[master] Makefile: use shallow clone

Makefile

@@ -23,7 +23,8 @@ src/github.com/docker/cli:
 	cp -r "$(CLI_DIR)" $@
 else
 src/github.com/docker/cli:
-	git clone -q "$(DOCKER_CLI_REPO)" $@
+	git init $@
+	git -C $@ remote add origin "$(DOCKER_CLI_REPO)"
 endif
 
 ifdef ENGINE_DIR
@@ -32,16 +33,17 @@ src/github.com/docker/docker:
 	cp -r "$(ENGINE_DIR)" $@
 else
 src/github.com/docker/docker:
-	git clone -q "$(DOCKER_ENGINE_REPO)" $@
+	git init $@
+	git -C $@ remote add origin "$(DOCKER_ENGINE_REPO)"
 endif
 
 .PHONY: checkout-cli
 checkout-cli: src/github.com/docker/cli
-	@git -C src/github.com/docker/cli checkout -q "$(DOCKER_CLI_REF)"
+	./scripts/checkout.sh src/github.com/docker/cli "$(DOCKER_CLI_REF)"
 
 .PHONY: checkout-docker
 checkout-docker: src/github.com/docker/docker
-	@git -C src/github.com/docker/docker checkout -q "$(DOCKER_ENGINE_REF)"
+	./scripts/checkout.sh src/github.com/docker/docker "$(DOCKER_ENGINE_REF)"
 
 .PHONY: checkout
 checkout: checkout-cli checkout-docker ## checkout source at the given reference(s)

scripts/checkout.sh

@@ -0,0 +1,39 @@
+#!/usr/bin/env sh
+
+#   Copyright 2018-2020 Docker Inc.
+
+#   Licensed under the Apache License, Version 2.0 (the "License");
+#   you may not use this file except in compliance with the License.
+#   You may obtain a copy of the License at
+
+#       http://www.apache.org/licenses/LICENSE-2.0
+
+#   Unless required by applicable law or agreed to in writing, software
+#   distributed under the License is distributed on an "AS IS" BASIS,
+#   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+#   See the License for the specific language governing permissions and
+#   limitations under the License.
+
+checkout() (
+	set -ex
+	SRC="$1"
+	REF="$2"
+	REF_FETCH="$REF"
+	# if ref is branch or tag, retrieve its canonical form
+	REF=$(git -C "$SRC" ls-remote --refs --heads --tags origin "$REF" | awk '{print $2}')
+	if [ -n "$REF" ]; then
+		# if branch or tag then create it locally too
+		REF_FETCH="$REF:$REF"
+	else
+		REF="FETCH_HEAD"
+	fi
+	git -C "$SRC" fetch --update-head-ok --depth 1 origin "$REF_FETCH"
+	git -C "$SRC" checkout -q "$REF"
+)
+
+
+# Only execute checkout function above if this file is executed, not sourced from another script
+prog=checkout.sh # needs to be in sync with this file's name
+if [ "$(basename -- $0)" = "$prog" ]; then
+	checkout $*
+fi