fix(api): allow empty Lua table for nested dicts #22268

Problem:
The Lua-API bridge allows Dict params to be empty Lua (list) tables at
the function-signature level. But not for _nested_ Dicts, because they
are not modeled:
https://github.com/neovim/neovim/blob/fae754073289566051433fae74ec65783f9e7a6a/src/nvim/api/keysets.lua#L184
Some API functions like nvim_cmd check for kObjectTypeDictionary and
don't handle the case of empty Lua tables (treated as "Array").

Solution:
Introduce VALIDATE_T_DICT and use it in places where
kObjectTypeDictionary was being checked directly.

fixes #21005

1 files changed, 23 insertions, 0 deletions

diff --git a/src/nvim/api/private/validate.h b/src/nvim/api/private/validate.h
index 469fed0f83..91a92c2762 100644
--- a/src/nvim/api/private/validate.h
+++ b/src/nvim/api/private/validate.h
@@ -38,12 +38,35 @@
 
 #define VALIDATE_T(name, expected_t, actual_t, code) \
   do { \
+    STATIC_ASSERT(expected_t != kObjectTypeDictionary, "use VALIDATE_T_DICT"); \
     if (expected_t != actual_t) { \
       api_err_exp(err, name, api_typename(expected_t), api_typename(actual_t)); \
       code; \
     } \
   } while (0)
 
+/// Checks that `obj_` has type `expected_t`.
+#define VALIDATE_T2(obj_, expected_t, code) \
+  do { \
+    STATIC_ASSERT(expected_t != kObjectTypeDictionary, "use VALIDATE_T_DICT"); \
+    if ((obj_).type != expected_t) { \
+      api_err_exp(err, STR(obj_), api_typename(expected_t), api_typename((obj_).type)); \
+      code; \
+    } \
+  } while (0)
+
+/// Checks that `obj_` has Dict type. Also allows empty Array in a Lua context.
+#define VALIDATE_T_DICT(name, obj_, code) \
+  do { \
+    if ((obj_).type != kObjectTypeDictionary \
+        && !(channel_id == LUA_INTERNAL_CALL \
+             && (obj_).type == kObjectTypeArray \
+             && (obj_).data.array.size == 0)) { \
+      api_err_exp(err, name, api_typename(kObjectTypeDictionary), api_typename((obj_).type)); \
+      code; \
+    } \
+  } while (0)
+
 #define VALIDATE_RANGE(cond, name, code) \
   do { \
     if (!(cond)) { \