From 474abbd65c9d66410976e9f816d37ffa545d0aa4 Mon Sep 17 00:00:00 2001
From: Yuan Fu <casouri@gmail.com>
Date: Sun, 1 Jun 2025 16:14:12 -0700
Subject: [PATCH] Fix typescript-ts-mode tenary indentation (bug#77901)

Fixes indentation for nested ternary expressions:

const a = cond1 ? 1 :
  cond2 ? 2 :
  cond3 ? 3 :
  cond 4: 5;

instead of

const a = cond1 ? 1 :
  cond2 ? 2 :
    cond3 ? 3 :
      cond 4: 5;

* lisp/progmodes/typescript-ts-mode.el:
(typescript-ts--standalone-parent-p): New function.
(typescript-ts-mode):
(tsx-ts-mode): Use new function.

(cherry picked from commit 8d132359d19b8efbdbd17786fa67c0c20efba35b)
---
 lisp/progmodes/typescript-ts-mode.el          | 24 +++++++++++++++++++
 .../typescript-ts-mode-resources/indent.erts  |  5 ++++
 2 files changed, 29 insertions(+)

diff --git a/lisp/progmodes/typescript-ts-mode.el b/lisp/progmodes/typescript-ts-mode.el
index eafaad876bd..c8efb4f771a 100644
--- a/lisp/progmodes/typescript-ts-mode.el
+++ b/lisp/progmodes/typescript-ts-mode.el
@@ -229,6 +229,26 @@ Argument LANGUAGE is either `typescript' or `tsx'."
     "&&" "||" "!" "?.")
   "TypeScript operators for tree-sitter font-locking.")
 
+(defun typescript-ts--standalone-parent-p (parent)
+  "Return t if PARENT can be considered standalone.
+This is used for `treesit-simple-indent-standalone-predicate'."
+  (save-excursion
+    (goto-char (treesit-node-start parent))
+    (cond
+     ;; Never allow nested ternary_expression node to be standalone
+     ;; parent, to avoid nested indentation.
+     ((equal (treesit-node-type (treesit-node-parent parent))
+             "ternary_expression")
+      nil)
+     ;; If there's only whitespace before node, consider
+     ;; this node standalone. To support function
+     ;; chaining, allow a dot to be before the node.
+     ((looking-back (rx bol (* whitespace) (? "."))
+                    (line-beginning-position))
+      (if (looking-back "\\.")
+          (1- (point))
+        (point))))))
+
 (defun tsx-ts-mode--font-lock-compatibility-bb1f97b (language)
   "Font lock rules helper, to handle different releases of tree-sitter-tsx.
 Check if a node type is available, then return the right font lock rules.
@@ -677,6 +697,8 @@ This mode is intended to be inherited by concrete major modes."
     ;; Indent.
     (setq-local treesit-simple-indent-rules
                 (typescript-ts-mode--indent-rules 'typescript))
+    (setq-local treesit-simple-indent-standalone-predicate
+                #'typescript-ts--standalone-parent-p)
 
     ;; Font-lock.
     (setq-local treesit-font-lock-settings
@@ -726,6 +748,8 @@ at least 3 (which is the default value)."
     ;; Indent.
     (setq-local treesit-simple-indent-rules
                 (typescript-ts-mode--indent-rules 'tsx))
+    (setq-local treesit-simple-indent-standalone-predicate
+                #'typescript-ts--standalone-parent-p)
 
     (setq-local treesit-thing-settings
                 `((tsx
diff --git a/test/lisp/progmodes/typescript-ts-mode-resources/indent.erts b/test/lisp/progmodes/typescript-ts-mode-resources/indent.erts
index 210bfcabd41..ba41c10c08c 100644
--- a/test/lisp/progmodes/typescript-ts-mode-resources/indent.erts
+++ b/test/lisp/progmodes/typescript-ts-mode-resources/indent.erts
@@ -96,6 +96,11 @@ const foo = () => {
 Name: Chained ternary expressions
 
 =-=
+const a = cond1 ? 1 :
+  cond2 ? 2 :
+  cond3 ? 3 :
+  cond 4: 5;
+
 const a = cond1 ? 1
   : cond2 ? 2
   : cond3 ? 3
-- 
2.39.5