From 07804d4759726da04020834502d37a8f4ac97a8f Mon Sep 17 00:00:00 2001
From: Eli Rose <really.eli@gmail.com>
Date: Sun, 17 Feb 2019 23:07:16 -0500
Subject: [PATCH] Add handling and tests.

---
 actionview/lib/action_view/template.rb        | 10 +++++++++-
 actionview/lib/action_view/template/error.rb  | 20 +++++++++++++++++++
 .../test/fixtures/test/syntax_error.html.erb  |  4 ++++
 actionview/test/template/render_test.rb       |  6 ++++++
 4 files changed, 39 insertions(+), 1 deletion(-)
 create mode 100644 actionview/test/fixtures/test/syntax_error.html.erb

diff --git a/actionview/lib/action_view/template.rb b/actionview/lib/action_view/template.rb
index 37f476e554..9f1ca42041 100644
--- a/actionview/lib/action_view/template.rb
+++ b/actionview/lib/action_view/template.rb
@@ -313,6 +313,7 @@ module ActionView
 
         # 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}
@@ -333,7 +334,14 @@ module ActionView
           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)
diff --git a/actionview/lib/action_view/template/error.rb b/actionview/lib/action_view/template/error.rb
index 4e3c02e05e..ff01e4cd83 100644
--- a/actionview/lib/action_view/template/error.rb
+++ b/actionview/lib/action_view/template/error.rb
@@ -138,4 +138,24 @@ module ActionView
   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
diff --git a/actionview/test/fixtures/test/syntax_error.html.erb b/actionview/test/fixtures/test/syntax_error.html.erb
new file mode 100644
index 0000000000..4004a2b187
--- /dev/null
+++ b/actionview/test/fixtures/test/syntax_error.html.erb
@@ -0,0 +1,4 @@
+<%= foo(
+  1,
+  2,
+%>
diff --git a/actionview/test/template/render_test.rb b/actionview/test/template/render_test.rb
index cda8c942d8..171650d0b5 100644
--- a/actionview/test/template/render_test.rb
+++ b/actionview/test/template/render_test.rb
@@ -263,6 +263,12 @@ module RenderTestCases
       "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