[PATCH] fsmonitor: fix two bugs in watchman hook retry path

[PATCH] fsmonitor: fix two bugs in watchman hook retry path

[Paul Tarjan via GitGitGadget]

From: Claude <noreply@anthropic.com>

The is_work_tree_watched() function in fsmonitor-watchman.sample has
two bugs:

1. Wrong variable in error check: After calling watchman_clock(), the
   result is stored in $o, but the code checks $output->{error} instead
   of $o->{error}. This means errors from the clock command are silently
   ignored.

2. Double output violates protocol: When the retry path triggers (the
   directory wasn't initially watched), output_result() is called with
   the "/" flag, then launch_watchman() is called recursively which
   calls output_result() again. This outputs two clock tokens to stdout,
   but git's fsmonitor v2 protocol expects exactly one response.

Fix #1 by checking $o->{error} after watchman_clock().

Fix #2 by removing the recursive launch_watchman() call. The "/"
"everything is dirty" flag already tells git to do a full scan, and
git will call the hook again on the next invocation with a valid clock
token.

Apply the same fixes to the test helper scripts in t/t7519/.

Signed-off-by: Paul Tarjan <github@paulisageek.com>
---
    fsmonitor-watchman: fix variable reference and remove redundant code
    
    The is_work_tree_watched() function in fsmonitor-watchman.sample has two
    bugs:
    
     1. Wrong variable in error check: After calling watchman_clock(), the
        result is stored in $o, but the code checks $output->{error} instead
        of $o->{error}. This means errors from the clock command are
        silently ignored.
    
     2. Double output violates protocol: When the retry path triggers (the
        directory wasn't initially watched), output_result() is called with
        the "/" flag, then launch_watchman() is called recursively which
        calls output_result() again. This outputs two clock tokens to
        stdout, but git's fsmonitor v2 protocol expects exactly one
        response.
    
    Fix #1 by checking $o->{error} after watchman_clock().
    
    Fix #2 by removing the recursive launch_watchman() call. The "/"
    "everything is dirty" flag already tells git to do a full scan, and git
    will call the hook again on the next invocation with a valid clock
    token.

Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-2180%2Fptarjan%2Fclaude%2Ffix-watchman-query-bug-sfbIw-v1
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-2180/ptarjan/claude/fix-watchman-query-bug-sfbIw-v1
Pull-Request: https://github.com/git/git/pull/2180

 t/t7519/fsmonitor-watchman                | 1 -
 t/t7519/fsmonitor-watchman-v2             | 5 +----
 templates/hooks/fsmonitor-watchman.sample | 5 +----
 3 files changed, 2 insertions(+), 9 deletions(-)

diff --git a/t/t7519/fsmonitor-watchman b/t/t7519/fsmonitor-watchman
index 264b9daf83..907bd1533c 100755
--- a/t/t7519/fsmonitor-watchman
+++ b/t/t7519/fsmonitor-watchman
@@ -109,7 +109,6 @@ sub launch_watchman {
 		close $fh;
 
 		print "/\0";
-		eval { launch_watchman() };
 		exit 0;
 	}
 
diff --git a/t/t7519/fsmonitor-watchman-v2 b/t/t7519/fsmonitor-watchman-v2
index 14ed0aa42d..2c59120c3d 100755
--- a/t/t7519/fsmonitor-watchman-v2
+++ b/t/t7519/fsmonitor-watchman-v2
@@ -141,15 +141,12 @@ sub is_work_tree_watched {
 		# Watchman query just to get it over with now so we won't pay
 		# the cost in git to look up each individual file.
 		my $o = watchman_clock();
-		$error = $output->{error};
+		$error = $o->{error};
 
 		die "Watchman: $error.\n" .
 		"Falling back to scanning...\n" if $error;
 
 		output_result($o->{clock}, ("/"));
-		$last_update_token = $o->{clock};
-
-		eval { launch_watchman() };
 		return 0;
 	}
 
