patch 9.0.1178: a child class cannot override functions from a base class

Problem:    A child class cannot override functions from a base class.
Solution:   Allow overriding and implement "super".

src/errors.h

@@ -3432,4 +3432,10 @@ EXTERN char e_class_name_not_found_str[]
 	INIT(= N_("E1353: Class name not found: %s"));
 EXTERN char e_cannot_extend_str[]
 	INIT(= N_("E1354: Cannot extend %s"));
+EXTERN char e_duplicate_function_str[]
+	INIT(= N_("E1355: Duplicate function: %s"));
+EXTERN char e_super_must_be_followed_by_dot[]
+	INIT(= N_("E1356: \"super\" must be followed by a dot"));
+EXTERN char e_using_super_not_in_class_function[]
+	INIT(= N_("E1357: Using \"super\" not in a class function"));
 #endif

src/globals.h

@@ -527,7 +527,10 @@ EXTERN int	garbage_collect_at_exit INIT(= FALSE);
 #define t_dict_string		(static_types[76])
 #define t_const_dict_string	(static_types[77])
 
-EXTERN type_T static_types[78]
+#define t_super			(static_types[78])
+#define t_const_super		(static_types[79])
+
+EXTERN type_T static_types[80]
 #ifdef DO_INIT
 = {
     // 0: t_unknown
@@ -685,6 +688,10 @@ EXTERN type_T static_types[78]
     // 76: t_dict_string
     {VAR_DICT, 0, 0, TTFLAG_STATIC, &t_string, NULL},
     {VAR_DICT, 0, 0, TTFLAG_STATIC|TTFLAG_CONST, &t_string, NULL},
+
+    // 78: t_super (VAR_CLASS with tt_member set to &t_bool
+    {VAR_CLASS, 0, 0, TTFLAG_STATIC, &t_bool, NULL},
+    {VAR_CLASS, 0, 0, TTFLAG_STATIC|TTFLAG_CONST, &t_bool, NULL},
 }
 #endif
 ;

src/structs.h

@@ -1465,6 +1465,7 @@ typedef struct {
 #define TTFLAG_NUMBER_OK    0x04    // tt_type is VAR_FLOAT, VAR_NUMBER is OK
 #define TTFLAG_STATIC	    0x08    // one of the static types, e.g. t_any
 #define TTFLAG_CONST	    0x10    // cannot be changed
+#define TTFLAG_SUPER	    0x20    // object from "super".
 
 typedef enum {
     ACCESS_PRIVATE,	// read/write only inside th class
@@ -1506,7 +1507,8 @@ struct class_S
     typval_T	*class_members_tv;	// allocated array of class member vals
 
     // class functions: "static def SomeMethod()"
-    int		class_class_function_count;
+    int		class_class_function_count;	    // total count
+    int		class_class_function_count_child;   // count without "extends"
     ufunc_T	**class_class_functions;	// allocated
 
     // object members: "this.varname"
@@ -1514,7 +1516,8 @@ struct class_S
     ocmember_T	*class_obj_members;	// allocated
 
     // object methods: "def SomeMethod()"
-    int		class_obj_method_count;
+    int		class_obj_method_count;		    // total count
+    int		class_obj_method_count_child;	    // count without "extends"
     ufunc_T	**class_obj_methods;	// allocated
 
     garray_T	class_type_list;	// used for type pointers

src/testdir/test_vim9_class.vim

@@ -817,6 +817,27 @@ def Test_class_extends()
       endclass
   END
   v9.CheckScriptFailure(lines, 'E1354: Cannot extend SomeVar')
+
+  lines =<< trim END
+      vim9script
+      class Base
+        this.name: string
+        def ToString(): string
+          return this.name
+        enddef
+      endclass
+
+      class Child extends Base
+        this.age: number
+        def ToString(): string
+          return super.ToString() .. ': ' .. this.age
+        enddef
+      endclass
+
+      var o = Child.new('John', 42)
+      assert_equal('John: 42', o.ToString())
+  END
+  v9.CheckScriptSuccess(lines)
 enddef
 
