Cleanup preproc indent for c-ts-mode (bug#61558)

* lisp/progmodes/c-ts-mode.el (c-ts-mode--indent-styles): Make sure we
indent to great-grand-parent if inside an #ifdef...#endif block.  If
grand-parent is root node, then don't indent one step.
(c-ts-mode--preproc-offset): New helper anchor function to calculate
indent offset.

2 files changed, 49 insertions, 0 deletions

diff --git a/test/lisp/progmodes/c-ts-mode-resources/indent-preproc.erts b/test/lisp/progmodes/c-ts-mode-resources/indent-preproc.erts
new file mode 100644
index 00000000000..5a4996f642e
--- /dev/null
+++ b/test/lisp/progmodes/c-ts-mode-resources/indent-preproc.erts
@@ -0,0 +1,45 @@
+Code:
+  (lambda ()
+    (c-ts-mode)
+    (newline)
+    (indent-for-tab-command))
+
+Point-Char: |
+
+Name: Indents inside #if preproc
+
+=-=
+static void
+free_glyph_pool (struct glyph_pool *pool)
+{
+  if (pool)
+    {
+#if defined GLYPH_DEBUG|
+#endif
+    }
+}
+=-=
+static void
+free_glyph_pool (struct glyph_pool *pool)
+{
+  if (pool)
+    {
+#if defined GLYPH_DEBUG
+      |
+#endif
+    }
+}
+=-=-=
+
+Name: Indents to 0 if #if preproc at root
+
+=-=
+#if 0|
+/* */
+static void
+=-=
+#if 0
+|
+/* */
+static void
+=-=-=
diff --git a/test/lisp/progmodes/c-ts-mode-tests.el b/test/lisp/progmodes/c-ts-mode-tests.el
index ddf64b40736..ea5fab4cbef 100644
--- a/test/lisp/progmodes/c-ts-mode-tests.el
+++ b/test/lisp/progmodes/c-ts-mode-tests.el
@@ -27,6 +27,10 @@
   (skip-unless (treesit-ready-p 'c))
   (ert-test-erts-file (ert-resource-file "indent.erts")))
 
+(ert-deftest c-ts-mode-test-indentation-preproc ()
+  (skip-unless (treesit-ready-p 'c))
+  (ert-test-erts-file (ert-resource-file "indent-preproc.erts")))
+
 (ert-deftest c-ts-mode-test-indentation-bsd ()
   (skip-unless (treesit-ready-p 'c))
   (ert-test-erts-file (ert-resource-file "indent-bsd.erts")))