bug#63829: 29.0.90; project-find-file's future history breaks with common-parent-directory

[Juri Linkov]

> +(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.