Infinite loop in a Makefile

I had to kick myself for writing this bug into a Makefile today. I am writing it down so that I remember to use &&, and not ; next time.

The Makefile had this target in it:

clean:
	cd folder; \
		make clean
	rm -f file

The problem here is that the statement cd folder; make clean counts as one "line", and make wont notice a problem (and stop) until that line has executed.

Unfortunately, the folder name had a typo, so this script had a chance to call make clean without changing directory, calling itself and becoming stuck in an infinite loop.

So long story short, this is why Makefiles should be littered with the "and" operator.

clean:
	cd folder && \
		make clean
	rm -f file