Better way to find deprecated method location

Instead of relying on hard coded indexes, we can look through the called method stack backwards (i.e. the first method called will be the first in the list). If it has a suffix for one of our APIs, then we check to see if there exists a `public_` prefix on the view, if it does it's the first method called that can be deprecated so we point to that.

Author: schneems

lib/sprockets/rails/helper.rb

@@ -284,24 +284,23 @@ def deprecate_invalid_asset_lookup(name, call_stack)
           message << "The public fallback behavior is being deprecated and will be removed.\n"
 
           append = nil
-          # Search for the most likely top level method where deprecation occured.
-          # Hash contains, in order, the suffix we're looking for, and where it would appear
-          # in the call stack.
-          # This is needed because every deprecated method eventually calls `asset_path`.
-          { "_url" => [0, 1] , "_tag" => [1, 2], "_path" => [0] }.detect do |suffix, positions|
-
-            positions.detect do |position|
-              public_method_name = "public_" + extract_method_from_call_frame(call_stack[position])
-
-              if public_method_name.end_with?(suffix) && respond_to?(public_method_name)
-                position.times { call_stack.shift }
-                append = "please use the `public_*` helper instead. For example `#{ public_method_name }`.\n"
-              else
-                false
-              end
+
+          # We need to figure out the actually deprecated method. This is complicated since
+          # the deprecation always comes from `asset_path` but that might not be the API that
+          # is being used. To solve this we look at the call stack methods backwards and figure out the first
+          # `*_url`, `*_tag` or `*_path` method that is called. If that method also has a `public_*`
+          # counterpart it is the first method that was called that could be deprecated.
+          call_stack.reverse_each.detect.with_index do |call_frame, index|
+            method_name = extract_method_from_call_frame(call_frame)
+            next if !method_name.end_with?("_url".freeze) &&
+                      !method_name.end_with?("_tag".freeze) &&
+                      !method_name.end_with?("_path".freeze)
+
+            if self.respond_to?("public_#{ method_name }")
+              append = "please use the `public_*` helper instead. For example `#{ "public_#{ method_name }" }`.\n"
+              call_stack.shift(call_stack.length - index - 1)
             end
           end
-
           append ||= "please use the `public_*` helper instead for example `public_asset_path`.\n"
           message << append