The source import in this module is a no-op and has no legitimate use:

module A where
import {-# SOURCE #-} A

It's also tricky to support properly, see #10182 (closed). So we will disable it.

However, there is one mode of use which cannot be legitimately done in normal Haskell: a qualified source import:

module A where
import {-# SOURCE #-} qualified A as MyA

The intended semantics is that the boot entities defined in A.hs-boot are available under the qualification MyA.

Fixing #7672 (closed) would get us most of the way here, but there is one more step to avoid regressing #10182 (closed). So this just seems not worth fixing, unless someone really wants it.

(Note: regular self imports could also be supported this way, but it would be even more complicated to do, since we don't even know what OccNames to add provenances for.)