Generate make helping message dynamicaly.

Generate make helping message dynamicaly by using
python code snippet inside Makefile.

All commented make targets will be added to the
help message. To be added to the helping message
comment need to start with '## '.

These specials comments are detected by the python code.
Python code generate the helping output from these results.

Notice that this commit introduce a dependency with python (compatible python 2 and 3).

Signed-off-by: Hervé Beraud <hberaud@redhat.com>

Makefile

@@ -72,15 +72,23 @@ all: binaries docs
 
 default: help
 
+define PRINT_HELP_PYSCRIPT
+import re, sys
+
+print("Usage: make <target>")
+cmds = {}
+for line in sys.stdin:
+	match = re.match(r'^([a-zA-Z_-]+):.*?## (.*)$$', line)
+	if match:
+	  target, help = match.groups()
+	  cmds.update({target: help})
+for cmd in sorted(cmds):
+		print(" * '%s' - %s" % (cmd, cmds[cmd]))
+endef
+export PRINT_HELP_PYSCRIPT
+
 help:
-	@echo "Usage: make <target>"
+	@python -c "$$PRINT_HELP_PYSCRIPT" < $(MAKEFILE_LIST)
-	@echo
-	@echo " * 'install' - Install binaries to system locations"
-	@echo " * 'binaries' - Build podman"
-	@echo " * 'integration' - Execute integration tests"
-	@echo " * 'clean' - Clean artifacts"
-	@echo " * 'lint' - Execute the source code linter"
-	@echo " * 'gofmt' - Verify the source code gofmt"
 
 .gopathok:
 ifeq ("$(wildcard $(GOPKGDIR))","")
@@ -89,11 +97,11 @@ ifeq ("$(wildcard $(GOPKGDIR))","")
 endif
 	touch $@
 
-lint: .gopathok varlink_generate
+lint: .gopathok varlink_generate ## Execute the source code linter
 	@echo "checking lint"
 	@./.tool/lint
 
-gofmt:
+gofmt: ## Verify the source code gofmt
 	find . -name '*.go' ! -path './vendor/*' -exec gofmt -s -w {} \+
 	git diff --exit-code
 
@@ -109,16 +117,16 @@ test/checkseccomp/checkseccomp: .gopathok $(wildcard test/checkseccomp/*.go)
 test/goecho/goecho: .gopathok $(wildcard test/goecho/*.go)
 	$(GO) build -ldflags '$(LDFLAGS)' -o $@ $(PROJECT)/test/goecho
 
-podman: .gopathok $(PODMAN_VARLINK_DEPENDENCIES)
+podman: .gopathok $(PODMAN_VARLINK_DEPENDENCIES) ## Build with podman
 	$(GO) build -ldflags '$(LDFLAGS_PODMAN)' -tags "$(BUILDTAGS)" -o bin/$@ $(PROJECT)/cmd/podman
 
-podman-remote: .gopathok $(PODMAN_VARLINK_DEPENDENCIES)
+podman-remote: .gopathok $(PODMAN_VARLINK_DEPENDENCIES) ## Build with podman on remote environment
 	$(GO) build -ldflags '$(LDFLAGS_PODMAN)' -tags "$(BUILDTAGS) remoteclient" -o bin/$@ $(PROJECT)/cmd/podman
 
-podman-remote-darwin: .gopathok $(PODMAN_VARLINK_DEPENDENCIES)
+podman-remote-darwin: .gopathok $(PODMAN_VARLINK_DEPENDENCIES) ## Build with podman on remote OSX environment
 	GOOS=darwin $(GO) build -ldflags '$(LDFLAGS_PODMAN)' -tags "remoteclient containers_image_openpgp exclude_graphdriver_devicemapper" -o bin/$@ $(PROJECT)/cmd/podman
 
-local-cross: $(CROSS_BUILD_TARGETS)
+local-cross: $(CROSS_BUILD_TARGETS) ## Cross local compilation
 
 bin/podman.cross.%: .gopathok
 	TARGET="$*"; \
@@ -126,7 +134,7 @@ bin/podman.cross.%: .gopathok
 	GOARCH="$${TARGET##*.}" \
 	$(GO) build -ldflags '$(LDFLAGS_PODMAN)' -tags '$(BUILDTAGS_CROSS)' -o "$@" $(PROJECT)/cmd/podman
 
-clean:
+clean: ## Clean artifacts
 	rm -rf \
 		.gopathok \
 		_output \
@@ -146,16 +154,16 @@ clean:
 	find . -name \*~ -delete
 	find . -name \#\* -delete
 
-libpodimage:
+libpodimage: ## Build the libpod image
 	${CONTAINER_RUNTIME} build -t ${LIBPOD_IMAGE} .
 
