view tests/test-sidedata-exchange.t @ 48068:bf8837e3d7ce

dirstate: Remove the flat Rust DirstateMap implementation

Before this changeset we had two Rust implementations of `DirstateMap`.
This removes the "flat" DirstateMap so that the "tree" DirstateMap is always
used when Rust enabled. This simplifies the code a lot, and will enable
(in the next changeset) further removal of a trait abstraction.

This is a performance regression when:

* Rust is enabled, and
* The repository uses the legacy dirstate-v1 file format, and
* For `hg status`, unknown files are not listed (such as with `-mard`)

The regression is about 100 milliseconds for `hg status -mard` on a
semi-large repository (mozilla-central), from ~320ms to ~420ms.
We deem this to be small enough to be worth it.

The new dirstate-v2 is still experimental at this point, but we aim to
stabilize it (though not yet enable it by default for new repositories)
in Mercurial 6.0. Eventually, upgrating repositories to dirsate-v2 will
eliminate this regression (and enable other performance improvements).


# Background

The flat DirstateMap was introduced with the first Rust implementation of the
status algorithm. It works similarly to the previous Python + C one, with a
single `HashMap` that associates file paths to a `DirstateEntry` (where Python
has a dict).

We later added the tree DirstateMap where the root of the tree contains nodes
for files and directories that are directly at the root of the repository,
and nodes for directories can contain child nodes representing the files and
directly that *they* contain directly. The shape of this tree mirrors that of
the working directory in the filesystem. This enables the status algorithm to
traverse this tree in tandem with traversing the filesystem tree, which in
turns enables a more efficient algorithm.

Furthermore, the new dirstate-v2 file format is also based on a tree of the
same shape. The tree DirstateMap can access a dirstate-v2 file without parsing
it: binary data in a single large (possibly memory-mapped) bytes buffer is
traversed on demand. This allows `DirstateMap` creation to take `O(1)` time.
(Mutation works by creating new in-memory nodes with copy-on-write semantics,
and serialization is append-mostly.)

The tradeoff is that for "legacy" repositories that use the dirstate-v1 file
format, parsing that file into a tree DirstateMap takes more time. Profiling
shows that this time is dominated by `HashMap`. For a dirstate containing `F`
files with an average `D` directory depth, the flat DirstateMap does parsing
in `O(F)` number of HashMap operations but the tree DirstateMap in `O(F × D)`
operations, since each node has its own HashMap containing its child nodes.
This slower costs ~140ms on an old snapshot of mozilla-central, and ~80ms
on an old snapshot of the Netbeans repository.

The status algorithm is faster, but with `-mard` (when not listing unknown
files) it is typically not faster *enough* to compensate the slower parsing.

Both Rust implementations are always faster than the Python + C implementation


# Benchmark results

All benchmarks are run on changeset 98c0408324e6, with repositories that use
the dirstate-v1 file format, on a server with 4 CPU cores and 4 CPU threads
(no HyperThreading).

`hg status` benchmarks show wall clock times of the entire command as the
average and standard deviation of serveral runs, collected by
https://github.com/sharkdp/hyperfine and reformated.

Parsing benchmarks are wall clock time of the Rust function that converts a
bytes buffer of the dirstate file into the `DirstateMap` data structure as
used by the status algorithm. A single run each, collected by running
`hg status` this environment variable:

