Fix decoding of directories when "~" includes non-ASCII chars

* src/fileio.c (Fexpand_file_name): Don't build multibyte strings
from unibyte non-ASCII strings when NAME and DEFAULT_DIRECTORY
have different multibyteness, as this adds bytes to the byte
sequence, and in some situations, e.g., when the home directory
includes non-ASCII characters, can fail file APIs.  (Bug#30755)

* lisp/startup.el (normal-top-level): Make sure default-directory
is set to a multibyte string when decoded on MS-Windows.

1 files changed, 11 insertions, 3 deletions

diff --git a/lisp/startup.el b/lisp/startup.el
index 5b2d3e58cba..83fd190ea2b 100644
--- a/lisp/startup.el
+++ b/lisp/startup.el
@@ -560,9 +560,17 @@ It is the default value of the variable `top-level'."
 	    (if default-directory
 		(setq default-directory
                       (if (eq system-type 'windows-nt)
-                          ;; Convert backslashes to forward slashes.
-                          (expand-file-name
-                           (decode-coding-string default-directory coding t))
+                          ;; We pass the decoded default-directory as
+                          ;; the 2nd arg to expand-file-name to make
+                          ;; sure it sees a multibyte string as the
+                          ;; default directory; this avoids the side
+                          ;; effect of returning a unibyte string from
+                          ;; expand-file-name because it still sees
+                          ;; the undecoded value of default-directory.
+                          (let ((defdir (decode-coding-string default-directory
+                                                              coding t)))
+                            ;; Convert backslashes to forward slashes.
+                            (expand-file-name defdir defdir))
                         (decode-coding-string default-directory coding t))))))
 
 	;; Decode all the important variables and directory lists, now