bug#51754: 29.0.50; [PATCH] tramp-compat-file-name-concat work in wrong way

[Aleksandr Vityazev <avityazev@posteo.org>]

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Hello, 

The current implementation of the tramp-compat-file-name-concat 
from lisp/net/tramp-compat.el fails test fileio-tests/file-name-concat
from file test/src/fileio-tests.el for file-name-concat on Emacs where no
file-name-concat.

#+begin_src elisp
(ert-deftest test-tramp-compat-file-name-concat ()
  (should (equal (tramp-compat-file-name-concat "foo" "bar") "foo/bar"))
  (should (equal (tramp-compat-file-name-concat "foo" "bar") "foo/bar"))
  (should (equal (tramp-compat-file-name-concat "foo" "bar" "zot") "foo/bar/zot"))
  (should (equal (tramp-compat-file-name-concat "foo/" "bar") "foo/bar"))
  (should (equal (tramp-compat-file-name-concat "foo//" "bar") "foo//bar"))
  (should (equal (tramp-compat-file-name-concat "foo/" "bar/" "zot") "foo/bar/zot"))
  (should (equal (tramp-compat-file-name-concat "fóo" "bar") "fóo/bar"))
  (should (equal (tramp-compat-file-name-concat "foo" "bár") "foo/bár"))
  (should (equal (tramp-compat-file-name-concat "fóo" "bár") "fóo/bár"))
  (let ((string (make-string 5 ?a)))
    (should (not (multibyte-string-p string)))
    (aset string 2 255)
    (should (not (multibyte-string-p string)))
    (should (equal (tramp-compat-file-name-concat "fóo" string) "fóo/aa\377aa")))
  (should (equal (tramp-compat-file-name-concat "foo") "foo"))
  (should (equal (tramp-compat-file-name-concat "foo/") "foo/"))
  (should (equal (tramp-compat-file-name-concat "foo" "") "foo"))
  (should (equal (tramp-compat-file-name-concat "foo" "" "" "" nil) "foo"))
  (should (equal (tramp-compat-file-name-concat "" "bar") "bar"))
  (should (equal (tramp-compat-file-name-concat "" "") "")))

(ert 'test-tramp-compat-file-name-concat)
#+end_src


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Selector: test-tramp-compat-file-name-concat
Passed:  0
Failed:  1 (1 unexpected)
Skipped: 0
Total:   1/1

Started at:   2021-11-10 21:21:24+0300
Finished.
Finished at:  2021-11-10 21:21:25+0300

F

F test-tramp-compat-file-name-concat
    (wrong-type-argument characterp "zot")



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Here is the patch to fix:

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From 1a0c540abfc129d67bf2e291c038c2163f7fee7f Mon Sep 17 00:00:00 2001
From: Aleksandr Vityazev <avityazev@posteo.org>
Date: Wed, 10 Nov 2021 21:36:16 +0300
Subject: [PATCH] * lisp/net/tramp-compat.el: Fix tramp-compat-file-name-concat

* lisp/net/tramp-compat.el: Make tramp-compat-file-name-concat
work like file-name-concat.
---
 lisp/net/tramp-compat.el | 19 +++++++++++--------
 1 file changed, 11 insertions(+), 8 deletions(-)

diff --git a/lisp/net/tramp-compat.el b/lisp/net/tramp-compat.el
index 213ab5857c..fbc3d684ce 100644
--- a/lisp/net/tramp-compat.el
+++ b/lisp/net/tramp-compat.el
@@ -386,14 +386,17 @@ CONDITION can also be a list of error conditions."
   (if (fboundp 'file-name-concat)
       #'file-name-concat
     (lambda (directory &rest components)
-      (unless (null directory)
-	(let ((components (delq nil components))
-	      file-name-handler-alist)
-	  (if (null components)
-	      directory
-	    (tramp-compat-file-name-concat
-	     (concat (file-name-as-directory directory) (car components))
-	     (cdr components))))))))
+      (let ((components (cl-remove-if (lambda (el)
+                                        (or (null el) (equal "" el)))
+                                      components))
+	    file-name-handler-alist)
+        (if (null components)
+	    directory
+          (apply #'tramp-compat-file-name-concat
+	         (concat (unless (or (equal "" directory) (null directory))
+                           (file-name-as-directory directory))
+                         (car components))
+	         (cdr components)))))))
 
 (dolist (elt (all-completions "tramp-compat-" obarray 'functionp))
   (put (intern elt) 'tramp-suppress-trace t))
-- 
2.33.1


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-- 
Best regards,
Aleksandr Vityazev