    RUST_LOG=hg::dirstate::dirstate_map=trace,hg::dirstate_tree::dirstate_map=trace


Benchmark 1: Rust flat DirstateMap → Rust tree DirstateMap

    hg status

    mozilla-clean    	562.3 ms ± 2.0 ms	→	462.5 ms ± 0.6 ms	 1.22 ± 0.00 times faster
    mozilla-dirty    	859.6 ms ± 2.2 ms	→	719.5 ms ± 3.2 ms	 1.19 ± 0.01 times faster
    mozilla-ignored  	558.2 ms ± 3.0 ms	→	457.9 ms ± 2.9 ms	 1.22 ± 0.01 times faster
    mozilla-unknowns 	859.4 ms ± 5.7 ms	→	716.0 ms ± 4.7 ms	 1.20 ± 0.01 times faster
    netbeans-clean   	336.5 ms ± 0.9 ms	→	339.5 ms ± 0.4 ms	 0.99 ± 0.00 times faster
    netbeans-dirty   	491.4 ms ± 1.6 ms	→	475.1 ms ± 1.2 ms	 1.03 ± 0.00 times faster
    netbeans-ignored 	343.7 ms ± 1.0 ms	→	347.8 ms ± 0.4 ms	 0.99 ± 0.00 times faster
    netbeans-unknowns	484.3 ms ± 1.0 ms	→	466.0 ms ± 1.2 ms	 1.04 ± 0.00 times faster

    hg status -mard

    mozilla-clean    	317.3 ms ± 0.6 ms	→	422.5 ms ± 1.2 ms	 0.75 ± 0.00 times faster
    mozilla-dirty    	315.4 ms ± 0.6 ms	→	417.7 ms ± 1.1 ms	 0.76 ± 0.00 times faster
    mozilla-ignored  	314.6 ms ± 0.6 ms	→	417.4 ms ± 1.0 ms	 0.75 ± 0.00 times faster
    mozilla-unknowns 	312.9 ms ± 0.9 ms	→	417.3 ms ± 1.6 ms	 0.75 ± 0.00 times faster
    netbeans-clean   	212.0 ms ± 0.6 ms	→	283.6 ms ± 0.8 ms	 0.75 ± 0.00 times faster
    netbeans-dirty   	211.4 ms ± 1.0 ms	→	283.4 ms ± 1.6 ms	 0.75 ± 0.01 times faster
    netbeans-ignored 	211.4 ms ± 0.9 ms	→	283.9 ms ± 0.8 ms	 0.74 ± 0.01 times faster
    netbeans-unknowns	211.1 ms ± 0.6 ms	→	283.4 ms ± 1.0 ms	 0.74 ± 0.00 times faster

    Parsing

    mozilla-clean       38.4ms → 177.6ms
    mozilla-dirty       38.8ms → 177.0ms
    mozilla-ignored     38.8ms → 178.0ms
    mozilla-unknowns    38.7ms → 176.9ms
    netbeans-clean      16.5ms → 97.3ms
    netbeans-dirty      16.5ms → 98.4ms
    netbeans-ignored    16.9ms → 97.4ms
    netbeans-unknowns   16.9ms → 96.3ms


Benchmark 2: Python + C dirstatemap → Rust tree DirstateMap

    hg status

    mozilla-clean    	1261.0 ms ± 3.6 ms	→	461.1 ms ± 0.5 ms	 2.73 ± 0.00 times faster
    mozilla-dirty    	2293.4 ms ± 9.1 ms	→	719.6 ms ± 3.6 ms	 3.19 ± 0.01 times faster
    mozilla-ignored  	1240.4 ms ± 2.3 ms	→	457.7 ms ± 1.9 ms	 2.71 ± 0.00 times faster
    mozilla-unknowns 	2283.3 ms ± 9.0 ms	→	719.7 ms ± 3.8 ms	 3.17 ± 0.01 times faster
    netbeans-clean   	879.7 ms ± 3.5 ms	→	339.9 ms ± 0.5 ms	 2.59 ± 0.00 times faster
    netbeans-dirty   	1257.3 ms ± 4.7 ms	→	474.6 ms ± 1.6 ms	 2.65 ± 0.01 times faster
    netbeans-ignored 	943.9 ms ± 1.9 ms	→	347.3 ms ± 1.1 ms	 2.72 ± 0.00 times faster
    netbeans-unknowns	1188.1 ms ± 5.0 ms	→	465.2 ms ± 2.3 ms	 2.55 ± 0.01 times faster

