Tramp's method "kubernetes" supports now optional namespace

* doc/misc/tramp.texi (Inline methods): Extend Kubernetes host
name syntax by an optional namespace.
(Kubernetes setup): Mention optional namespace part of the host name.

* etc/NEWS: Tramp's method "kubernetes" supports now optional namespace.
Fix typos.

* lisp/net/tramp-container.el (tramp-kubernetes-namespace):
Initialize with nil.  Adapt docstring.
(tramp-kubernetes--name-regexp): New defconst.
(tramp-kubernetes--host-name-regexp): Change in order to cover
also an optional namespace.  (Bug#59797)
(tramp-kubernetes--namespace): New defun.
(tramp-kubernetes--context-namespace): Use it.
(tramp-skeleton-kubernetes-vector): Add sanity check for
superfluous user name or port number.

3 files changed, 78 insertions, 41 deletions

diff --git a/doc/misc/tramp.texi b/doc/misc/tramp.texi
index eddf0272641..e548432700f 100644
--- a/doc/misc/tramp.texi
+++ b/doc/misc/tramp.texi
@@ -999,9 +999,11 @@ if desired.
 @cindex @option{kubernetes} method
 
 Integration for containers in Kubernetes pods.  The host name is
-@samp{@var{pod}}, or @samp{@var{container}.@var{pod}} if an
-explicit container name shall be used.  Otherwise, the first container
-in a pod is used.
+@samp{@var{pod}}, or @samp{@var{container}.@var{pod}} if an explicit
+container name shall be used.  Otherwise, the first container in a pod
+is used.  @samp{@var{pod}%@var{namespace}} as host name allows to use
+another namespace but the default one.  This can also be combined with
+the @samp{@var{container}.} prefix.
 
 This method does not support user names.
 
@@ -3246,7 +3248,9 @@ by setting the pod annotation
 @vindex tramp-kubernetes-namespace
 @value{tramp} uses the default Kubernetes context and namespace.  If
 another context or namespace shall be used, configure the user options
-@code{tramp-kubernetes-context} and @code{tramp-kubernetes-namespace}.
+@code{tramp-kubernetes-context} or @code{tramp-kubernetes-namespace},
+respectively.  An explicit @samp{%@var{namespace}} postfix in the host
+name takes precedence.
 
 
 @node Auto-save File Lock and Backup
diff --git a/etc/NEWS b/etc/NEWS
index f133769bebf..607244b4b4b 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -24,11 +24,12 @@ applies, and please also update docstrings as needed.
 
 * Installation Changes in Emacs 31.1
 
-** When using GCC 4 or later to build Emacs on 32-bit x86 systems,
-'configure' now defaults to using the GCC options -mfpmath=sse (if the
-host system supports SSE2) or -fno-tree-sra (if not).  These GCC options
-work around GCC bug 58416, which can cause Emacs to behave incorrectly
-in rare cases.
+** Changed GCC default options on 32-bit x86 systems.
+When using GCC 4 or later to build Emacs on 32-bit x86 systems,
+'configure' now defaults to using the GCC options '-mfpmath=sse' (if the
+host system supports SSE2) or '-fno-tree-sra' (if not).  These GCC
+options work around GCC bug 58416, which can cause Emacs to behave
+incorrectly in rare cases.
 
 
 * Startup Changes in Emacs 31.1
@@ -37,7 +38,7 @@ in rare cases.
 * Changes in Emacs 31.1
 
 ---
-** "find-func.el" commands now have history enabled.
+** find-func.el commands now have history enabled.
 The 'find-function', 'find-library', 'find-face-definition', and
 'find-variable' commands now allow retrieving previous input using the
 usual minibuffer history commands.  Each command has a separate history.
@@ -52,13 +53,13 @@ usual minibuffer history commands.  Each command has a separate history.
 
 ---
 *** 'whitespace-cleanup' now adds missing newline at end of file.
-If 'whitespace-style' includes 'missing-newline-at-eof (which is the
+If 'whitespace-style' includes 'missing-newline-at-eof' (which is the
 default), the 'whitespace-cleanup' function will now add the newline.
 
 ** Eshell
 
 ---
-*** New option 'eshell-command-async-buffer'.
+*** New user option 'eshell-command-async-buffer'.
 This option lets you tell 'eshell-command' how to respond if its output
 buffer is already in use by another invocation of 'eshell-command', much
 like 'async-shell-command-buffer' does for 'shell-command'.  By default,
@@ -68,7 +69,7 @@ necessary.  To restore the previous behavior, set this option to
 
 +++
 *** 'eshell-execute-file' is now an interactive command.
-Interactively, this now prompts for a script file to execute. With the
+Interactively, this now prompts for a script file to execute.  With the
 prefix argument, it will also insert any output into the current buffer
 at point.
 
