Subject: bug#35899: 26.1; move-beginning-of-line sometimes does not move to beginning of line

From: Noam Postavsky <[email-masked]>
Date: Fri, 21 Jun 2019 06:05:22 -0400

Eli Zaretskii <[email-masked]> writes:

>> However, the documentation of move-beginning-of-line includes:
>> 
>>    (If there’s an image in the line, this disregards newlines
>>    which are part of the text that the image rests on.)
>> 
>> Hence, I expect this to move to position 1. For comparison, when I press
>> C-a, it does move to position 1, as expected.
>
> "the text that the image rests on" refers to the text which is
> "covered" by the display property, not the newlines in the binary data
> that constitutes the image file's data.

If I create an image which rests on some newlines like this:

    (let ((img (create-image "bug-35899-hello.png")))
      (insert "abc")
      (insert-image img "foo\nbar\nbaz")
      (insert "def"))

Then with point after "def", move-beginning-of-line stops "inside" the
image.  And I don't see anything in its code which would allow it to
skip the image.  Isn't this just a doc bug?

>From f64d539780c0aa8e1a3322afa518eb768f468e16 Mon Sep 17 00:00:00 2001
From: Noam Postavsky <[email-masked]>
Date: Fri, 21 Jun 2019 05:52:14 -0400
Subject: [PATCH] Clarify docs about line movement (Bug#35899)

* doc/lispref/positions.texi (Text Lines, Screen Lines): Add index
entries.
* lisp/simple.el (move-beginning-of-line): Remove incorrect mention of
images, and reference beginning-of-visual-line.
* src/editfns.c (Fline_beginning_position): Reference
`vertical-motion'.
---
 doc/lispref/positions.texi | 3 +++
 lisp/simple.el             | 8 ++++----
 src/editfns.c              | 3 ++-
 3 files changed, 9 insertions(+), 5 deletions(-)

diff --git a/doc/lispref/positions.texi b/doc/lispref/positions.texi
index 7707793467..128685800f 100644
--- a/doc/lispref/positions.texi
+++ b/doc/lispref/positions.texi
@@ -332,6 +332,8 @@ Buffer End Motion
 @node Text Lines
 @subsection Motion by Text Lines
 @cindex lines
+@cindex logical lines, moving by
+@cindex physical lines, moving by
 
   Text lines are portions of the buffer delimited by newline characters,
 which are regarded as part of the previous line.  The first text line
@@ -515,6 +517,7 @@ Text Lines
 @node Screen Lines
 @subsection Motion by Screen Lines
 @cindex screen lines, moving by
+@cindex visual lines, moving by
 
   The line functions in the previous section count text lines, delimited
 only by newline characters.  By contrast, these functions count screen
diff --git a/lisp/simple.el b/lisp/simple.el
index a0f2da7152..010a7ae563 100644
--- a/lisp/simple.el
+++ b/lisp/simple.el
@@ -6638,15 +6638,15 @@ (defun move-end-of-line (arg)
 	    (setq done t)))))))
 
 (defun move-beginning-of-line (arg)
-  "Move point to beginning of current line as displayed.
-\(If there's an image in the line, this disregards newlines
-which are part of the text that the image rests on.)
+  "Move point to visible beginning of current logical line.
+This disregards any invisible newline characters.
 
 With argument ARG not nil or 1, move forward ARG - 1 lines first.
 If point reaches the beginning or end of buffer, it stops there.
 \(But if the buffer doesn't end in a newline, it stops at the
 beginning of the last line.)
-To ignore intangibility, bind `inhibit-point-motion-hooks' to t."
+To ignore intangibility, bind `inhibit-point-motion-hooks' to t.
+For motion by visual lines, see `beginning-of-visual-line'."
   (interactive "^p")
   (or arg (setq arg 1))
 
diff --git a/src/editfns.c b/src/editfns.c
index 9b76ae23ff..7e16fbd0ed 100644
--- a/src/editfns.c
+++ b/src/editfns.c
@@ -910,7 +910,8 @@ DEFUN ("line-beginning-position",
 
 This function ignores text display directionality; it returns the
 position of the first character in logical order, i.e. the smallest
-character position on the line.
+character position on the logical line.  See `vertical-motion' for
+movement by screen lines.
 
 This function constrains the returned position to the current field
 unless that position would be on a different line than the original,
-- 
2.11.0