Consolidate cross-referencing commands

Move autoloaded bindings for `M-.', `M-,', `C-x 4 .' and
`C-x 5 .' from etags.el to xref.el.

* progmodes/xref.el: New file.

* progmodes/elisp-mode.el (elisp--identifier-types): New variable.
(elisp--identifier-location): New function, extracted from
`elisp--company-location'.
(elisp--company-location): Use it.
(elisp--identifier-completion-table): New variable.
(elisp-completion-at-point): Use it.
(emacs-lisp-mode): Set the local values of `xref-find-function'
and `xref-identifier-completion-table-function'.
(elisp-xref-find, elisp--xref-find-definitions)
(elisp--xref-identifier-completion-table): New functions.

* progmodes/etags.el (find-tag-marker-ring): Mark obsolete in
favor of `xref--marker-ring'.
(tags-lazy-completion-table): Autoload.
(tags-reset-tags-tables): Use `xref-clear-marker-stack'.
(find-tag-noselect): Use `xref-push-marker-stack'.
(pop-tag-mark): Make an alias for `xref-pop-marker-stack'.
(etags--xref-limit): New constant.
(etags-xref-find, etags--xref-find-definitions): New functions.

1 files changed, 19 insertions, 0 deletions

diff --git a/etc/NEWS b/etc/NEWS
index 16aa297aed0..37806a7fe56 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -434,6 +434,25 @@ By default, 32 spaces and four TABs are considered to be too much but
 `tildify-ignored-environments-alist' variables (as well as a few
 helper functions) obsolete.
 
+** xref
+The new package provides generic framework and new commands to find
+and move to definitions, as well as pop back to the original location.
+
+*** New key bindings
+`xref-find-definitions' replaces `find-tag' and provides an interface
+to pick one destination among several.  Hence, `tags-toop-continue' is
+unbound.  `xref-pop-marker-stack' replaces `pop-tag-mark', but uses an
+easier binding, which is now unoccupied (`M-,').
+`xref-find-definitions-other-window' replaces `find-tag-other-window'.
+`xref-find-definitions-other-frame' replaces `find-tag-other-frame'.
+`xref-find-apropos' replaces `find-tag-regexp'.
+
+*** New variables
+`find-tag-marker-ring-length' is now an obsolete alias for
+`xref-marker-ring-length'.  `find-tag-marker-ring' is now an obsolete
+alias for a private variable.  `xref-push-marker-stack' and
+`xref-pop-marker-stack' should be used to mutate it instead.
+
 ** Obsolete packages
 
 ---