api/lua: make nvim_execute_lua use native lua floats, not special tables

Rationale: the purpose of nvim_execute_lua is to simply call lua code with lua
values. If a lua function expects a floating point value, it should be enough
to specify a float as argument to nvim_execute_lua.

However, make sure to preserve the existing roundtripping behavior of
API values when using `vim.api` functions. This is covered by existing
lua/api_spec.lua tests.

src/nvim/generators/gen_api_dispatch.lua

@@ -441,7 +441,7 @@ local function process_function(fn)
     end
     write_shifted_output(output, string.format([[
     const %s ret = %s(%s);
-    nlua_push_%s(lstate, ret);
+    nlua_push_%s(lstate, ret, true);
     api_free_%s(ret);
   %s
   %s

src/nvim/lua/converter.c

@@ -615,7 +615,7 @@ static inline void nlua_create_typed_table(lua_State *lstate,
 /// Convert given String to lua string
 ///
 /// Leaves converted string on top of the stack.
-void nlua_push_String(lua_State *lstate, const String s)
+void nlua_push_String(lua_State *lstate, const String s, bool special)
   FUNC_ATTR_NONNULL_ALL
 {
   lua_pushlstring(lstate, s.data, s.size);
@@ -624,7 +624,7 @@ void nlua_push_String(lua_State *lstate, const String s)
 /// Convert given Integer to lua number
 ///
 /// Leaves converted number on top of the stack.
-void nlua_push_Integer(lua_State *lstate, const Integer n)
+void nlua_push_Integer(lua_State *lstate, const Integer n, bool special)
   FUNC_ATTR_NONNULL_ALL
 {
   lua_pushnumber(lstate, (lua_Number)n);
@@ -633,19 +633,23 @@ void nlua_push_Integer(lua_State *lstate, const Integer n)
 /// Convert given Float to lua table
 ///
 /// Leaves converted table on top of the stack.
-void nlua_push_Float(lua_State *lstate, const Float f)
+void nlua_push_Float(lua_State *lstate, const Float f, bool special)
   FUNC_ATTR_NONNULL_ALL
 {
-  nlua_create_typed_table(lstate, 0, 1, kObjectTypeFloat);
+  if (special) {
-  nlua_push_val_idx(lstate);
+    nlua_create_typed_table(lstate, 0, 1, kObjectTypeFloat);
-  lua_pushnumber(lstate, (lua_Number)f);
+    nlua_push_val_idx(lstate);
-  lua_rawset(lstate, -3);
+    lua_pushnumber(lstate, (lua_Number)f);
+    lua_rawset(lstate, -3);
+  } else {
+    lua_pushnumber(lstate, (lua_Number)f);
+  }
 }
 
 /// Convert given Float to lua boolean
 ///
 /// Leaves converted value on top of the stack.
-void nlua_push_Boolean(lua_State *lstate, const Boolean b)
+void nlua_push_Boolean(lua_State *lstate, const Boolean b, bool special)
   FUNC_ATTR_NONNULL_ALL
 {
   lua_pushboolean(lstate, b);
@@ -654,17 +658,18 @@ void nlua_push_Boolean(lua_State *lstate, const Boolean b)
 /// Convert given Dictionary to lua table
 ///
 /// Leaves converted table on top of the stack.
-void nlua_push_Dictionary(lua_State *lstate, const Dictionary dict)
+void nlua_push_Dictionary(lua_State *lstate, const Dictionary dict,
+                          bool special)
   FUNC_ATTR_NONNULL_ALL
 {
-  if (dict.size == 0) {
+  if (dict.size == 0 && special) {
     nlua_create_typed_table(lstate, 0, 0, kObjectTypeDictionary);
   } else {
     lua_createtable(lstate, 0, (int)dict.size);
   }
   for (size_t i = 0; i < dict.size; i++) {
-    nlua_push_String(lstate, dict.items[i].key);
+    nlua_push_String(lstate, dict.items[i].key, special);
-    nlua_push_Object(lstate, dict.items[i].value);
+    nlua_push_Object(lstate, dict.items[i].value, special);
     lua_rawset(lstate, -3);
   }
 }
@@ -672,18 +677,18 @@ void nlua_push_Dictionary(lua_State *lstate, const Dictionary dict)
 /// Convert given Array to lua table
 ///
 /// Leaves converted table on top of the stack.
-void nlua_push_Array(lua_State *lstate, const Array array)
+void nlua_push_Array(lua_State *lstate, const Array array, bool special)
   FUNC_ATTR_NONNULL_ALL
 {
   lua_createtable(lstate, (int)array.size, 0);
   for (size_t i = 0; i < array.size; i++) {
-    nlua_push_Object(lstate, array.items[i]);
+    nlua_push_Object(lstate, array.items[i], special);
     lua_rawseti(lstate, -2, (int)i + 1);
   }
 }
 
