Report when a Sass type used in a function is unsupported

Author: Edward Ocampo-Gooding

lib/sassc/functions_handler.rb

@@ -17,40 +17,40 @@ def setup(native_options)
         @callbacks[custom_function] = FFI::Function.new(:pointer, [:pointer, :pointer]) do |native_argument_list, cookie|
           native_argument_list_length = Native.list_get_length(native_argument_list)
           custom_function_arguments = []
+          errorTag = nil
 
           (0...native_argument_list_length).each do |i|
             native_value = Native.list_get_value(native_argument_list, i)
 
-            case Native.value_get_tag(native_value)
+            case value_tag = Native.value_get_tag(native_value)
+            when :sass_null
+              # no-op
             when :sass_string
               native_string = Native.string_get_value(native_value)
               argument = Script::String.new(Script::String.unquote(native_string), Script::String.type(native_string))
 
               custom_function_arguments << argument
+            else
+              errorTag = error(message: "Sass argument of type #{value_tag} unsupported")
+              break
             end
           end
 
-          begin
-            value = functions.send(custom_function, *custom_function_arguments)
-
-            if value
-              value = Script::String.new(Script::String.unquote(value.to_s), value.type)
-              value.to_native
-            else
-              Script::String.new("").to_native
+          if errorTag
+            errorTag
+          else
+            begin
+              value = functions.send(custom_function, *custom_function_arguments)
+
+              if value
+                value = Script::String.new(Script::String.unquote(value.to_s), value.type)
+                value.to_native
+              else
+                Script::String.new("").to_native
+              end
+            rescue StandardError => exception
+              error(message: exception.message)
             end
-          rescue StandardError => exception
-            value = Native::SassValue.new
-            value[:unknown] = Native::SassUnknown.new
-
-            error = Native::SassError.new
-            error[:tag] = :sass_error
-
-            Native.error_set_message(error, Native.native_string(exception))
-
-            value[:unknown][:tag] = :sass_error
-            value[:error] = error
-            value.pointer
           end
         end
 
@@ -70,6 +70,21 @@ def setup(native_options)
 
     private
 
+    def error(message:)
+      value = Native::SassValue.new
+      value[:unknown] = Native::SassUnknown.new
+
+      error = Native::SassError.new
+      error[:tag] = :sass_error
+
+      Native.error_set_message(error, Native.native_string(message))
+      $stderr.puts "[SassC::FunctionsHandler] #{message}"
+
+      value[:unknown][:tag] = :sass_error
+      value[:error] = error
+      value.pointer
+    end
+
     class FunctionWrapper
       class << self
         attr_accessor :options

test/functions_test.rb

@@ -1,42 +1,16 @@
 require_relative "test_helper"
+require "stringio"
 
 module SassC
   class FunctionsTest < MiniTest::Test
     include FixtureHelper
 
-    SassString = Struct.new(:value, :type) do
-      def to_s
-        value
-      end
+    def setup
+      @real_stderr, $stderr = $stderr, StringIO.new
     end
 
-    module Script::Functions
-      def javascript_path(path)
-        Script::String.new("/js/#{path.value}", :string)
-      end
-
-      def no_return_path(path)
-        nil
-      end
-
-      def sass_return_path(path)
-        return SassString.new("'#{path.value}'", :string)
-      end
-
-      def optional_arguments(path, optional = "bar")
-        return SassString.new("#{path}/#{optional}", :string)
-      end
-
-      def function_that_raises_errors()
-        raise StandardError, "Intentional wrong thing happened somewhere inside the custom function"
-      end
-
-      module Compass
-        def stylesheet_path(path)
-          Script::String.new("/css/#{path.value}", :identifier)
-        end
-      end
-      include Compass
+    def teardown
+      $stderr = @real_stderr
     end
 
     def test_functions_may_return_sass_string_type
@@ -88,9 +62,21 @@ def test_function_with_optional_arguments
       EOS
     end
 
+    def test_function_with_unsupported_tag
+      engine = Engine.new("div {url: function_with_unsupported_tag(red);}")
+
+      exception = assert_raises(SassC::SyntaxError) do
+        engine.render
+      end
+
+      assert_equal "Error: error in C function function_with_unsupported_tag: Sass argument of type sass_color unsupported\n\n       Backtrace:\n       \tstdin:1, in function `function_with_unsupported_tag`\n       \tstdin:1\n        on line 1 of stdin\n>> div {url: function_with_unsupported_tag(red);}\n   ----------^\n", exception.message
+
+      assert_equal "[SassC::FunctionsHandler] Sass argument of type sass_color unsupported", stderr_output
+    end
+
     def test_function_with_error
       engine = Engine.new("div {url: function_that_raises_errors();}")
-      exception = assert_raises(SassC::SyntaxError, "") do
+      exception = assert_raises(SassC::SyntaxError) do
         engine.render
       end
 
@@ -103,6 +89,52 @@ def test_function_with_error
 >> div {url: function_that_raises_errors();}
    ----------^
 ", exception.message
+
+      assert_equal "[SassC::FunctionsHandler] Intentional wrong thing happened somewhere inside the custom function", stderr_output
+    end
+
+    private
+
+    SassString = Struct.new(:value, :type) do
+      def to_s
+        value
+      end
+    end
+
+    module Script::Functions
+      def javascript_path(path)
+        Script::String.new("/js/#{path.value}", :string)
+      end
+
+      def no_return_path(path)
+        nil
+      end
+
+      def sass_return_path(path)
+        return SassString.new("'#{path.value}'", :string)
+      end
+
+      def optional_arguments(path, optional = "bar")
+        return SassString.new("#{path}/#{optional}", :string)
+      end
+
+      def function_that_raises_errors()
+        raise StandardError, "Intentional wrong thing happened somewhere inside the custom function"
+      end
+
+      def function_with_unsupported_tag(color)
+      end
+
+      module Compass
+        def stylesheet_path(path)
+          Script::String.new("/css/#{path.value}", :identifier)
+        end
+      end
+      include Compass
+    end
+
+    def stderr_output
+      $stderr.string.gsub("\u0000\n", '')
     end
   end
 end