 dbuild: libpodimage
 	${CONTAINER_RUNTIME} run --name=${LIBPOD_INSTANCE} --privileged -v ${PWD}:/go/src/${PROJECT} --rm ${LIBPOD_IMAGE} make all
 
-test: libpodimage
+test: libpodimage ## Run tests on built image
 	${CONTAINER_RUNTIME} run -e STORAGE_OPTIONS="--storage-driver=vfs" -e TESTFLAGS -e OCI_RUNTIME -e CGROUP_MANAGER=cgroupfs -e TRAVIS -t --privileged --rm -v ${CURDIR}:/go/src/${PROJECT} ${LIBPOD_IMAGE} make clean all localunit install.catatonit localintegration
 
-integration: libpodimage
+integration: libpodimage ## Execute integration tests
 	${CONTAINER_RUNTIME} run -e STORAGE_OPTIONS="--storage-driver=vfs" -e TESTFLAGS -e OCI_RUNTIME -e CGROUP_MANAGER=cgroupfs -e TRAVIS -t --privileged --rm -v ${CURDIR}:/go/src/${PROJECT} ${LIBPOD_IMAGE} make clean all install.catatonit localintegration
 
 integration.fedora:
@@ -164,10 +172,10 @@ integration.fedora:
 integration.centos:
 	DIST=CentOS sh .papr_prepare.sh
 
-shell: libpodimage
+shell: libpodimage ## Run the built image and attach a shell
 	${CONTAINER_RUNTIME} run -e STORAGE_OPTIONS="--storage-driver=vfs" -e CGROUP_MANAGER=cgroupfs -e TESTFLAGS -e OCI_RUNTIME -e TRAVIS -it --privileged --rm -v ${CURDIR}:/go/src/${PROJECT} ${LIBPOD_IMAGE} sh
 
-testunit: libpodimage
+testunit: libpodimage ## Run unittest on the built image
 	${CONTAINER_RUNTIME} run -e STORAGE_OPTIONS="--storage-driver=vfs" -e TESTFLAGS -e CGROUP_MANAGER=cgroupfs -e OCI_RUNTIME -e TRAVIS -t --privileged --rm -v ${CURDIR}:/go/src/${PROJECT} ${LIBPOD_IMAGE} make localunit
 
 localunit: test/goecho/goecho varlink_generate
@@ -188,16 +196,16 @@ localsystem: .install.ginkgo .install.gomega
 system.test-binary: .install.ginkgo .install.gomega
 	$(GO) test -c ./test/system
 
-perftest:
+perftest:  ## Build perf tests
 	$ cd contrib/perftest;go build
 
-run-perftest: perftest
+run-perftest: perftest ## Build and run perf tests
 	$ contrib/perftest/perftest
 
 vagrant-check:
 	BOX=$(BOX) sh ./vagrant.sh
 
-binaries: varlink_generate podman podman-remote
+binaries: varlink_generate podman podman-remote  ## Build podman
 
 install.catatonit:
 	./hack/install_catatonit.sh
@@ -210,12 +218,12 @@ MANPAGES ?= $(MANPAGES_MD:%.md=%)
 $(MANPAGES): %: %.md .gopathok
 	@sed -e 's/\((podman.*\.md)\)//' -e 's/\[\(podman.*\)\]/\1/' $<  | $(GOMD2MAN) -in /dev/stdin -out $@
 
-docs: $(MANPAGES)
+docs: $(MANPAGES) ## Generate documentation
 
 docker-docs: docs
 	(cd docs; ./dckrman.sh *.1)
 
-changelog:
+changelog: ## Generate changelog
 	@echo "Creating changelog from $(CHANGELOG_BASE) to $(CHANGELOG_TARGET)"
 	$(eval TMPFILE := $(shell mktemp))
 	$(shell cat changelog.txt > $(TMPFILE))
@@ -225,7 +233,7 @@ changelog:
 	$(shell cat $(TMPFILE) >> changelog.txt)
 	$(shell rm $(TMPFILE))
 
-install: .gopathok install.bin install.man install.cni install.systemd
+install: .gopathok install.bin install.man install.cni install.systemd  ## Install binaries to system locations
 
 install.bin:
 	install ${SELINUXOPT} -d -m 755 $(BINDIR)
@@ -278,7 +286,7 @@ uninstall:
 
 .PHONY: install.tools
 
-install.tools: .install.gitvalidation .install.gometalinter .install.md2man .install.ginkgo
+install.tools: .install.gitvalidation .install.gometalinter .install.md2man .install.ginkgo ## Install needed tools
 
 .install.vndr: .gopathok
 	$(GO) get github.com/LK4D4/vndr