    hg status -mard

    mozilla-clean    	903.2 ms ± 3.6 ms	→	423.4 ms ± 2.2 ms	 2.13 ± 0.01 times faster
    mozilla-dirty    	884.6 ms ± 4.5 ms	→	417.3 ms ± 1.4 ms	 2.12 ± 0.01 times faster
    mozilla-ignored  	881.9 ms ± 1.3 ms	→	417.3 ms ± 0.8 ms	 2.11 ± 0.00 times faster
    mozilla-unknowns 	878.5 ms ± 1.9 ms	→	416.4 ms ± 0.9 ms	 2.11 ± 0.00 times faster
    netbeans-clean   	434.9 ms ± 1.8 ms	→	284.0 ms ± 0.8 ms	 1.53 ± 0.01 times faster
    netbeans-dirty   	434.1 ms ± 0.8 ms	→	283.1 ms ± 0.8 ms	 1.53 ± 0.00 times faster
    netbeans-ignored 	431.7 ms ± 1.1 ms	→	283.6 ms ± 1.8 ms	 1.52 ± 0.01 times faster
    netbeans-unknowns	433.0 ms ± 1.3 ms	→	283.5 ms ± 0.7 ms	 1.53 ± 0.00 times faster

Differential Revision: https://phab.mercurial-scm.org/D11516

===========================
Tests for sidedata exchange
===========================

Check simple exchange behavior
==============================

Pusher and pushed have sidedata enabled
---------------------------------------

  $ hg init sidedata-source --config experimental.revlogv2=enable-unstable-format-and-corrupt-my-data
  $ cat << EOF >> sidedata-source/.hg/hgrc
  > [extensions]
  > testsidedata=$TESTDIR/testlib/ext-sidedata-5.py
  > EOF
  $ hg init sidedata-target --config experimental.revlogv2=enable-unstable-format-and-corrupt-my-data
  $ cat << EOF >> sidedata-target/.hg/hgrc
  > [extensions]
  > testsidedata=$TESTDIR/testlib/ext-sidedata-5.py
  > EOF
  $ cd sidedata-source
  $ echo a > a
  $ echo b > b
  $ echo c > c
  $ hg commit -Am "initial"
  adding a
  adding b
  adding c
  $ echo aa > a
  $ hg commit -m "other"
  $ hg push -r . ../sidedata-target
  pushing to ../sidedata-target
  searching for changes
  adding changesets
  adding manifests
  adding file changes
  added 2 changesets with 4 changes to 3 files
  $ hg -R ../sidedata-target debugsidedata -c 0
  2 sidedata entries
   entry-0001 size 4
   entry-0002 size 32
  $ hg -R ../sidedata-target debugsidedata -c 1 -v
  2 sidedata entries
   entry-0001 size 4
    '\x00\x00\x00:'
   entry-0002 size 32
    '\xa3\xee4v\x99\x85$\x9f\x1f\x8dKe\x0f\xc3\x9d-\xc9\xb5%[\x15=h\xe9\xf2O\xb5\xd9\x1f*\xff\xe5'
  $ hg -R ../sidedata-target debugsidedata -m 0
  2 sidedata entries
   entry-0001 size 4
   entry-0002 size 32
  $ hg -R ../sidedata-target debugsidedata -m 1 -v
  2 sidedata entries
   entry-0001 size 4
    '\x00\x00\x00\x81'
   entry-0002 size 32
    '-bL\xc5\xa4uu"#\xac\x1b`,\xc0\xbc\x9d\xf5\xac\xf0\x1d\x89)2\xf8N\xb1\x14m\xce\xd7\xbc\xae'
  $ hg -R ../sidedata-target debugsidedata a 0
  2 sidedata entries
   entry-0001 size 4
   entry-0002 size 32
  $ hg -R ../sidedata-target debugsidedata a 1 -v
  2 sidedata entries
   entry-0001 size 4
    '\x00\x00\x00\x03'
   entry-0002 size 32
    '\xd9\xcd\x81UvL5C\xf1\x0f\xad\x8aH\rt17Fo\x8dU!<\x8e\xae\xfc\xd1/\x06\xd4:\x80'
  $ cd ..

