make-directory now returns t if dir already exists

This new feature will help fix a copy-directory bug (Bug#58919).
Its implementation does not rely on make-directory handlers
supporting the new feature, as it no longer uses a make-directory
handler H in any way other than (funcall H DIR), thus using
only the intersection of the old and new behavior for handlers.
This will give us time to fix handlers at our leisure.
* lisp/files.el (files--ensure-directory): New arg MKDIR.
All uses changed.
(files--ensure-directory, make-directory):
Return non-nil if DIR is already a directory.  All uses changed.
* test/lisp/files-tests.el (files-tests-make-directory):
Test new return-value convention.

1 files changed, 5 insertions, 0 deletions

diff --git a/etc/NEWS b/etc/NEWS
index 72421b03191..c5820a5f045 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -4486,6 +4486,11 @@ and cannot work with regular styles such as 'basic' or 'flex'.
 ** Magic file handlers for make-directory-internal are no longer needed.
 Instead, Emacs uses the already-existing make-directory handlers.
 
++++
+** (make-directory DIR t) returns non-nil if DIR already exists.
+This can let a caller know whether it created DIR.  Formerly,
+make-directory's return value was unspecified.
+
 
 * Changes in Emacs 29.1 on Non-Free Operating Systems