@@ -79,8 +80,8 @@ where to send the standard error output.  See the "(eshell) Entry
 Points" node in the Eshell manual for more details.
 
 +++
-*** Eshell's built-in "wait" command now accepts a timeout.
-By passing "-t" or "--timeout", you can specify a maximum time to wait
+*** Eshell's built-in 'wait' command now accepts a timeout.
+By passing '-t' or '--timeout', you can specify a maximum time to wait
 for the processes to exit.  Additionally, you can now wait for external
 processes by passing their PIDs.
 
@@ -91,7 +92,7 @@ processes by passing their PIDs.
 Sliced images allow for more intuitive scrolling up/down by letting you
 scroll past each slice, instead of jumping past the entire image.
 Previously, SHR sliced images when zoomed to their original size, no
-matter how large or small that was).  Now, SHR slices any images taller
+matter how large or small that was.  Now, SHR slices any images taller
 than 'shr-sliced-image-height'.  For more information, see the "(eww)
 Advanced" node in the EWW manual.
 
@@ -111,13 +112,13 @@ point.  If a region is active, it runs all the unit tests under the
 region.  It is bound to 'C-c C-t t' in 'go-ts-mode'.
 
 The 'go-ts-mode-test-this-file' command runs all unit tests in the current
-file. It is bound to 'C-c C-t f' in 'go-ts-mode'.
+file.  It is bound to 'C-c C-t f' in 'go-ts-mode'.
 
 The 'go-ts-mode-test-this-package' command runs all unit tests under the
 package of the current buffer.  It is bound to 'C-c C-t p' in 'go-ts-mode'.
 
-The 'go-ts-mode-build-tags' variable is available to set a list of build
-tags for the test commands.
+The 'go-ts-mode-build-tags' user option is available to set a list of
+build tags for the test commands.
 
 ** Emacs Lisp mode
 
@@ -154,8 +155,18 @@ positives.
 ---
 *** Dedicated buffer for plain text contents.
 When switching to the plain text contents with 'doc-view-open-text',
-DocView now creates a dedicated buffer to display it. 'C-c C-c' gets you
+DocView now creates a dedicated buffer to display it.  'C-c C-c' gets you
 back to real DocView buffer if it still exists.
+
+** Tramp
+
++++
+*** Connection method "kubernetes" supports now optional namespace.
+The host name for Kubernetes connections can be of kind
+[CONTAINER.]POD[%NAMESPACE], in order to specify the namespace to be
+used.  This overrides the setiing in 'tramp-kubernetes-namespace', if
+any.
+
 
 * New Modes and Packages in Emacs 31.1
 
@@ -182,9 +193,9 @@ It has been obsolete since Emacs 26.1.  Use the group 'text' instead.
 
 ---
 ** Process execution has been optimized on Android.
-The run-time performance of subprocesses on recent Android releases
-where a userspace executable loader is required has been optimized on
-systems featuring Linux 3.5.0 and above.
+The run-time performance of subprocesses on recent Android releases,
+where a userspace executable loader is required, has been optimized on
+systems featuring GNU/Linux 3.5.0 and above.
 
 
 ----------------------------------------------------------------------
diff --git a/lisp/net/tramp-container.el b/lisp/net/tramp-container.el
index 02512e64ef6..27bad70753c 100644
--- a/lisp/net/tramp-container.el
+++ b/lisp/net/tramp-container.el
@@ -50,18 +50,14 @@
 ;;
 ;; Open file in a Kubernetes container:
 ;;
-;;     C-x C-f /kubernetes:[CONTAINER.]POD:/path/to/file
+;;     C-x C-f /kubernetes:[CONTAINER.]POD[%NAMESPACE]:/path/to/file
 ;;
 ;; Where:
 ;;     POD           is the pod to connect to.
 ;;     CONTAINER     is the container to connect to (optional).
 ;;                   By default, the first container in that pod will
 ;;                   be used.
-;;
-;; Completion for POD and accessing it operate in the current
-;; namespace, use this command to change it:
-;;
-;; "kubectl config set-context --current --namespace=<name>"
+;;     NAMESPACE     is the namespace to be used (optional).
 ;;
 ;;
 ;;
@@ -151,11 +147,14 @@ If it is nil, the default context will be used."
   :type '(choice (const :tag "Use default" nil)
                  (string)))
 
