[Emacs-diffs] emacs-26 cb93a6c: Improve documentation of 'copy-sequence'

[Eli Zaretskii]

branch: emacs-26
commit cb93a6ce72c5d238c6f120192aaba1554363dfe9
Author: Eli Zaretskii <address@hidden>
Commit: Eli Zaretskii <address@hidden>

    Improve documentation of 'copy-sequence'
    
    * src/fns.c (Fcopy_sequence):
    * doc/lispref/sequences.texi (Sequence Functions): Mention the
    exception when copying an empty sequence.  (Bug#28627)
---
 doc/lispref/sequences.texi | 5 ++++-
 src/fns.c                  | 4 +++-
 2 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/doc/lispref/sequences.texi b/doc/lispref/sequences.texi
index c7cf9f5..5ae1567 100644
--- a/doc/lispref/sequences.texi
+++ b/doc/lispref/sequences.texi
@@ -155,7 +155,10 @@ This function generalizes @code{aref} (@pxref{Array 
Functions}) and
 @cindex copying sequences
 This function returns a copy of @var{seqr}, which should be either a
 sequence or a record.  The copy is the same type of object as the
-original, and it has the same elements in the same order.
+original, and it has the same elements in the same order.  However, if
address@hidden is empty, like a string or a vector of zero length, the
+value returned by this function might not be a copy, but an empty
+object of the same type and identical to @var{seqr}.
 
 Storing a new element into the copy does not affect the original
 @var{seqr}, and vice versa.  However, the elements of the copy
diff --git a/src/fns.c b/src/fns.c
index 4524ff9..2311a6e 100644
--- a/src/fns.c
+++ b/src/fns.c
@@ -482,7 +482,9 @@ usage: (vconcat &rest SEQUENCES)   */)
 DEFUN ("copy-sequence", Fcopy_sequence, Scopy_sequence, 1, 1, 0,
        doc: /* Return a copy of a list, vector, string, char-table or record.
 The elements of a list, vector or record are not copied; they are
-shared with the original.  */)
+shared with the original.
+If the original sequence is empty, this function may return
+the same empty object instead of its copy.  */)
   (Lisp_Object arg)
 {
   if (NILP (arg)) return arg;