Improve performance of computing indexables (#1129)

* Avoid searching LOAD_PATH for entries that are related to the same pattern

* Avoid using Pathname#relative_path_from when instantiating indexable paths

Author: vinistock

lib/ruby_indexer/lib/ruby_indexer/configuration.rb

@@ -67,8 +67,12 @@ def indexables
 
       # Add user specified patterns
       indexables = @included_patterns.flat_map do |pattern|
+        load_path_entry = T.let(nil, T.nilable(String))
+
         Dir.glob(pattern, File::FNM_PATHNAME | File::FNM_EXTGLOB).map! do |path|
-          load_path_entry = $LOAD_PATH.find { |load_path| path.start_with?(load_path) }
+          # All entries for the same pattern match the same $LOAD_PATH entry. Since searching the $LOAD_PATH for every
+          # entry is expensive, we memoize it for the entire pattern
+          load_path_entry ||= $LOAD_PATH.find { |load_path| path.start_with?(load_path) }
           IndexablePath.new(load_path_entry, path)
         end
       end

lib/ruby_indexer/lib/ruby_indexer/indexable_path.rb

@@ -21,7 +21,7 @@ class IndexablePath
     def initialize(load_path_entry, full_path)
       @full_path = full_path
       @require_path = T.let(
-        load_path_entry ? Pathname.new(full_path).relative_path_from(load_path_entry).to_s.delete_suffix(".rb") : nil,
+        load_path_entry ? full_path.delete_prefix("#{load_path_entry}/").delete_suffix(".rb") : nil,
         T.nilable(String),
       )
     end