Properly indent the body of compound expressions, even when then
compound expression is not at the beginning of line and the parent is
not an if/for/while/etc., and matches the behavior of c-mode.
This fixes a problem that is common with macros and in testing
frameworks. For example, you expect this to indent:
TEST_CASE(1) {
    assert (...);
}
If the compound statement is the function body itself, don't apply this
new rule and instead guide by the parent and first sibling.
I'm sure there are subtle interactions that aren't handled properly by
checking for "function_definition" rather than something more general,
but it does fix the test case and the check can be improved as more
cases are found.
* lisp/progmodes/c-ts-mode.el:
(c-ts-mode--parent-is-not-top-compound): New function.
(c-ts-mode--indent-styles): Use it.
* test/lisp/progmodes/c-ts-mode-resources/indent.erts: New
compound statement test.
---
 lisp/progmodes/c-ts-mode.el                   |  9 ++++++
 .../progmodes/c-ts-mode-resources/indent.erts | 30 +++++++++++++++++++
 2 files changed, 39 insertions(+)
diff --git a/lisp/progmodes/c-ts-mode.el b/lisp/progmodes/c-ts-mode.el
index 3823c553fda..b635e621b03 100644
--- a/lisp/progmodes/c-ts-mode.el
+++ b/lisp/progmodes/c-ts-mode.el
@@ -402,6 +402,12 @@ c-ts-mode--first-sibling
               (treesit-node-start parent)
               (line-end-position))))))
+(defun c-ts-mode--parent-is-not-top-compound (_n parent &rest _)
+  "Matches when PARENT is not the top level compound statement.
+The top-level compound is the {} that immediately follows the function
+signature."
+  (not (equal "function_definition" (treesit-node-type (treesit-node-parent parent)))))
+
 (defun c-ts-mode--indent-styles (mode)
   "Indent rules supported by `c-ts-mode'.
 MODE is either `c' or `cpp'."
@@ -478,6 +484,7 @@ c-ts-mode--indent-styles
            ;; Closing bracket.  This should be before initializer_list
            ;; (and probably others) rule because that rule (and other
            ;; similar rules) will match the closing bracket.  (Bug#61398)
+           ((and (node-is "}") c-ts-mode--parent-is-not-top-compound) parent-bol 0)
            ((node-is "}") standalone-parent 0)
            ,@(when (eq mode 'cpp)
                '(((node-is "access_specifier") parent-bol 0)
@@ -497,6 +504,8 @@ c-ts-mode--indent-styles
            ((parent-is "field_declaration_list") c-ts-mode--anchor-prev-sibling 0)
            ;; Statement in {} blocks.
+           ((and (parent-is "compound_statement") c-ts-mode--parent-is-not-top-compound)
+            parent-bol c-ts-mode-indent-offset)
            ((or (and (parent-is "compound_statement")
                      ;; If the previous sibling(s) are not on their
                      ;; own line, indent as if this node is the first
diff --git a/test/lisp/progmodes/c-ts-mode-resources/indent.erts b/test/lisp/progmodes/c-ts-mode-resources/indent.erts
index 2f3540c3970..61e61677ed7 100644
--- a/test/lisp/progmodes/c-ts-mode-resources/indent.erts
+++ b/test/lisp/progmodes/c-ts-mode-resources/indent.erts
@@ -223,6 +223,36 @@ make_pair(int long_identifier_a[], int long_identifier_b[],
 =-=-=
+Name: Compound Statement after code
+
+=-=
+#define IOTA(var, n) for (int var = 0; var != (n); ++var)
+int main()
+{
+IOTA (v, 10) {
+printf("%d ", v);
+}
+
+const char *msg = "Hello, world!"; {
+puts("Hello, world!");
+}
+}
+
+=-=
+#define IOTA(var, n) for (int var = 0; var != (n); ++var)
+int main()
+{
+  IOTA (v, 10) {
+    printf("%d ", v);
+  }
+
+  const char *msg = "Hello, world!"; {
+    puts("Hello, world!");
+  }
+}
+
+=-=-=
+
 Name: Switch-Case statement
 =-=
-- 
2.39.5