Fix protobuf regeneration script. (#5291)

release/v20.03-specific change: use dgo/v2 instead of dgo/v200.

This fixes the make regenerate command that should create the generated
protobuf code.

1. make regenerate fails to run (error log attached in PR)
2. The protobuf dependencies are unintentionally updated to the latest
   version.
3. It was referencing protobuf definitions from GOPATH. So, if a package
   was not updated to the right version (e.g., updating
   github.com/dgraph-io/badger to the latest master), then there could
   be errors like the following when referencing the wrong version of a
   proto:

      pb.proto:285:18: "badgerpb2.KV" is not defined.
      pb.proto:297:11: "badgerpb2.KV" is not defined.
      pb.proto:545:5: "badgerpb2.KVList" is not defined.
      pb.proto:537:60: "badgerpb2.KVList" is not defined.
      pb.proto:28:1: warning: Import github.com/dgraph-io/badger/pb/pb.proto is unused.

Changes

* Include proto path /usr/local/include in protoc command to fix (1).
* Update depcheck.sh to check that this directory exists. Error out with
  installation instructions otherwise if it's missing.
* Install protobuf libraries from the versions in go.mod, and use go install
  instead of go get so the protobuf versions aren't updated automatically to fix
  (2).
* Copy to temporary directory for proper import paths from go mod versions to
  remove any dependencies on $GOPATH to fix (3).
  * protos from proto library
  * proto from badger
  * proto from dgo
* Regenerate protos

protos/Makefile

@@ -14,10 +14,14 @@
 # limitations under the License.
 #
 
-PROTO_PATH := ${GOPATH}/src:.
-PROTO_PATH := ${PROTO_PATH}:${GOPATH}/src/github.com/dgraph-io/dgraph
-PROTO_PATH := ${PROTO_PATH}:${GOPATH}/src/github.com/dgraph-io/dgo/protos
-PROTO_PATH := ${PROTO_PATH}:${GOPATH}/src/github.com/dgraph-io/badger/pb
+DGO_PATH    := github.com/dgraph-io/dgo/v2
+BADGER_PATH := github.com/dgraph-io/badger/v2
+GOGO_PATH   := github.com/gogo/protobuf
+
+TMPDIR     := $(shell mktemp -d)
+PROTO_PATH := ${TMPDIR}/src:.
+PROTO_PATH := ${PROTO_PATH}:${TMPDIR}/src/${DGO_PATH}/protos
+PROTO_PATH := ${PROTO_PATH}:${TMPDIR}/src/${BADGER_PATH}/pb
 
 .PHONY: help
 help:
@@ -30,21 +34,25 @@ clean:
 .PHONY: check
 check:
 	@./depcheck.sh && \
-		(echo "Upgrading proto libraries before regenerating." ; \
-		go get -u github.com/golang/protobuf/protoc-gen-go ; \
-		go get -u github.com/gogo/protobuf/protoc-gen-gofast)
+		(echo "Installing proto libraries to versions in go.mod." ; \
+		go install github.com/golang/protobuf/protoc-gen-go ; \
+		go install github.com/gogo/protobuf/protoc-gen-gofast)
+
+.PHONY: copy-protos
+copy-protos:
+	@mkdir -p ${TMPDIR}/src/${DGO_PATH}/protos
+	@mkdir -p ${TMPDIR}/src/${BADGER_PATH}/pb
+	@mkdir -p ${TMPDIR}/src/${GOGO_PATH}/gogoproto
+	@cp $(shell go list -m -f "{{.Dir}}" ${BADGER_PATH})/pb/pb.proto ${TMPDIR}/src/${BADGER_PATH}/pb/pb.proto
+	@cp $(shell go list -m -f "{{.Dir}}" ${DGO_PATH})/protos/api.proto ${TMPDIR}/src/${DGO_PATH}/protos/api.proto
+	@cp $(shell go list -m -f "{{.Dir}}" ${GOGO_PATH})/gogoproto/gogo.proto ${TMPDIR}/src/${GOGO_PATH}/gogoproto/gogo.proto
 
 .PHONY: regenerate
-regenerate: check clean
-#	These sed replacements are necessary to use Badger v2 via Go modules.
-#	The protoc tool doesn't recognize Go module import paths, so we need to
-#	specify the filesystem-level import path (without "v2") to generate the
-#	protos and then set "v2" in the generated code (pb/pb.pb.go).
-	@sed -i'' -e 's;github.com/dgraph-io/badger/v2/pb/pb.proto;github.com/dgraph-io/badger/pb/pb.proto;' pb.proto
+regenerate: copy-protos check clean
 	@protoc \
+		--proto_path=/usr/local/include \
 		--proto_path=${PROTO_PATH} \
-		--gofast_out=plugins=grpc,Mapi.proto=github.com/dgraph-io/dgo/v2/protos/api:pb \
+		--gofast_out=plugins=grpc,Mapi.proto=${DGO_PATH}/protos/api:pb \
 		pb.proto
-	@sed -i'' -e 's;github.com/dgraph-io/badger/pb/pb.proto;github.com/dgraph-io/badger/v2/pb/pb.proto;' pb.proto
-	@sed -i'' -e 's;github.com/dgraph-io/badger/pb;github.com/dgraph-io/badger/v2/pb;' pb/pb.pb.go
+	@rm -rf ${TMPDIR}
 	@echo Done.

protos/depcheck.sh

@@ -4,7 +4,7 @@ set -e
 
 readonly PROTOCMINVER="3.6.1"
 
-which protoc &>/dev/null || (echo "Error: protoc not found" ; exit 1)
+which protoc &>/dev/null || (echo "Error: protoc not found" >&2; exit 1)
 
 PROTOCVER=`protoc --version | awk '{printf $2}'`
 
@@ -14,22 +14,34 @@ function CompareSemVer() {
 	local minver=(${1//./ })
 	local curver=(${2//./ })
 
-	echo "Checking for semantic version $1 or newer"
+	echo -n "Checking protoc for semantic version $1 or newer... "
 
 	for i in 0 1 2; do
 		if [ ${minver[$i]} -gt ${curver[$i]} ]; then
-			echo "Error: version $2 is lower than the required version $1"
+			echo "FAIL" >&2
+			echo "Error: version $2 is lower than the required version $1" >&2
 			exit 1
 		elif [ ${curver[$i]} -gt ${minver[$i]} ]; then
 			break
 		fi
 	done
 }
 
-CompareSemVer $PROTOCMINVER $PROTOCVER
+function CheckProtobufIncludes() {
+	echo -n "Checking for directory /usr/local/include/google/protobuf... "
+	if [ ! -d /usr/local/include/google/protobuf ]; then
+		echo "FAIL" >&2
+		echo "Missing protobuf types in /usr/local/include/google/protobuf: directory not found" >&2
+		echo "Download and install protoc and the protobuf types from protobuf releases page:" >&2
+		echo "https://github.com/protocolbuffers/protobuf/releases/" >&2
+		exit 1
+	fi
+}
 
-# TODO: check proto api versions
+CompareSemVer $PROTOCMINVER $PROTOCVER
+echo "OK"
 
+CheckProtobufIncludes
 echo "OK"
 
 exit 0