diff --git a/templates/hooks/fsmonitor-watchman.sample b/templates/hooks/fsmonitor-watchman.sample
index 23e856f5de..21c81b6804 100755
--- a/templates/hooks/fsmonitor-watchman.sample
+++ b/templates/hooks/fsmonitor-watchman.sample
@@ -142,15 +142,12 @@ sub is_work_tree_watched {
 		# Watchman query just to get it over with now so we won't pay
 		# the cost in git to look up each individual file.
 		my $o = watchman_clock();
-		$error = $output->{error};
+		$error = $o->{error};
 
 		die "Watchman: $error.\n" .
 		"Falling back to scanning...\n" if $error;
 
 		output_result($o->{clock}, ("/"));
-		$last_update_token = $o->{clock};
-
-		eval { launch_watchman() };
 		return 0;
 	}
 

base-commit: 68cb7f9e92a5d8e9824f5b52ac3d0a9d8f653dbe
-- 
gitgitgadget

Re: [PATCH] fsmonitor: fix two bugs in watchman hook retry path

[Paul Tarjan]

Friendly ping on this patch.

Thanks,
Paul

Re: [PATCH] fsmonitor-watchman: fix variable reference and remove redundant code

[Paul Tarjan]

Friendly ping on this patch. Happy to address any feedback.

Thanks,
Paul

Re: [PATCH] fsmonitor: fix two bugs in watchman hook retry path

[Koji Nakamaru]

