patch 9.0.2170: Vim9: no support for const/final class/objects vars

Problem:  Vim9: no support for const/final class/objects vars
Solution: Support final and const object and class variables

closes: #13655

Signed-off-by: Yegappan Lakshmanan <yegappan@yahoo.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

runtime/doc/tags

@@ -4505,7 +4505,10 @@ E1401	vim9class.txt	/*E1401*
 E1402	vim9class.txt	/*E1402*
 E1403	vim9class.txt	/*E1403*
 E1407	vim9class.txt	/*E1407*
+E1408	vim9class.txt	/*E1408*
+E1409	vim9class.txt	/*E1409*
 E141	message.txt	/*E141*
+E1410	vim9class.txt	/*E1410*
 E142	message.txt	/*E142*
 E143	autocmd.txt	/*E143*
 E144	various.txt	/*E144*
@@ -9096,6 +9099,8 @@ o_V	motion.txt	/*o_V*
 o_object-select	motion.txt	/*o_object-select*
 o_v	motion.txt	/*o_v*
 object	vim9class.txt	/*object*
+object-const-variable	vim9class.txt	/*object-const-variable*
+object-final-variable	vim9class.txt	/*object-final-variable*
 object-motions	motion.txt	/*object-motions*
 object-select	motion.txt	/*object-select*
 objects	index.txt	/*objects*

runtime/doc/todo.txt

@@ -1,4 +1,4 @@
-*todo.txt*      For Vim version 9.0.  Last change: 2023 Jun 08
+*todo.txt*      For Vim version 9.0.  Last change: 2023 Dec 14
 
 
 		  VIM REFERENCE MANUAL	  by Bram Moolenaar
@@ -122,7 +122,6 @@ Upcoming larger works:
 
 Further Vim9 improvements:
 - Classes and Interfaces. See |vim9-classes|
-  - "final" object members - can only be set in the constructor.
   - Cannot use class type of itself in the method (Issue #12369)
   - Getting member of variable with "any" type should be handled at runtime.
     Remove temporary solution from #12096 / patch 9.0.1375.

runtime/doc/vim9class.txt

@@ -364,6 +364,78 @@ super class.  Depending on the class where the member is used the
 corresponding class member will be used.  The type of the class member in a
 child class can be different from that in the super class.
 
+					*object-final-variable* *E1409*
+The |:final| keyword can be used to make a class or object variable a
+constant.  Examples: >
+
+    class A
+	final v1 = [1, 2]		# final object variable
+	public final v2 = {x: 1}	# final object variable
+	static final v3 = 'abc'		# final class variable
+	public static final v4 = 0z10	# final class variable
+    endclass
+<
+A final variable can be changed only from a constructor function.  Example: >
+
+    class A
+	final v1: list<number>
+	def new()
+	    this.v1 = [1, 2]
+	enddef
+    endclass
+    var a = A.new()
+    echo a.v1
+<
+Note that the value of a final variable can be changed.  Example: >
+
+    class A
+	public final v1 = [1, 2]
+    endclass
+    var a = A.new()
+    a.v1[0] = 6			# OK
+    a.v1->add(3)		# OK
+    a.v1 = [3, 4]		# Error
+<
+							*E1408*
+Final variables are not supported in an interface.  A class or object method
+cannot be final.
+
+					*object-const-variable*
+The |:const| keyword can be used to make a class or object variable and the
+value a constant.  Examples: >
+
+    class A
+	const v1 = [1, 2]		# const object variable
+	public const v2 = {x: 1}	# const object variable
+	static const v3 = 'abc'		# const class variable
+	public static const v4 = 0z10	# const class variable
+    endclass
+<
+A const variable can be changed only from a constructor function. Example: >
+
+    class A
+	const v1: list<number>
+	def new()
+	    this.v1 = [1, 2]
+	enddef
+    endclass
+    var a = A.new()
+    echo a.v1
+<
+A const variable and its value cannot be changed.  Example: >
+
+    class A
+	public const v1 = [1, 2]
+    endclass
+    var a = A.new()
+    a.v1[0] = 6			# Error
+    a.v1->add(3)		# Error
+    a.v1 = [3, 4]		# Error
+<
+							 *E1410*
+Const variables are not supported in an interface.  A class or object method
+cannot be a const.
+
 ==============================================================================
 
 4.  Using an abstract class			*Vim9-abstract-class*
@@ -982,8 +1054,6 @@ function declaration syntax for class/object variables and methods.  Vim9 also
 reuses the general function declaration syntax for methods.  So, for the sake
 of consistency, we require "var" in these declarations.
 