Puller and pulled have sidedata enabled
---------------------------------------

  $ rm -rf sidedata-source sidedata-target
  $ hg init sidedata-source --config experimental.revlogv2=enable-unstable-format-and-corrupt-my-data
  $ cat << EOF >> sidedata-source/.hg/hgrc
  > [extensions]
  > testsidedata=$TESTDIR/testlib/ext-sidedata-5.py
  > EOF
  $ hg init sidedata-target --config experimental.revlogv2=enable-unstable-format-and-corrupt-my-data
  $ cat << EOF >> sidedata-target/.hg/hgrc
  > [extensions]
  > testsidedata=$TESTDIR/testlib/ext-sidedata-5.py
  > EOF
  $ cd sidedata-source
  $ echo a > a
  $ echo b > b
  $ echo c > c
  $ hg commit -Am "initial"
  adding a
  adding b
  adding c
  $ echo aa > a
  $ hg commit -m "other"
  $ hg pull -R ../sidedata-target ../sidedata-source
  pulling from ../sidedata-source
  requesting all changes
  adding changesets
  adding manifests
  adding file changes
  added 2 changesets with 4 changes to 3 files
  new changesets 05da661850d7:7ec8b4049447
  (run 'hg update' to get a working copy)
  $ hg -R ../sidedata-target debugsidedata -c 0
  2 sidedata entries
   entry-0001 size 4
   entry-0002 size 32
  $ hg -R ../sidedata-target debugsidedata -c 1 -v
  2 sidedata entries
   entry-0001 size 4
    '\x00\x00\x00:'
   entry-0002 size 32
    '\xa3\xee4v\x99\x85$\x9f\x1f\x8dKe\x0f\xc3\x9d-\xc9\xb5%[\x15=h\xe9\xf2O\xb5\xd9\x1f*\xff\xe5'
  $ hg -R ../sidedata-target debugsidedata -m 0
  2 sidedata entries
   entry-0001 size 4
   entry-0002 size 32
  $ hg -R ../sidedata-target debugsidedata -m 1 -v
  2 sidedata entries
   entry-0001 size 4
    '\x00\x00\x00\x81'
   entry-0002 size 32
    '-bL\xc5\xa4uu"#\xac\x1b`,\xc0\xbc\x9d\xf5\xac\xf0\x1d\x89)2\xf8N\xb1\x14m\xce\xd7\xbc\xae'
  $ hg -R ../sidedata-target debugsidedata a 0
  2 sidedata entries
   entry-0001 size 4
   entry-0002 size 32
  $ hg -R ../sidedata-target debugsidedata a 1 -v
  2 sidedata entries
   entry-0001 size 4
    '\x00\x00\x00\x03'
   entry-0002 size 32
    '\xd9\xcd\x81UvL5C\xf1\x0f\xad\x8aH\rt17Fo\x8dU!<\x8e\xae\xfc\xd1/\x06\xd4:\x80'
  $ cd ..

Now on to asymmetric configs.

Pusher has sidedata enabled, pushed does not
--------------------------------------------

  $ rm -rf sidedata-source sidedata-target
  $ hg init sidedata-source --config experimental.revlogv2=enable-unstable-format-and-corrupt-my-data
  $ cat << EOF >> sidedata-source/.hg/hgrc
  > [extensions]
  > testsidedata=$TESTDIR/testlib/ext-sidedata-5.py
  > EOF
  $ hg init sidedata-target --config experimental.revlogv2=no
  $ cd sidedata-source
  $ echo a > a
  $ echo b > b
  $ echo c > c
  $ hg commit -Am "initial"
  adding a
  adding b
  adding c
  $ echo aa > a
  $ hg commit -m "other"
  $ hg push -r . ../sidedata-target --traceback
  pushing to ../sidedata-target
  searching for changes
  adding changesets
  adding manifests
  adding file changes
  added 2 changesets with 4 changes to 3 files
  $ hg -R ../sidedata-target log -G
  o  changeset:   1:7ec8b4049447
  |  tag:         tip
  |  user:        test
  |  date:        Thu Jan 01 00:00:00 1970 +0000
  |  summary:     other
  |
  o  changeset:   0:05da661850d7
     user:        test
     date:        Thu Jan 01 00:00:00 1970 +0000
     summary:     initial
  

