Resolve all paths to absolute paths

When paths were sent in as relative paths from the CLI, `Exclude`
directives within a rubocop config yml were not correctly applied. This
is because Rubocop internally turns those excludes into absolute paths,
and it seems like it was then trying to match the being-analyzed
relative path against the had-been-made-absolute excluded path.

lib/cc/engine/file_list_resolver.rb

@@ -29,20 +29,24 @@ def exclude_due_to_config?(path)
       end
 
       def include_based_files_to_inspect
-        @include_paths.map do |path|
-          if path =~ %r{/$}
+        absolute_include_paths.flat_map do |path|
+          if Dir.exist?(path)
             rubocop_runner.send(:find_target_files, [path])
           elsif rubocop_file_to_include?(path)
             path
           end
-        end.flatten.compact
+        end.compact
       end
 
       def local_path(path)
         realpath = Pathname.new(@root).realpath.to_s
         path.gsub(%r{^#{realpath}/}, '')
       end
 
+      def absolute_include_paths
+        @include_paths.map { |path| Pathname.new(path).realpath.to_s }
+      end
+
       def rubocop_file_to_include?(file)
         if file =~ /\.rb$/
           true

spec/cc/engine/rubocop_spec.rb

@@ -62,6 +62,37 @@ def method
         expect(includes_check?(output, "Lint/UselessAssignment")).to be false
       end
 
+      it "respects excludes in an inherit_from directive" do
+        create_source_file("foo.rb", <<-EORUBY)
+          def method
+            unused = "x"
+            return false
+          end
+        EORUBY
+        create_source_file("bar.rb", <<-EORUBY)
+          def method
+            unused = 42
+            return true
+          end
+        EORUBY
+
+        create_source_file(
+          ".rubocop.yml",
+          "inherit_from: .rubocop_todo.yml\nAllCops:\n  DisabledByDefault: true\nLint/UselessAssignment:\n  Enabled: true\n"
+        )
+        create_source_file(
+          ".rubocop_todo.yml",
+          "Lint/UselessAssignment:\n  Exclude:\n    - bar.rb\n"
+        )
+
+        output = run_engine("include_paths" => ["foo.rb", "bar.rb"])
+        issues = output.split("\0").map { |istr| JSON.parse(istr) }
+        lint_issues = issues.select { |issue| issue["check_name"] == "Rubocop/Lint/UselessAssignment" }
+
+        expect(lint_issues.detect { |i| i["location"]["path"] == "foo.rb" }).to be_present
+        expect(lint_issues.detect { |i| i["location"]["path"] == "bar.rb" }).to be_nil
+      end
+
       it "reads a file with a #!.*ruby declaration at the top" do
         create_source_file("my_script", <<-EORUBY)
           #!/usr/bin/env ruby