Replace manual mock generation with go generate

This uses the builtin Go method for generating mocks; read more in:
https://blog.codecentric.de/en/2017/08/gomock-tutorial/#using-gomock-with-gogenerate

As a result, we can clean up quite a bit of code and manual workarounds,
and the generated code is identical (minus the copyright header); that
said, this feature was added on 25 Dec 2018 in
golang/mock#234 which was after the most-recent
release of v1.2.0 on 8 Dec 2018, so it's not available to us just yet.

.travis.yml

@@ -29,6 +29,8 @@ before_script:
   # Install dependencies for testing.
   - go get github.com/golang/mock/gomock@v1.2.0
   - go get github.com/golang/mock/mockgen@v1.2.0
+  # Generate the mocks for testing.
+  - go generate ./...
 
 script:
   - make test

Makefile

@@ -25,13 +25,8 @@ gofmt_test:
 	$(VERB) echo "Running 'go fmt' test ..."
 	$(VERB) ./gofmt_test.sh
 
-ghutil_test:
-	$(VERB) echo
-	$(VERB) echo "Running tests in 'ghutil' recursively ..."
-	$(VERB) $(MAKE) VERBOSE=$(VERBOSE) -s -C ghutil test
-
 go_mod_tidy_test:
 	$(VERB) echo "Running 'go mod tidy' test ..."
 	$(VERB) ./go_mod_tidy_test.sh
 
-test: go_test gofmt_test ghutil_test go_mod_tidy_test
+test: go_test gofmt_test go_mod_tidy_test

README.md

@@ -50,6 +50,12 @@ $ go get github.com/golang/mock/gomock@v1.2.0
 $ go get github.com/golang/mock/mockgen@v1.2.0
 ```
 
+Generate the mocks:
+
+```bash
+$ go generate ./...
+```
+
 This specific version of both `gomock` and `mockgen` tools is what's used in
 this repo, and tests will fail if your version of these tools generates
 different code, including comments.
@@ -59,18 +65,9 @@ To update the versions of these tools used in this repo:
 1. update the version numbers in this file (above) and in
    [`.travis.yml`](.travis.yml) to match
 1. run the commands above to get those specific versions of the tools
-1. update the generated code in this repo via:
-
-   ```bash
-   $ cd ghutil
-   $ rm -f mock_ghutil.go
-   $ make mock
-   ```
-
 1. [run the tests](#testing) from the top-level of the tree
-1. commit your changes to this file (`README.md`), `.travis.yml`, and
-   `ghutil/mock_ghutil.go` and make sure the build passes on Travis CI before
-   merging the change
+1. commit your changes to this file (`README.md`) and `.travis.yml`, making
+   sure that the build passes on Travis CI before merging the change
 
 ## Testing
 

ghutil/.gitignore

@@ -0,0 +1 @@
+mock_ghutil.go

ghutil/ghutil.go

@@ -12,6 +12,10 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+// TODO(mbrukman): in the future, consider using the recently-added
+// `-copyright_filename` flag: https://github.com/golang/mock/pull/234
+
+//go:generate mockgen -source ghutil.go -destination mock_ghutil.go -package ghutil
 package ghutil
 
 import (