-This also allows for a natural use of "final" and "const" in the future.
-
 
 Using "ClassName.new()" to construct an object ~
 

src/errors.h

@@ -3406,8 +3406,8 @@ EXTERN char e_invalid_class_variable_declaration_str[]
 	INIT(= N_("E1329: Invalid class variable declaration: %s"));
 EXTERN char e_invalid_type_for_object_variable_str[]
 	INIT(= N_("E1330: Invalid type for object variable: %s"));
-EXTERN char e_public_must_be_followed_by_var_or_static[]
-	INIT(= N_("E1331: Public must be followed by \"var\" or \"static\""));
+EXTERN char e_public_must_be_followed_by_var_static_final_or_const[]
+	INIT(= N_("E1331: Public must be followed by \"var\" or \"static\" or \"final\" or \"const\""));
 EXTERN char e_public_variable_name_cannot_start_with_underscore_str[]
 	INIT(= N_("E1332: Public variable name cannot start with underscore: %s"));
 EXTERN char e_cannot_access_protected_variable_str[]
@@ -3488,8 +3488,8 @@ EXTERN char e_cannot_access_protected_method_str[]
 	INIT(= N_("E1366: Cannot access protected method: %s"));
 EXTERN char e_variable_str_of_interface_str_has_different_access[]
 	INIT(= N_("E1367: Access level of variable \"%s\" of interface \"%s\" is different"));
-EXTERN char e_static_must_be_followed_by_var_or_def[]
-	INIT(= N_("E1368: Static must be followed by \"var\" or \"def\""));
+EXTERN char e_static_must_be_followed_by_var_def_final_or_const[]
+	INIT(= N_("E1368: Static must be followed by \"var\" or \"def\" or \"final\" or \"const\""));
 EXTERN char e_duplicate_variable_str[]
 	INIT(= N_("E1369: Duplicate variable: %s"));
 EXTERN char e_cannot_define_new_method_as_static[]
@@ -3568,8 +3568,14 @@ EXTERN char e_using_class_as_var_val[]
 	INIT(= N_("E1406: Cannot use a Class as a variable or value"));
 EXTERN char e_using_typealias_as_var_val[]
 	INIT(= N_("E1407: Cannot use a Typealias as a variable or value"));
-#endif
-// E1408 - E1499 unused (reserved for Vim9 class support)
+EXTERN char e_final_variable_not_supported_in_interface[]
+	INIT(= N_("E1408: Final variable not supported in an interface"));
+EXTERN char e_cannot_change_readonly_variable_str_in_class_str[]
+	INIT(= N_("E1409: Cannot change read-only variable \"%s\" in class \"%s\""));
+EXTERN char e_const_variable_not_supported_in_interface[]
+	INIT(= N_("E1410: Const variable not supported in an interface"));
+#endif
+// E1411 - E1499 unused (reserved for Vim9 class support)
 EXTERN char e_cannot_mix_positional_and_non_positional_str[]
 	INIT(= N_("E1500: Cannot mix positional and non-positional arguments: %s"));
 EXTERN char e_fmt_arg_nr_unused_str[]

src/eval.c

@@ -1778,6 +1778,13 @@ get_lval(
 							  p, flags) == FAIL)
 			    return NULL;
 
+			// When lhs is used to modify the variable, check it is
+			// not a read-only variable.
+			if ((flags & GLV_READ_ONLY) == 0
+				&& (*p != '.' && *p != '[')
+				&& oc_var_check_ro(cl, om))
+			    return NULL;
+
 			lp->ll_valtype = om->ocm_type;
 
 			if (v_type == VAR_OBJECT)

src/proto/vim9class.pro

@@ -18,6 +18,8 @@ ocmember_T *member_lookup(class_T *cl, vartype_T v_type, char_u *name, size_t na
 void emsg_var_cl_define(char *msg, char_u *name, size_t len, class_T *cl);
 ufunc_T *method_lookup(class_T *cl, vartype_T v_type, char_u *name, size_t namelen, int *idx);
 int inside_class(cctx_T *cctx_arg, class_T *cl);
+int oc_var_check_ro(class_T *cl, ocmember_T *m);
+void obj_lock_const_vars(object_T *obj);
 void copy_object(typval_T *from, typval_T *to);
 void copy_class(typval_T *from, typval_T *to);
 void class_unref(class_T *cl);

src/structs.h

@@ -1523,14 +1523,18 @@ typedef enum {
     VIM_ACCESS_ALL	// read/write everywhere
 } omacc_T;
 
+#define OCMFLAG_HAS_TYPE	0x01	// type specified explicitly
+#define OCMFLAG_FINAL		0x02	// "final" object/class member
+#define OCMFLAG_CONST		0x04	// "const" object/class member
+
 /*
  * Entry for an object or class member variable.
  */
 typedef struct {
     char_u	*ocm_name;	// allocated
     omacc_T	ocm_access;
-    int		ocm_has_type;	// type specified explicitly
     type_T	*ocm_type;
+    int		ocm_flags;
     char_u	*ocm_init;	// allocated
 } ocmember_T;