org-agenda: Set restriction lock from agenda

* lisp/org-agenda.el (org-agenda-set-restriction-lock-from-agenda):
  New function.  Allows to set the restriction lock from an agenda
  buffer.

Further bind C-c C-x < to
`org-agenda-set-restriction-lock-from-agenda' in the
`org-agenda-mode-map'.  This is the same binding as for Org files.

etc/ORG-NEWS

@@ -64,7 +64,7 @@ list as their first argument.
 *** Agenda
 **** New variable : ~org-agenda-show-future-repeats~
 **** New variable : ~org-agenda-prefer-last-repeat~
-
+**** Binding C-c C-x < for ~org-agenda-set-restriction-lock-from-agenda~
 *** New value for ~org-publish-sitemap-sort-folders~
 
 The new ~ignore~ value effectively allows toggling inclusion of
@@ -115,7 +115,7 @@ value of the code will be displayed in the results section.
 A new engine was added to support ~sqsh~ command line utility for use
 against Microsoft SQL Server or Sybase SQL server.
 
-More information on ~sqsh~ can be found here: [[https://sourceforge.net/projects/sqsh/][sourceforge/sqsh]] 
+More information on ~sqsh~ can be found here: [[https://sourceforge.net/projects/sqsh/][sourceforge/sqsh]]
 
 To use ~sqsh~ in an *sql* =SRC_BLK= set the =:engine= like this:
 
@@ -135,7 +135,7 @@ Where clue > 0
 This new function is meant to be used in back-ends supporting images
 as descriptions of links, a.k.a. image links.  See its docstring for
 details.
-**** Add global macros through ~org-export-global-macros~ 
+**** Add global macros through ~org-export-global-macros~
 With this variable, one can define macros available for all documents.
 **** New keyword ~#+EXPORT_FILE_NAME~
 Simiralry to ~:EXPORT_FILE_NAME:~ property, this keyword allows the
@@ -180,6 +180,10 @@ in addition to ~org-publish-find-title~ and ~org-publish-find-date~.
 
 It is the reciprocal of ~org-list-to-lisp~, which see.
 
+*** ~org-agenda-set-restriction-lock-from-agenda~
+
+Call ~org-agenda-set-restriction-lock~ from the agenda.
+
 * Version 9.0
 
 ** Incompatible changes
@@ -518,7 +522,7 @@ If you want to use the *trusted connection* feature, omit *both* the
 If your Emacs is running in a Cygwin environment, the =ob-sql= library
 can pass the converted path to the =sqlcmd= tool.
 
-**** Improved support of header arguments for postgresql 
+**** Improved support of header arguments for postgresql
 
 The postgresql engine in a sql code block supports now ~:dbport~ nd
 ~:dbpassword~ as header arguments.

lisp/org-agenda.el

@@ -2320,6 +2320,7 @@ The following commands are available:
 (org-defkey org-agenda-mode-map "b" 'org-agenda-earlier)
 (org-defkey org-agenda-mode-map "\C-c\C-x\C-c" 'org-agenda-columns)
 (org-defkey org-agenda-mode-map "\C-c\C-x>" 'org-agenda-remove-restriction-lock)
+(org-defkey org-agenda-mode-map "\C-c\C-x<" 'org-agenda-set-restriction-lock-from-agenda)
 
 (org-defkey org-agenda-mode-map "[" 'org-agenda-manipulate-query-add)
 (org-defkey org-agenda-mode-map "]" 'org-agenda-manipulate-query-subtract)
@@ -7027,6 +7028,22 @@ their type."
 	     'help-echo "Agendas are currently limited to this subtree.")
 (delete-overlay org-agenda-restriction-lock-overlay)
 
+(defun org-agenda-set-restriction-lock-from-agenda (arg)
+  "Set the restriction lock to the agenda item at point from within the agenda.
+When called with a `\\[universal-argument]' prefix, restrict to
+the file which contains the item.
+Argument ARG is the prefix argument."
+  (interactive "P")
+  (unless  (derived-mode-p 'org-agenda-mode)
+    (user-error "Not in an Org agenda buffer"))
+  (let* ((marker (or (org-get-at-bol 'org-marker)
+                     (org-agenda-error)))
+         (buffer (marker-buffer marker))
+         (pos (marker-position marker)))
+    (with-current-buffer buffer
+      (goto-char pos)
+      (org-agenda-set-restriction-lock arg))))
+
 ;;;###autoload
 (defun org-agenda-set-restriction-lock (&optional type)
   "Set restriction lock for agenda, to current subtree or file.