Hi,
I’m trying to use make to render some files with VPATH employed:
Source files
```
foo/1.tpl
foo/1.data
bar/2.tpl
bar/2.data
baz/3
```
Makefile
```
.SECONDEXPANSION:
VPATH := foo bar baz
build/%: %.tpl $$(patsubst %.tpl,%.data,$$<)
render --data $(word 2,$^) $< $@
build/%: %
cp $< $@
```
I’d like for make to automatically list the corresponding data file as a
prerequisite for the pattern rule, but apparently this doesn’t work, because
$$< expands to an empty string.
I also tried this:
Makefile
```
.SECONDEXPANSION:
VPATH := foo bar
build/%: %.tpl
build/%: $$(patsubst %.tpl,%.data,$$<)
render --data $(word 2,$^) $< $@
build/%: %
cp $< $@
```
But since an implicit rule only applies when both the target and requisites are
found, this also doesn’t work.
I read the official doc on topics about secondary expansion, VPATH and search
algorithm, but couldn’t come up with a way to get the prerequisite path and
turn it into another prerequisite. I’d be really grateful if anyone could shed
some light.
Regards,
Glen
