From d6623cf2da1bdb49dc9019818ab7593f1fbd1f80 Mon Sep 17 00:00:00 2001
From: Todd Derr <salty@bandcamp.com>
Date: Fri, 17 Jun 2022 18:25:55 -0400
Subject: [PATCH] feat: use watchman's `watch-project` if available

If watchman is bersion 3.3 or later, use `watch-project` rather than
the deprecated `watch`. The main advantage is eliminating redundant
nested watches (i.e.  where one is a subtree of another), which reduces
RAM and CPU usage in the `watchman` daemon and eliminates the indexing
delay when invoking Command-T after moving down the directory hierarchy.

Although `watch-project` was introduced in 3.1 it is awkward/inefficient
to use without the `relative_root` query which was introduced in 3.3.
3.3 was released in June 2015, so most users should have a newer version
but backward compatibility with older versions is maintained.

Fixes #389

Tested:
* Tested the new code under various scenarios by invoking Command-T in my homedir
  and various subdirectories, as well as other paths (/tmp).
* Manually tested the fallback path to `watch`, which is unchanged from existing code.
* Tested various version numbers by manually simulating the output of `--version`
    * If the version number is missing or malformed, it will end up as version 0.0
    * test cases: nil, "", "foo.bar", "-5.2", "1", "3.2", 3.3.449", "4", "2022.06.13.00"
---
 .../file_scanner/watchman_file_scanner.rb     | 36 ++++++++++++++-----
 1 file changed, 27 insertions(+), 9 deletions(-)

diff --git a/ruby/command-t/lib/command-t/scanner/file_scanner/watchman_file_scanner.rb b/ruby/command-t/lib/command-t/scanner/file_scanner/watchman_file_scanner.rb
index 60f412a7..330bc3c9 100644
--- a/ruby/command-t/lib/command-t/scanner/file_scanner/watchman_file_scanner.rb
+++ b/ruby/command-t/lib/command-t/scanner/file_scanner/watchman_file_scanner.rb
@@ -25,20 +25,29 @@ def paths!
 
           UNIXSocket.open(sockname) do |socket|
             root = Pathname.new(@path).realpath.to_s
-            roots = Watchman::Utils.query(['watch-list'], socket)['roots']
-            if !roots.include?(root)
-              # this path isn't being watched yet; try to set up watch
-              result = Watchman::Utils.query(['watch', root], socket)
+            # use `watch-project` for efficiency if it's available
+            if use_watch_project?
+                result = Watchman::Utils.query(['watch-project', root], socket)
+                root = extract_value(result, 'watch')
+                relative_root = extract_value(result, 'relative_path') if result.has_key?('relative_path')
+            else
+              roots = Watchman::Utils.query(['watch-list'], socket)['roots']
+              if !roots.include?(root)
+                # this path isn't being watched yet; try to set up watch
+                result = Watchman::Utils.query(['watch', root], socket)
 
-              # root_restrict_files setting may prevent Watchman from working
-              # or enforce_root_files/root_files (>= version 3.1)
-              extract_value(result)
+                # root_restrict_files setting may prevent Watchman from working
+                # or enforce_root_files/root_files (>= version 3.1)
+                extract_value(result)
+              end
             end
 
-            query = ['query', root, {
+            query_params = {
               'expression' => ['type', 'f'],
               'fields'     => ['name'],
-            }]
+            }
+            query_params['relative_root'] = relative_root if relative_root;
+            query = ['query', root, query_params]
             paths = Watchman::Utils.query(query, socket)
 
             # could return error if watch is removed
@@ -68,6 +77,15 @@ def get_raw_sockname
           end
           raw_sockname
         end
+
+        # watch_project is available in 3.1+ but it's awkward to use without
+        # relative_root (3.3+), so use the latter as our minimum version.
+        def use_watch_project?
+          return @use_watch_project if defined?(@use_watch_project)
+          version = %x{watchman --version 2>/dev/null}
+          major, minor = version.split('.')[0..1] if !$?.exitstatus.nil? && $?.exitstatus.zero? && version
+          @use_watch_project = major.to_i > 3 || (major.to_i == 3 && minor.to_i >= 3)
+        end
       end
     end
   end