Add some dependency logic around generators. (#1966)

This isn't 100% correct, but it's a pretty good approximation.
Specifically, it doesn't know about transitive dependencies from other
go packages.  But it'll rebuild a generator if any code inside its
package changes (or build them all if anything in gengo changes).

Author: vin

Makefile

@@ -146,42 +146,26 @@ $(BINDIR)/service-catalog: .init .generate_files cmd/service-catalog
 
 # This section contains the code generation stuff
 #################################################
-.generate_exes: $(BINDIR)/defaulter-gen \
-                $(BINDIR)/deepcopy-gen \
-                $(BINDIR)/conversion-gen \
-                $(BINDIR)/client-gen \
-                $(BINDIR)/lister-gen \
-                $(BINDIR)/informer-gen \
-                $(BINDIR)/openapi-gen
-	touch $@
-
-$(BINDIR)/defaulter-gen: .init
-	$(DOCKER_CMD) go build -o $@ $(SC_PKG)/vendor/k8s.io/code-generator/cmd/defaulter-gen
-
-$(BINDIR)/deepcopy-gen: .init
-	$(DOCKER_CMD) go build -o $@ $(SC_PKG)/vendor/k8s.io/code-generator/cmd/deepcopy-gen
-
-$(BINDIR)/conversion-gen: .init
-	$(DOCKER_CMD) go build -o $@ $(SC_PKG)/vendor/k8s.io/code-generator/cmd/conversion-gen
-
-$(BINDIR)/client-gen: .init
-	$(DOCKER_CMD) go build -o $@ $(SC_PKG)/vendor/k8s.io/code-generator/cmd/client-gen
+GENERATORS = $(addprefix $(BINDIR)/, defaulter-gen deepcopy-gen conversion-gen \
+	     client-gen lister-gen informer-gen openapi-gen)
 
-$(BINDIR)/lister-gen: .init
-	$(DOCKER_CMD) go build -o $@ $(SC_PKG)/vendor/k8s.io/code-generator/cmd/lister-gen
+.PHONY: generators
+generators: $(GENERATORS)
 
-$(BINDIR)/informer-gen: .init
-	$(DOCKER_CMD) go build -o $@ $(SC_PKG)/vendor/k8s.io/code-generator/cmd/informer-gen
+.SECONDEXPANSION:
 
-$(BINDIR)/openapi-gen: vendor/k8s.io/code-generator/cmd/openapi-gen
-	$(DOCKER_CMD) go build -o $@ $(SC_PKG)/$^
+# We specify broad dependencies for these generator binaries: each one depends
+# on everything under its source tree as well as gengo's.  This uses GNU Make's
+# secondary expansion feature to pass $* to `find`.
+$(BINDIR)/%-gen: $$(shell find vendor/k8s.io/code-generator/cmd/$$*-gen vendor/k8s.io/gengo) .init
+	$(DOCKER_CMD) go build -o $@ $(SC_PKG)/vendor/k8s.io/code-generator/cmd/$*-gen
 
 .PHONY: $(BINDIR)/e2e.test
 $(BINDIR)/e2e.test: .init
 	$(DOCKER_CMD) go test -c -o $@ $(SC_PKG)/test/e2e
 
 # Regenerate all files if the gen exes changed or any "types.go" files changed
-.generate_files: .init .generate_exes $(TYPES_FILES)
+.generate_files: .init generators $(TYPES_FILES)
 	# generate apiserver deps
 	$(DOCKER_CMD) $(BUILD_DIR)/update-apiserver-gen.sh
 	# generate all pkg/client contents
@@ -242,10 +226,10 @@ verify-docs: .init
 	@echo Running href checker$(SKIP_COMMENT):
 	@$(DOCKER_CMD) verify-links.sh -s .pkg -s .bundler -s _plugins -s _includes -t $(SKIP_HTTP) .
 
-verify-generated: .init .generate_exes
+verify-generated: .init generators
 	$(DOCKER_CMD) $(BUILD_DIR)/update-apiserver-gen.sh --verify-only
 
-verify-client-gen: .init .generate_exes
+verify-client-gen: .init generators
 	$(DOCKER_CMD) $(BUILD_DIR)/verify-client-gen.sh
 
 format: .init
@@ -302,7 +286,6 @@ clean: clean-bin clean-build-image clean-generated clean-coverage
 
 clean-bin: .init $(scBuildImageTarget)
 	$(DOCKER_CMD) rm -rf $(BINDIR)
-	rm -f .generate_exes
 
 clean-build-image: .init $(scBuildImageTarget)
 	$(DOCKER_CMD) rm -rf .pkg