master 9480169 1/2: Change the string-limit parameter semantics

[Lars Ingebrigtsen]

branch: master
commit 9480169f1b8a27ed61db0913989c9a81339ccd9d
Author: Lars Ingebrigtsen <larsi@gnus.org>
Commit: Lars Ingebrigtsen <larsi@gnus.org>

    Change the string-limit parameter semantics
    
    * lisp/emacs-lisp/subr-x.el (string-limit): Alter the calling
    convention.
---
 doc/lispref/strings.texi             | 13 ++++++-------
 lisp/emacs-lisp/shortdoc.el          |  2 +-
 lisp/emacs-lisp/subr-x.el            | 19 +++++++++++--------
 test/lisp/emacs-lisp/subr-x-tests.el |  7 ++++---
 4 files changed, 22 insertions(+), 19 deletions(-)

diff --git a/doc/lispref/strings.texi b/doc/lispref/strings.texi
index 17cc1a4..80e936e 100644
--- a/doc/lispref/strings.texi
+++ b/doc/lispref/strings.texi
@@ -405,13 +405,12 @@ there are individual words that are longer than 
@var{length}, these
 will not be shortened.
 @end defun
 
-@defun string-limit string length
-Return a string that's shorter than @var{length}.  If @var{string} is
-shorter than @var{length}, @var{string} is returned as is.  If
-@var{length} is positive, return a substring of @var{string}
-consisting of the first @var{length} characters.  If @var{length} is
-negative, return a string of the @var{-length} last characters
-instead.
+@defun string-limit string length &optional end
+If @var{string} is shorter than @var{length}, @var{string} is returned
+as is.  Otherwise, return a substring of @var{string} consisting of
+the first @var{length} characters.  If the optional @var{end}
+parameter is given, return a string of the @var{length} last
+characters instead.
 @end defun
 
 @defun string-lines string &optional omit-nulls
diff --git a/lisp/emacs-lisp/shortdoc.el b/lisp/emacs-lisp/shortdoc.el
index 7bb7d23..eb57e70 100644
--- a/lisp/emacs-lisp/shortdoc.el
+++ b/lisp/emacs-lisp/shortdoc.el
@@ -145,7 +145,7 @@ There can be any number of :example/:result elements."
    :eval (substring "foobar" 3))
   (string-limit
    :eval (string-limit "foobar" 3)
-   :eval (string-limit "foobar" -3)
+   :eval (string-limit "foobar" 3 t)
    :eval (string-limit "foobar" 10))
   (split-string
    :eval (split-string "foo bar")
diff --git a/lisp/emacs-lisp/subr-x.el b/lisp/emacs-lisp/subr-x.el
index 6f4f7ed..b79482f 100644
--- a/lisp/emacs-lisp/subr-x.el
+++ b/lisp/emacs-lisp/subr-x.el
@@ -286,17 +286,20 @@ result will have lines that are longer than LENGTH."
       (fill-region (point-min) (point-max)))
     (buffer-string)))
 
-(defun string-limit (string length)
+(defun string-limit (string length &optional end)
   "Return (up to) a LENGTH substring of STRING.
 If STRING is shorter than or equal to LENGTH, the entire string
-is returned unchanged.  If STRING is longer than LENGTH, and
-LENGTH is a positive number, return a substring consisting of the
-first LENGTH characters of STRING.  If LENGTH is negative, return
-a substring consisting of the last LENGTH characters of STRING."
+is returned unchanged.
+
+If STRING is longer than LENGTH, return a substring consisting of
+the first LENGTH characters of STRING.  If END is non-nil, return
+the last LENTGH characters instead."
+  (unless (natnump length)
+    (signal 'wrong-type-argument (list 'natnump length)))
   (cond
-   ((<= (length string) (abs length)) string)
-   ((>= length 0) (substring string 0 length))
-   ((substring string length))))
+   ((<= (length string) length) string)
+   (end (substring string (- (length string) length)))
+   (t (substring string 0 length))))
 
 (defun string-lines (string &optional omit-nulls)
   "Split STRING into a list of lines.
diff --git a/test/lisp/emacs-lisp/subr-x-tests.el 
b/test/lisp/emacs-lisp/subr-x-tests.el
index 2e16cd0..52b4809 100644
--- a/test/lisp/emacs-lisp/subr-x-tests.el
+++ b/test/lisp/emacs-lisp/subr-x-tests.el
@@ -595,9 +595,10 @@
 (ert-deftest subr-string-limit ()
   (should (equal (string-limit "foo" 10) "foo"))
   (should (equal (string-limit "foo" 2) "fo"))
-  (should (equal (string-limit "foo" -2) "oo"))
-  (should (equal (string-limit "abc" -10) "abc"))
-  (should (equal (string-limit "foo" 0) "")))
+  (should (equal (string-limit "foo" 2 t) "oo"))
+  (should (equal (string-limit "abc" 10 t) "abc"))
+  (should (equal (string-limit "foo" 0) ""))
+  (should-error (string-limit "foo" -1)))
 
 (ert-deftest subr-string-lines ()
   (should (equal (string-lines "foo") '("foo")))