bug#62974: 29.0.60; New buffers created with project-switch-to-buffer aren't in the project

[Dmitry Gutov <dmitry@gutov.dev>]

On 21/04/2023 16:17, sbaugh@catern.com wrote:
> Eli Zaretskii<eliz@gnu.org>  writes:
>>> From: Spencer Baugh<sbaugh@janestreet.com>
>>> Date: Fri, 21 Apr 2023 07:46:14 -0400
>>> Cc: Dmitry Gutov<dmitry@gutov.dev>,62974@debbugs.gnu.org
>>>
>>>   But if it is in a subdirectory of the root, it also belongs to the
>>>   project, doesn't it?  Exactly like the buffer from which this command
>>>   is invoked, whose default-directory was a subdirectory of the root.
>>>   No?
>>>
>>> That's fine, I wouldn't want to change that behavior, the behavior I'd want to change is when invoking
>>> the command from a buffer which is not in a project, or by invoking it after C-x p p to switch projects.
>> The recipe you posted didn't include "C-x p p", though.
> My recipe was an example of "command from a buffer which is not in a
> project".  Here's a recipe for the issue using C-x p p:
> 
> 1. (setq project-switch-use-entire-map t)
> 2. Be in a buffer in project A
> 3. C-x p p b to switch to project B and select a buffer in project B
> 4. Type a buffer name which doesn't exist
> 5. The resulting buffer is in project A, not B

Thanks.

How does this look?

diff --git a/lisp/progmodes/project.el b/lisp/progmodes/project.el
index a18b918db62..94c7f8f547a 100644
--- a/lisp/progmodes/project.el
+++ b/lisp/progmodes/project.el
@@ -1314,13 +1314,17 @@ project--read-project-buffer
              (and (memq (cdr buffer) buffers)
                   (not
                    (project--buffer-check
-                   (cdr buffer) project-ignore-buffer-conditions))))))
-    (read-buffer
-     "Switch to buffer: "
-     (when (funcall predicate (cons other-name other-buffer))
-       other-name)
-     nil
-     predicate)))
+                   (cdr buffer) project-ignore-buffer-conditions)))))
+         (buffer (read-buffer
+                  "Switch to buffer: "
+                  (when (funcall predicate (cons other-name other-buffer))
+                    other-name)
+                  nil
+                  predicate)))
+    (if (get-buffer buffer)
+        buffer
+      (let ((default-directory (project-root pr)))
+        (get-buffer-create buffer)))))

  ;;;###autoload
  (defun project-switch-to-buffer (buffer-or-name)