compilation--previous-directory-cache

compilation--previous-directory-cache is a variable defined in `compile.el'.
Its value is

nil

• Automatically becomes buffer-local when set.

Documentation:
A pair (POS . RES) caching the result of previous directory search.
Basically, this pair says that calling
(previous-single-property-change POS 'compilation-directory)
returned RES, i.e. there is no change of `compilation-directory' between
POS and RES.