Re: Mysterious fontification/C++ context issue - Patch for c-basic-common-init

[Alan Mackenzie]

Hi, Martin, and everybody else.

On Sun, Dec 17, 2006 at 12:55:22PM +0000, Alan Mackenzie wrote:

[ .... ]

> OK, you've convinced me.  I now agree with you that CC Mode should not
> itself set that horrible variable to nil, not even as a default.  I
> should remove the offending line from cc-mode.el, and put some extra
> explanation into cc-mode.texi and programs.texi.

Here's a pair of patches to do the job.  I think most people will be
happy about them.  ;-)

Richard, please review my change to programs.texi.

I'll have a look at cc-mode.texi ASAP.

Thanks to Chong, Stefan and Martin for talking me through this at such
great length and persuading me to do the right thing.


2006-12-17  Alan Mackenzie  <address@hidden>

        * progmodes/cc-mode.el (c-basic-common-init): don't set
        open-paren-in-column-0-is-defun-start to nil any more.


Index: cc-mode.el
===================================================================
RCS file: /cvsroot/emacs/emacs/lisp/progmodes/cc-mode.el,v
retrieving revision 1.50
diff -c -r1.50 cc-mode.el
*** cc-mode.el  3 Dec 2006 00:59:33 -0000       1.50
--- cc-mode.el  17 Dec 2006 18:10:38 -0000
***************
*** 531,539 ****
    ;; heuristic that open parens in column 0 are defun starters.  Since
    ;; we have c-state-cache, that heuristic isn't useful and only causes
    ;; trouble, so turn it off.
!   (when (memq 'col-0-paren c-emacs-features)
!     (make-local-variable 'open-paren-in-column-0-is-defun-start)
!     (setq open-paren-in-column-0-is-defun-start nil))
  
    (c-clear-found-types)
  
--- 531,541 ----
    ;; heuristic that open parens in column 0 are defun starters.  Since
    ;; we have c-state-cache, that heuristic isn't useful and only causes
    ;; trouble, so turn it off.
! ;; 2006/12/17: This facility is somewhat confused, and doesn't really seem
! ;; helpful.  Comment it out for now.
! ;;   (when (memq 'col-0-paren c-emacs-features)
! ;;     (make-local-variable 'open-paren-in-column-0-is-defun-start)
! ;;     (setq open-paren-in-column-0-is-defun-start nil))
  
    (c-clear-found-types)
  


2006-12-17  Alan Mackenzie  <address@hidden>

        * programs.texi (Left Margin Paren): Remove the bit which says
        that CC Mode sets open-paren-in-column-0-is-defun-start to nil.
        Discuss some of the issues of setting this option to nil.


Index: programs.texi
===================================================================
RCS file: /cvsroot/emacs/emacs/man/programs.texi,v
retrieving revision 1.121
diff -c -r1.121 programs.texi
*** programs.texi       30 Sep 2006 21:07:21 -0000      1.121
--- programs.texi       17 Dec 2006 18:28:40 -0000
***************
*** 156,178 ****
  @cindex open-parenthesis in leftmost column
  @cindex ( in leftmost column
    Emacs assumes by default that any opening delimiter found at the
! left margin is the start of a top-level definition, or defun.  You can
! override this default by setting this user option:
! 
! @defvar open-paren-in-column-0-is-defun-start
! If this user option is set to @code{t} (the default), opening
! parentheses or braces at column zero always start defuns.  When it's
! @code{nil}, defuns are found by searching for parens or braces at the
! outermost level.  Some major modes, including C and related modes, set
! @code{open-paren-in-column-0-is-defun-start} buffer-locally to
! @code{nil}
! @end defvar
! 
!   In modes where @code{open-paren-in-column-0-is-defun-start} is
! @code{t}, @strong{don't put an opening delimiter at the left margin
! unless it is a defun start}.  For instance, never put an
  open-parenthesis at the left margin in a Lisp file unless it is the
! start of a top-level list.
  
    If you don't follow this convention, not only will you have trouble
  when you explicitly use the commands for motion by defuns; other
--- 156,166 ----
  @cindex open-parenthesis in leftmost column
  @cindex ( in leftmost column
    Emacs assumes by default that any opening delimiter found at the
! left margin is the start of a top-level definition, or defun.
! Therefore, @strong{don't put an opening delimiter at the left margin
! unless it should have that significance}.  For instance, never put an
  open-parenthesis at the left margin in a Lisp file unless it is the
! start of a top-level list.  
  
    If you don't follow this convention, not only will you have trouble
  when you explicitly use the commands for motion by defuns; other
***************
*** 182,191 ****
  
    The most likely problem case is when you want an opening delimiter
  at the start of a line inside a string.  To avoid trouble, put an
! escape character (@samp{\}, in Emacs Lisp, @samp{/} in some other Lisp
! dialects) before the opening delimiter.  This will not affect the
! contents of the string, but will prevent that opening delimiter from
! starting a defun.  Here's an example:
  
  @example
    (insert "Foo:
--- 170,179 ----
  
    The most likely problem case is when you want an opening delimiter
  at the start of a line inside a string.  To avoid trouble, put an
! escape character (@samp{\}, in C and Emacs Lisp, @samp{/} in some
! other Lisp dialects) before the opening delimiter.  This will not
! affect the contents of the string, but will prevent that opening
! delimiter from starting a defun.  Here's an example:
  
  @example
    (insert "Foo:
***************
*** 197,202 ****
--- 185,209 ----
  highlights confusing opening delimiters (those that ought to be
  quoted) in bold red.
  
+ If you need to override this convention, you can so by setting this
+ user option:
+ 
+ @defvar open-paren-in-column-0-is-defun-start
+ If this user option is set to @code{t} (the default), opening
+ parentheses or braces at column zero always start defuns.  When it's
+ @code{nil}, defuns are found by searching for parens or braces at the
+ outermost level.
+ @end defvar
+ 
+   Usually, you shouldn't need to set
+ @code{open-paren-in-column-0-is-defun-start} to @code{nil}.  However,
+ if your buffer contains parentheses or braces in column zero which
+ don't start defuns and this confuses Emacs, it sometimes helps to set
+ the option to @code{nil}.  Be aware, though, that this will make
+ scrolling and display in large buffers quite sluggish, and that
+ parentheses and braces must be correctly matched throughout the buffer
+ for it to work properly.
+ 
    In the earliest days, the original Emacs found defuns by moving
  upward a level of parentheses or braces until there were no more
  levels to go up.  This always required scanning all the way back to
***************
*** 1557,1566 ****
  @table @kbd
  @item C-c address@hidden
  @itemx C-c @key{DEL}
! @findex c-hungry-backspace
  @kindex C-c address@hidden (C Mode)
  @kindex C-c @key{DEL} (C Mode)
! @code{c-hungry-backspace}---Delete the entire block of whitespace
  preceding point.
  
  @item C-c C-d
--- 1564,1573 ----
  @table @kbd
  @item C-c address@hidden
  @itemx C-c @key{DEL}
! @findex c-hungry-delete-backwards
  @kindex C-c address@hidden (C Mode)
  @kindex C-c @key{DEL} (C Mode)
! @code{c-hungry-delete-backwards}---Delete the entire block of whitespace
  preceding point.
  
  @item C-c C-d

-- 
Alan.