On Mon, Jan 26, 2026 at 10:33 AM Paul Tarjan via GitGitGadget
<gitgitgadget@gmail.com> wrote:
>
> From: Claude <noreply@anthropic.com>
>
> The is_work_tree_watched() function in fsmonitor-watchman.sample has
> two bugs:
>
> 1. Wrong variable in error check: After calling watchman_clock(), the
>    result is stored in $o, but the code checks $output->{error} instead
>    of $o->{error}. This means errors from the clock command are silently
>    ignored.
>
> 2. Double output violates protocol: When the retry path triggers (the
>    directory wasn't initially watched), output_result() is called with
>    the "/" flag, then launch_watchman() is called recursively which
>    calls output_result() again. This outputs two clock tokens to stdout,
>    but git's fsmonitor v2 protocol expects exactly one response.
>
> Fix #1 by checking $o->{error} after watchman_clock().
>
> Fix #2 by removing the recursive launch_watchman() call. The "/"
> "everything is dirty" flag already tells git to do a full scan, and
> git will call the hook again on the next invocation with a valid clock
> token.
>
> Apply the same fixes to the test helper scripts in t/t7519/.
>
> Signed-off-by: Paul Tarjan <github@paulisageek.com>
> ---
>     fsmonitor-watchman: fix variable reference and remove redundant code
>
>     The is_work_tree_watched() function in fsmonitor-watchman.sample has two
>     bugs:
>
>      1. Wrong variable in error check: After calling watchman_clock(), the
>         result is stored in $o, but the code checks $output->{error} instead
>         of $o->{error}. This means errors from the clock command are
>         silently ignored.
>
>      2. Double output violates protocol: When the retry path triggers (the
>         directory wasn't initially watched), output_result() is called with
>         the "/" flag, then launch_watchman() is called recursively which
>         calls output_result() again. This outputs two clock tokens to
>         stdout, but git's fsmonitor v2 protocol expects exactly one
>         response.
>
>     Fix #1 by checking $o->{error} after watchman_clock().
>
>     Fix #2 by removing the recursive launch_watchman() call. The "/"
>     "everything is dirty" flag already tells git to do a full scan, and git
>     will call the hook again on the next invocation with a valid clock
>     token.
>
> Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-2180%2Fptarjan%2Fclaude%2Ffix-watchman-query-bug-sfbIw-v1
> Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-2180/ptarjan/claude/fix-watchman-query-bug-sfbIw-v1
> Pull-Request: https://github.com/git/git/pull/2180
>
>  t/t7519/fsmonitor-watchman                | 1 -
>  t/t7519/fsmonitor-watchman-v2             | 5 +----
>  templates/hooks/fsmonitor-watchman.sample | 5 +----
>  3 files changed, 2 insertions(+), 9 deletions(-)
>
> diff --git a/t/t7519/fsmonitor-watchman b/t/t7519/fsmonitor-watchman
> index 264b9daf83..907bd1533c 100755
> --- a/t/t7519/fsmonitor-watchman
> +++ b/t/t7519/fsmonitor-watchman
> @@ -109,7 +109,6 @@ sub launch_watchman {
>                 close $fh;
>
>                 print "/\0";
> -               eval { launch_watchman() };
>                 exit 0;
>         }
>
> diff --git a/t/t7519/fsmonitor-watchman-v2 b/t/t7519/fsmonitor-watchman-v2
> index 14ed0aa42d..2c59120c3d 100755
> --- a/t/t7519/fsmonitor-watchman-v2
> +++ b/t/t7519/fsmonitor-watchman-v2
> @@ -141,15 +141,12 @@ sub is_work_tree_watched {
>                 # Watchman query just to get it over with now so we won't pay
>                 # the cost in git to look up each individual file.
>                 my $o = watchman_clock();
> -               $error = $output->{error};
> +               $error = $o->{error};
>
>                 die "Watchman: $error.\n" .
>                 "Falling back to scanning...\n" if $error;
>
>                 output_result($o->{clock}, ("/"));
> -               $last_update_token = $o->{clock};
> -
> -               eval { launch_watchman() };
>                 return 0;
>         }
>
> diff --git a/templates/hooks/fsmonitor-watchman.sample b/templates/hooks/fsmonitor-watchman.sample
> index 23e856f5de..21c81b6804 100755
> --- a/templates/hooks/fsmonitor-watchman.sample
> +++ b/templates/hooks/fsmonitor-watchman.sample
> @@ -142,15 +142,12 @@ sub is_work_tree_watched {
>                 # Watchman query just to get it over with now so we won't pay
>                 # the cost in git to look up each individual file.
>                 my $o = watchman_clock();
> -               $error = $output->{error};
> +               $error = $o->{error};
>
>                 die "Watchman: $error.\n" .
>                 "Falling back to scanning...\n" if $error;
>
>                 output_result($o->{clock}, ("/"));
> -               $last_update_token = $o->{clock};
> -
> -               eval { launch_watchman() };
>                 return 0;
>         }
>
>
> base-commit: 68cb7f9e92a5d8e9824f5b52ac3d0a9d8f653dbe
> --
> gitgitgadget
>

Although I don't have much experience with the Watchman backend, the
fixes look correct to me.

One suggestion: it seems we can make the code even cleaner by removing
$retry and its associated logic, as they appear to be no longer
necessary after these changes.

--
Koji Nakamaru

Re: [PATCH] fsmonitor: fix two bugs in watchman hook retry path

[brian m. carlson]

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On 2026-01-26 at 01:33:22, Paul Tarjan via GitGitGadget wrote:
> From: Claude <noreply@anthropic.com>

This looks like it was written by an LLM.  Is that the case, and if so,
how does it line up with https://git-scm.com/docs/SubmittingPatches#ai?
-- 
brian m. carlson (they/them)
Toronto, Ontario, CA

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Re: [PATCH] fsmonitor-watchman: fix variable reference and remove redundant code

[Paul Tarjan]

"brian m. carlson" <sandals@crustytoothpaste.net> writes:

> This looks like it was written by an LLM.  Is that the case, and if so,
> how does it line up with https://git-scm.com/docs/SubmittingPatches#ai?

I found these bugs during code review at my company where we use
the watchman hook. The $output vs $o mixup and the double
output_result() from the recursive call were both causing real
issues. I used Claude to help with the mechanics of formatting
and submitting the patch, and it ended up as the commit author,
which was a mistake on my part. I'll fix that in v2 with myself
as the author.

