view tests/test-convert-cvs-synthetic.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

#require cvs112

This feature requires use of builtin cvsps!

  $ echo "[extensions]" >> $HGRCPATH
  $ echo "convert = " >> $HGRCPATH

create cvs repository with one project

  $ mkdir cvsrepo
  $ cd cvsrepo
  $ CVSROOT=`pwd`
  $ export CVSROOT
  $ CVS_OPTIONS=-f
  $ export CVS_OPTIONS
  $ cd ..
  $ rmdir cvsrepo
  $ cvscall()
  > {
  >     cvs -f "$@"
  > }

output of 'cvs ci' varies unpredictably, so just discard it

  $ cvsci()
  > {
  >     sleep 1
  >     cvs -f ci "$@" >/dev/null
  > }
  $ cvscall -d "$CVSROOT" init
  $ mkdir cvsrepo/proj
  $ cvscall -q co proj

create file1 on the trunk

  $ cd proj
  $ touch file1
  $ cvscall -Q add file1
  $ cvsci -m"add file1 on trunk" file1

create two branches

  $ cvscall -q tag -b v1_0
  T file1
  $ cvscall -q tag -b v1_1
  T file1

create file2 on branch v1_0

  $ cvscall -Q up -rv1_0
  $ touch file2
  $ cvscall -Q add file2
  $ cvsci -m"add file2" file2

create file3, file4 on branch v1_1

  $ cvscall -Q up -rv1_1
  $ touch file3
  $ touch file4
  $ cvscall -Q add file3 file4
  $ cvsci -m"add file3, file4 on branch v1_1" file3 file4

merge file2 from v1_0 to v1_1

  $ cvscall -Q up -jv1_0
  $ cvsci -m"MERGE from v1_0: add file2"
  cvs commit: Examining .

Step things up a notch: now we make the history really hairy, with
changes bouncing back and forth between trunk and v1_2 and merges
going both ways.  (I.e., try to model the real world.)
create branch v1_2

  $ cvscall -Q up -A
  $ cvscall -q tag -b v1_2
  T file1

create file5 on branch v1_2

  $ cvscall -Q up -rv1_2
  $ touch file5
  $ cvs -Q add file5
  $ cvsci -m"add file5 on v1_2"
  cvs commit: Examining .

create file6 on trunk post-v1_2

  $ cvscall -Q up -A
  $ touch file6
  $ cvscall -Q add file6
  $ cvsci -m"add file6 on trunk post-v1_2"
  cvs commit: Examining .

merge file5 from v1_2 to trunk

  $ cvscall -Q up -A
  $ cvscall -Q up -jv1_2 file5
  $ cvsci -m"MERGE from v1_2: add file5"
  cvs commit: Examining .

merge file6 from trunk to v1_2

  $ cvscall -Q up -rv1_2
  $ cvscall up -jHEAD file6
  U file6
  $ cvsci -m"MERGE from HEAD: add file6"
  cvs commit: Examining .

cvs rlog output

  $ cvscall -q rlog proj | egrep '^(RCS file|revision)'
  RCS file: $TESTTMP/cvsrepo/proj/file1,v
  revision 1.1
  RCS file: $TESTTMP/cvsrepo/proj/Attic/file2,v
  revision 1.1
  revision 1.1.4.2
  revision 1.1.4.1
  revision 1.1.2.1
  RCS file: $TESTTMP/cvsrepo/proj/Attic/file3,v
  revision 1.1
  revision 1.1.2.1
  RCS file: $TESTTMP/cvsrepo/proj/Attic/file4,v
  revision 1.1
  revision 1.1.2.1
  RCS file: $TESTTMP/cvsrepo/proj/file5,v
  revision 1.2
  revision 1.1
  revision 1.1.2.1
  RCS file: $TESTTMP/cvsrepo/proj/file6,v
  revision 1.1
  revision 1.1.2.2
  revision 1.1.2.1

convert to hg (#1)

  $ cd ..
  $ hg convert --datesort proj proj.hg
  initializing destination proj.hg repository
  connecting to $TESTTMP/cvsrepo
  scanning source...
  collecting CVS rlog
  15 log entries
  creating changesets
  9 changeset entries
  sorting...
  converting...
  8 add file1 on trunk
  7 add file2
  6 MERGE from v1_0: add file2
  5 file file3 was initially added on branch v1_1.
  4 add file3, file4 on branch v1_1
  3 add file5 on v1_2
  2 add file6 on trunk post-v1_2
  1 MERGE from HEAD: add file6
  0 MERGE from v1_2: add file5

hg log -G output (#1)

  $ hg -R proj.hg log -G --template "{rev} {desc}\n"
  o  8 MERGE from v1_2: add file5
  |
  | o  7 MERGE from HEAD: add file6
  | |
  o |  6 add file6 on trunk post-v1_2
  | |
  | o  5 add file5 on v1_2
  | |
  | | o  4 add file3, file4 on branch v1_1
  | | |
  o | |  3 file file3 was initially added on branch v1_1.
  |/ /
  | o  2 MERGE from v1_0: add file2
  |/
  | o  1 add file2
  |/
  o  0 add file1 on trunk
  

convert to hg (#2: with merge detection)

  $ hg convert \
  >   --config convert.cvsps.mergefrom='"^MERGE from (\S+):"' \
  >   --datesort \
  >   proj proj.hg2
  initializing destination proj.hg2 repository
  connecting to $TESTTMP/cvsrepo
  scanning source...
  collecting CVS rlog
  15 log entries
  creating changesets
  9 changeset entries
  sorting...
  converting...
  8 add file1 on trunk
  7 add file2
  6 MERGE from v1_0: add file2
  5 file file3 was initially added on branch v1_1.
  4 add file3, file4 on branch v1_1
  3 add file5 on v1_2
  2 add file6 on trunk post-v1_2
  1 MERGE from HEAD: add file6
  0 MERGE from v1_2: add file5

hg log -G output (#2)

  $ hg -R proj.hg2 log -G --template "{rev} {desc}\n"
  o  8 MERGE from v1_2: add file5
  |
  | o  7 MERGE from HEAD: add file6
  | |
  o |  6 add file6 on trunk post-v1_2
  | |
  | o  5 add file5 on v1_2
  | |
  | | o  4 add file3, file4 on branch v1_1
  | | |
  o | |  3 file file3 was initially added on branch v1_1.
  |/ /
  | o  2 MERGE from v1_0: add file2
  |/
  | o  1 add file2
  |/
  o  0 add file1 on trunk