Idiom: whitespace

make has a rather ad-hoc approach to whitespace. Most of the time it ignores it, e.g.

FOO = bar

sets FOO to "bar", not " bar". However, sometimes whitespace is significant, and calling macros is one example. For example, we used to have a call

$(call all-target, $$($1_$2_INPLACE))

and this passed " $$($1_$2_INPLACE)" as the argument to all-target. This in turn generated

.PHONY: all_ inplace/bin/ghc-asm

which caused an infinite loop, as make continually thought that ghc-asm was out-of-date, rebuilt it, reinvoked make, and then thought it was out of date again.

The moral of the story is, avoid white space unless you're sure it'll be OK!