Add treesit-explore-mode

This mode is basically the tree-sitter playground[1] in Emacs:
displays the syntax tree with the source side-by-side, kept in sync in
real-time.

[1] https://tree-sitter.github.io/tree-sitter/playground

* doc/lispref/parsing.texi (Language Definitions): Mention in manual.
* lisp/treesit.el (treesit--explorer-buffer)
(treesit--explorer-source-buffer)
(treesit--explorer-language)
(treesit--explorer-refresh-timer)
(treesit--explorer-highlight-overlay)
(treesit--explorer-last-node): New variables.
* lisp/treesit.el (treesit--explorer--nodes-to-highlight)
(treesit--explorer-refresh)
(treesit--explorer-post-command)
(treesit--explorer-jump)
(treesit--explorer-highlight-node)
(treesit--explorer-draw-node): New functions.
(treesit--explorer-tree-mode)
(treesit-explore-mode): New modes.

1 files changed, 16 insertions, 0 deletions

diff --git a/doc/lispref/parsing.texi b/doc/lispref/parsing.texi
index 9fcf488da10..0f4a004ee90 100644
--- a/doc/lispref/parsing.texi
+++ b/doc/lispref/parsing.texi
@@ -223,6 +223,22 @@ assign @dfn{field names} to child nodes.  For example, a
 @end group
 @end example
 
+@heading Exploring the syntax tree
+
+To aid understanding the syntax of a language and debugging, Emacs
+provides a ``explore'' mode, which displays the syntax tree of the
+source in the current buffer in real time.  Emacs also comes with a
+``inspect mode'', which displays information of the nodes at point in
+the mode-line.
+
+@deffn Command treesit-explore-mode
+This mode pops up a window displaying the syntax tree of the source in
+the current buffer.  Emacs highlights nodes in the syntax tree if
+their corresponding text in the source buffer is selected.  Clicking
+on nodes in the syntax tree highlights the corresponding text in the
+source buffer.
+@end deffn
+
 @deffn Command treesit-inspect-mode
 This minor mode displays on the mode-line the node that @emph{starts}
 at point.  The mode-line will display