Fix c-ts-mode indentation (bug#67357)

1. In a compund_statement, we indent the first sibling against the
parent, and the rest siblings against their previous sibling.  But
this strategy falls apart when the first sibling is not on its own
line.  We should regard the first sibling that is on its own line as
the "first sibling"", and indent it against the parent.

2. In linux style, in a do-while statement, if the do-body is
bracket-less, the "while" keyword is indented to the same level as the
do-body.  It should be indented to align with the "do" keyword
instead.

* lisp/progmodes/c-ts-mode.el:
(c-ts-mode--no-prev-standalone-sibling): New function.
(c-ts-mode--indent-styles): Use
c-ts-mode--no-prev-standalone-sibling. Add while keyword indent rule.
* test/lisp/progmodes/c-ts-mode-resources/indent.erts: New tests.

1 files changed, 47 insertions, 1 deletions

diff --git a/test/lisp/progmodes/c-ts-mode-resources/indent.erts b/test/lisp/progmodes/c-ts-mode-resources/indent.erts
index bac76fb7378..2fd26d75844 100644
--- a/test/lisp/progmodes/c-ts-mode-resources/indent.erts
+++ b/test/lisp/progmodes/c-ts-mode-resources/indent.erts
@@ -330,7 +330,7 @@ label:
 
 Name: Bracket-less Block-Statement (Linux Style) (bug#61026)
 
-=-=-=
+=-=
 int main() {
   while (true)
     if (true) {
@@ -351,6 +351,8 @@ int main() {
     if (true) {
       puts ("Hello");
     }
+    else
+      puts("Hello");
 }
 =-=-=
 
@@ -399,6 +401,34 @@ void foo(
 }
 =-=-=
 
+Name: Block-Statement where first siblings are comments (Linux Style)
+
+=-=
+int main() {
+  while (true) { /* foo */
+    if (true) { // bar
+      puts ("Hello");
+    }
+  }
+  for (;;) {  // 1. fooo
+    /* 2. baaa */
+    /* 3. rrr */
+    if (true)
+      // 2. baaa
+      puts ("Hello");
+  }
+  if (1) { // 1
+    /*
+     * 2
+     */
+    if (1) /*3*/ {
+      /* 4 */
+      puts("Hello");
+    }
+  }
+}
+=-=-=
+
 Name: Initializer List (Linux Style) (Bug#61398)
 
 =-=
@@ -498,3 +528,19 @@ main (void)
 {
   |
 =-=-=
+
+Code:
+  (lambda ()
+    (c-ts-mode)
+    (setq-local indent-tabs-mode nil)
+    (goto-line 3)
+    (indent-for-tab-command))
+
+Name: Block-Statement where previous sibling is comment
+
+=-=
+int main() {
+    puts ("Hello"); // unusual indent and has trailing comment.
+    return true; // Should align with previous non-comment sibling (rather than one level up against parent).
+}
+=-=-=