Set asset finder from callable

lib/inline_svg.rb

@@ -19,7 +19,7 @@ module InlineSvg
   class Configuration
     class Invalid < ArgumentError; end
 
-    attr_reader :asset_file, :asset_finder, :custom_transformations, :svg_not_found_css_class
+    attr_reader :asset_file, :custom_transformations, :svg_not_found_css_class
 
     def initialize
       @custom_transformations = {}
@@ -41,8 +41,15 @@ def asset_file=(custom_asset_file)
       end
     end
 
+    def asset_finder
+      set_asset_finder_from_callable
+      @asset_finder
+    end
+
     def asset_finder=(finder)
-      @asset_finder = if finder.respond_to?(:find_asset)
+      @asset_finder = if finder.respond_to?(:call)
+                        finder
+                      elsif finder.respond_to?(:find_asset)
                         finder
                       elsif finder.class.name == "Propshaft::Assembly"
                         InlineSvg::PropshaftAssetFinder
@@ -52,7 +59,6 @@ def asset_finder=(finder)
                         # See: https://github.com/jamesmartin/inline_svg/issues/25
                         InlineSvg::StaticAssetFinder
                       end
-      asset_finder
     end
 
     def svg_not_found_css_class=(css_class)
@@ -82,6 +88,11 @@ def incompatible_transformation?(klass)
       !klass.is_a?(Class) || !klass.respond_to?(:create_with_value) || !klass.instance_methods.include?(:transform)
     end
 
+    def set_asset_finder_from_callable
+      if @asset_finder && @asset_finder.respond_to?(:call)
+        self.asset_finder = @asset_finder.call
+      end
+    end
   end
 
   @configuration = InlineSvg::Configuration.new

lib/inline_svg/railtie.rb

@@ -10,14 +10,12 @@ class Railtie < ::Rails::Railtie
 
     config.after_initialize do |app|
       InlineSvg.configure do |config|
-        # Configure the asset_finder:
-        # Only set this when a user-configured asset finder has not been
-        # configured already.
-        if config.asset_finder.nil?
-          # In default Rails apps, this will be a fully operational
-          # Sprockets::Environment instance
-          config.asset_finder = app.instance_variable_get(:@assets)
-        end
+        # Configure an asset finder for Rails. This will be evaluated when the
+        # first SVG is rendered, giving time to the asset pipeline to be done
+        # loading.
+        config.asset_finder = proc {
+          app.instance_variable_get(:@assets)
+        }
       end
     end
   end

spec/inline_svg_spec.rb

@@ -19,6 +19,10 @@ def self.named(filename); end
 
 describe InlineSvg do
   describe "configuration" do
+    before do
+      InlineSvg.reset_configuration!
+    end
+
     context "when a block is not given" do
       it "complains" do
         expect do
@@ -29,14 +33,24 @@ def self.named(filename); end
 
     context "asset finder" do
       it "allows an asset finder to be assigned" do
-        sprockets = double('SomethingLikeSprockets', find_asset: 'some asset')
+        sprockets = double("Something like sprockets", find_asset: "some asset")
         InlineSvg.configure do |config|
           config.asset_finder = sprockets
         end
 
         expect(InlineSvg.configuration.asset_finder).to eq sprockets
       end
 
+      it "allows to give a callable object that returns an asset finder" do
+        propshaft = double("Something like propshaft", class: double(name: "Propshaft::Assembly"))
+        callable = -> { propshaft }
+        InlineSvg.configure do |config|
+          config.asset_finder = callable
+        end
+
+        expect(InlineSvg.configuration.asset_finder).to eq InlineSvg::PropshaftAssetFinder
+      end
+
       it "falls back to StaticAssetFinder when the provided asset finder does not implement #find_asset" do
         InlineSvg.configure do |config|
           config.asset_finder = 'Not a real asset finder'