 

src/version.c

@@ -695,6 +695,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1178,
 /**/
     1177,
 /**/

src/vim9class.c

@@ -487,9 +487,21 @@ early_ret:
 
 	    if (uf != NULL)
 	    {
-		int is_new = STRNCMP(uf->uf_name, "new", 3) == 0;
+		char_u *name = uf->uf_name;
+		int is_new = STRNCMP(name, "new", 3) == 0;
 		garray_T *fgap = has_static || is_new
 					       ? &classfunctions : &objmethods;
+		// Check the name isn't used already.
+		for (int i = 0; i < fgap->ga_len; ++i)
+		{
+		    char_u *n = ((ufunc_T **)fgap->ga_data)[i]->uf_name;
+		    if (STRCMP(name, n) == 0)
+		    {
+			semsg(_(e_duplicate_function_str), name);
+			break;
+		    }
+		}
+
 		if (ga_grow(fgap, 1) == OK)
 		{
 		    if (is_new)
@@ -793,7 +805,8 @@ early_ret:
 
 	    if (nf != NULL && ga_grow(&classfunctions, 1) == OK)
 	    {
-		((ufunc_T **)classfunctions.ga_data)[classfunctions.ga_len] = nf;
+		((ufunc_T **)classfunctions.ga_data)[classfunctions.ga_len]
+									  = nf;
 		++classfunctions.ga_len;
 
 		nf->uf_flags |= FC_NEW;
@@ -808,6 +821,7 @@ early_ret:
 	    }
 	}
 
+	// Move all the functions into the created class.
 	// loop 1: class functions, loop 2: object methods
 	for (int loop = 1; loop <= 2; ++loop)
 	{
@@ -834,26 +848,52 @@ early_ret:
 	    if (*fup == NULL)
 		goto cleanup;
 
+	    mch_memmove(*fup, gap->ga_data, sizeof(ufunc_T *) * gap->ga_len);
+	    vim_free(gap->ga_data);
+	    if (loop == 1)
+		cl->class_class_function_count_child = gap->ga_len;
+	    else
+		cl->class_obj_method_count_child = gap->ga_len;
+
 	    int skipped = 0;
 	    for (int i = 0; i < parent_count; ++i)
 	    {
 		// Copy functions from the parent.  Can't use the same
 		// function, because "uf_class" is different and compilation
 		// will have a different result.
+		// Put them after the functions in the current class, object
+		// methods may be overruled, then "super.Method()" is used to
+		// find a method from the parent.
 		// Skip "new" functions. TODO: not all of them.
 		if (loop == 1 && STRNCMP(
 			    extends_cl->class_class_functions[i]->uf_name,
 								"new", 3) == 0)
 		    ++skipped;
 		else
-		    *fup[i - skipped] = copy_function((loop == 1
+		{
+		    ufunc_T *pf = (loop == 1
 					? extends_cl->class_class_functions
-					: extends_cl->class_obj_methods)[i]);
+					: extends_cl->class_obj_methods)[i];
+		    (*fup)[gap->ga_len + i - skipped] = copy_function(pf);
+
+		    // If the child class overrides a function from the parent
+		    // the signature must be equal.
+		    char_u *pname = pf->uf_name;
+		    for (int ci = 0; ci < gap->ga_len; ++ci)
+		    {
+			ufunc_T *cf = (*fup)[ci];
+			char_u *cname = cf->uf_name;
+			if (STRCMP(pname, cname) == 0)
+			{
+			    where_T where = WHERE_INIT;
+			    where.wt_func_name = (char *)pname;
+			    (void)check_type(pf->uf_func_type, cf->uf_func_type,
+								  TRUE, where);
+			}
+		    }
+		}
 	    }
 
-	    mch_memmove(*fup + parent_count - skipped, gap->ga_data,
-					      sizeof(ufunc_T *) * gap->ga_len);
-	    vim_free(gap->ga_data);
 	    *fcount -= skipped;
 
 	    // Set the class pointer on all the functions and object methods.

src/vim9compile.c

@@ -43,16 +43,31 @@ lookup_local(char_u *name, size_t len, lvar_T *lvar, cctx_T *cctx)
     if (len == 0)
 	return FAIL;
 
