Subject: Re: [PATCH] fsmonitor: query watchman with right valid json

From: Ævar Arnfjörð Bjarmason <[email-masked]>
Date: Tue, 07 Jun 2022 10:40:10 +0200

On Tue, Jun 07 2022, Son Luong Ngoc wrote:

> In rare circumstances where the current git index does not carry the
> last_update_token, the fsmonitor v2 hook will be invoked with an
> empty string which would caused the final rendered json to be invalid.
>
>   ["query", "/path/to/my/git/repository/", {
>           "since": ,
>           "fields": ["name"],
>           "expression": ["not", ["dirname", ".git"]]
>   }]
>
> Which will left user with the following error message
>
>   > git status
>   failed to parse command from stdin: line 2, column 13, position 67: unexpected token near ','
>   Watchman: command returned no output.
>   Falling back to scanning...
>
> Hide the "since" field in json query when "last_update_token" is empty.
>
> Signed-off-by: Son Luong Ngoc <[email-masked]>
> ---
>  templates/hooks--fsmonitor-watchman.sample | 21 +++++++++++++--------
>  1 file changed, 13 insertions(+), 8 deletions(-)
>
> diff --git a/templates/hooks--fsmonitor-watchman.sample b/templates/hooks--fsmonitor-watchman.sample
> index 14ed0aa42d..b4ee86dfc4 100755
> --- a/templates/hooks--fsmonitor-watchman.sample
> +++ b/templates/hooks--fsmonitor-watchman.sample
> @@ -79,6 +79,12 @@ sub watchman_query {
>  	or die "open2() failed: $!\n" .
>  	"Falling back to scanning...\n";
>  
> +	my $query = <<"	END";
> +		["query", "$git_work_tree", {
> +			"fields": ["name"],
> +			"expression": ["not", ["dirname", ".git"]]
> +		}]
> +	END

Wouldn't a more minimal & obvious patch here be....

>  	# In the query expression below we're asking for names of files that
>  	# changed since $last_update_token but not from the .git folder.
>  	#
> @@ -87,15 +93,14 @@ sub watchman_query {
>  	# output to file names only. Then we're using the "expression" term to
>  	# further constrain the results.
>  	if (substr($last_update_token, 0, 1) eq "c") {
> -		$last_update_token = "\"$last_update_token\"";

To just change this to be:

	# same as now:
	$last_update_token = "\"$last_update_token\"";
        $last_update_line = qq["since": $last_update_token,];

Of course having declared the new $last_update_line variable earlier, then:

> +		$query = <<"		END";
> +			["query", "$git_work_tree", {
> +				"since": "$last_update_token",
> +				"fields": ["name"],
> +				"expression": ["not", ["dirname", ".git"]]
> +			}]
> +		END
>  	}
> -	my $query = <<"	END";
> -		["query", "$git_work_tree", {
> -			"since": $last_update_token,

Just change this line to:

	$last_update_line

I.e. you don't need to duplicate the whole query just to omit/include a
single line in it, or am I missing something?

(This suggestion *would* include a redundant line, but I'm assuming
JSON/watchman deals with that just fine...).