Fix recently extended delete-indentation behavior

* doc/lispref/text.texi (User-Level Deletion): Document new optional
arguments of delete-indentation.

* lisp/simple.el (delete-indentation): Do not barf if called
interactively when region is inactive. (bug#35021)
Do not skip blank lines. (bug#35036)
Consistently deactivate mark even when no text was changed.
Handle active region spanning a single line.

* test/lisp/simple-tests.el (simple-test--buffer-substrings):
New convenience function.
(simple-test--dummy-buffer, simple-test--transpositions): Use it.
(simple-delete-indentation-no-region)
(simple-delete-indentation-inactive-region): Update commentary.
Call delete-indentation interactively when testing for behavior with
inactive region and region is not explicitly defined.
(simple-delete-indentation-blank-line)
(simple-delete-indentation-boundaries)
(simple-delete-indentation-region)
(simple-delete-indentation-prefix): New tests.

1 files changed, 8 insertions, 2 deletions

diff --git a/doc/lispref/text.texi b/doc/lispref/text.texi
index 21c5a73f887..b430adf5976 100644
--- a/doc/lispref/text.texi
+++ b/doc/lispref/text.texi
@@ -723,12 +723,18 @@ You thought
 @end example
 @end deffn
 
-@deffn Command delete-indentation &optional join-following-p
+@deffn Command delete-indentation &optional join-following-p beg end
 This function joins the line point is on to the previous line, deleting
 any whitespace at the join and in some cases replacing it with one
 space.  If @var{join-following-p} is non-@code{nil},
 @code{delete-indentation} joins this line to the following line
-instead.  The function returns @code{nil}.
+instead.  Otherwise, if @var{beg} and @var{end} are non-@code{nil},
+this function joins all lines in the region they define.
+
+In an interactive call, @var{join-following-p} is the prefix argument,
+and @var{beg} and @var{end} are, respectively, the start and end of
+the region if it is active, else @code{nil}.  The function returns
+@code{nil}.
 
 If there is a fill prefix, and the second of the lines being joined
 starts with the prefix, then @code{delete-indentation} deletes the