view tests/test-histedit-base.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/histedit-helpers.sh"

  $ cat >> $HGRCPATH <<EOF
  > [alias]
  > tglog = log -G --template "{rev}:{node}:{phase} '{desc}'\n"
  > [extensions]
  > histedit=
  > EOF

Create repo a:

  $ hg init a
  $ cd a
  $ hg unbundle "$TESTDIR/bundles/rebase.hg"
  adding changesets
  adding manifests
  adding file changes
  added 8 changesets with 7 changes to 7 files (+2 heads)
  new changesets cd010b8cd998:02de42196ebe (8 drafts)
  (run 'hg heads' to see heads, 'hg merge' to merge)
  $ hg up tip
  3 files updated, 0 files merged, 0 files removed, 0 files unresolved

  $ hg tglog
  @  7:02de42196ebee42ef284b6780a87cdc96e8eaab6:draft 'H'
  |
  | o  6:eea13746799a9e0bfd88f29d3c2e9dc9389f524f:draft 'G'
  |/|
  o |  5:24b6387c8c8cae37178880f3fa95ded3cb1cf785:draft 'F'
  | |
  | o  4:9520eea781bcca16c1e15acc0ba14335a0e8e5ba:draft 'E'
  |/
  | o  3:32af7686d403cf45b5d95f2d70cebea587ac806a:draft 'D'
  | |
  | o  2:5fddd98957c8a54a4d436dfe1da9d87f21a1b97b:draft 'C'
  | |
  | o  1:42ccdea3bb16d28e1848c95fe2e44c000f3f21b1:draft 'B'
  |/
  o  0:cd010b8cd998f3981a5a8115f94f8da4ab506089:draft 'A'
  
Verify that implicit base command and help are listed

  $ HGEDITOR=cat hg histedit |grep base
  #  b, base = checkout changeset and apply further changesets from there

Go to D
  $ hg update 3
  3 files updated, 0 files merged, 2 files removed, 0 files unresolved
edit the history to rebase B onto H


Rebase B onto H
  $ hg histedit 1 --commands - 2>&1 << EOF | fixbundle
  > base 02de42196ebe
  > pick 42ccdea3bb16 B
  > pick 5fddd98957c8 C
  > pick 32af7686d403 D
  > EOF

  $ hg tglog
  @  7:0937e82309df47d14176ee15e45dbec5fbdef340:draft 'D'
  |
  o  6:f778d1cbddac4ab679d9983c9bb92e4c5e09e7fa:draft 'C'
  |
  o  5:3d41b7cc708545206213a842f96d812d2e73d818:draft 'B'
  |
  o  4:02de42196ebee42ef284b6780a87cdc96e8eaab6:draft 'H'
  |
  | o  3:eea13746799a9e0bfd88f29d3c2e9dc9389f524f:draft 'G'
  |/|
  o |  2:24b6387c8c8cae37178880f3fa95ded3cb1cf785:draft 'F'
  | |
  | o  1:9520eea781bcca16c1e15acc0ba14335a0e8e5ba:draft 'E'
  |/
  o  0:cd010b8cd998f3981a5a8115f94f8da4ab506089:draft 'A'
  
Rebase back and drop something
  $ hg histedit 5 --commands - 2>&1 << EOF | fixbundle
  > base cd010b8cd998
  > pick 3d41b7cc7085 B
  > drop f778d1cbddac C
  > pick 0937e82309df D
  > EOF

  $ hg tglog
  @  6:476cc3e4168da2d036b141f7f7dcff7f8e3fe846:draft 'D'
  |
  o  5:d273e35dcdf21a7eb305192ef2e362887cd0a6f8:draft 'B'
  |
  | o  4:02de42196ebee42ef284b6780a87cdc96e8eaab6:draft 'H'
  | |
  | | o  3:eea13746799a9e0bfd88f29d3c2e9dc9389f524f:draft 'G'
  | |/|
  | o |  2:24b6387c8c8cae37178880f3fa95ded3cb1cf785:draft 'F'
  |/ /
  | o  1:9520eea781bcca16c1e15acc0ba14335a0e8e5ba:draft 'E'
  |/
  o  0:cd010b8cd998f3981a5a8115f94f8da4ab506089:draft 'A'
  
