Raise BranchNotFound error when getting a branch's head commit fails

Author: greysteil

lib/dependabot/errors.rb

@@ -3,6 +3,28 @@
 module Dependabot
   class DependabotError < StandardError; end
 
+  #####################
+  # Repo leval errors #
+  #####################
+
+  class BranchNotFound < DependabotError
+    attr_reader :branch_name
+
+    def initialize(branch_name, msg = nil)
+      @branch_name = branch_name
+      super(msg)
+    end
+
+    def file_name
+      branch_name.split("/").last
+    end
+
+    def directory
+      # Directory should always start with a `/`
+      branch_name.split("/")[0..-2].join("/").sub(%r{^/*}, "/")
+    end
+  end
+
   #####################
   # File level errors #
   #####################

lib/dependabot/file_fetchers/base.rb

@@ -48,6 +48,8 @@ def commit
             gitlab_client.branch(repo, branch).commit.id
           else raise "Unsupported host '#{host}'."
           end
+      rescue Octokit::NotFound
+        raise Dependabot::BranchNotFound, branch
       end
 
       private

spec/dependabot/file_fetchers/base_spec.rb

@@ -77,6 +77,22 @@ def fetch_files
         end
 
         it { is_expected.to eq("bb218f56b14c9653891f9e74264a383fa43fefbd") }
+
+        context "that can't be found" do
+          before do
+            stub_request(:get, url + "/git/refs/heads/my_branch").
+              with(headers: { "Authorization" => "token token" }).
+              to_return(status: 404,
+                        headers: { "content-type" => "application/json" })
+          end
+
+          it "raises a custom error" do
+            expect { file_fetcher_instance.files }.
+              to raise_error(Dependabot::BranchNotFound) do |error|
+                expect(error.branch_name).to eq("my_branch")
+              end
+          end
+        end
       end
     end