fsmonitor: read entirety of watchman output

In Perl, setting $/ sets the string that is used as the "record
separator," which sets the boundary that the `<>` construct reads to.
Setting `local $/ = 0666;` evaluates the octal, getting 438, and
stringifies it.  Thus, the later read from `<CHLD_OUT>` stops as soon
as it encounters the string "438" in the watchman output, yielding
invalid JSON; repositories containing filenames with SHA1 hashes are
able to trip this easily.

Set `$/` to undefined, thus slurping all output from watchman.  Also
close STDIN which is provided to watchman, to better guarantee that we
cannot deadlock with watchman while both attempting to read.

Signed-off-by: Alex Vandiver <alexmv@dropbox.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t7519/fsmonitor-watchman

diff --git a/t/t7519/fsmonitor-watchman b/t/t7519/fsmonitor-watchman
index cca3d71..51330f8 100755
--- a/t/t7519/fsmonitor-watchman
+++ b/t/t7519/fsmonitor-watchman
@@ -50,9 +50,6 @@
 
 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";
@@ -83,7 +80,8 @@
 	close $fh;
 
 	print CHLD_IN $query;
-	my $response = <CHLD_OUT>;
+	close CHLD_IN;
+	my $response = do {local $/; <CHLD_OUT>};
 
 	open ($fh, ">", ".git/watchman-response.json");
 	print $fh $response;

templates/hooks--fsmonitor-watchman.sample

diff --git a/templates/hooks--fsmonitor-watchman.sample b/templates/hooks--fsmonitor-watchman.sample
index c68038ef0..9eba8a7 100755
--- a/templates/hooks--fsmonitor-watchman.sample
+++ b/templates/hooks--fsmonitor-watchman.sample
@@ -49,9 +49,6 @@
 
 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";
@@ -78,7 +75,8 @@
 	END
 
 	print CHLD_IN $query;
-	my $response = <CHLD_OUT>;
+	close CHLD_IN;
+	my $response = do {local $/; <CHLD_OUT>};
 
 	die "Watchman: command returned no output.\n" .
 	    "Falling back to scanning...\n" if $response eq "";