tools/lookup: Support implementations lookup handlers

modules/tools/lookup/config.el

@@ -3,6 +3,8 @@
 ;; "What am I looking at?" This module helps you answer this question.
 ;;
 ;;   + `+lookup/definition': a jump-to-definition that should 'just work'
+;;   + `+lookup/implementations': find a symbol's implementations in the current
+;;                                project
 ;;   + `+lookup/references': find a symbol's references in the current project
 ;;   + `+lookup/file': open the file referenced at point
 ;;   + `+lookup/online'; look up a symbol on online resources
@@ -52,6 +54,15 @@ If the argument is interactive (satisfies `commandp'), it is called with
 argument: the identifier at point. See `set-lookup-handlers!' about adding to
 this list.")
 
+(defvar +lookup-implementations-functions ()
+  "Function for `+lookup/implementations' to try. Stops at the first function to
+return non-nil or change the current window/point.
+
+If the argument is interactive (satisfies `commandp'), it is called with
+`call-interactively' (with no arguments). Otherwise, it is called with one
+argument: the identifier at point. See `set-lookup-handlers!' about adding to
+this list.")
+
 (defvar +lookup-references-functions
   '(+lookup-xref-references-backend-fn
     +lookup-project-search-backend-fn)