  $ hg -R ../sidedata-target debugsidedata -c 0
  $ hg -R ../sidedata-target debugsidedata -c 1 -v
  $ hg -R ../sidedata-target debugsidedata -m 0
  $ hg -R ../sidedata-target debugsidedata -m 1 -v
  $ hg -R ../sidedata-target debugsidedata a 0
  $ hg -R ../sidedata-target debugsidedata a 1 -v
  $ cd ..

Pulled has sidedata enabled, puller does not
--------------------------------------------

  $ rm -rf sidedata-source sidedata-target
  $ hg init sidedata-source --config experimental.revlogv2=enable-unstable-format-and-corrupt-my-data
  $ cat << EOF >> sidedata-source/.hg/hgrc
  > [extensions]
  > testsidedata=$TESTDIR/testlib/ext-sidedata-5.py
  > EOF
  $ hg init sidedata-target --config experimental.revlogv2=no
  $ cd sidedata-source
  $ echo a > a
  $ echo b > b
  $ echo c > c
  $ hg commit -Am "initial"
  adding a
  adding b
  adding c
  $ echo aa > a
  $ hg commit -m "other"
  $ hg pull -R ../sidedata-target ../sidedata-source
  pulling from ../sidedata-source
  requesting all changes
  adding changesets
  adding manifests
  adding file changes
  added 2 changesets with 4 changes to 3 files
  new changesets 05da661850d7:7ec8b4049447
  (run 'hg update' to get a working copy)
  $ hg -R ../sidedata-target log -G
  o  changeset:   1:7ec8b4049447
  |  tag:         tip
  |  user:        test
  |  date:        Thu Jan 01 00:00:00 1970 +0000
  |  summary:     other
  |
  o  changeset:   0:05da661850d7
     user:        test
     date:        Thu Jan 01 00:00:00 1970 +0000
     summary:     initial
  

  $ hg -R ../sidedata-target debugsidedata -c 0
  $ hg -R ../sidedata-target debugsidedata -c 1 -v
  $ hg -R ../sidedata-target debugsidedata -m 0
  $ hg -R ../sidedata-target debugsidedata -m 1 -v
  $ hg -R ../sidedata-target debugsidedata a 0
  $ hg -R ../sidedata-target debugsidedata a 1 -v
  $ cd ..


Check sidedata exchange with on-the-fly generation and removal
==============================================================

(Push) Target has strict superset of the source
-----------------------------------------------

  $ hg init source-repo --config experimental.revlogv2=enable-unstable-format-and-corrupt-my-data
  $ hg init target-repo --config experimental.revlogv2=enable-unstable-format-and-corrupt-my-data
  $ cat << EOF >> target-repo/.hg/hgrc
  > [extensions]
  > testsidedata=$TESTDIR/testlib/ext-sidedata.py
  > EOF
  $ cd source-repo
  $ echo aaa > a
  $ hg add a
  $ hg commit -m a
  $ echo aaa > b
  $ hg add b
  $ hg commit -m b
  $ echo xxx >> a
  $ hg commit -m aa

No sidedata is generated in the source
  $ hg debugsidedata -c 0

Check that sidedata capabilities are advertised
  $ hg debugcapabilities ../target-repo | grep sidedata
    exp-wanted-sidedata=1,2