Split stack
  $ hg histedit 5 --commands - 2>&1 << EOF | fixbundle
  > base cd010b8cd998
  > pick d273e35dcdf2 B
  > base cd010b8cd998
  > pick 476cc3e4168d D
  > EOF

  $ hg tglog
  @  6:d7a6f907a822c4ce6f15662ae45a42aa46d3818a:draft 'D'
  |
  | o  5:d273e35dcdf21a7eb305192ef2e362887cd0a6f8:draft 'B'
  |/
  | o  4:02de42196ebee42ef284b6780a87cdc96e8eaab6:draft 'H'
  | |
  | | o  3:eea13746799a9e0bfd88f29d3c2e9dc9389f524f:draft 'G'
  | |/|
  | o |  2:24b6387c8c8cae37178880f3fa95ded3cb1cf785:draft 'F'
  |/ /
  | o  1:9520eea781bcca16c1e15acc0ba14335a0e8e5ba:draft 'E'
  |/
  o  0:cd010b8cd998f3981a5a8115f94f8da4ab506089:draft 'A'
  
Abort
  $ echo x > B
  $ hg add B
  $ hg commit -m "X"
  $ hg tglog
  @  7:591369deedfdcbf57471e894999a70d7f676186d:draft 'X'
  |
  o  6:d7a6f907a822c4ce6f15662ae45a42aa46d3818a:draft 'D'
  |
  | o  5:d273e35dcdf21a7eb305192ef2e362887cd0a6f8:draft 'B'
  |/
  | o  4:02de42196ebee42ef284b6780a87cdc96e8eaab6:draft 'H'
  | |
  | | o  3:eea13746799a9e0bfd88f29d3c2e9dc9389f524f:draft 'G'
  | |/|
  | o |  2:24b6387c8c8cae37178880f3fa95ded3cb1cf785:draft 'F'
  |/ /
  | o  1:9520eea781bcca16c1e15acc0ba14335a0e8e5ba:draft 'E'
  |/
  o  0:cd010b8cd998f3981a5a8115f94f8da4ab506089:draft 'A'
  
  $ hg histedit 6 --commands - 2>&1 << EOF | fixbundle
  > base d273e35dcdf2 B
  > drop d7a6f907a822 D
  > pick 591369deedfd X
  > EOF
  merging B
  warning: conflicts while merging B! (edit, then use 'hg resolve --mark')
  Fix up the change (pick 591369deedfd)
  (hg histedit --continue to resume)
  $ hg histedit --abort | fixbundle
  2 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg tglog
  @  7:591369deedfdcbf57471e894999a70d7f676186d:draft 'X'
  |
  o  6:d7a6f907a822c4ce6f15662ae45a42aa46d3818a:draft 'D'
  |
  | o  5:d273e35dcdf21a7eb305192ef2e362887cd0a6f8:draft 'B'
  |/
  | o  4:02de42196ebee42ef284b6780a87cdc96e8eaab6:draft 'H'
  | |
  | | o  3:eea13746799a9e0bfd88f29d3c2e9dc9389f524f:draft 'G'
  | |/|
  | o |  2:24b6387c8c8cae37178880f3fa95ded3cb1cf785:draft 'F'
  |/ /
  | o  1:9520eea781bcca16c1e15acc0ba14335a0e8e5ba:draft 'E'
  |/
  o  0:cd010b8cd998f3981a5a8115f94f8da4ab506089:draft 'A'
  
