Tweak regexp for object initializers in csharp-mode (bug#69571)

* lisp/progmodes/csharp-mode.el (csharp-guess-basic-syntax): Add
handling to not consider ended statements as object init openers.
* test/lisp/progmodes/csharp-mode-resources/indent.erts: New test
resources.
* test/lisp/progmodes/csharp-mode-tests.el: Add test for this particular
issue.

lisp/progmodes/csharp-mode.el

@@ -495,9 +495,12 @@ compilation and evaluation time conflicts."
        (unless (eq (char-after) ?{)
          (ignore-errors (backward-up-list 1 t t)))
        (save-excursion
-         ;; 'new' should be part of the line
+         ;; 'new' should be part of the line, but should not trigger if
+         ;; statement has already ended, like for 'var x = new X();'.
+         ;; Also, deal with the possible end of line obscured by a
+         ;; trailing comment.
          (goto-char (c-point 'iopl))
-         (looking-at ".*new.*")))
+         (looking-at "^[^//]*new[^//]*;$")))
      ;; Line should not already be terminated
      (save-excursion
        (goto-char (c-point 'eopl))

test/lisp/progmodes/csharp-mode-resources/indent.erts

@@ -0,0 +1,19 @@
+Code:
+  (lambda ()
+    (csharp-mode)
+    (indent-region (point-min) (point-max)))
+
+Point-Char: |
+
+Name: Don't consider closed statements as object initializers. (bug#69571)
+
+=-=
+public class Foo {
+    void Bar () {
+        var x = new X();            // [1]
+        for (;;) {
+            x();
+        }  // [2]
+    }
+}
+=-=-=

test/lisp/progmodes/csharp-mode-tests.el

@@ -0,0 +1,30 @@
+;;; csharp-mode-tests.el --- Tests for CC Mode C# mode  -*- lexical-binding: t; -*-
+
+;; Copyright (C) 2024 Free Software Foundation, Inc.
+
+;; This file is part of GNU Emacs.
+
+;; GNU Emacs is free software: you can redistribute it and/or modify
+;; it under the terms of the GNU General Public License as published by
+;; the Free Software Foundation, either version 3 of the License, or
+;; (at your option) any later version.
+
+;; GNU Emacs is distributed in the hope that it will be useful,
+;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;; GNU General Public License for more details.
+
+;; You should have received a copy of the GNU General Public License
+;; along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>.
+
+;;; Code:
+
+(require 'ert)
+(require 'ert-x)
+(require 'csharp-mode)
+
+(ert-deftest csharp-mode-test-indentation ()
+  (ert-test-erts-file (ert-resource-file "indent.erts")))
+
+(provide 'csharp-mode-tests)
+;;; csharp-mode-tests.el ends here