Allow querying font by name for its height and other info. (Bug#19395)

 src/font.c (Ffont_info): Add more font information to the vector
 returned by the function, inspired by query-font.  Doc fix.

 doc/lispref/display.texi (Low-Level Font): Document font-info and query-font.

 lisp/international/mule-diag.el (describe-font-internal): Display
 additional info returned by font-info.
 lisp/linum.el (linum--face-width): Rename from linum--face-height,
 and use the new functionality of font-info.
 (linum-update-window): Use linum--face-width and frame-char-width,
 instead of approximating with height.

 etc/NEWS: Mention the enhancement in font-info.

3 files changed, 28 insertions, 7 deletions

diff --git a/lisp/ChangeLog b/lisp/ChangeLog
index 89a92f6454f..cb8348e1d51 100644
--- a/lisp/ChangeLog
+++ b/lisp/ChangeLog
@@ -1,3 +1,13 @@
+2014-12-18  Eli Zaretskii  <eliz@gnu.org>
+
+        * international/mule-diag.el (describe-font-internal): Display
+        additional info returned by font-info.
+
+        * linum.el (linum--face-width): Rename from linum--face-height,
+        and use the new functionality of font-info.
+        (linum-update-window): Use linum--face-width and frame-char-width,
+        instead of approximating with height.
+
 2014-12-18  Dmitry Gutov  <dgutov@yandex.ru>
 
         * vc/vc-svn.el (vc-svn-dir-status-files): Revert the 2014-12-02
diff --git a/lisp/international/mule-diag.el b/lisp/international/mule-diag.el
index 13a178531bc..ead2decb771 100644
--- a/lisp/international/mule-diag.el
+++ b/lisp/international/mule-diag.el
@@ -825,10 +825,18 @@ but still contains full information about each coding system."
 The IGNORED argument is ignored."
   (print-list "name (opened by):" (aref font-info 0))
   (print-list "       full name:" (aref font-info 1))
+  (and (aref font-info 12)
+       (print-list "       file name:" (aref font-info 12)))
   (print-list "            size:" (format "%2d" (aref font-info 2)))
   (print-list "          height:" (format "%2d" (aref font-info 3)))
   (print-list " baseline-offset:" (format "%2d" (aref font-info 4)))
-  (print-list "relative-compose:" (format "%2d" (aref font-info 5))))
+  (print-list "relative-compose:" (format "%2d" (aref font-info 5)))
+  (print-list "  default-ascent:" (format "%2d" (aref font-info 6)))
+  (print-list "          ascent:" (format "%2d" (aref font-info 8)))
+  (print-list "         descent:" (format "%2d" (aref font-info 9)))
+  (print-list "   average-width:" (format "%2d" (aref font-info 11)))
+  (print-list "     space-width:" (format "%2d" (aref font-info 10)))
+  (print-list "       max-width:" (format "%2d" (aref font-info 7))))
 
 ;;;###autoload
 (defun describe-font (fontname)
diff --git a/lisp/linum.el b/lisp/linum.el
index b13bd8dbbb6..fb2cda6c506 100644
--- a/lisp/linum.el
+++ b/lisp/linum.el
@@ -138,8 +138,13 @@ Linum mode is a buffer-local minor mode."
       (mapc #'delete-overlay linum-available)
       (setq linum-available nil))))
 
-(defun linum--face-height (face)
-  (aref (font-info (face-font face)) 2))
+(defun linum--face-width (face)
+  (let ((info (font-info (face-font face)))
+        width)
+    (setq width (aref info 11))
+    (if (<= width 0)
+        (setq width (aref info 10)))
+    width))
 
 (defun linum-update-window (win)
   "Update line numbers for the portion visible in window WIN."
@@ -183,10 +188,8 @@ Linum mode is a buffer-local minor mode."
       (setq line (1+ line)))
     (when (display-graphic-p)
       (setq width (ceiling
-                   ;; We'd really want to check the widths rather than the
-                   ;; heights, but it's a start.
-                   (/ (* width 1.0 (linum--face-height 'linum))
-                      (frame-char-height)))))
+                   (/ (* width 1.0 (linum--face-width 'linum))
+                      (frame-char-width)))))
     (set-window-margins win width (cdr (window-margins win)))))
 
 (defun linum-after-change (beg end _len)