[Emacs-diffs] master a96731d: * lisp/emacs-lisp/tabulated-list.el: Don't error on nil header-string

[Artur Malabarba]

branch: master
commit a96731d7f0f0616e500583a1d3eaa912a7f0ec16
Author: Artur Malabarba <address@hidden>
Commit: Artur Malabarba <address@hidden>

    * lisp/emacs-lisp/tabulated-list.el: Don't error on nil header-string
    
    (tabulated-list-init-header): Document new behavior.
    (tabulated-list-print-fake-header): No nothing if
    `tabulated-list--header-string' is nil.
    (tabulated-list--header-string): Add a docstring.
    
    * doc/lispref/modes.texi (Tabulated List Mode): Document it.
    * etc/NEWS: Document it.
---
 doc/lispref/modes.texi            |    6 +++---
 etc/NEWS                          |    4 ++++
 lisp/emacs-lisp/tabulated-list.el |   24 ++++++++++++++----------
 3 files changed, 21 insertions(+), 13 deletions(-)

diff --git a/doc/lispref/modes.texi b/doc/lispref/modes.texi
index 8cb0f3d..c325506 100644
--- a/doc/lispref/modes.texi
+++ b/doc/lispref/modes.texi
@@ -958,9 +958,9 @@ Menu,,, emacs, The GNU Emacs Manual}).
 way, specifying @code{tabulated-list-mode} as the second argument
 (@pxref{Derived Modes}).  The body of the @code{define-derived-mode}
 form should specify the format of the tabulated data, by assigning
-values to the variables documented below; then, it should call the
-function @code{tabulated-list-init-header} to initialize the header
-line.
+values to the variables documented below; optionally, it can then call
+the function @code{tabulated-list-init-header}, which will populate a
+header with the names of the columns.
 
   The derived mode should also define a @dfn{listing command}.  This,
 not the mode command, is what the user calls (e.g., @kbd{M-x
diff --git a/etc/NEWS b/etc/NEWS
index 2888c16..fdd0c87 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -205,6 +205,10 @@ font, and (iii) the specified window.
    `message' and related functions from displaying messages the Echo
    Area.  The output is still logged to the *Messages* buffer.
 
+** It is now safe for a mode that derives `tabulated-list-mode' to not
+call `tabulated-list-init-header', in which case it will have no
+header.
+
 
 * Editing Changes in Emacs 25.1
 
diff --git a/lisp/emacs-lisp/tabulated-list.el 
b/lisp/emacs-lisp/tabulated-list.el
index b12edc8..5d10b55 100644
--- a/lisp/emacs-lisp/tabulated-list.el
+++ b/lisp/emacs-lisp/tabulated-list.el
@@ -179,7 +179,9 @@ If ADVANCE is non-nil, move forward by one line afterwards."
     table)
   "The `glyphless-char-display' table in Tabulated List buffers.")
 
-(defvar tabulated-list--header-string nil)
+(defvar tabulated-list--header-string nil
+  "Holds the header if `tabulated-list-use-header-line' is nil.
+Populated by `tabulated-list-init-header'.")
 (defvar tabulated-list--header-overlay nil)
 
 (defun tabulated-list-init-header ()
@@ -243,15 +245,17 @@ If ADVANCE is non-nil, move forward by one line 
afterwards."
       (setq-local tabulated-list--header-string cols))))
 
 (defun tabulated-list-print-fake-header ()
-  "Insert a fake Tabulated List \"header line\" at the start of the buffer."
-  (goto-char (point-min))
-  (let ((inhibit-read-only t))
-    (insert tabulated-list--header-string "\n")
-    (if tabulated-list--header-overlay
-       (move-overlay tabulated-list--header-overlay (point-min) (point))
-      (setq-local tabulated-list--header-overlay
-                  (make-overlay (point-min) (point))))
-    (overlay-put tabulated-list--header-overlay 'face 'underline)))
+  "Insert a fake Tabulated List \"header line\" at the start of the buffer.
+Do nothing if `tabulated-list--header-string' is nil."
+  (when tabulated-list--header-string
+    (goto-char (point-min))
+    (let ((inhibit-read-only t))
+      (insert tabulated-list--header-string "\n")
+      (if tabulated-list--header-overlay
+          (move-overlay tabulated-list--header-overlay (point-min) (point))
+        (setq-local tabulated-list--header-overlay
+                    (make-overlay (point-min) (point))))
+      (overlay-put tabulated-list--header-overlay 'face 'underline))))
 
 (defun tabulated-list-revert (&rest ignored)
   "The `revert-buffer-function' for `tabulated-list-mode'.