Thanks for flagging it,
Paul

Re: [PATCH] fsmonitor-watchman: fix variable reference and remove redundant code

[Paul Tarjan]

Koji Nakamaru <koji.nakamaru@gree.net> writes:

> Although I don't have much experience with the Watchman backend, the
> fixes look correct to me.
>
> One suggestion: it seems we can make the code even cleaner by removing
> $retry and its associated logic, as they appear to be no longer
> necessary after these changes.

Good point. $retry only existed to prevent the infinite recursion
from the recursive launch_watchman() call, so now that we've
removed that call it's dead code. Cleaned it up in v2.

Thanks for the review,
Paul

[PATCH v2] fsmonitor-watchman: fix variable reference and remove redundant code

[Paul Tarjan via GitGitGadget]

From: Paul Tarjan <github@paulisageek.com>

The is_work_tree_watched() function in fsmonitor-watchman.sample has
two bugs:

1. Wrong variable in error check: After calling watchman_clock(), the
   result is stored in $o, but the code checks $output->{error} instead
   of $o->{error}. This means errors from the clock command are silently
   ignored.

2. Double output violates protocol: When the retry path triggers (the
   directory wasn't initially watched), output_result() is called with
   the "/" flag, then launch_watchman() is called recursively which
   calls output_result() again. This outputs two clock tokens to stdout,
   but git's fsmonitor v2 protocol expects exactly one response.

Fix #1 by checking $o->{error} after watchman_clock().

Fix #2 by removing the recursive launch_watchman() call. The "/"
"everything is dirty" flag already tells git to do a full scan, and
git will call the hook again on the next invocation with a valid clock
token.

With the recursive call removed, the $retry guard is no longer needed
since it only existed to prevent infinite recursion. Remove it.

Apply the same fixes to the test helper scripts in t/t7519/.

Signed-off-by: Paul Tarjan <github@paulisageek.com>
---
    fsmonitor-watchman: fix variable reference and remove redundant code
    
    fsmonitor-watchman: fix variable reference and remove redundant code
    
    The is_work_tree_watched() function in fsmonitor-watchman.sample has two
    bugs:
    
     1. Wrong variable in error check: After calling watchman_clock(), the
        result is stored in $o, but the code checks $output->{error} instead
        of $o->{error}. This means errors from the clock command are
        silently ignored.
    
     2. Double output violates protocol: When the retry path triggers (the
        directory wasn't initially watched), output_result() is called with
        the "/" flag, then launch_watchman() is called recursively which
        calls output_result() again. This outputs two clock tokens to
        stdout, but git's fsmonitor v2 protocol expects exactly one
        response.
    
    Fix #1 by checking $o->{error} after watchman_clock().
    
    Fix #2 by removing the recursive launch_watchman() call. The "/"
    "everything is dirty" flag already tells git to do a full scan, and git
    will call the hook again on the next invocation with a valid clock
    token.
    
    Apply the same fixes to the test helper scripts in t/t7519/.
    
    Changes since v1:
    
     * Removed $retry variable and associated logic, which only existed to
       prevent infinite recursion from the now-removed recursive
       launch_watchman() call
     * Fixed commit authorship

Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-2180%2Fptarjan%2Fclaude%2Ffix-watchman-query-bug-sfbIw-v2
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-2180/ptarjan/claude/fix-watchman-query-bug-sfbIw-v2
Pull-Request: https://github.com/git/git/pull/2180

Range-diff vs v1:

 1:  116d26287f ! 1:  b9e00b8ab5 fsmonitor: fix two bugs in watchman hook retry path
     @@
       ## Metadata ##
     -Author: Claude <noreply@anthropic.com>
     +Author: Paul Tarjan <github@paulisageek.com>
      
       ## Commit message ##
     -    fsmonitor: fix two bugs in watchman hook retry path
     +    fsmonitor-watchman: fix variable reference and remove redundant code
      
          The is_work_tree_watched() function in fsmonitor-watchman.sample has
          two bugs:
     @@ Commit message
          git will call the hook again on the next invocation with a valid clock
          token.
      