We expect the client to abort the push since it's not capable of generating
what the server is asking
  $ hg push -r . ../target-repo
  pushing to ../target-repo
  abort: cannot push: required sidedata category not supported by this client: '1'
  [255]

Add the required capabilities
  $ cat << EOF >> .hg/hgrc
  > [extensions]
  > testsidedata2=$TESTDIR/testlib/ext-sidedata-2.py
  > EOF

We expect the target to have sidedata that was generated by the source on push
  $ hg push -r . ../target-repo
  pushing to ../target-repo
  searching for changes
  adding changesets
  adding manifests
  adding file changes
  added 3 changesets with 3 changes to 2 files
  $ cd ../target-repo
  $ hg debugsidedata -c 0
  2 sidedata entries
   entry-0001 size 4
   entry-0002 size 32
  $ hg debugsidedata -c 1 -v
  2 sidedata entries
   entry-0001 size 4
    '\x00\x00\x006'
   entry-0002 size 32
    '\x98\t\xf9\xc4v\xf0\xc5P\x90\xf7wRf\xe8\xe27e\xfc\xc1\x93\xa4\x96\xd0\x1d\x97\xaaG\x1d\xd7t\xfa\xde'
  $ hg debugsidedata -m 2
  2 sidedata entries
   entry-0001 size 4
   entry-0002 size 32
  $ hg debugsidedata a 1
  2 sidedata entries
   entry-0001 size 4
   entry-0002 size 32
  $ cd ..

(Push) Difference is not subset/superset
----------------------------------------

Source has one in common, one missing and one more sidedata category with the
target.

  $ rm -rf source-repo target-repo
  $ hg init source-repo --config experimental.revlogv2=enable-unstable-format-and-corrupt-my-data
  $ cat << EOF >> source-repo/.hg/hgrc
  > [extensions]
  > testsidedata3=$TESTDIR/testlib/ext-sidedata-3.py
  > EOF
  $ hg init target-repo --config experimental.revlogv2=enable-unstable-format-and-corrupt-my-data
  $ cat << EOF >> target-repo/.hg/hgrc
  > [extensions]
  > testsidedata4=$TESTDIR/testlib/ext-sidedata-4.py
  > EOF
  $ cd source-repo
  $ echo aaa > a
  $ hg add a
  $ hg commit -m a
  $ echo aaa > b
  $ hg add b
  $ hg commit -m b
  $ echo xxx >> a
  $ hg commit -m aa

Check that sidedata capabilities are advertised
  $ hg debugcapabilities . | grep sidedata
    exp-wanted-sidedata=1,2
  $ hg debugcapabilities ../target-repo | grep sidedata
    exp-wanted-sidedata=2,3

Sidedata is generated in the source, but only the right categories (entry-0001 and entry-0002)
  $ hg debugsidedata -c 0
  2 sidedata entries
   entry-0001 size 4
   entry-0002 size 32
  $ hg debugsidedata -c 1 -v
  2 sidedata entries
   entry-0001 size 4
    '\x00\x00\x006'
   entry-0002 size 32
    '\x98\t\xf9\xc4v\xf0\xc5P\x90\xf7wRf\xe8\xe27e\xfc\xc1\x93\xa4\x96\xd0\x1d\x97\xaaG\x1d\xd7t\xfa\xde'
  $ hg debugsidedata -m 2
  2 sidedata entries
   entry-0001 size 4
   entry-0002 size 32
  $ hg debugsidedata a 1
  2 sidedata entries
   entry-0001 size 4
   entry-0002 size 32


We expect the target to have sidedata that was generated by the source on push,
and also removed the sidedata categories that are not supported by the target.
Namely, we expect entry-0002 (only exchanged) and entry-0003 (generated),
but not entry-0001.