-(defcustom tramp-kubernetes-namespace "default"
-  "Namespace of Kubernetes."
+(defcustom tramp-kubernetes-namespace nil
+  "Namespace of Kubernetes.
+If it is nil, the current namespace will be used.  An explicit NAMESPACE
+in the remote file name host part will override it."
   :group 'tramp
-  :version "30.1"
-  :type 'string)
+  :version "31.1"
+  :type '(choice (const :tag "Use default" nil)
+                 (string)))
 
 ;;;###tramp-autoload
 (defcustom tramp-toolbox-program "toolbox"
@@ -324,10 +323,18 @@ see its function help for a description of the format."
             (push (concat elt "." (car line)) names)))
         (mapcar (lambda (name) (list nil name)) (delq nil names))))))
 
+;; <https://kubernetes.io/docs/concepts/overview/working-with-objects/names/>
+;; `lower' could also match non-ascii letters.  But since this regexp
+;; is only used for strings matching `tramp-host-regexp', this doesn't
+;; hurt.
+(defconst tramp-kubernetes--name-regexp (rx (** 1 63 (any lower digit "-")))
+  "Regexp matching kubernetes names.")
+
 (defconst tramp-kubernetes--host-name-regexp
-  (rx (? (group (regexp tramp-host-regexp)) ".")
-      (group (regexp tramp-host-regexp)))
-  "The CONTAINER.POD syntax of kubernetes host names in Tramp.")
+  (rx bos (? (group (regexp tramp-kubernetes--name-regexp)) ".")
+      (group (regexp tramp-kubernetes--name-regexp))
+      (? "%" (group (regexp tramp-kubernetes--name-regexp))) eos)
+  "The CONTAINER.POD%NAMESPACE syntax of kubernetes host names in Tramp.")
 
 ;;;###tramp-autoload
 (defun tramp-kubernetes--container (vec)
@@ -345,6 +352,16 @@ see its function help for a description of the format."
              (match-string 2 host)))
       ""))
 
+;;;###tramp-autoload
+(defun tramp-kubernetes--namespace (vec)
+  "Extract the namespace from a kubernetes host name in VEC.
+Use `tramp-kubernetes-namespace' otherwise."
+  (or (when-let ((_ vec)
+                 (host (tramp-file-name-host vec)))
+        (and (string-match tramp-kubernetes--host-name-regexp host)
+             (match-string 3 host)))
+      tramp-kubernetes-namespace))
+
 ;; We must change `vec' and `default-directory' to the previous hop,
 ;; in order to run `process-file' in a proper environment.
 (defmacro tramp-skeleton-kubernetes-vector (vec &rest body)
@@ -355,6 +372,11 @@ BODY is the backend specific code."
            (cond
             ((null ,vec) tramp-null-hop)
             ((equal (tramp-file-name-method ,vec) tramp-kubernetes-method)
+             ;; Sanity check.  We don't support `user' or `port' in
+             ;; Kubernetes file names.
+             (when (or (tramp-file-name-user-domain ,vec)
+                       (tramp-file-name-port ,vec))
+               (tramp-user-error ,vec "Wrong kubernetes file name syntax"))
              (if (tramp-file-name-hop ,vec)
                  (tramp-dissect-hop-name (tramp-file-name-hop ,vec))
                tramp-null-hop))
@@ -400,8 +422,8 @@ Obey `tramp-kubernetes-context'"
    #'identity
    `(,(when-let ((context (tramp-kubernetes--current-context vec)))
         (format "--context=%s" context))
-     ,(when tramp-kubernetes-namespace
-        (format "--namespace=%s" tramp-kubernetes-namespace)))
+     ,(when-let ((namespace (tramp-kubernetes--namespace vec)))
+        (format "--namespace=%s" namespace)))
    " "))
 
 ;;;###tramp-autoload
@@ -617,9 +639,9 @@ see its function help for a description of the format."
      ;; This variable will be eval'ed in `tramp-expand-args'.
      (tramp-extra-expand-args
       . (?a (tramp-kubernetes--container (car tramp-current-connection))
-            ?h (tramp-kubernetes--pod (car tramp-current-connection))
-            ?x (tramp-kubernetes--context-namespace
-                (car tramp-current-connection)))))
+         ?h (tramp-kubernetes--pod (car tramp-current-connection))
+         ?x (tramp-kubernetes--context-namespace
+             (car tramp-current-connection)))))
    "Default connection-local variables for remote kubernetes connections.")
 
  (connection-local-set-profile-variables