     +    With the recursive call removed, the $retry guard is no longer needed
     +    since it only existed to prevent infinite recursion. Remove it.
     +
          Apply the same fixes to the test helper scripts in t/t7519/.
      
          Signed-off-by: Paul Tarjan <github@paulisageek.com>
      
       ## t/t7519/fsmonitor-watchman ##
     +@@ t/t7519/fsmonitor-watchman: if ($^O =~ 'msys' || $^O =~ 'cygwin') {
     + 	$git_work_tree = Cwd::cwd();
     + }
     + 
     +-my $retry = 1;
     +-
     + launch_watchman();
     + 
     + sub launch_watchman {
     +@@ t/t7519/fsmonitor-watchman: sub launch_watchman {
     + 
     + 	my $o = $json_pkg->new->utf8->decode($response);
     + 
     +-	if ($retry > 0 and $o->{error} and $o->{error} =~ m/unable to resolve root .* directory (.*) is not watched/) {
     ++	if ($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;
      @@ t/t7519/fsmonitor-watchman: sub launch_watchman {
       		close $fh;
       
     @@ t/t7519/fsmonitor-watchman: sub launch_watchman {
       
      
       ## t/t7519/fsmonitor-watchman-v2 ##
     +@@ t/t7519/fsmonitor-watchman-v2: if ($version ne 2) {
     + 
     + my $git_work_tree = get_working_dir();
     + 
     +-my $retry = 1;
     +-
     + my $json_pkg;
     + eval {
     + 	require JSON::XS;
     +@@ t/t7519/fsmonitor-watchman-v2: sub watchman_query {
     + sub is_work_tree_watched {
     + 	my ($output) = @_;
     + 	my $error = $output->{error};
     +-	if ($retry > 0 and $error and $error =~ m/unable to resolve root .* directory (.*) is not watched/) {
     +-		$retry--;
     ++	if ($error and $error =~ m/unable to resolve root .* directory (.*) is not watched/) {
     + 		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;
      @@ t/t7519/fsmonitor-watchman-v2: sub is_work_tree_watched {
       		# Watchman query just to get it over with now so we won't pay
       		# the cost in git to look up each individual file.
     @@ t/t7519/fsmonitor-watchman-v2: sub is_work_tree_watched {
       
      
       ## templates/hooks/fsmonitor-watchman.sample ##
     +@@ templates/hooks/fsmonitor-watchman.sample: if ($version ne 2) {
     + 
     + my $git_work_tree = get_working_dir();
     + 
     +-my $retry = 1;
     +-
     + my $json_pkg;
     + eval {
     + 	require JSON::XS;
     +@@ templates/hooks/fsmonitor-watchman.sample: sub watchman_query {
     + sub is_work_tree_watched {
     + 	my ($output) = @_;
     + 	my $error = $output->{error};
     +-	if ($retry > 0 and $error and $error =~ m/unable to resolve root .* directory (.*) is not watched/) {
     +-		$retry--;
     ++	if ($error and $error =~ m/unable to resolve root .* directory (.*) is not watched/) {
     + 		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;
      @@ templates/hooks/fsmonitor-watchman.sample: sub is_work_tree_watched {
       		# Watchman query just to get it over with now so we won't pay
       		# the cost in git to look up each individual file.


 t/t7519/fsmonitor-watchman                |  6 +-----
 t/t7519/fsmonitor-watchman-v2             | 10 ++--------
 templates/hooks/fsmonitor-watchman.sample | 10 ++--------
 3 files changed, 5 insertions(+), 21 deletions(-)

diff --git a/t/t7519/fsmonitor-watchman b/t/t7519/fsmonitor-watchman
index 264b9daf83..bcc055c1e0 100755
--- a/t/t7519/fsmonitor-watchman
+++ b/t/t7519/fsmonitor-watchman
@@ -38,8 +38,6 @@ if ($^O =~ 'msys' || $^O =~ 'cygwin') {
 	$git_work_tree = Cwd::cwd();
 }
 