-    if (len == 4 && STRNCMP(name, "this", 4) == 0
+    if (((len == 4 && STRNCMP(name, "this", 4) == 0)
+		|| (len == 5 && STRNCMP(name, "super", 5) == 0))
 	    && cctx->ctx_ufunc != NULL
 	    && (cctx->ctx_ufunc->uf_flags & (FC_OBJECT|FC_NEW)))
     {
+	int is_super = *name == 's';
 	if (lvar != NULL)
 	{
 	    CLEAR_POINTER(lvar);
-	    lvar->lv_name = (char_u *)"this";
+	    lvar->lv_name = (char_u *)(is_super ? "super" : "this");
 	    if (cctx->ctx_ufunc->uf_class != NULL)
+	    {
 		lvar->lv_type = &cctx->ctx_ufunc->uf_class->class_object_type;
+		if (is_super)
+		{
+		    type_T *type = get_type_ptr(cctx->ctx_type_list);
+
+		    if (type != NULL)
+		    {
+			*type = *lvar->lv_type;
+			lvar->lv_type = type;
+			type->tt_flags |= TTFLAG_SUPER;
+		    }
+		}
+	    }
 	}
 	return OK;
     }

src/vim9expr.c

@@ -263,7 +263,21 @@ compile_class_object_index(cctx_T *cctx, char_u **arg, type_T *type)
 	return FAIL;
     }
 
-    if (type->tt_type == VAR_CLASS)
+    class_T *cl = (class_T *)type->tt_member;
+    int is_super = type->tt_flags & TTFLAG_SUPER;
+    if (type == &t_super)
+    {
+	if (cctx->ctx_ufunc == NULL || cctx->ctx_ufunc->uf_class == NULL)
+	    emsg(_(e_using_super_not_in_class_function));
+	else
+	{
+	    is_super = TRUE;
+	    cl = cctx->ctx_ufunc->uf_class;
+	    // Remove &t_super from the stack.
+	    --cctx->ctx_type_stack.ga_len;
+	}
+    }
+    else if (type->tt_type == VAR_CLASS)
     {
 	garray_T *instr = &cctx->ctx_instr;
 	if (instr->ga_len > 0)
@@ -286,26 +300,28 @@ compile_class_object_index(cctx_T *cctx, char_u **arg, type_T *type)
 	return FAIL;
     size_t len = name_end - name;
 
-    class_T *cl = (class_T *)type->tt_member;
     if (*name_end == '(')
     {
 	int	function_count;
+	int	child_count;
 	ufunc_T	**functions;
 
 	if (type->tt_type == VAR_CLASS)
 	{
 	    function_count = cl->class_class_function_count;
+	    child_count = cl->class_class_function_count_child;
 	    functions = cl->class_class_functions;
 	}
 	else
 	{
 	    // type->tt_type == VAR_OBJECT: method call
 	    function_count = cl->class_obj_method_count;
+	    child_count = cl->class_obj_method_count_child;
 	    functions = cl->class_obj_methods;
 	}
 
 	ufunc_T *ufunc = NULL;
-	for (int i = 0; i < function_count; ++i)
+	for (int i = is_super ? child_count : 0; i < function_count; ++i)
 	{
 	    ufunc_T *fp = functions[i];
 	    // Use a separate pointer to avoid that ASAN complains about
@@ -643,7 +659,17 @@ compile_load(
 	if (name == NULL)
 	    return FAIL;
 
-	if (vim_strchr(name, AUTOLOAD_CHAR) != NULL)
+	if (STRCMP(name, "super") == 0
+		&& cctx->ctx_ufunc != NULL
+		&& (cctx->ctx_ufunc->uf_flags & (FC_OBJECT|FC_NEW)) == 0)
+	{
+	    // super.SomeFunc() in a class function: push &t_super type, this
+	    // is recognized in compile_subscript().
+	    res = push_type_stack(cctx, &t_super);
+	    if (*end != '.')
+		emsg(_(e_super_must_be_followed_by_dot));
+	}
+	else if (vim_strchr(name, AUTOLOAD_CHAR) != NULL)
 	{
 	    script_autoload(name, FALSE);
 	    res = generate_LOAD(cctx, ISN_LOADAUTO, 0, name, &t_any);