Fix ERB template highlighting crash when compiled longer than source

This ensures that the debug template will be shown even if the error
highlighting is on the wrong line. When the compiled template is much
longer than the source, errors can occur on lines that don't exist on
the source. Avoid crashing so the exception middleware can display.

Author: martinemde

actionview/CHANGELOG.md

@@ -1,3 +1,8 @@
+*   Fix a crash in ERB template error highlighting when the error occurs on a
+    line in the compiled template that is past the end of the source template.
+
+    *Martin Emde*
+
 *   Improve reliability of ERB template error highlighting.
     Fix infinite loops and crashes in highlighting and
     improve tolerance for alternate ERB handlers.

actionview/lib/action_view/template/handlers/erb.rb

@@ -42,7 +42,9 @@ def handles_encoding?
         # source location inside the template.
         def translate_location(spot, backtrace_location, source)
           # Tokenize the source line
-          tokens = ::ERB::Util.tokenize(source.lines[backtrace_location.lineno - 1])
+          source_lines = source.lines
+          return nil if source_lines.size < backtrace_location.lineno
+          tokens = ::ERB::Util.tokenize(source_lines[backtrace_location.lineno - 1])
           new_first_column = find_offset(spot[:snippet], tokens, spot[:first_column])
           lineno_delta = spot[:first_lineno] - backtrace_location.lineno
           spot[:first_lineno] -= lineno_delta
@@ -51,7 +53,7 @@ def translate_location(spot, backtrace_location, source)
           column_delta = spot[:first_column] - new_first_column
           spot[:first_column] -= column_delta
           spot[:last_column] -= column_delta
-          spot[:script_lines] = source.lines
+          spot[:script_lines] = source_lines
 
           spot
         rescue NotImplementedError, LocationParsingError

actionview/test/template/template_test.rb

@@ -339,10 +339,11 @@ def test_template_translate_location
     assert_equal expected, new_template(source).translate_location(backtrace_location, spot)
   end
 
+  # merely tests for the case where the backtrace and spot disagree about lineno
   def test_template_translate_location_lineno_offset
     highlight = "nomethoderror"
     source = "<%= nomethoderror %>"
-    compiled = "\n'.freeze; @output_buffer.append=  nomethoderror ; @output_buffer.safe_append='\n"
+    compiled = "'.freeze; @output_buffer.append=  nomethoderror ; @output_buffer.safe_append='"
 
     backtrace_location = Data.define(:lineno).new(lineno: 1)
     spot = spot_highlight(compiled, highlight, first_lineno: 2, last_lineno: 2)
@@ -351,6 +352,21 @@ def test_template_translate_location_lineno_offset
     assert_equal expected, new_template(source).translate_location(backtrace_location, spot)
   end
 
+  # We are testing the failure case here. `find_offset` doesn't correctly handle the case
+  # where the line number is not the same in the backtrace and template.
+  def test_template_translate_location_with_multiline_code_source
+    highlight = "nomethoderror"
+    source = "<%=\ngood(\n nomethoderror\n) %>"
+    extracted_line = " nomethoderror\n"
+    compiled = "ValidatedOutputBuffer.wrap(@output_buffer, ({}), ' \ngood(\n nomethoderror\n" \
+               ") '.freeze, true).safe_none_append=( \ngood(\n nomethoderror\n) );\n@output_buffer"
+
+    backtrace_location = Data.define(:lineno).new(lineno: 6)
+    spot = spot_highlight(compiled, highlight, first_column: 1, first_lineno: 6, last_lineno: 6, snippet: extracted_line)
+
+    assert_equal spot, new_template(source).translate_location(backtrace_location, spot)
+  end
+
   def test_template_translate_location_with_multibye_string_before_highlight
     highlight = "nomethoderror"
     source = String.new("\u{a5}<%= nomethoderror %>", encoding: Encoding::UTF_8) # yen symbol