Remove `string-slice' -- it's not very well defined

* doc/lispref/strings.texi (Creating Strings): Ditto.

* lisp/emacs-lisp/subr-x.el (string-slice): Remove.

doc/lispref/strings.texi

@@ -381,17 +381,6 @@ The default value of @var{separators} for @code{split-string}.  Its
 usual value is @w{@code{"[ \f\t\n\r\v]+"}}.
 @end defvar
 
-@defun string-slice string regexp
-Split @var{string} into a list of strings on @var{regexp} boundaries.
-As opposed to @code{split-string}, the boundaries are included in the
-result set:
-
-@example
-(string-slice "  two words " " +")
-     @result{} ("  two" " words" " ")
-@end example
-@end defun
-
 @defun string-clean-whitespace string
 Clean up the whitespace in @var{string} by collapsing stretches of
 whitespace to a single space character, as well as removing all

etc/NEWS

@@ -1467,7 +1467,7 @@ This can be set to nil to inhibit hiding passwords in .authinfo files.
 +++
 *** A number of new string manipulation functions have been added.
 'string-clean-whitespace', 'string-fill', 'string-limit',
-'string-lines', 'string-pad', 'string-chop-newline' and 'string-slice'.
+'string-lines', 'string-pad' and 'string-chop-newline'.
 
 +++
 *** New variable 'current-minibuffer-command'.

lisp/emacs-lisp/shortdoc.el

@@ -154,9 +154,6 @@ There can be any number of :example/:result elements."
    :eval (split-string "foo bar")
    :eval (split-string "|foo|bar|" "|")
    :eval (split-string "|foo|bar|" "|" t))
-  (string-slice
-   :eval (string-slice "foo-bar" "-")
-   :eval (string-slice "foo-bar--zot-" "-+"))
   (string-lines
    :eval (string-lines "foo\n\nbar")
    :eval (string-lines "foo\n\nbar" t))

lisp/emacs-lisp/subr-x.el

@@ -310,19 +310,6 @@ than this function."
 If OMIT-NULLS, empty lines will be removed from the results."
   (split-string string "\n" omit-nulls))
 
-(defun string-slice (string regexp)
-  "Split STRING at REGEXP boundaries and return a list of slices.
-The boundaries that match REGEXP are included in the result.
-
-Also see `split-string'."
-  (if (zerop (length string))
-      (list "")
-    (let ((i (string-match-p regexp string 1)))
-      (if i
-          (cons (substring string 0 i)
-                (string-slice (substring string i) regexp))
-        (list string)))))
-
 (defun string-pad (string length &optional padding start)
   "Pad STRING to LENGTH using PADDING.
 If PADDING is nil, the space character is used.  If not nil, it

test/lisp/emacs-lisp/subr-x-tests.el

@@ -604,14 +604,6 @@
   (should (equal (string-lines "foo") '("foo")))
   (should (equal (string-lines "foo \nbar") '("foo " "bar"))))
 
-(ert-deftest subr-string-slice ()
-  (should (equal (string-slice "foo-bar" "-") '("foo" "-bar")))
-  (should (equal (string-slice "foo-bar-" "-") '("foo" "-bar" "-")))
-  (should (equal (string-slice "-foo-bar-" "-") '("-foo" "-bar" "-")))
-  (should (equal (string-slice "ooo" "lala") '("ooo")))
-  (should (equal (string-slice "foo bar" "\\b") '("foo" " " "bar" "")))
-  (should (equal (string-slice "foo bar" "\\b\\|a") '("foo" " " "b" "ar" ""))))
-
 (ert-deftest subr-string-pad ()
   (should (equal (string-pad "foo" 5) "foo  "))
   (should (equal (string-pad "foo" 5 ?-) "foo--"))