Merge pull request #35308 from erose/better-error-reporting-for-syntax-errors-in-templates

Display a more helpful error message when an ERB template has a Ruby syntax error.

actionview/lib/action_view/template.rb

@@ -331,6 +331,7 @@ def compile(mod)
 
         # Make sure that the resulting String to be eval'd is in the
         # encoding of the code
+        original_source = source
         source = +<<-end_src
           def #{method_name}(local_assigns, output_buffer)
             @virtual_path = #{@virtual_path.inspect};#{locals_code};#{code}
@@ -351,7 +352,14 @@ def #{method_name}(local_assigns, output_buffer)
           raise WrongEncodingError.new(source, Encoding.default_internal)
         end
 
-        mod.module_eval(source, identifier, 0)
+        begin
+          mod.module_eval(source, identifier, 0)
+        rescue SyntaxError
+          # Account for when code in the template is not syntactically valid; e.g. if we're using
+          # ERB and the user writes <%= foo( %>, attempting to call a helper `foo` and interpolate
+          # the result into the template, but missing an end parenthesis.
+          raise SyntaxErrorInTemplate.new(self, original_source)
+        end
       end
 
       def handle_render_error(view, e)

actionview/lib/action_view/template/error.rb

@@ -138,4 +138,24 @@ def formatted_code_for(source_code, line_counter, indent, output)
   end
 
   TemplateError = Template::Error
+
+  class SyntaxErrorInTemplate < TemplateError #:nodoc
+    def initialize(template, offending_code_string)
+      @offending_code_string = offending_code_string
+      super(template)
+    end
+
+    def message
+      <<~MESSAGE
+        Encountered a syntax error while rendering template: check #{@offending_code_string}
+      MESSAGE
+    end
+
+    def annoted_source_code
+      @offending_code_string.split("\n").map.with_index(1) { |line, index|
+        indentation = " " * 4
+        "#{index}:#{indentation}#{line}"
+      }
+    end
+  end
 end

actionview/test/fixtures/test/syntax_error.html.erb

+<%= foo(
+  1,
+  2,
+%>

actionview/test/template/render_test.rb

@@ -259,6 +259,12 @@ def test_render_partial_with_hyphen_and_invalid_option_as
       "and is followed by any combination of letters, numbers and underscores.", e.message
   end
 
+  def test_render_template_with_syntax_error
+    e = assert_raises(ActionView::Template::Error) { @view.render(template: "test/syntax_error") }
+    assert_match %r!syntax!, e.message
+    assert_equal "1:    <%= foo(", e.annoted_source_code[0].strip
+  end
+
   def test_render_partial_with_errors
     e = assert_raises(ActionView::Template::Error) { @view.render(partial: "test/raise") }
     assert_match %r!method.*doesnt_exist!, e.message