From 389e85c020e7e59977e3c832a281f8b7844fecd4 Mon Sep 17 00:00:00 2001
From: Craig Jennings <c@cjennings.net>
Date: Sun, 3 May 2026 19:24:40 -0500
Subject: fix: use file basename when moving buffer + file

`cj/--move-buffer-and-file` was building the destination as `(concat dir "/" (buffer-name))`. If the buffer had been renamed via `M-x rename-buffer`, or uniquified by Emacs with a `<2>` suffix when a second buffer visited the same filename, the move wrote a file with the wrong name on disk.

I derived the destination basename from `buffer-file-name` instead, in both the internal helper and the interactive wrapper. The wrapper's overwrite-prompt now also formats the real target filename rather than the buffer name.

I added two regression tests: one for a renamed buffer visiting `original.txt`, and one for a `<2>` uniquified buffer with a trailing-slash target directory.
---
 modules/custom-buffer-file.el                      |  8 +++--
 ...test-custom-buffer-file-move-buffer-and-file.el | 40 ++++++++++++++++++++++
 2 files changed, 46 insertions(+), 2 deletions(-)

diff --git a/modules/custom-buffer-file.el b/modules/custom-buffer-file.el
index f99a0ee4..ce635cd0 100644
--- a/modules/custom-buffer-file.el
+++ b/modules/custom-buffer-file.el
@@ -110,11 +110,12 @@ If OK-IF-EXISTS is non-nil, overwrite existing file.
 Returns t on success, nil if buffer not visiting a file."
   (let* ((name (buffer-name))
          (filename (buffer-file-name))
+         (basename (and filename (file-name-nondirectory filename)))
          (dir (expand-file-name dir))
          (dir
           (if (string-match "[/\\\\]$" dir)
               (substring dir 0 -1) dir))
-         (newname (concat dir "/" name)))
+         (newname (and basename (expand-file-name basename dir))))
     (if (not filename)
         (progn
           (message "Buffer '%s' is not visiting a file!" name)
@@ -129,7 +130,10 @@ Returns t on success, nil if buffer not visiting a file."
   "Move both current buffer and the file it visits to DIR.
 When called interactively, prompts for confirmation if target file exists."
   (interactive (list (read-directory-name "Move buffer and file (to new directory): ")))
-  (let* ((target (expand-file-name (buffer-name) (expand-file-name dir))))
+  (let* ((filename (buffer-file-name))
+         (target (expand-file-name
+                  (file-name-nondirectory (or filename (buffer-name)))
+                  (expand-file-name dir))))
     (condition-case _
         (cj/--move-buffer-and-file dir nil)
       (file-already-exists
diff --git a/tests/test-custom-buffer-file-move-buffer-and-file.el b/tests/test-custom-buffer-file-move-buffer-and-file.el
index e8f4563d..8331db5c 100644
--- a/tests/test-custom-buffer-file-move-buffer-and-file.el
+++ b/tests/test-custom-buffer-file-move-buffer-and-file.el
@@ -225,6 +225,46 @@
         (kill-buffer (current-buffer)))
     (test-move-buffer-and-file-teardown)))
 
+(ert-deftest test-move-buffer-and-file-renamed-buffer-uses-file-basename ()
+  "Should use visited file basename when buffer name differs."
+  (test-move-buffer-and-file-setup)
+  (unwind-protect
+      (let* ((source-dir (cj/create-test-subdirectory "source"))
+             (target-dir (cj/create-test-subdirectory "target"))
+             (source-file (expand-file-name "original.txt" source-dir))
+             (target-file (expand-file-name "original.txt" target-dir))
+             (wrong-target (expand-file-name "renamed-buffer" target-dir)))
+        (with-temp-file source-file
+          (insert "content"))
+        (find-file source-file)
+        (rename-buffer "renamed-buffer")
+        (cj/--move-buffer-and-file target-dir)
+        (should (file-exists-p target-file))
+        (should-not (file-exists-p wrong-target))
+        (should (string= (buffer-file-name) target-file))
+        (kill-buffer (current-buffer)))
+    (test-move-buffer-and-file-teardown)))
+
+(ert-deftest test-move-buffer-and-file-uniquified-buffer-uses-file-basename ()
+  "Should not use uniquified buffer names such as <2> as filenames."
+  (test-move-buffer-and-file-setup)
+  (unwind-protect
+      (let* ((source-dir (cj/create-test-subdirectory "source"))
+             (target-dir (cj/create-test-subdirectory "target"))
+             (source-file (expand-file-name "duplicate.txt" source-dir))
+             (target-file (expand-file-name "duplicate.txt" target-dir))
+             (wrong-target (expand-file-name "duplicate.txt<2>" target-dir)))
+        (with-temp-file source-file
+          (insert "content"))
+        (find-file source-file)
+        (rename-buffer "duplicate.txt<2>")
+        (cj/--move-buffer-and-file (concat target-dir "/"))
+        (should (file-exists-p target-file))
+        (should-not (file-exists-p wrong-target))
+        (should (string= (buffer-file-name) target-file))
+        (kill-buffer (current-buffer)))
+    (test-move-buffer-and-file-teardown)))
+
 (ert-deftest test-move-buffer-and-file-deeply-nested-target ()
   "Should move to deeply nested target directory."
   (test-move-buffer-and-file-setup)
-- 
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