lisp/emacs-lisp/track-changes.el: New filescratch/track-changes

This new package provides an API that is easier to use right than
our `*-change-functions` hooks.

The patch includes changes to `diff-mode.el` and `eglot.el` to
make use of this new package.

* lisp/emacs-lisp/track-changes.el: New file.
* test/lisp/emacs-lisp/track-changes-tests.el: New file.
* doc/lispref/text.texi (Tracking changes): New subsection.

* lisp/progmodes/eglot.el: Require `track-changes`.
(eglot--virtual-pos-to-lsp-position): New function.
(eglot--track-changes): New var.
(eglot--managed-mode): Use `track-changes-register` i.s.o
`after/before-change-functions` when available.
(eglot--track-changes-signal): New function, partly extracted from
`eglot--after-change`.
(eglot--after-change): Use it.
(eglot--track-changes-fetch): New function.
(eglot--signal-textDocument/didChange): Use it.

* lisp/vc/diff-mode.el: Require `track-changes`.
Also require `easy-mmode` before the `eval-when-compile`s.
(diff-unhandled-changes): Delete variable.
(diff-after-change-function): Delete function.
(diff--track-changes-function): Rename from `diff-post-command-hook`
and adjust to new calling convention.
(diff--track-changes): New variable.
(diff--track-changes-signal): New function.
(diff-mode, diff-minor-mode): Use it with `track-changes-register`.

1 files changed, 18 insertions, 0 deletions

diff --git a/etc/NEWS b/etc/NEWS
index a2a3fe494cb..2cf6477ba99 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -15,6 +15,12 @@ in older Emacs versions.
 You can narrow news to a specific version by calling 'view-emacs-news'
 with a prefix argument or by typing 'C-u C-h C-n'.
 
+Temporary note:
++++ indicates that all relevant manuals in doc/ have been updated.
+--- means no change in the manuals is needed.
+When you add a new item, use the appropriate mark if you are sure it
+applies, and please also update docstrings as needed.
+
 
 * Installation Changes in Emacs 30.1
 
@@ -1586,6 +1592,18 @@ options of GNU 'ls'.
 
 * New Modes and Packages in Emacs 30.1
 
++++
+** New package Track-Changes.
+This library is a layer of abstraction above 'before-change-functions'
+and 'after-change-functions' which provides a superset of
+the functionality of 'after-change-functions':
+- It provides the actual previous text rather than only its length.
+- It takes care of accumulating and bundling changes until a time when
+  its client finds it convenient to react to them.
+- It detects most cases where some changes were not properly
+  reported (calls to 'before/after-change-functions' that are
+  incorrectly paired, missing, etc...) and reports them adequately.
+
 ** New major modes based on the tree-sitter library
 
 +++