move to use virtual workspace

[Skgland]

• fixes num tests starting from 1.51.0 aka current beta
  • cargo stabilized feature package-features making --feature and --no-default-features
    work as expected for virtual workspaces, though apparently not workspaces with
    a root package

[triska]

Thank you! However, does this once again break all external links to library files that occur in existing blog posts, tweets, emails, discussions etc. which point to the source files of Scryer Prolog on github, and which also occur in the README.md file of Scryer itself?

Please aim for a suitable balance between progress and breakage. If at all possible, I would prefer existing links to source files to keep working. If that is not possible, maybe it can at least be set up in such a way that the paths remain more stable in the future. The most recent such breakage occurred less than a year ago in 33325f1.

[Skgland]

Does this once again break all external links to library files that occur in existing blog posts, tweets, emails, discussions etc. which point to the source files of Scryer Prolog on github?

Oh, I hadn't considered link breakage.
Unless permanent links to a specific commit where used this will likely break links. Github may be smart with redirects if the original file is not re-created like it is with project/user renames, but I couldn't find anything like that having been documented.

Please aim for a suitable balance between progress and breakage. If at all possible, I would prefer existing links to source files to keep working. If that is not possible, maybe it can at least be set up in such a way that the paths remain more stable in the future.

I am not sure what future breakage you have in mind. Though I would assume the paths to be stable unless one would move back to not use a virtual workspace or change the workspace layout.

It appears that most Issues regarding --no-default-features and --features in conjunction with workspaces have been closed now that the flags work with virtual workspaces. It may be that workspaces with a root package where overlooked. rust-lang/cargo#7160 is still open, though somewhat stale and the comment that the now stabilized feature should solve it is apparently false.

[Skgland]

I have found a workaround that is less disruptive, will open it in a separate pr

[triska]

Thank you a lot!