-my $retry = 1;
-
 launch_watchman();
 
 sub launch_watchman {
@@ -92,9 +90,8 @@ sub launch_watchman {
 
 	my $o = $json_pkg->new->utf8->decode($response);
 
-	if ($retry > 0 and $o->{error} and $o->{error} =~ m/unable to resolve root .* directory (.*) is not watched/) {
+	if ($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;
@@ -109,7 +106,6 @@ sub launch_watchman {
 		close $fh;
 
 		print "/\0";
-		eval { launch_watchman() };
 		exit 0;
 	}
 
diff --git a/t/t7519/fsmonitor-watchman-v2 b/t/t7519/fsmonitor-watchman-v2
index 14ed0aa42d..368604c278 100755
--- a/t/t7519/fsmonitor-watchman-v2
+++ b/t/t7519/fsmonitor-watchman-v2
@@ -29,8 +29,6 @@ if ($version ne 2) {
 
 my $git_work_tree = get_working_dir();
 
-my $retry = 1;
-
 my $json_pkg;
 eval {
 	require JSON::XS;
@@ -122,8 +120,7 @@ sub watchman_query {
 sub is_work_tree_watched {
 	my ($output) = @_;
 	my $error = $output->{error};
-	if ($retry > 0 and $error and $error =~ m/unable to resolve root .* directory (.*) is not watched/) {
-		$retry--;
+	if ($error and $error =~ m/unable to resolve root .* directory (.*) is not watched/) {
 		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;
@@ -141,15 +138,12 @@ sub is_work_tree_watched {
 		# Watchman query just to get it over with now so we won't pay
 		# the cost in git to look up each individual file.
 		my $o = watchman_clock();
-		$error = $output->{error};
+		$error = $o->{error};
 
 		die "Watchman: $error.\n" .
 		"Falling back to scanning...\n" if $error;
 
 		output_result($o->{clock}, ("/"));
-		$last_update_token = $o->{clock};
-
-		eval { launch_watchman() };
 		return 0;
 	}
 
diff --git a/templates/hooks/fsmonitor-watchman.sample b/templates/hooks/fsmonitor-watchman.sample
index 23e856f5de..429e0a51c1 100755
--- a/templates/hooks/fsmonitor-watchman.sample
+++ b/templates/hooks/fsmonitor-watchman.sample
@@ -29,8 +29,6 @@ if ($version ne 2) {
 
 my $git_work_tree = get_working_dir();
 
-my $retry = 1;
-
 my $json_pkg;
 eval {
 	require JSON::XS;
@@ -123,8 +121,7 @@ sub watchman_query {
 sub is_work_tree_watched {
 	my ($output) = @_;
 	my $error = $output->{error};
-	if ($retry > 0 and $error and $error =~ m/unable to resolve root .* directory (.*) is not watched/) {
-		$retry--;
+	if ($error and $error =~ m/unable to resolve root .* directory (.*) is not watched/) {
 		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;
@@ -142,15 +139,12 @@ sub is_work_tree_watched {
 		# Watchman query just to get it over with now so we won't pay
 		# the cost in git to look up each individual file.
 		my $o = watchman_clock();
-		$error = $output->{error};
+		$error = $o->{error};
 
 		die "Watchman: $error.\n" .
 		"Falling back to scanning...\n" if $error;
 
 		output_result($o->{clock}, ("/"));
-		$last_update_token = $o->{clock};
-
-		eval { launch_watchman() };
 		return 0;
 	}
 

base-commit: 68cb7f9e92a5d8e9824f5b52ac3d0a9d8f653dbe
-- 
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