--search-dir is not expanded prior to passing to external module

[unode]

external(file="<data>/input.fa")

called with ngless --search-dir data=/somedir results in calling external() with <data>/input.fa instead of /somedir/input.fa.

Testcase here

[unode]

Possibly related, if a path doesn't exist an error:

Line X: Could not find necessary input file <references>/path/to/file

is shown. It might be useful to also display the resolved path in the error.

When I first saw this I wasn't sure if I did a mistake specifying --search-dir or a typo on /path/to/file. Turned out to be neither and the file was simply missing.

[unode]

Now that we have a few external modules we should fix this before next release.

[unode]

This is still not complete as the current implementation doesn't fail if it was not possible to resolve search-dir.

[unode]

On offline discussions we realized the current approach doesn't allow distinguishing between a file path and an string argument to be passed as-is.

All solutions discussed would require changes on the API of external modules.
Some of the alternatives mentioned:

• Add atype=path to distinguish from atype=str - path would be searchdir expanded while str reverts to the old behavior and wouldn't be expanded.
• Add a expand_searchdir=true attribute that explicitly specifies which API arguments should be searchdir expanded.