emacs-29 64fee21d5f8 1/2: Fix dockerfile-ts-mode line continuation indentation (bug#61131)

[Yuan Fu]

branch: emacs-29
commit 64fee21d5f85db465198970a4d636cb17d500f26
Author: Randy Taylor <dev@rjt.dev>
Commit: Yuan Fu <casouri@gmail.com>

    Fix dockerfile-ts-mode line continuation indentation (bug#61131)
    
    Without this rule, line continuations are only indented after entering
    the contents for the line and hitting TAB or RET.
    
    For example:
    ```
    EXPOSE 1 \
    ```
    
    After hitting RET to go to the next line, point would end up at BOL
    instead of lining up with the previous entry, like so:
    ```
    EXPOSE 1 \
    2
    ```
    
    The new rule will indent it as so:
    ```
    EXPOSE 1 \
           2
    ```
    
    * lisp/progmodes/dockerfile-ts-mode.el:
    (dockerfile-ts-mode--indent-rules): New rule.
    (dockerfile-ts-mode--line-continuation-p)
    (dockerfile-ts-mode--line-continuation-anchor): New functions.
---
 lisp/progmodes/dockerfile-ts-mode.el | 20 +++++++++++++++++++-
 1 file changed, 19 insertions(+), 1 deletion(-)

diff --git a/lisp/progmodes/dockerfile-ts-mode.el 
b/lisp/progmodes/dockerfile-ts-mode.el
index 2a295e885b0..f2f30cf2617 100644
--- a/lisp/progmodes/dockerfile-ts-mode.el
+++ b/lisp/progmodes/dockerfile-ts-mode.el
@@ -51,9 +51,27 @@
      ((parent-is "expose_instruction") (nth-sibling 1) 0)
      ((parent-is "label_instruction") (nth-sibling 1) 0)
      ((parent-is "shell_command") first-sibling 0)
-     ((parent-is "string_array") first-sibling 1)))
+     ((parent-is "string_array") first-sibling 1)
+     ((dockerfile-ts-mode--line-continuation-p) 
dockerfile-ts-mode--line-continuation-anchor 0)))
   "Tree-sitter indent rules.")
 
+(defun dockerfile-ts-mode--line-continuation-p ()
+  "Return t if the current node is a line continuation node."
+  (lambda (node _ _ &rest _)
+    (string= (treesit-node-type node) "\n")))
+
+(defun dockerfile-ts-mode--line-continuation-anchor (_ _ &rest _)
+  "This anchor is used to align any nodes that are part of a line
+continuation to the previous entry."
+  (save-excursion
+    (forward-line -1)
+    (let ((prev-node (treesit-node-at (point))))
+      (if (string= (treesit-node-type prev-node) "\\\n")
+          (back-to-indentation)
+        (forward-word)
+        (forward-char))
+      (+ 1 (- (point) (pos-bol))))))
+
 (defvar dockerfile-ts-mode--keywords
   '("ADD" "ARG" "AS" "CMD" "COPY" "CROSS_BUILD" "ENTRYPOINT" "ENV"
     "EXPOSE" "FROM" "HEALTHCHECK" "LABEL" "MAINTAINER" "ONBUILD" "RUN"