Makefile: throw error when linting fails (#249)

This affects the GitHub linting workflow, which is just calling the Makefile.

Makefile

@@ -3,8 +3,10 @@ SHELL := /bin/bash
 
 .SILENT: build clean devenv docs publish test lint
 .IGNORE: clean
+.ONESHELL:
 
 BLUE:=\033[0;34m
+RED:=\033[0;31m
 NC:=\033[0m # No Color
 BOLD:=$(tput bold)
 NORM:=$(tput sgr0)
@@ -14,8 +16,8 @@ DIR:=$(shell dirname $(realpath $(firstword $(MAKEFILE_LIST))))
 
 # build the package from the source
 build: devenv
-	. venv/bin/activate; \
-		python -m build; \
+	. venv/bin/activate;
+		python -m build;
 		twine check --strict dist/*
 
 clean:
@@ -28,38 +30,46 @@ clean:
 	rm -f test-*.yml
 
 devenv:
-	if [ ! -d "$(DIR)/venv" ]; then \
-		echo "Creating venv"; \
-		python -m venv venv/; \
+	if [ ! -d "$(DIR)/venv" ]; then
+		echo "Creating venv";
+		python -m venv venv/;
 	fi
-	@if ! venv/bin/python -c "import kafe2" 2>/dev/null; then \
-		echo "Installing kafe2 in editable mode"; \
-		. venv/bin/activate; \
-		pip install --upgrade -e .[dev]; \
+	@if ! venv/bin/python -c "import kafe2" 2>/dev/null; then
+		echo "Installing kafe2 in editable mode";
+		. venv/bin/activate;
+		pip install --upgrade -e .[dev];
 	fi
 
 docs:	devenv
 	echo "Generating Docs"
-	. venv/bin/activate; \
-		cd doc; \
-		$(MAKE) html; \
+	. venv/bin/activate;
+		cd doc;
+		$(MAKE) html;
 		$(MAKE) latex;
 
 publish: build
 	echo "uploading build to PyPI"
-	. venv/bin/activate; twine upload ./dist/*
+	. venv/bin/activate;
+		twine upload ./dist/*
 
 test: devenv
 	echo "Running Pytest and Coverage"
-	. venv/bin/activate; \
-		pytest; \
+	. venv/bin/activate;
+		pytest;
 		coverage run
 
 lint: devenv
-	. venv/bin/activate; \
-		echo -e "$(BLUE)${BOLD}ISORT${NC}$(NORM)"; \
-		isort --check --diff ./kafe2; \
-		echo -e "$(BLUE)${BOLD}BLACK${NC}$(NORM)"; \
-		black --check --diff ./kafe2; \
-		echo -e "$(BLUE)${BOLD}FLAKE8${NC}$(NORM)"; \
+	. venv/bin/activate;
+		echo -e "$(BLUE)${BOLD}ISORT${NC}$(NORM)";
+		isort --check --diff ./kafe2;
+		RET_Isort=$$?;
+		echo -e "$(BLUE)${BOLD}BLACK${NC}$(NORM)";
+		black --check --color --diff ./kafe2;
+		RET_Black=$$?;
+		echo -e "$(BLUE)${BOLD}FLAKE8${NC}$(NORM)";
 		flake8 --config .flake8 ./kafe2;
+		RET_Flake8=$$?;
+		if [ $$RET_Isort -ne 0 ] || [ $$RET_Black -ne 0 ] || [ $$RET_Flake8 -ne 0 ]; then
+			echo -e "$(RED)${BOLD}Linting failed${NC}$(NORM)";
+			exit 1;
+		fi