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

["Ævar Arnfjörð Bjarmason" <avarab@gmail.com>]

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').
>
> 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"}}));'

I couldn't get watchman to work for me (built from source, keep
getting [1]), but I hacked up something you can hopefully test &
squash on top of this:

 # Query Watchman for all the changes since the requested time
-echo "[\"query\", \"$GIT_WORK_TREE\", {\"since\": $time_t,
\"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-
+echo "[\"query\", \"$GIT_WORK_TREE\", {\"since\": $time_t,
\"fields\":[\"name\"]}]" |
+       watchman -j |
+       perl -0666 -e '
+               use strict;
+               use warnings;
+
+               my $stdin = <>;
+               die "Watchman: The watchman command returned no
output, error above?\n" if $stdin eq "";
+               die "Watchman: Invalid input: $stdin\n" unless $stdin =~ /^\{/;
+
+               my $json_pkg;
+               eval {
+                       require JSON::XS;
+                       $json_pkg = "JSON::XS";
+                       1;
+               } or do {
+                       require JSON::PP;
+                       $json_pkg = "JSON::PP";
+               };
+
+               my $o = $json_pkg->new->utf8->decode($stdin);
+               die "Watchman: $o->{error}.\nFalling back to scanning...\n"
+                       if $o->{error};
+
+               local $, = "\0";
+               print @{$o->{files}};
+       '

Rationale:

 * We use the much faster JSON::XS if it's installed.
 * We use strict/warnings
 * Micro optimization: Replace joining stdin with an equivalent -0666
   invocation. See "perldoc perlrun".
 * Micro optimization: No need to join up the possibly large list of
   files into one big string, just set $, to \0 and stream out the
   array.
 * Error handling: My watchman is broken (so actually this isn't
   tested), it only spews to stderr and exits. Handle that by checking
   whether stdin is "".

Those changes are available at
https://github.com/avar/git/commits/avar/fsmonitor



1. watchman: /usr/lib/x86_64-linux-gnu/libstdc++.so.6: version
`CXXABI_1.3.11' not found (required by watchman)