* lisp/net/tramp.el (tramp-file-name-for-operation):
Add `file-system-info'.

* lisp/net/tramp-adb.el (tramp-adb-handle-file-system-info): New defun.
(tramp-adb-file-name-handler-alist): Use it.

* lisp/net/tramp-gvfs.el (tramp-gvfs-file-system-attributes)
(tramp-gvfs-file-system-attributes-regexp): New defconst.
(tramp-gvfs-handle-file-system-info): New defun.
(tramp-gvfs-file-name-handler-alist): Use it.
(tramp-gvfs-get-directory-attributes): Fix property name.
(tramp-gvfs-get-root-attributes): Support also file system attributes.

* lisp/net/tramp-sh.el (tramp-sh-handle-file-system-info): New defun.
(tramp-sh-file-name-handler-alist): Use it.
(tramp-sh-handle-insert-directory): Insert size information.
(tramp-get-remote-df): New defun.

* lisp/net/tramp-smb.el (tramp-smb-handle-file-system-info): New defun.
(tramp-smb-file-name-handler-alist): Use it.
(tramp-smb-handle-insert-directory): Insert size information.

* test/lisp/net/tramp-tests.el (tramp-test37-file-system-info):
New test.
(tramp-test38-asynchronous-requests)
(tramp-test39-recursive-load, tramp-test40-remote-load-path)
(tramp-test41-unload): Rename.

* lisp/net/tramp.el (tramp-interrupt-process): Better error handling.

* lisp/net/tramp-compat.el (default-toplevel-value): Move up.
(top): Do not call `tramp-change-syntax' anymore.
(tramp-compat-directory-name-p): New defalias.

* lisp/net/tramp-adb.el (tramp-adb-handle-copy-file):
* lisp/net/tramp-sh.el (tramp-sh-handle-copy-directory):
* lisp/net/tramp-smb.el (tramp-smb-handle-copy-directory)
(tramp-smb-handle-copy-file): Use it.

* test/lisp/net/tramp-tests.el (tramp-test28-interrupt-process):
Modify test.

Most of this change is to boilerplate commentary such as license URLs.
This change was prompted by ftp://ftp.gnu.org's going-away party,
planned for November.  Change these FTP URLs to https://ftp.gnu.org
instead.  Make similar changes for URLs to other organizations moving
away from FTP.  Also, change HTTP to HTTPS for URLs to gnu.org and
fsf.org when this works, as this will further help defend against
man-in-the-middle attacks (for this part I omitted the MS-DOS and
MS-Windows sources and the test tarballs to keep the workload down).
HTTPS is not fully working to lists.gnu.org so I left those URLs alone
for now.

* test/lisp/net/tramp-tests.el (seq): Don't require.
(tramp--test-emacs26-p): New defun.
(tramp-test10-write-region, tramp-test11-copy-file)
(tramp-test12-rename-file, tramp-test15-copy-directory)
(tramp-test21-file-links): Use it.
(tramp-test16-file-expand-wildcards): Use `copy-sequence'.

* test/lisp/net/tramp-tests.el (tramp-test11-copy-file)
(tramp-test12-rename-file, tramp-test15-copy-directory)
(tramp-test21-file-links): Extend tests.
(tramp-test13-make-directory, tramp-test14-delete-directory):
Specifiy error symbol in `should-error'.

* lisp/net/tramp.el (tramp-syntax): Recompute all file name
components.  Call `custom-set-variables' after loading.
(tramp-build-prefix-format, tramp-build-prefix-regexp)
(tramp-build-method-regexp)
(tramp-build-postfix-method-format)
(tramp-build-postfix-method-regexp)
(tramp-build-prefix-ipv6-format)
(tramp-build-prefix-ipv6-regexp)
(tramp-build-postfix-ipv6-format)
(tramp-build-postfix-ipv6-regexp)
(tramp-build-postfix-host-format)
(tramp-build-postfix-host-regexp)
(tramp-build-file-name-regexp)
(tramp-build-completion-file-name-regexp): New defuns.
(tramp-prefix-format, tramp-prefix-regexp)
(tramp-method-regexp, tramp-postfix-method-format)
(tramp-postfix-method-regexp, tramp-prefix-ipv6-format)
(tramp-prefix-ipv6-regexp, tramp-postfix-ipv6-format)
(tramp-postfix-ipv6-regexp, tramp-postfix-host-format)
(tramp-postfix-host-regexp)
(tramp-remote-file-name-spec-regexp)
(tramp-file-name-structure, tramp-file-name-regexp)
(tramp-completion-file-name-regexp): Convert defuns into defvars.
(tramp-prefix-regexp-alist)
(tramp-postfix-method-regexp-alist)
(tramp-prefix-ipv6-regexp-alist)
(tramp-postfix-ipv6-regexp-alist)
(tramp-postfix-host-regexp-alist)
(tramp-remote-file-name-spec-regexp-alist): Remove.
(tramp-build-remote-file-name-spec-regexp)
(tramp-build-file-name-structure): Simplify.
(tramp-completion-file-name-regexp-alist): New defconst.
(tramp-tramp-file-p, tramp-dissect-file-name)
(tramp-make-tramp-file-name)
(tramp-completion-make-tramp-file-name)
(tramp-rfn-eshadow-update-overlay-regexp)
(tramp-register-file-name-handlers)
(tramp-completion-handle-file-name-all-completions)
(tramp-completion-dissect-file-name, tramp-clear-passwd):
* lisp/net/tramp-ftp.el (tramp-ftp-file-name-handler):
* lisp/net/tramp-sh.el (tramp-sh-handle-vc-registered)
(tramp-compute-multi-hops): Use variables but functions for
file name components.

* test/lisp/net/tramp-tests.el (tramp-test24-file-name-completion):
Use variables but functions for file name components.

* test/lisp/net/tramp-tests.el (tramp-test15-copy-directory):
Use directory name as arg for copy-directory when we want
the special behavior.

This changes the behavior of rename-file etc. slightly.
The old behavior mostly disagreed with the documentation, and had
a race condition bug that could allow attackers to modify victims'
write-protected directories (Bug#27986).
* doc/lispref/files.texi (Changing Files): Document that in
rename-file etc., NEWFILE is special if it is a directory name.
* etc/NEWS: Document the change in behavior.
* src/fileio.c (directory_like): Remove.  All uses removed.
(expand_cp_target): Test only whether NEWNAME is a directory name,
not whether it is currently a directory.  This avoids a race.
(Fcopy_file, Frename_file, Fadd_name_to_file, Fmake_symbolic_link):
Document behavior if NEWNAME is a directory name.
(Frename_file): Simplify now that the destdir behavior occurs
only when NEWNAME is a directory name.
* test/lisp/net/tramp-tests.el (tramp-test11-copy-file)
(tramp-test12-rename-file, tramp--test-check-files):
Adjust tests to match new behavior.