Fix up checks in Makefile and make them portable

.gitattributes

@@ -1,2 +1,3 @@
 test/fixtures/* eol=lf
-init-tests-after-clone.sh
+init-tests-after-clone.sh eol=lf
+Makefile eol=lf

Makefile

@@ -7,16 +7,45 @@ clean:
 	rm -rf build/ dist/ .eggs/ .tox/
 
 release: clean
-	# Check if latest tag is the current head we're releasing
-	echo "Latest tag = $$(git tag | sort -nr | head -n1)"
-	echo "HEAD SHA       = $$(git rev-parse head)"
-	echo "Latest tag SHA = $$(git tag | sort -nr | head -n1 | xargs git rev-parse)"
-	@test "$$(git rev-parse head)" = "$$(git tag | sort -nr | head -n1 | xargs git rev-parse)"
+	# Check that VERSION and changes.rst exist and have no uncommitted changes
+	test -f VERSION
+	test -f doc/source/changes.rst
+	git status -s VERSION doc/source/changes.rst
+	@test -z "$$(git status -s VERSION doc/source/changes.rst)"
+
+	# Check that ALL changes are commited (can comment out if absolutely necessary)
+	git status -s
+	@test -z "$$(git status -s)"
+
+	# Check that latest tag matches version and is the current head we're releasing
+	@version_file="$$(cat VERSION)" && \
+	changes_file="$$(awk '/^[0-9]/ {print $$0; exit}' doc/source/changes.rst)" && \
+	config_opts="$$(printf ' -c versionsort.suffix=-%s' alpha beta pre rc RC)" && \
+	latest_tag=$$(git $$config_opts tag -l '[0-9]*' --sort=-v:refname | head -n1) && \
+	head_sha=$$(git rev-parse HEAD) latest_tag_sha=$$(git rev-parse "$$latest_tag") && \
+	printf '%-14s = %s\n' 'VERSION file'   "$$version_file" \
+	                      'changes.rst'    "$$changes_file" \
+	                      'Latest tag'     "$$latest_tag" \
+	                      'HEAD SHA'       "$$head_sha" \
+	                      'Latest tag SHA' "$$latest_tag_sha" && \
+	test "$$version_file" = "$$changes_file" && \
+	test "$$latest_tag" = "$$version_file" && \
+	test "$$head_sha" = "$$latest_tag_sha"
+
 	make force_release
 
 force_release: clean
 	# IF we're in a virtual environment, add build tools
 	test -z "$$VIRTUAL_ENV" || pip install -U build twine
-	python3 -m build --sdist --wheel || echo "Use a virtual-env with 'python -m venv env && source env/bin/activate' instead"
+
+	# Build the sdist and wheel that will be uploaded to PyPI.
+	if test -n "$$VIRTUAL_ENV"; then \
+		python -m build --sdist --wheel; \
+	else \
+		python3 -m build --sdist --wheel || \
+		{ echo "Use a virtual-env with 'python -m venv env && source env/bin/activate' instead" && false; }; \
+	fi
+
+	# Upload to PyPI and push the tag.
 	twine upload dist/*
 	git push --tags origin main