Use table summary for large groups

When five or more dependencies are being updated in a pull request, render the updates as a table for legibility.

common/lib/dependabot/pull_request_creator/message_builder.rb

@@ -315,12 +315,19 @@ def transitive_removed_dependency_intro
       def group_intro
         update_count = dependencies.map(&:name).uniq.count
 
-        msg = "Bumps the #{dependency_group.name} group#{pr_name_directory} with #{update_count} update"
-        msg += if update_count > 1
-                 "s: #{dependency_links[0..-2].join(', ')} and #{dependency_links[-1]}."
+        msg = "Bumps the #{dependency_group.name} group#{pr_name_directory} " \
+          "with #{update_count} update#{update_count > 1 ? 's' : ''}:"
+
+        msg += if update_count >= 5
+                header = ["Package", "Update"]
+                rows = dependencies.map { |dep| [dependency_link(dep), dependency_version_update(dep)] }
+                "\n\n#{table([header] + rows)}"
+               elsif update_count > 1
+                 " #{dependency_links[0..-2].join(', ')} and #{dependency_links[-1]}."
                else
-                 ": #{dependency_links.first}."
+                 " #{dependency_links.first}."
                end
+
         msg += "\n"
 
         msg
@@ -390,6 +397,10 @@ def dependency_link(dependency)
         end
       end
 
+      def dependency_version_update(dependency)
+        "#{dependency.humanized_previous_version} to #{dependency.humanized_version}"
+      end
+
       def metadata_links
         return metadata_links_for_dep(dependencies.first) if dependencies.count == 1
 
@@ -414,6 +425,24 @@ def metadata_links_for_dep(dep)
         msg
       end
 
+      def table(rows)
+        [
+          table_header(rows[0]),
+          rows[1..].map { |r| table_row(r) },
+        ].join("\n")
+      end
+
+      def table_header(row)
+        [
+          table_row(row),
+          table_row(["---"] * row.count),
+        ].join("\n")
+      end
+
+      def table_row(row)
+        "| #{row.join(' | ')} |"
+      end
+
       def metadata_cascades
         return metadata_cascades_for_dep(dependencies.first) if dependencies.one?
 

common/spec/dependabot/pull_request_creator/message_builder_spec.rb

@@ -2078,6 +2078,106 @@ def commits_details(base:, head:)
           end
         end
 
+        context "with five or more dependencies", :vcr do
+          let(:dependency2) do
+            Dependabot::Dependency.new(
+              name: "business2",
+              version: "1.8.0",
+              previous_version: "1.7.0",
+              package_manager: "dummy",
+              requirements: [],
+              previous_requirements: []
+            )
+          end
+          let(:dependency3) do
+            Dependabot::Dependency.new(
+              name: "business3",
+              version: "1.5.0",
+              previous_version: "1.4.0",
+              package_manager: "dummy",
+              requirements: [],
+              previous_requirements: []
+            )
+          end
+          let(:dependency4) do
+            Dependabot::Dependency.new(
+              name: "business4",
+              version: "2.1.1",
+              previous_version: "2.1.0",
+              package_manager: "dummy",
+              requirements: [],
+              previous_requirements: []
+            )
+          end
+          let(:dependency5) do
+            Dependabot::Dependency.new(
+              name: "business5",
+              version: "0.17.0",
+              previous_version: "0.16.2",
+              package_manager: "dummy",
+              requirements: [],
+              previous_requirements: []
+            )
+          end
+          let(:dependencies) { [dependency, dependency2, dependency3, dependency4, dependency5] }
+
+          before do
+            (2..5).each do |i|
+              repo_url = "https://api.github.com/repos/gocardless/business#{i}"
+
+              stub_request(:get, repo_url).
+                to_return(status: 200,
+                          body: fixture("github", "business_repo.json"),
+                          headers: json_header)
+              stub_request(:get, "#{repo_url}/contents/").
+                to_return(status: 200,
+                          body: fixture("github", "business_files.json"),
+                          headers: json_header)
+              stub_request(:get, "#{repo_url}/releases?per_page=100").
+                to_return(status: 200,
+                          body: fixture("github", "business_releases.json"),
+                          headers: json_header)
+              stub_request(:get, "https://api.github.com/repos/gocardless/" \
+                                "business#{i}/contents/CHANGELOG.md?ref=master").
+                to_return(status: 200,
+                          body: fixture("github", "changelog_contents.json"),
+                          headers: json_header)
+              stub_request(:get, "https://rubygems.org/api/v1/gems/business#{i}.json").
+                to_return(
+                  status: 200,
+                  body: fixture("ruby", "rubygems_response_statesman.json")
+                )
+
+              service_pack_url =
+                "https://github.com/gocardless/business#{i}.git/info/refs" \
+                "?service=git-upload-pack"
+
+              stub_request(:get, service_pack_url).
+                to_return(
+                  status: 200,
+                  body: fixture("git", "upload_packs", "no_tags"),
+                  headers: {
+                    "content-type" => "application/x-git-upload-pack-advertisement"
+                  }
+                )
+            end
+          end
+
+          it "has the correct message" do
+            expect(pr_message).to start_with(
+              "Bumps the all-the-things group with 5 updates:\n\n" \
+              "| Package | Update |\n" \
+              "| --- | --- |\n" \
+              "| [business](https://github.com/gocardless/business) | 1.4.0 to 1.5.0 |\n" \
+              "| [business2](https://github.com/gocardless/business2) | 1.7.0 to 1.8.0 |\n" \
+              "| [business3](https://github.com/gocardless/business3) | 1.4.0 to 1.5.0 |\n" \
+              "| [business4](https://github.com/gocardless/business4) | 2.1.0 to 2.1.1 |\n" \
+              "| [business5](https://github.com/gocardless/business5) | 0.16.2 to 0.17.0 |"
+            )
+          end
+        end
+
+
         context "with a directory specified" do
           let(:gemfile) do
             Dependabot::DependencyFile.new(