fsmonitor: add a sample integration script for Watchman
authorBen Peart <benpeart@microsoft.com>
Fri, 22 Sep 2017 16:35:47 +0000 (12:35 -0400)
committerJunio C Hamano <gitster@pobox.com>
Sun, 1 Oct 2017 08:23:05 +0000 (17:23 +0900)
This 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/.
Rename the sample integration hook from fsmonitor-watchman.sample to
fsmonitor-watchman. Configure git to use the extension:

git config core.fsmonitor .git/hooks/fsmonitor-watchman

Optionally turn on the untracked cache for optimal performance.

Signed-off-by: Ben Peart <benpeart@microsoft.com>
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Christian Couder <christian.couder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
templates/hooks--fsmonitor-watchman.sample [new file with mode: 0755]

diff --git a/templates/hooks--fsmonitor-watchman.sample b/templates/hooks--fsmonitor-watchman.sample
new file mode 100755 (executable)
index 0000000..870a59d
--- /dev/null
@@ -0,0 +1,122 @@
+#!/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
+       $time = int $time / 1000000000;
+} else {
+       die "Unsupported query-fsmonitor hook version '$version'.\n" .
+           "Falling back to scanning...\n";
+}
+
+# Convert unix style paths to escaped Windows style paths when running
+# in Windows command prompt
+
+my $system = `uname -s`;
+$system =~ s/[\r\n]+//g;
+my $git_work_tree;
+
+if ($system =~ m/^MSYS_NT/) {
+       $git_work_tree = `cygpath -aw "\$PWD"`;
+       $git_work_tree =~ s/[\r\n]+//g;
+       $git_work_tree =~ s,\\,/,g;
+} else {
+       $git_work_tree = $ENV{'PWD'};
+}
+
+my $retry = 1;
+
+launch_watchman();
+
+sub launch_watchman {
+
+       # Set input record separator
+       local $/ = 0666;
+
+       my $pid = open2(\*CHLD_OUT, \*CHLD_IN, 'watchman -j')
+           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. Then we're using the "expression" term to
+       # further constrain the results.
+       #
+       # The category of transient files that we want to ignore will have a
+       # creation clock (cclock) newer than $time_t value and will also not
+       # currently exist.
+
+       my $query = <<" END";
+               ["query", "$git_work_tree", {
+                       "since": $time,
+                       "fields": ["name"],
+                       "expression": ["not", ["allof", ["since", $time, "cclock"], ["not", "exists"]]]
+               }]
+       END
+
+       print CHLD_IN $query;
+       my $response = <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}};
+}