Continue
  $ hg histedit 6 --commands - 2>&1 << EOF | fixbundle
  > base d273e35dcdf2 B
  > drop d7a6f907a822 D
  > pick 591369deedfd X
  > EOF
  merging B
  warning: conflicts while merging B! (edit, then use 'hg resolve --mark')
  Fix up the change (pick 591369deedfd)
  (hg histedit --continue to resume)
  $ echo b2 > B
  $ hg resolve --mark B
  (no more unresolved files)
  continue: hg histedit --continue
  $ hg histedit --continue | fixbundle
  $ hg tglog
  @  6:03772da75548bb42a8f1eacd8c91d0717a147fcd:draft 'X'
  |
  o  5:d273e35dcdf21a7eb305192ef2e362887cd0a6f8:draft 'B'
  |
  | o  4:02de42196ebee42ef284b6780a87cdc96e8eaab6:draft 'H'
  | |
  | | o  3:eea13746799a9e0bfd88f29d3c2e9dc9389f524f:draft 'G'
  | |/|
  | o |  2:24b6387c8c8cae37178880f3fa95ded3cb1cf785:draft 'F'
  |/ /
  | o  1:9520eea781bcca16c1e15acc0ba14335a0e8e5ba:draft 'E'
  |/
  o  0:cd010b8cd998f3981a5a8115f94f8da4ab506089:draft 'A'
  

base on a previously picked changeset
  $ echo i > i
  $ hg add i
  $ hg commit -m "I"
  $ echo j > j
  $ hg add j
  $ hg commit -m "J"
  $ hg tglog
  @  8:e8c55b19d366b335626e805484110d1d5f6f2ea3:draft 'J'
  |
  o  7:b2f90fd8aa85db5569e3cfc30cd1d7739546368e:draft 'I'
  |
  o  6:03772da75548bb42a8f1eacd8c91d0717a147fcd:draft 'X'
  |
  o  5:d273e35dcdf21a7eb305192ef2e362887cd0a6f8:draft 'B'
  |
  | o  4:02de42196ebee42ef284b6780a87cdc96e8eaab6:draft 'H'
  | |
  | | o  3:eea13746799a9e0bfd88f29d3c2e9dc9389f524f:draft 'G'
  | |/|
  | o |  2:24b6387c8c8cae37178880f3fa95ded3cb1cf785:draft 'F'
  |/ /
  | o  1:9520eea781bcca16c1e15acc0ba14335a0e8e5ba:draft 'E'
  |/
  o  0:cd010b8cd998f3981a5a8115f94f8da4ab506089:draft 'A'
  
  $ hg histedit 5 --commands - 2>&1 << EOF | fixbundle
  > pick d273e35dcdf2 B
  > pick 03772da75548 X
  > base d273e35dcdf2 B
  > pick e8c55b19d366 J
  > base d273e35dcdf2 B
  > pick b2f90fd8aa85 I
  > EOF
  hg: parse error: base "d273e35dcdf2" changeset was an edited list candidate
  (base must only use unlisted changesets)

  $ hg tglog
  @  8:e8c55b19d366b335626e805484110d1d5f6f2ea3:draft 'J'
  |
  o  7:b2f90fd8aa85db5569e3cfc30cd1d7739546368e:draft 'I'
  |
  o  6:03772da75548bb42a8f1eacd8c91d0717a147fcd:draft 'X'
  |
  o  5:d273e35dcdf21a7eb305192ef2e362887cd0a6f8:draft 'B'
  |
  | o  4:02de42196ebee42ef284b6780a87cdc96e8eaab6:draft 'H'
  | |
  | | o  3:eea13746799a9e0bfd88f29d3c2e9dc9389f524f:draft 'G'
  | |/|
  | o |  2:24b6387c8c8cae37178880f3fa95ded3cb1cf785:draft 'F'
  |/ /
  | o  1:9520eea781bcca16c1e15acc0ba14335a0e8e5ba:draft 'E'
  |/
  o  0:cd010b8cd998f3981a5a8115f94f8da4ab506089:draft 'A'