Automatic setup/cleanup in Makefile.

- Automatically set up poetry environment when needed.  Can still be
  explicitly run using `make setup`.

- Added `make clean` to remove the poetry environment.

- Added `make require`, run during setup, to check environment for the
  presence of python3/poetry, and the python3 version.

.gitignore

@@ -105,6 +105,7 @@ celerybeat-schedule
 *.sage.py
 
 # Environments
+.setup_complete
 .env
 .venv
 env/

Makefile

@@ -3,26 +3,52 @@ help:  ## Print this help menu
 	@grep -E '^[a-zA-Z_-]+:.*?## .*$$' $(MAKEFILE_LIST) | sort | \
 		awk 'BEGIN {FS = ":.*?## "}; {printf "\033[36m%-30s\033[0m %s\n", $$1, $$2}'
 
+.PHONY: require
+require: ## Check that prerequisites are installed.
+	@if ! command -v python3 > /dev/null; then \
+            printf "\033[1m\033[31mERROR\033[0m: python3 not installed\n" >&2 ; \
+	    exit 1; \
+	fi
+	@if ! python3 -c "import sys; sys.exit(sys.version_info < (3,6))"; then \
+            printf "\033[1m\033[31mERROR\033[0m: python 3.6+ required\n" >&2 ; \
+	    exit 1; \
+	fi
+	@if ! command -v poetry > /dev/null; then \
+	    printf "\033[1m\033[31mERROR\033[0m: poetry not installed.\n" >&2 ; \
+	    printf "Please install with 'python3 -mpip install --user poetry'\n" >&2 ; \
+	    exit 1; \
+	fi
+
 .PHONY: setup
-setup:  ## Set up the local development environment
+setup:  require .setup_complete ## Set up the local development environment
+
+.setup_complete:  poetry.lock ## Internal helper to run the setup.
 	poetry install
 	poetry run pre-commit install
+	touch .setup_complete
 
 .PHONY: test
-test:  ## Run the tests, but only for current Python version
+test:  setup ## Run the tests, but only for current Python version
 	poetry run tox -e py
 
 .PHONY: test-all
-test-all:  ## Run the tests for all relevant Python version
+test-all:  setup ## Run the tests for all relevant Python version
 	poetry run tox
 
 .PHONY: publish
-publish:  ## Build & publish the new version
+publish:  setup ## Build & publish the new version
 	poetry build
 	poetry publish
 
 .PHONY: format
-format:  ## Autoformat all files in the repo. WARNING: changes files in-place
+format:  setup ## Autoformat all files in the repo. WARNING: changes files in-place
 	poetry run black jedi_language_server tests
 	poetry run isort jedi_language_server tests
 	poetry run docformatter --recursive --in-place jedi_language_server tests
+
+.PHONY:  clean
+clean: ## Remove local development environment
+	if poetry env list | grep -q Activated; then \
+	    poetry env remove python3; \
+	fi
+	rm -f .setup_complete