prow.sh: use vendor directory if available

This avoids dependencies on the Go module cache or the upstream code
hosting.

Author: pohly

Diff for: build.make

@@ -22,6 +22,9 @@
 # including build.make.
 REGISTRY_NAME=quay.io/k8scsi
 
+# Can be set to -mod=vendor to ensure that the "vendor" directory is used.
+GOFLAGS_VENDOR=
+
 # Revision that gets built into each binary via the main.version
 # string. Uses the `git describe` output based on the most recent
 # version tag with a short revision suffix or, if nothing has been
@@ -64,9 +67,9 @@ ARCH := $(if $(GOARCH),$(GOARCH),$(shell go env GOARCH))
 
 build-%: check-go-version-go
 	mkdir -p bin
-	CGO_ENABLED=0 GOOS=linux go build -a -ldflags '-X main.version=$(REV) -extldflags "-static"' -o ./bin/$* ./cmd/$*
+	CGO_ENABLED=0 GOOS=linux go build $(GOFLAGS_VENDOR) -a -ldflags '-X main.version=$(REV) -extldflags "-static"' -o ./bin/$* ./cmd/$*
 	if [ "$$ARCH" = "amd64" ]; then \
-		CGO_ENABLED=0 GOOS=windows go build -a -ldflags '-X main.version=$(REV) -extldflags "-static"' -o ./bin/$*.exe ./cmd/$* ; \
+		CGO_ENABLED=0 GOOS=windows go build $(GOFLAGS_VENDOR) -a -ldflags '-X main.version=$(REV) -extldflags "-static"' -o ./bin/$*.exe ./cmd/$* ; \
 	fi
 
 container-%: build-%
@@ -103,13 +106,13 @@ test: check-go-version-go
 test: test-go
 test-go:
 	@ echo; echo "### $@:"
-	go test `go list ./... | grep -v -e 'vendor' -e '/test/e2e$$' $(TEST_GO_FILTER_CMD)` $(TESTARGS)
+	go test $(GOFLAGS_VENDOR) `go list $(GOFLAGS_VENDOR) ./... | grep -v -e 'vendor' -e '/test/e2e$$' $(TEST_GO_FILTER_CMD)` $(TESTARGS)
 
 .PHONY: test-vet
 test: test-vet
 test-vet:
 	@ echo; echo "### $@:"
-	go vet `go list ./... | grep -v vendor $(TEST_VET_FILTER_CMD)`
+	go test $(GOFLAGS_VENDOR) `go list $(GOFLAGS_VENDOR) ./... | grep -v vendor $(TEST_VET_FILTER_CMD)`
 
 .PHONY: test-fmt
 test: test-fmt

Diff for: prow.sh

@@ -85,6 +85,12 @@ get_versioned_variable () {
     echo "$value"
 }
 
+# If we have a vendor directory, then use it. We must be careful to only
+# use this for "make" invocations inside the project's repo itself because
+# setting it globally can break other go usages (like "go get <some command>"
+# which is disabled with GOFLAGS=-mod=vendor).
+configvar GOFLAGS_VENDOR "$( [ -d vendor ] && echo '-mod=vendor' )" "Go flags for using the vendor directory"
+
 # Go versions can be specified seperately for different tasks
 # If the pre-installed Go is missing or a different
 # version, the required version here will get installed
@@ -928,7 +934,7 @@ main () {
     images=
     if ${CSI_PROW_BUILD_JOB}; then
         # A successful build is required for testing.
-        run_with_go "${CSI_PROW_GO_VERSION_BUILD}" make all || die "'make all' failed"
+        run_with_go "${CSI_PROW_GO_VERSION_BUILD}" make all "GOFLAGS_VENDOR=${GOFLAGS_VENDOR}" || die "'make all' failed"
         # We don't want test failures to prevent E2E testing below, because the failure
         # might have been minor or unavoidable, for example when experimenting with
         # changes in "release-tools" in a PR (that fails the "is release-tools unmodified"
@@ -938,13 +944,13 @@ main () {
                 warn "installing 'dep' failed, cannot test vendoring"
                 ret=1
             fi
-            if ! run_with_go "${CSI_PROW_GO_VERSION_BUILD}" make -k test 2>&1 | make_test_to_junit; then
+            if ! run_with_go "${CSI_PROW_GO_VERSION_BUILD}" make -k test "GOFLAGS_VENDOR=${GOFLAGS_VENDOR}" 2>&1 | make_test_to_junit; then
                 warn "'make test' failed, proceeding anyway"
                 ret=1
             fi
         fi
         # Required for E2E testing.
-        run_with_go "${CSI_PROW_GO_VERSION_BUILD}" make container || die "'make container' failed"
+        run_with_go "${CSI_PROW_GO_VERSION_BUILD}" make container "GOFLAGS_VENDOR=${GOFLAGS_VENDOR}" || die "'make container' failed"
     fi
 
     if tests_need_kind; then