Re: M-w, then C-y. C-y inserts text properties that aren't on original.

[Alan Mackenzie]

Hi, Eli,

On Fri, Feb 19, 2010 at 11:22:55AM +0200, Eli Zaretskii wrote:
> > Date: Thu, 18 Feb 2010 20:29:02 +0000
> > From: Alan Mackenzie <address@hidden>

> > In a C++ Mode buffer, I create a region containing a template-opener <,
> > M-w it, then C-y it.

> > The C-y puts a syntax-table property on the (copy of) the <, but this
> > property didn't exist on the original.

> > What _was_ on the original was a category property whose symbol had a
> > syntax-table property.

> > This is the root cause of bug 5570 (indentation messed up in C++).

> > Would somebody please suggest the part of Emacs I should be looking at
> > to debug this problem.

> Can you please give a precise recipe, starting with "emacs -Q", for
> reproducing the problem?  I don't know enough about C++ Mode internals
> to understand what you say.

#########################################################################
emacs -Q
(defvar propp-var nil)
(put 'propp-var 'foo t)

Create buffer "foo" and put a line of text (including NL) into it.

(with-current-buffer "foo" (put-text-property 1 2 'category 'propp-var))

In foo:
M-<                                     ; goto BOB
C-<space> C-n M-w                       ; Copy L1 into the kill ring
C-y                                     ; Yank it as L2

M-<   C-u C-x =                         ; Get details of char at BOB
    There are text properties here:
      category             propp-var    ; <==============================
      fontified            t

C-n   C-u C-x =                         ; Get details of char at BOL 2
    There are text properties here:
      fontified            t
      foo                  t            ; <==============================
#########################################################################

Note that where the original "had" a 'foo property by indirection through
the 'category, the copy has spuriously short-circuited the 'category
indirection.

> Thanks.

-- 
Alan Mackenzie (Nuremberg, Germany).