1 files changed, 38 insertions, 0 deletions
diff --git a/activesupport/lib/active_support/core_ext/name_error.rb b/activesupport/lib/active_support/core_ext/name_error.rb
new file mode 100644
index 0000000000..6d37cd9dfd
--- /dev/null
+++ b/activesupport/lib/active_support/core_ext/name_error.rb
@@ -0,0 +1,38 @@
+# frozen_string_literal: true
+
+class NameError
+  # Extract the name of the missing constant from the exception message.
+  #
+  #   begin
+  #     HelloWorld
+  #   rescue NameError => e
+  #     e.missing_name
+  #   end
+  #   # => "HelloWorld"
+  def missing_name
+    # Since ruby v2.3.0 `did_you_mean` gem is loaded by default.
+    # It extends NameError#message with spell corrections which are SLOW.
+    # We should use original_message message instead.
+    message = respond_to?(:original_message) ? original_message : self.message
+
+    if /undefined local variable or method/ !~ message
+      $1 if /((::)?([A-Z]\w*)(::[A-Z]\w*)*)$/ =~ message
+    end
+  end
+
+  # Was this exception raised because the given name was missing?
+  #
+  #   begin
+  #     HelloWorld
+  #   rescue NameError => e
+  #     e.missing_name?("HelloWorld")
+  #   end
+  #   # => true
+  def missing_name?(name)
+    if name.is_a? Symbol
+      self.name == name
+    else
+      missing_name == name.to_s
+    end
+  end
+end