  $ hg push -r . ../target-repo --traceback
  pushing to ../target-repo
  searching for changes
  adding changesets
  adding manifests
  adding file changes
  added 3 changesets with 3 changes to 2 files
  $ cd ../target-repo
  $ hg log -G
  o  changeset:   2:40f977031323
  |  tag:         tip
  |  user:        test
  |  date:        Thu Jan 01 00:00:00 1970 +0000
  |  summary:     aa
  |
  o  changeset:   1:2707720c6597
  |  user:        test
  |  date:        Thu Jan 01 00:00:00 1970 +0000
  |  summary:     b
  |
  o  changeset:   0:7049e48789d7
     user:        test
     date:        Thu Jan 01 00:00:00 1970 +0000
     summary:     a
  
  $ hg debugsidedata -c 0
  2 sidedata entries
   entry-0002 size 32
   entry-0003 size 48
  $ hg debugsidedata -c 1 -v
  2 sidedata entries
   entry-0002 size 32
    '\x98\t\xf9\xc4v\xf0\xc5P\x90\xf7wRf\xe8\xe27e\xfc\xc1\x93\xa4\x96\xd0\x1d\x97\xaaG\x1d\xd7t\xfa\xde'
   entry-0003 size 48
    '\x87\xcf\xdfI/\xb5\xed\xeaC\xc1\xf0S\xf3X\x1c\xcc\x00m\xee\xe6#\xc1\xe3\xcaB8Fk\x82e\xfc\xc01\xf6\xb7\xb9\xb3([\xf6D\xa6\xcf\x9b\xea\x11{\x08'
  $ hg debugsidedata -m 2
  2 sidedata entries
   entry-0002 size 32
   entry-0003 size 48
  $ hg debugsidedata a 1
  2 sidedata entries
   entry-0002 size 32
   entry-0003 size 48
  $ cd ..

(Pull) Target has strict superset of the source
-----------------------------------------------

  $ rm -rf source-repo target-repo
  $ hg init source-repo --config experimental.revlogv2=enable-unstable-format-and-corrupt-my-data
  $ hg init target-repo --config experimental.revlogv2=enable-unstable-format-and-corrupt-my-data
  $ cat << EOF >> target-repo/.hg/hgrc
  > [extensions]
  > testsidedata=$TESTDIR/testlib/ext-sidedata.py
  > EOF
  $ cd source-repo
  $ echo aaa > a
  $ hg add a
  $ hg commit -m a
  $ echo aaa > b
  $ hg add b
  $ hg commit -m b
  $ echo xxx >> a
  $ hg commit -m aa

No sidedata is generated in the source
  $ hg debugsidedata -c 0

Check that sidedata capabilities are advertised
  $ hg debugcapabilities ../target-repo | grep sidedata
    exp-wanted-sidedata=1,2

  $ cd ../target-repo

Add the required capabilities
  $ cat << EOF >> .hg/hgrc
  > [extensions]
  > testsidedata2=$TESTDIR/testlib/ext-sidedata-2.py
  > EOF

We expect the target to have sidedata that it generated on-the-fly during pull
  $ hg pull -r . ../source-repo  --traceback
  pulling from ../source-repo
  adding changesets
  adding manifests
  adding file changes
  added 3 changesets with 3 changes to 2 files
  new changesets 7049e48789d7:40f977031323
  (run 'hg update' to get a working copy)
  $ hg debugsidedata -c 0 --traceback
  2 sidedata entries
   entry-0001 size 4
   entry-0002 size 32
  $ hg debugsidedata -c 1 -v --traceback
  2 sidedata entries
   entry-0001 size 4
    '\x00\x00\x006'
   entry-0002 size 32
    '\x98\t\xf9\xc4v\xf0\xc5P\x90\xf7wRf\xe8\xe27e\xfc\xc1\x93\xa4\x96\xd0\x1d\x97\xaaG\x1d\xd7t\xfa\xde'
  $ hg debugsidedata -m 2
  2 sidedata entries
   entry-0001 size 4
   entry-0002 size 32
  $ hg debugsidedata a 1
  2 sidedata entries
   entry-0001 size 4
   entry-0002 size 32
  $ cd ..