emacs: Add "View build log" action to build popup.

* emacs/guix-command.el (guix-run-view-build-log): New function.
  (guix-command-additional-execute-arguments,
  guix-command-special-executors): Add entries for "View build log"
  action.
* emacs/guix-utils.el (guix-find-file-or-url): New function.

emacs/guix-command.el

@@ -497,7 +497,10 @@ to be modified."
   "List of default 'execute' action arguments.")
 
 (defvar guix-command-additional-execute-arguments
-  `((("graph")
+  `((("build")
+     ,(guix-command-make-argument
+       :name "log" :char ?l :doc "View build log"))
+    (("graph")
      ,(guix-command-make-argument
        :name "view" :char ?v :doc "View graph")))
   "Alist of guix commands and additional 'execute' action arguments.")
@@ -518,6 +521,8 @@ to be modified."
      ("repl" . guix-run-environment-command-in-repl))
     (("pull")
      ("repl" . guix-run-pull-command-in-repl))
+    (("build")
+     ("log" . guix-run-view-build-log))
     (("graph")
      ("view" . guix-run-view-graph)))
   "Alist of guix commands and alists of special executers for them.
@@ -556,6 +561,18 @@ Perform pull-specific actions after operation, see
    (apply #'guix-make-guile-expression 'guix-command args)
    nil 'pull))
 
+(defun guix-run-view-build-log (args)
+  "Add --log-file to ARGS, run 'guix ARGS ...' build command, and
+open the log file(s)."
+  (let* ((args (if (member "--log-file" args)
+                   args
+                 (apply #'list (car args) "--log-file" (cdr args))))
+         (output (guix-command-output args))
+         (files  (split-string output "\n" t)))
+    (dolist (file files)
+      (guix-find-file-or-url file)
+      (guix-build-log-mode))))
+
 (defun guix-run-view-graph (args)
   "Run 'guix ARGS ...' graph command, make the image and open it."
   (let* ((graph-file (guix-dot-file-name))

emacs/guix-utils.el

@@ -208,6 +208,16 @@ single argument."
       (funcall guix-find-file-function file)
     (message "File '%s' does not exist." file)))
 
+(defvar url-handler-regexp)
+
+(defun guix-find-file-or-url (file-or-url)
+  "Find FILE-OR-URL."
+  (require 'url-handlers)
+  (let ((file-name-handler-alist
+         (cons (cons url-handler-regexp 'url-file-handler)
+               file-name-handler-alist)))
+    (find-file file-or-url)))
+
 (defmacro guix-while-search (regexp &rest body)
   "Evaluate BODY after each search for REGEXP in the current buffer."
   (declare (indent 1) (debug t))