master 55aad592e17: Improve computation of indent depth in SHR and 'visual-wrap-prefix-mode'

[Jim Porter]

branch: master
commit 55aad592e177dc2c503ebe9ad2a46e227683315e
Author: Jim Porter <jporterbugs@gmail.com>
Commit: Jim Porter <jporterbugs@gmail.com>

    Improve computation of indent depth in SHR and 'visual-wrap-prefix-mode'
    
    Now, we get the average-width of the current font using
    'string-pixel-width' and a specified space display spec, which doesn't
    require the buffer to be displayed in a window (bug#72771).
    
    * lisp/net/shr.el (shr-indent):
    * lisp/visual-wrap.el (visual-wrap--content-prefix): Fix getting the
    font when the buffer isn't displayed in a window.
    (visual-wrap-fill-context-prefix): Fix indentation.
---
 lisp/net/shr.el     | 22 +++++++++++-----------
 lisp/visual-wrap.el | 20 +++++++-------------
 2 files changed, 18 insertions(+), 24 deletions(-)

diff --git a/lisp/net/shr.el b/lisp/net/shr.el
index b9ac9f0c8c0..cd0e482aee7 100644
--- a/lisp/net/shr.el
+++ b/lisp/net/shr.el
@@ -1051,17 +1051,17 @@ When `shr-fill-text' is nil, only indent."
       (if (not shr-use-fonts)
           (insert-char ?\s shr-indentation)
         (insert ?\s)
-        (put-text-property
-         (1- (point)) (point) 'display
-         ;; Set the specified space width in terms of the default width
-         ;; of the current face, like (N . width).  That way, the
-         ;; indentation is calculated correctly when using
-         ;; `text-scale-adjust'.
-         `(space :width (,(if-let ((font (font-at (1- (point))))
-                                   (info (query-font font)))
-                              (/ (float shr-indentation) (aref info 7))
-                            shr-indentation)
-                         . width))))
+        ;; Set the specified space width in units of the average-width
+        ;; of the current font, like (N . width).  That way, the
+        ;; indentation is calculated correctly when using
+        ;; `text-scale-adjust'.
+        (let ((avg-space (propertize (buffer-substring (1- (point)) (point))
+                                     'display '(space :width 1))))
+          (put-text-property
+           (1- (point)) (point) 'display
+           `(space :width (,(/ (float shr-indentation)
+                               (string-pixel-width avg-space (current-buffer)))
+                           . width)))))
       (put-text-property start (+ (point) prefix)
                          'shr-prefix-length (+ prefix (- (point) start))))))
 
diff --git a/lisp/visual-wrap.el b/lisp/visual-wrap.el
index 902a9e41c5e..76276c0f474 100644
--- a/lisp/visual-wrap.el
+++ b/lisp/visual-wrap.el
@@ -160,20 +160,14 @@ PREFIX was empty."
     prefix)
    (t
     ;; Otherwise, we want the prefix to be whitespace of the same width
-    ;; as the first-line prefix.  If possible, compute the real pixel
-    ;; width of the first-line prefix in canonical-width characters.
-    ;; This is useful if the first-line prefix uses some very-wide
-    ;; characters.
-    (if-let ((font (font-at position))
-             (info (query-font font)))
+    ;; as the first-line prefix.  We want to return an integer width (in
+    ;; units of the font's average-width) large enough to fit the
+    ;; first-line prefix.
+    (let ((avg-space (propertize (buffer-substring position (1+ position))
+                                 'display '(space :width 1))))
         (max (string-width prefix)
              (ceiling (string-pixel-width prefix (current-buffer))
-                      (aref info 7)))
-      ;; We couldn't get the font, so we're in a terminal and
-      ;; `string-pixel-width' is really returning the number of columns.
-      ;; (This is different from `string-width', since that doesn't
-      ;; respect specified spaces.)
-      (string-pixel-width prefix)))))
+                      (string-pixel-width avg-space (current-buffer))))))))
 
 (defun visual-wrap-fill-context-prefix (beg end)
   "Compute visual wrap prefix from text between BEG and END.
@@ -189,7 +183,7 @@ by `visual-wrap-extra-indent'."
           ;; make much sense (and is positively harmful in
           ;; taskpaper-mode where paragraph-start matches everything).
           (or (let ((paragraph-start regexp-unmatchable))
-                    (fill-context-prefix beg end))
+                (fill-context-prefix beg end))
                   ;; Note: fill-context-prefix may return nil; See:
                   ;; http://article.gmane.org/gmane.emacs.devel/156285
               ""))