src/f1
  dir/src/f10
  dir/src/f11
  dir/src/f12
  dir/src/f13
  dir/src/f14
  dir/src/f15
  dir/src/f16
  dir/src/f17
  dir/src/f18
  dir/src/f19
  dir/src/f2
  dir/src/f20
  dir/src/f3
  dir/src/f4
  dir/src/f5
  dir/src/f6
  dir/src/f7
  dir/src/f8
  dir/src/f9

  $ cd ..

Testing the --narrowspec flag to clone

  $ cat >> narrowspecs <<EOF
  > %include foo
  > [include]
  > path:dir/tests/
  > path:dir/src/f12
  > EOF

  $ hg clone ssh://user@dummy/master specfile --narrowspec narrowspecs
  reading narrowspec from '$TESTTMP/narrowspecs'
  abort: cannot specify other files using '%include' in narrowspec
  [255]

  $ cat > narrowspecs <<EOF
  > [include]
  > path:dir/tests/
  > path:dir/src/f12
  > EOF

  $ hg clone ssh://user@dummy/master specfile --narrowspec narrowspecs
  reading narrowspec from '$TESTTMP/narrowspecs'
  requesting all changes
  adding changesets
  adding manifests
  adding file changes
  added 40 changesets with 21 changes to 21 files
  new changesets 681085829a73:26ce255d5b5d
  updating to branch default
  21 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ cd specfile
  $ hg tracked
  I path:dir/src/f12
  I path:dir/tests
  $ cd ..