Apply BUNDLE_RETRY to lazy gemspec downloads

lib/bundler/fetcher.rb

@@ -157,7 +157,15 @@ def fetch_spec(spec)
       elsif cached_spec_path = gemspec_cached_path(spec_file_name)
         Bundler.load_gemspec(cached_spec_path)
       else
-        Bundler.safe_load_marshal Bundler.rubygems.inflate(downloader.fetch(uri).body)
+        # Lazily downloading a single gemspec is a network operation like any
+        # other, so it gets the same retry treatment as `specs_with_retry`.
+        # Without this a single transient failure aborts the whole resolution,
+        # which is most painful without a lockfile, where a resolve can fetch
+        # a great many gemspecs one at a time.
+        body = Bundler::Retry.new("fetcher", FAIL_ERRORS).attempts do
+          downloader.fetch(uri).body
+        end
+        Bundler.safe_load_marshal Bundler.rubygems.inflate(body)
       end
       raise MarshalError, "is #{spec.inspect}" unless spec.is_a?(Gem::Specification)
       spec

spec/bundler/fetcher_spec.rb

@@ -205,6 +205,33 @@ def configured_connection
       end
     end
 
+    context "when the download fails transiently" do
+      let(:spec) { Gem::Specification.new(name, version) }
+      let(:downloaded_data) { Zlib::Deflate.deflate(Marshal.dump(spec)) }
+
+      it "retries the download and returns the spec" do
+        expect(Bundler::Fetcher::Downloader).to receive(:new).and_return(downloader)
+        expect(downloader).to receive(:fetch).twice do
+          @attempts = (@attempts || 0) + 1
+          raise Bundler::HTTPError, "transient network failure" if @attempts == 1
+          body
+        end
+
+        result = fetcher.fetch_spec([name, version, platform])
+        expect(result).to eq(spec)
+      end
+
+      it "does not retry an error that bypasses retries" do
+        expect(Bundler::Fetcher::Downloader).to receive(:new).and_return(downloader)
+        expect(downloader).to receive(:fetch).once.and_raise(
+          Bundler::Fetcher::AuthenticationRequiredError.new("http://example.org")
+        )
+
+        expect { fetcher.fetch_spec([name, version, platform]) }.
+          to raise_error(Bundler::Fetcher::AuthenticationRequiredError)
+      end
+    end
+
     context "when attempting to load an unexpected class" do
       let(:downloaded_data) { Zlib::Deflate.deflate(Marshal.dump(3)) }