Includeexpr + substitute not behaving as I would expect

Question

I am using includeexpr and substitute() in a ftplugin to remove a portion of an include string for gf functionality (in twig template files, for the curious), but I get an error instead.

Twig includes look like this:

{% include "@mynamespace/footer/footer.twig" %}

I already have my path setup to include the twig template directory, and I want to remove the @mynamespace/ piece to properly map to the filesystem.

I used this expression, adapted from the helpdocs example for Java.

setlocal includeexpr=substitute(v:fname,'@mynamespace/','','')

However, when I try to gf an include, I get this error:

E447: Can't find file "mynamespace/footer/footer.twig" in path

I would have expected substitute() to remove the @mynamespace/ piece. I looked at the documentation, and couldn't see anything I was doing wrong. I tried messing around with different invocations, using \ to escape the @ or /, but always got the same error.

Any help would be greatly appreciated. Thanks in advance.

Answer 1

Vim is separating out the @ when extracting the filename. Why? Per :h gf...

[Vim] uses the 'isfname' option to find out which characters are supposed to be in a file name.

You can demonstrate this another way by putting your cursor on the filename and running

:echo expand('<cfile>')

The response is "mynamespace/footer/footer.twig". <cfile> is determined the same way as for v:fname. That means you can proceed with your substitution with the same assumption....

:setlocal includeexpr=substitute(v:fname,'mynamespace/','','')

...and gf will look for footer/footer.twig.