source: LMDZ6/branches/cirrus/libf/phylmd/ecrad/.git/hooks/fsmonitor-watchman.sample

#!/usr/bin/perl

use strict;
use warnings;
use IPC::Open2;

# An example hook script to integrate Watchman
# (https://facebook.github.io/watchman/) with git to speed up detecting
# new and modified files.
#
# The hook is passed a version (currently 1) and a time in nanoseconds
# 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-watchman" and set
# 'git config core.fsmonitor .git/hooks/query-watchman'
#
my ($version, $time) = @ARGV;

# Check the hook interface version

if ($version == 1) {
        # convert nanoseconds to seconds
        # subtract one second to make sure watchman will return all changes
        $time = int ($time / 1000000000) - 1;
} else {
        die "Unsupported query-fsmonitor hook version '$version'.\n" .
            "Falling back to scanning...\n";
}

my $git_work_tree;
if ($^O =~ 'msys' || $^O =~ 'cygwin') {
        $git_work_tree = Win32::GetCwd();
        $git_work_tree =~ tr/\\/\//;
} else {
        require Cwd;
        $git_work_tree = Cwd::cwd();
}

my $retry = 1;

launch_watchman();

sub launch_watchman {

        my $pid = open2(\*CHLD_OUT, \*CHLD_IN, 'watchman -j --no-pretty')
            or die "open2() failed: $!\n" .
            "Falling back to scanning...\n";

        # In the query expression below we're asking for names of files that
        # changed since $time but were not transient (ie created after
        # $time but no longer exist).
        #
        # To accomplish this, we're using the "since" generator to use the
        # recency index to select candidate nodes and "fields" to limit the
        # output to file names only.

        my $query = <<" END";
                ["query", "$git_work_tree", {
                        "since": $time,
                        "fields": ["name"]
                }]
        END

        print CHLD_IN $query;
        close CHLD_IN;
        my $response = do {local $/; <CHLD_OUT>};

        die "Watchman: command returned no output.\n" .
            "Falling back to scanning...\n" if $response eq "";
        die "Watchman: command returned invalid output: $response\n" .
            "Falling back to scanning...\n" unless $response =~ /^\{/;

        my $json_pkg;
        eval {
                require JSON::XS;
                $json_pkg = "JSON::XS";
                1;
        } or do {
                require JSON::PP;
                $json_pkg = "JSON::PP";
        };

        my $o = $json_pkg->new->utf8->decode($response);

        if ($retry > 0 and $o->{error} and $o->{error} =~ m/unable to resolve root .* directory (.*) is not watched/) {
                print STDERR "Adding '$git_work_tree' to watchman's watch list.\n";
                $retry--;
                qx/watchman watch "$git_work_tree"/;
                die "Failed to make watchman watch '$git_work_tree'.\n" .
                    "Falling back to scanning...\n" if $? != 0;

                # Watchman will always return all files on the first query so
                # return the fast "everything is dirty" flag to git and do the
                # Watchman query just to get it over with now so we won't pay
                # the cost in git to look up each individual file.
                print "/\0";
                eval { launch_watchman() };
                exit 0;
        }

        die "Watchman: $o->{error}.\n" .
            "Falling back to scanning...\n" if $o->{error};

        binmode STDOUT, ":utf8";
        local $, = "\0";
        print @{$o->{files}};
}