see https://www.gnu.org/software/make/manual/html_node/General-Search.html
from the perspective of a recipe (i.e. automatic variables), prerequisites are "rewritten"; if they're resolved to a directory in VPATH, the prereq is prefixed with that directory
| use nix -p gnumake |
| /out/ | |
| local.in | |
| /.direnv |
| $(shell mkdir -p /tmp/foo/bar) | |
| $(shell touch /tmp/foo/bar/abs.in) | |
| $(shell touch local.in) | |
| VPATH += :/tmp/foo | |
| out/%.out: %.in | |
| @echo "$< -> $@" | |
| @mkdir -p $(@D); touch $@ | |
| all: out/bar/abs.out out/local.out | |
| .DEFAULT_GOAL := all |