Weird method location shouldn't match unknown location

Methods that don't have a source location (e.g., C methods, or methods
created via metaprogramming or even `alias_method` to C methods) are not
reasonable possible matching methods for a "weird method" we need to
locate.

In this case `renamed_method_source_location` can also return `nil` if
the actual code in question is a bare script (i.e., no methods). If that
script is loaded via `eval` then we'll end up in the weird method path
in the first place, but no method matching can be found, and if a
no-source-location method exists, we'll return that.

Down the line that's particularly painful because the source loading
thinks it's a C method, but it can actually be from metaprogramming (and
`alias_method`!), and then `Pry::Method#pry_doc_info` raises an error,
and `wherami` breaks even though we already have valid `__FILE__` and
`__LINE__` values.

3 files changed, 42 insertions, 1 deletions

diff --git a/lib/pry/method/weird_method_locator.rb b/lib/pry/method/weird_method_locator.rb
index e4f58c8f..85614aec 100644
--- a/lib/pry/method/weird_method_locator.rb
+++ b/lib/pry/method/weird_method_locator.rb
@@ -158,7 +158,7 @@ class Pry
 
         alias_name = all_methods_for(target_self).find do |v|
           location = target_self.method(v).source_location
-          expanded_source_location(location) == renamed_method_source_location
+          location && expanded_source_location(location) == renamed_method_source_location
         end
 
         alias_name && Pry::Method(target_self.method(alias_name))
diff --git a/spec/fixtures/test_task.rb b/spec/fixtures/test_task.rb
new file mode 100644
index 00000000..dfa86941
--- /dev/null
+++ b/spec/fixtures/test_task.rb
@@ -0,0 +1,3 @@
+task :test_task do
+  binding
+end
diff --git a/spec/method_spec.rb b/spec/method_spec.rb
index 95ac075c..8f06c484 100644
--- a/spec/method_spec.rb
+++ b/spec/method_spec.rb
@@ -208,6 +208,44 @@ describe Pry::Method do
       m = Pry::Method.from_binding(o.borscht)
       expect(m.source).to eq Pry::Method(o.method(:paella)).source
     end
+
+    it 'should not find a wrong method by matching on nil source location' do
+      included_module = Module.new do
+        def self.included(base)
+          base.send :alias_method, "respond_to_without_variables?", "respond_to?"
+          base.send :alias_method, "respond_to?", "respond_to_with_variables?"
+        end
+
+        def respond_to_with_variables?(sym, include_priv=false)
+          respond_to_without_variables?(sym, include_priv)
+        end
+      end
+
+      o = Object.new
+      class << o
+        attr_reader :tasks
+        def task(name, &block)
+          @tasks ||= {}
+          @tasks[name] = block
+        end
+
+        def load
+          path = File.expand_path("../fixtures/test_task.rb", __FILE__)
+          instance_eval File.read(path), path
+        end
+      end
+
+      o.load
+
+      o2 = Object.new
+      o2.singleton_class.send(:include, included_module)
+
+      # Verify preconditions.
+      expect(o2.method(:respond_to_without_variables?).source_location).to be_nil
+
+      b = o2.instance_eval(&o.tasks[:test_task])
+      expect(Pry::Method.from_binding(b).name).to eq "load"
+    end
   end
 
   describe 'super' do