+(defcustom project-file-name-history-relativize nil
+ "If non-nil, paths in `file-name-history' are adjusted for the current
project.
+
+When non-nil and in `project-find-file' or `project-find-dir',
+paths in `file-name-history' are adjusted to be relative to
+whatever the current project is, instead of the project which
+added those paths. This only affects history entries added by
+earlier calls to `project-find-file' or `project-find-dir'.
+
+When `project-read-file-name-function' is
+`project--read-file-cpd-relative' (the default), this has the
+effect of sharing more history between projects.")
Instead of, or in addition to 'project-file-name-history-relativize',
another option may be needed to define whether to check the
existence of the constructed file name. This could help
to filter out irrelevant file names constructed from
different projects.