 #define GENERATE_INDEX_FUNCTION(type) \
-void nlua_push_##type(lua_State *lstate, const type item) \
+void nlua_push_##type(lua_State *lstate, const type item, bool special) \
   FUNC_ATTR_NONNULL_ALL \
 { \
   lua_pushnumber(lstate, (lua_Number)(item)); \
@@ -698,7 +703,7 @@ GENERATE_INDEX_FUNCTION(Tabpage)
 /// Convert given Object to lua value
 ///
 /// Leaves converted value on top of the stack.
-void nlua_push_Object(lua_State *lstate, const Object obj)
+void nlua_push_Object(lua_State *lstate, const Object obj, bool special)
   FUNC_ATTR_NONNULL_ALL
 {
   switch (obj.type) {
@@ -712,7 +717,7 @@ void nlua_push_Object(lua_State *lstate, const Object obj)
     }
 #define ADD_TYPE(type, data_key) \
     case kObjectType##type: { \
-      nlua_push_##type(lstate, obj.data.data_key); \
+      nlua_push_##type(lstate, obj.data.data_key, special); \
       break; \
     }
     ADD_TYPE(Boolean,      boolean)
@@ -724,7 +729,7 @@ void nlua_push_Object(lua_State *lstate, const Object obj)
 #undef ADD_TYPE
 #define ADD_REMOTE_TYPE(type) \
     case kObjectType##type: { \
-      nlua_push_##type(lstate, (type)obj.data.integer); \
+      nlua_push_##type(lstate, (type)obj.data.integer, special); \
       break; \
     }
     ADD_REMOTE_TYPE(Buffer)

src/nvim/lua/executor.c

@@ -562,7 +562,7 @@ Object executor_exec_lua_api(const String str, const Array args, Error *err)
   }
 
   for (size_t i = 0; i < args.size; i++) {
-    nlua_push_Object(lstate, args.items[i]);
+    nlua_push_Object(lstate, args.items[i], false);
   }
 
   if (lua_pcall(lstate, (int)args.size, 1, 0)) {
@@ -583,7 +583,7 @@ Object executor_exec_lua_cb(LuaRef ref, const char *name, Array args,
   nlua_pushref(lstate, ref);
   lua_pushstring(lstate, name);
   for (size_t i = 0; i < args.size; i++) {
-    nlua_push_Object(lstate, args.items[i]);
+    nlua_push_Object(lstate, args.items[i], false);
   }
 
   if (lua_pcall(lstate, (int)args.size+1, retval ? 1 : 0, 0)) {

test/functional/api/vim_spec.lua

@@ -339,6 +339,15 @@ describe('API', function()
                  "did\nthe\nfail"},
          meth_pcall(meths.execute_lua, 'error("did\\nthe\\nfail")', {}))
     end)
+
+    it('uses native float values', function()
+      eq(2.5, meths.execute_lua("return select(1, ...)", {2.5}))
+      eq("2.5", meths.execute_lua("return vim.inspect(...)", {2.5}))
+
+      -- "special" float values are still accepted as return values.
+      eq(2.5, meths.execute_lua("return vim.api.nvim_eval('2.5')", {}))
+      eq("{\n  [false] = 2.5,\n  [true] = 3\n}", meths.execute_lua("return vim.inspect(vim.api.nvim_eval('2.5'))", {}))
+    end)
   end)
 
   describe('nvim_input', function()