Re: master daea9b3 1/2: Read mailcaps again only when necessary

[Stefan Monnier <monnier@iro.umontreal.ca>]

> +(defun file-has-changed-p (file)
> +  "Return non-nil if FILE has changed.
> +The modification time of FILE is compared to the modification
> +time of FILE during a previous invocation of `file-has-changed-p'.
> +Therefore the first invocation of `file-has-changed-p' always
> +returns non-nil."
> +  (let* ((attr (file-attributes file 'integer))
> +	  (mtime (file-attribute-modification-time attr))
> +	  (saved-mtime (gethash (intern file)
> +				file-has-changed-p--hash-table)))
> +     (when (not (equal mtime saved-mtime))
> +       (puthash (intern file) mtime file-has-changed-p--hash-table))))

This API doesn't seem safe.
If two packages read&parse the same file and both rely on this function
to decide when to reparse, the second package can get a nil value
(because the first has caused the mtime to be reset in the hash table)
even though the file has changed since it last parsed it.

So I think the function needs a second argument which represents the
"since when".  It could be the hash-table.

Side question: why use `intern`?
Why not just pass `:test #'equal` to the `make-hash-table`?


        Stefan