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.

diff --git a/lisp/progmodes/dockerfile-ts-mode.el b/lisp/progmodes/dockerfile-ts-mode.el
index 2a295e885b06f208549a42158973dcf049f255ec..f2f30cf2617e8bbd3e14e64b619e1468766e23bc 100644 (file)
--- 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"