Re: [PATCH v2 6/6] fsmonitor: add a sample query-fsmonitor hook script for Watchman

> On Wed, May 24, 2017 at 3:12 PM, Christian Couder
> <christian.couder@gmail.com> wrote:
>> On Thu, May 18, 2017 at 10:13 PM, Ben Peart <peartben@gmail.com> wrote:
>>> This hook script integrates the new fsmonitor capabilities of git with
>>> the cross platform Watchman file watching service. To use the script:
>>>
>>> Download and install Watchman from https://facebook.github.io/watchman/
>>> and instruct Watchman to watch your working directory for changes
>>> ('watchman watch-project /usr/src/git').
>>>
>>> Rename the sample integration hook from query-fsmonitor.sample to
>>> query-fsmonitor.
>>>
>>> Configure git to use the extension ('git config core.fsmonitor true')
>>> and optionally turn on the untracked cache for optimal performance
>>> ('git config core.untrackedcache true').
>>
>> Ok, it looks like the untracked cache can be used, but it could work without it.
>>
>>> Signed-off-by: Ben Peart <benpeart@microsoft.com>
>>> Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
>>> ---
>>>   templates/hooks--query-fsmonitor.sample | 27 +++++++++++++++++++++++++++
>>>   1 file changed, 27 insertions(+)
>>>   create mode 100644 templates/hooks--query-fsmonitor.sample
>>>
>>> diff --git a/templates/hooks--query-fsmonitor.sample b/templates/hooks--query-fsmonitor.sample
>>> new file mode 100644
>>> index 0000000000..4bd22f21d8
>>> --- /dev/null
>>> +++ b/templates/hooks--query-fsmonitor.sample
>>> @@ -0,0 +1,27 @@
>>> +#!/bin/sh
>>> +#
>>> +# An example hook script to integrate Watchman
>>> +# (https://facebook.github.io/watchman/) with git to provide fast
>>> +# git status.
>>> +#
>>> +# The hook is passed a time_t formatted as a string and outputs to
>>> +# stdout all files that have been modified since the given time.
>>> +# Paths must be relative to the root of the working tree and
>>> +# separated by a single NUL.
>>> +#
>>> +# To enable this hook, rename this file to "query-fsmonitor"
>>> +
>>> +# Convert unix style paths to escaped Windows style paths
>>> +case "$(uname -s)" in
>>> +MINGW*|MSYS_NT*)
>>> +  GIT_WORK_TREE="$(cygpath -aw "$PWD" | sed 's,\\,\\\\,g')"
>>> +  ;;
>>> +*)
>>> +  GIT_WORK_TREE="$PWD"
>>> +  ;;
>>> +esac
>>> +
>>> +# Query Watchman for all the changes since the requested time
>>> +echo "[\"query\", \"$GIT_WORK_TREE\", {\"since\": $1, \"fields\":[\"name\"]}]" | \
>>> +watchman -j | \
>>> +perl -e 'use JSON::PP; my $o = JSON::PP->new->utf8->decode(join("", <>)); die "Watchman: $o->{'error'}.\nFalling back to scanning...\n" if defined($o->{"error"}); print(join("\0", @{$o->{"files"}}));'
>>
>> Maybe put the above small perl script on multiple lines for improved
>> readability.
>>

>> Is JSON::PP always available in Perl >= 5.8?
> 
> No, it's shipped with perl as of 5.14.0, which came out in May 2011.
> 
> I think depending on that is fine. FWIW we bumped the required core
> dependency (but you might still need to install modules) in 2010 in my
> d48b284183 ("perl: bump the required Perl version to 5.8 from
> 5.6.[21]", 2010-09-24). Maybe we should be bumping that again...
> 
>> What happens if watchman is not installed or not in the PATH?
>> It seems to me that the git process will not die, and will just work
>> as if the hook does not exist, except that it will call the hook which
>> will probably output error messages.
> 
> I think a good solution to this is to just add "set -euo pipefail" to
> that script.
> 
> Then we'll print out on stderr that we couldn't find the watchman
> command. Right now (with my patch) it'll make its way to the perl
> program and get empty input.
>