"Inconsitent Pipeline" error when workspace is open

Summary

When trying to build an element that has had a workspace open against it, i am seeing this error:

Inconsistent pipeline

    Exact versions are missing for the following elements
    Try tracking these elements first with `bst track`

      desktop/sdl2.bst

Steps to reproduce

After some investigation i found these steps caused the issues:

• modify a .bst element
• create a workspace
• build the element
• rm -r the workspace directory
• try to build the element again

What is the current bug behavior?

When you try to build the element after removing the workspace directory you see the error above, and running bst track on the element does not fox the dependency issue.

When you close the bst workspace, the error no longer occurs and the element builds as expected.

What is the expected correct behavior?

Alert the user that a workspace is open against this element and that they should close it.

Relevant logs and/or screenshots

Bst error

Inconsistent pipeline

    Exact versions are missing for the following elements
    Try tracking these elements first with `bst track`

      desktop/sdl2.bst

Possible fixes

Other relevant information

• BuildStream version affected: /milestone %BuildStream_v1.2 x

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