merge(3p/git): Merge git subtree at v2.29.2 r/1890

This also bumps the stable nixpkgs to 20.09 as of 2020-11-21, because
there is some breakage in the git build related to the netrc
credentials helper which someone has taken care of in nixpkgs.

The stable channel is not used for anything other than git, so this
should be fine.

Change-Id: I3575a19dab09e1e9556cf8231d717de9890484fb

1 files changed, 113 insertions, 54 deletions

diff --git a/third_party/git/templates/hooks--fsmonitor-watchman.sample b/third_party/git/templates/hooks--fsmonitor-watchman.sample
index e673bb3980..14ed0aa42d 100755
--- a/third_party/git/templates/hooks--fsmonitor-watchman.sample
+++ b/third_party/git/templates/hooks--fsmonitor-watchman.sample
@@ -8,107 +8,166 @@ use IPC::Open2;
 # (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.
+# The hook is passed a version (currently 2) and last update token
+# formatted as a string and outputs to stdout a new update token and
+# all files that have been modified since the update token. 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, $time) = @ARGV;
+my ($version, $last_update_token) = @ARGV;
 
-# Check the hook interface version
+# Uncomment for debugging
+# print STDERR "$0 $version $last_update_token\n";
 
-if ($version == 1) {
-	# convert nanoseconds to seconds
-	$time = int $time / 1000000000;
-} else {
+# Check the hook interface version
+if ($version ne 2) {
 	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 $git_work_tree = get_working_dir();
 
 my $retry = 1;
 
+my $json_pkg;
+eval {
+	require JSON::XS;
+	$json_pkg = "JSON::XS";
+	1;
+} or do {
+	require JSON::PP;
+	$json_pkg = "JSON::PP";
+};
+
 launch_watchman();
 
 sub launch_watchman {
+	my $o = watchman_query();
+	if (is_work_tree_watched($o)) {
+		output_result($o->{clock}, @{$o->{files}});
+	}
+}
+
+sub output_result {
+	my ($clockid, @files) = @_;
 
+	# Uncomment for debugging watchman output
+	# open (my $fh, ">", ".git/watchman-output.out");
+	# binmode $fh, ":utf8";
+	# print $fh "$clockid\n@files\n";
+	# close $fh;
+
+	binmode STDOUT, ":utf8";
+	print $clockid;
+	print "\0";
+	local $, = "\0";
+	print @files;
+}
+
+sub watchman_clock {
+	my $response = qx/watchman clock "$git_work_tree"/;
+	die "Failed to get clock id on '$git_work_tree'.\n" .
+		"Falling back to scanning...\n" if $? != 0;
+
+	return $json_pkg->new->utf8->decode($response);
+}
+
+sub watchman_query {
 	my $pid = open2(\*CHLD_OUT, \*CHLD_IN, 'watchman -j --no-pretty')
-	    or die "open2() failed: $!\n" .
-	    "Falling back to scanning...\n";
+	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).
+	# changed since $last_update_token but not from the .git folder.
 	#
 	# 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 $time_t value and will also not
-	# currently exist.
-
+	if (substr($last_update_token, 0, 1) eq "c") {
+		$last_update_token = "\"$last_update_token\"";
+	}
 	my $query = <<"	END";
 		["query", "$git_work_tree", {
-			"since": $time,
+			"since": $last_update_token,
 			"fields": ["name"],
-			"expression": ["not", ["allof", ["since", $time, "cclock"], ["not", "exists"]]]
+			"expression": ["not", ["dirname", ".git"]]
 		}]
 	END
 
+	# Uncomment for debugging the watchman query
+	# open (my $fh, ">", ".git/watchman-query.json");
+	# print $fh $query;
+	# close $fh;
+
 	print CHLD_IN $query;
 	close CHLD_IN;
 	my $response = do {local $/; <CHLD_OUT>};
 
+	# Uncomment for debugging the watch response
+	# open ($fh, ">", ".git/watchman-response.json");
+	# print $fh $response;
+	# close $fh;
+
 	die "Watchman: command returned no output.\n" .
-	    "Falling back to scanning...\n" if $response eq "";
+	"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";
+	"Falling back to scanning...\n" unless $response =~ /^\{/;
+
+	return $json_pkg->new->utf8->decode($response);
+}
+
+sub is_work_tree_watched {
+	my ($output) = @_;
+	my $error = $output->{error};
+	if ($retry > 0 and $error and $error =~ m/unable to resolve root .* directory (.*) is not watched/) {
 		$retry--;
-		qx/watchman watch "$git_work_tree"/;
+		my $response = qx/watchman watch "$git_work_tree"/;
 		die "Failed to make watchman watch '$git_work_tree'.\n" .
 		    "Falling back to scanning...\n" if $? != 0;
+		$output = $json_pkg->new->utf8->decode($response);
+		$error = $output->{error};
+		die "Watchman: $error.\n" .
+		"Falling back to scanning...\n" if $error;
+
+		# Uncomment for debugging watchman output
+		# open (my $fh, ">", ".git/watchman-output.out");
+		# close $fh;
 
 		# 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";
+		my $o = watchman_clock();
+		$error = $output->{error};
+
+		die "Watchman: $error.\n" .
+		"Falling back to scanning...\n" if $error;
+
+		output_result($o->{clock}, ("/"));
+		$last_update_token = $o->{clock};
+
 		eval { launch_watchman() };
-		exit 0;
+		return 0;
 	}
 
-	die "Watchman: $o->{error}.\n" .
-	    "Falling back to scanning...\n" if $o->{error};
+	die "Watchman: $error.\n" .
+	"Falling back to scanning...\n" if $error;
 
-	binmode STDOUT, ":utf8";
-	local $, = "\0";
-	print @{$o->{files}};
+	return 1;
+}
+
+sub get_working_dir {
+	my $working_dir;
+	if ($^O =~ 'msys' || $^O =~ 'cygwin') {
+		$working_dir = Win32::GetCwd();
+		$working_dir =~ tr/\\/\//;
+	} else {
+		require Cwd;
+		$working_dir = Cwd::cwd();
+	}
+
+	return $working_dir;
 }