Add simplistic vc-p4-switch-client command

p4-lowlevel.el

@@ -726,4 +726,45 @@ already exists."
       (setq default-directory caller-default-directory))
     buf))
 
+(defun p4-lowlevel-local-clients ()
+  (mapcar (lambda (client) (alist-get "client" client nil nil #'string=))
+          (seq-filter (lambda (client) (string= (alist-get "Host" client nil nil #'string=)
+                                                (system-name)))
+                      (p4-lowlevel-clients))))
+
+(defun p4-lowlevel-clients ()
+  "Get the clients available."
+  (let ((lines (p4-lowlevel-command-to-alist `("-z" "tag" "clients" "-u" ,(user-login-name)))))
+    (seq-reduce (lambda (acc itm)
+                  (p4-lowlevel-clients-parse-line acc itm))
+                lines nil)))
+
+(defun p4-lowlevel-clients-parse-line (acc line)
+  (pcase (car line)
+    ((pred (string= "info1"))
+     (let ((values (split-string (cdr line) " ")))
+       (pcase (car values)
+         ((pred (string= "client"))
+          (cons (list (cons (car values) (cadr values))) acc))
+         ((or (pred (string= "Update"))
+              (pred (string= "Access"))
+              (pred (string= "Owner"))
+              (pred (string= "Options"))
+              (pred (string= "SubmitOptions"))
+              (pred (string= "LineEnd"))
+              (pred (string= "Root"))
+              (pred (string= "Host"))
+              (pred (string= "Stream"))
+              (pred (string= "Type"))
+              (pred (string= "Description")))
+          (cons (cons (cons (car values)
+                            (cadr values))
+                      (car acc))
+                (cdr acc)))
+         (_ acc))))
+    (`("exit" . ,result)
+     (if (not (= result 0))
+         (error "Clients returned non-zero exit code.")))
+    (_ acc)))
+
 (provide 'p4-lowlevel)

vc-p4.el

@@ -980,4 +980,9 @@ third subblock in each conflict block."
 The difference to vc-do-command is that this function always invokes `p4'."
   (apply 'vc-do-command buffer okstatus "p4" file flags))
 
+(defun vc-p4-switch-client (client)
+  (interactive
+   (list (completing-read "Client: " (p4-lowlevel-local-clients))))
+  (p4-lowlevel-command-or-error `("set" ,(format "P4CLIENT=%s" client))))
+
 (provide 'vc-p4)