From def1671ce4993cac32cbc329be3d4c7685b7a1d4 Mon Sep 17 00:00:00 2001
From: Taichi Ishitani <taichi730@gmail.com>
Date: Wed, 23 Oct 2019 02:29:58 +0900
Subject: [PATCH] Filter Docile's source files from backtrace (#36)

Extend any raised NoMethodError with a module to filter out Docile code
from the {#backtrace} and {#backtrace_locations} methods.

* Fixed #35
---
 lib/docile.rb                        |  1 +
 lib/docile/backtrace_filter.rb       | 22 ++++++++++++++++++++++
 lib/docile/fallback_context_proxy.rb |  7 ++++++-
 spec/docile_spec.rb                  | 19 +++++++++++++++++++
 4 files changed, 48 insertions(+), 1 deletion(-)
 create mode 100644 lib/docile/backtrace_filter.rb

diff --git a/lib/docile.rb b/lib/docile.rb
index f5b3f77..85e348d 100644
--- a/lib/docile.rb
+++ b/lib/docile.rb
@@ -2,6 +2,7 @@ require "docile/version"
 require "docile/execution"
 require "docile/fallback_context_proxy"
 require "docile/chaining_fallback_context_proxy"
+require "docile/backtrace_filter"
 
 # Docile keeps your Ruby DSLs tame and well-behaved.
 module Docile
diff --git a/lib/docile/backtrace_filter.rb b/lib/docile/backtrace_filter.rb
new file mode 100644
index 0000000..fd8f1f0
--- /dev/null
+++ b/lib/docile/backtrace_filter.rb
@@ -0,0 +1,22 @@
+module Docile
+  # @api private
+  #
+  # This is used to remove entries pointing to Docile's source files
+  # from {Exception#backtrace} and {Exception#backtrace_locations}.
+  #
+  # If {NoMethodError} is caught then the exception object will be extended
+  # by this module to add filter functionalities.
+  module BacktraceFilter
+    FILTER_PATTERN = /lib\/docile/
+
+    def backtrace
+      super.select { |trace| trace !~ FILTER_PATTERN }
+    end
+
+    if ::Exception.public_method_defined?(:backtrace_locations)
+      def backtrace_locations
+        super.select { |location| location.absolute_path !~ FILTER_PATTERN }
+      end
+    end
+  end
+end
diff --git a/lib/docile/fallback_context_proxy.rb b/lib/docile/fallback_context_proxy.rb
index 6d04607..db8a608 100644
--- a/lib/docile/fallback_context_proxy.rb
+++ b/lib/docile/fallback_context_proxy.rb
@@ -86,7 +86,12 @@ module Docile
       if @__receiver__.respond_to?(method.to_sym)
         @__receiver__.__send__(method.to_sym, *args, &block)
       else
-        @__fallback__.__send__(method.to_sym, *args, &block)
+        begin
+          @__fallback__.__send__(method.to_sym, *args, &block)
+        rescue NoMethodError => e
+          e.extend(BacktraceFilter)
+          raise e
+        end
       end
     end
   end
diff --git a/spec/docile_spec.rb b/spec/docile_spec.rb
index 70454e6..34b72e5 100644
--- a/spec/docile_spec.rb
+++ b/spec/docile_spec.rb
@@ -416,6 +416,25 @@ describe Docile do
       end
     end
 
+    context "when NoMethodError is raised" do
+      specify "#backtrace does not include path to Docile's source file" do
+        begin
+          Docile.dsl_eval(Object.new) { foo }
+        rescue NoMethodError => e
+          expect(e.backtrace).not_to include(match(/lib\/docile/))
+        end
+      end
+
+      if ::Exception.public_method_defined?(:backtrace_locations)
+        specify "#backtrace_locations also does not include path to Docile's source file" do
+          begin
+            Docile.dsl_eval(Object.new) { foo }
+          rescue NoMethodError => e
+            expect(e.backtrace_locations.map(&:absolute_path)).not_to include(match(/lib\/docile/))
+          end
+        end
+      end
+    end
   end
 
   describe ".dsl_eval_with_block_return" do