Empty array instead of nil for source_extract

The source_extract method will return nil when it can't find the file name in
the backtrace, methods that consume this method expect an array and the nil ends
up causing type errors down the road like it happened here: #36341. This
patch refactors the source_extract method so that it returns an empty
array instead of nil when it can't find the source code.

Co-authored-by: Kasper Timm Hansen <kaspth@gmail.com>

3 files changed, 29 insertions, 12 deletions

diff --git a/actionview/CHANGELOG.md b/actionview/CHANGELOG.md
index f2f57e6a36..504b1d3e98 100644
--- a/actionview/CHANGELOG.md
+++ b/actionview/CHANGELOG.md
@@ -1,3 +1,8 @@
+*   annotated_source_code returns an empty array so TemplateErrors without a
+    template in the backtrace are surfaced properly by DebugExceptions.
+
+    *Guilherme Mansur*, *Kasper Timm Hansen*
+
 *   Add autoload for SyntaxErrorInTemplate so syntax errors are correctly raised by DebugExceptions.
 
     *Guilherme Mansur*, *Gannon McGibbon*
diff --git a/actionview/lib/action_view/template/error.rb b/actionview/lib/action_view/template/error.rb
index feceef15f9..7fc74a5502 100644
--- a/actionview/lib/action_view/template/error.rb
+++ b/actionview/lib/action_view/template/error.rb
@@ -81,8 +81,8 @@ module ActionView
         end
       end
 
-      def source_extract(indentation = 0, output = :console)
-        return unless num = line_number
+      def source_extract(indentation = 0)
+        return [] unless num = line_number
         num = num.to_i
 
         source_code = @template.source.split("\n")
@@ -91,9 +91,9 @@ module ActionView
         end_on_line   = [ num + SOURCE_CODE_RADIUS - 1, source_code.length].min
 
         indent = end_on_line.to_s.size + indentation
-        return unless source_code = source_code[start_on_line..end_on_line]
+        return [] unless source_code = source_code[start_on_line..end_on_line]
 
-        formatted_code_for(source_code, start_on_line, indent, output)
+        formatted_code_for(source_code, start_on_line, indent)
       end
 
       def sub_template_of(template_path)
@@ -122,15 +122,11 @@ module ActionView
           end + file_name
         end
 
-        def formatted_code_for(source_code, line_counter, indent, output)
-          start_value = (output == :html) ? {} : []
-          source_code.inject(start_value) do |result, line|
+        def formatted_code_for(source_code, line_counter, indent)
+          indent_template = "%#{indent}s: %s"
+          source_code.map do |line|
             line_counter += 1
-            if output == :html
-              result.update(line_counter.to_s => "%#{indent}s %s\n" % ["", line])
-            else
-              result << "%#{indent}s: %s" % [line_counter, line]
-            end
+            indent_template % [line_counter, line]
           end
         end
     end
diff --git a/actionview/test/template/template_error_test.rb b/actionview/test/template/template_error_test.rb
index c4dc88e4aa..643c29602b 100644
--- a/actionview/test/template/template_error_test.rb
+++ b/actionview/test/template/template_error_test.rb
@@ -34,4 +34,20 @@ class TemplateErrorTest < ActiveSupport::TestCase
 
     assert_equal "#<ActionView::Template::Error: original>", error.inspect
   end
+
+  def test_annotated_source_code_returns_empty_array_if_source_cant_be_found
+    template = Class.new do
+      def identifier
+        "something"
+      end
+    end.new
+
+    error = begin
+      raise
+    rescue
+      raise ActionView::Template::Error.new(template) rescue $!
+    end
+
+    assert_equal [], error.annotated_source_code
+  end
 end