make does not realize that a relative path name dependency is the same as an absolute pathname target

Question

The following is a simplified makefile for a problem I'm having:

all: /tmp/makey/../filey
    @echo All done
/tmp/filey:
    @echo Filey

When I run make it says:

make-3.79.1-p7: * No rule to make target /tmp/makey/../filey', needed byall'. Stop.

Clearly it does not realize that /tmp/makey/../filey is the same as /tmp/filey. Any ideas how I can make this work?

Thanks

Ciao -- Murali

Answer 1

Newer versions of GNU make have $(abspath ...) and $(realpath ...) functions you can apply to your prerequisites and targets to resolve the paths to the same string. If you've constructed these names yourself (for example, $(PREFIX)/../filey) then you can use $(dir $(PREFIX))filey instead.

Other than that, there's no way to solve this problem. Make uses string matching on targets and if the strings are not identical, they don't match (there's a special case to ignore the simple prefix ./) Even if make understood this distinction (by applying abspath itself to each target name, maybe) it would still not help in the face of symbolic links for example.

The only "real" answer would be for make to understand something about the underlying file system (device IDs and inodes for example) that let you talk about files without referring to their pathname. However, in a portable program like make doing this is problematic.