Re: paragraph-start in Shell mode and Ielm.

[Luc Teirlinck]

Richard Stallman wrote:

   Have you checked all the uses of paragraph-start to make sure they
   really work when paragraph-start does not match separator lines?

Actually, another problem is that some modes apparently _relied_ on the
fact that paragraph-separate used to be meaningless if it did not also
match paragraph-start.  The recent 22.0.50 changes in paragraph
behavior have broken paragraphs at least in Shell mode and Ielm.
Although I do not know any further examples, it is likely that
paragraphs in other modes are now broken too for the same reason.

In my proposed changes to misc.texi, I documented the fact that blank
lines in Shell mode also separated paragraphs.  But I now realize that
this was documenting a bug.  To be useful in shell mode, paragraphs
should cover prompt, input and output.  That was the behavior in 21.3
and earlier and we should revert to that correct behavior.  If we do
not want to revert the changes Stefan referred to then we should set
paragraph-separate to something that does not match anything (what is
the standard regexp for that? "\\'"?), in Shell mode and Ielm and
possibly in some other modes.

Below is the proposed new last paragraph of the new "Shell Prompts"
node.  It assumes that the above bug will be fixed.  The description
of the behavior of paragraph commands if comint-use-prompt-regexp is
nil (the default) is deliberately vague, as it is messy (for people
not familiar with fields, it could easily appear to be buggy,
especially in as far as numeric arguments and such are concerned).
But that behavior is already present in 21.3, so people could actually
be used to it.

    In Shell mode, only shell prompts start new paragraphs.  Thus, a
  paragraph consists of a prompt and the input and output that follow
  it.  However, if @code{comint-use-prompt-regexp} is @code{nil}, the
  default, most paragraph commands do not cross field boundaries.  Thus,
  with this setting, prompt, input and output behave mostly as if they
  were separate paragraphs and most numeric arguments to paragraph
  commands are ignored.  For the purpose of finding paragraph
  boundaries, Shell mode uses @code{shell-prompt-pattern}, regardless of
  @code{comint-use-prompt-regexp}.