patch 9.2.1136: Vim9: cannot change an item of a read-only v: variable in :def

Problem:  Assigning to an item of a read-only v: variable, gives E46 in
          a :def function, while it works at the script level and
          ":help clipboard-providers-define" does it.
Solution: Check that a v: variable is read-only only when no index
          follows, as for a script variable.  Make v:clipproviders an
          empty dict at startup, as v:colornames, so that a :def function
          can add the first item.

closes: #21391

Assisted-by: Claude
Signed-off-by: Hirohito Higashi <h.east.727@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

src/evalvars.c

@@ -273,6 +273,7 @@ evalvars_init(void)
     set_vim_var_nr(VV_ECHOSPACE,    sc_col - 1);
 
     set_vim_var_dict(VV_COLORNAMES, dict_alloc());
+    set_vim_var_dict(VV_CLIPPROVIDERS, dict_alloc());
 
 #ifdef FEAT_PYTHON3
     set_vim_var_nr(VV_PYTHON3_VERSION, python3_version());

src/proto/vim9compile.pro

@@ -22,7 +22,7 @@ char_u *compile_one_expr_in_str(char_u *p, cctx_T *cctx);
 int compile_all_expr_in_str(char_u *str, int evalstr, cctx_T *cctx);
 int assignment_len(char_u *p, int *heredoc);
 void vim9_declare_error(char_u *name);
-int get_var_dest(char_u *name, assign_dest_T *dest, cmdidx_T cmdidx, int *option_scope, int *vimvaridx, type_T **type, cctx_T *cctx);
+int get_var_dest(char_u *name, assign_dest_T *dest, cmdidx_T cmdidx, int has_index, int *option_scope, int *vimvaridx, type_T **type, cctx_T *cctx);
 int compile_lhs(char_u *var_start, lhs_T *lhs, cmdidx_T cmdidx, int heredoc, int has_cmd, int oplen, cctx_T *cctx);
 int compile_assign_lhs(char_u *var_start, lhs_T *lhs, cmdidx_T cmdidx, int is_decl, int heredoc, int has_cmd, int oplen, cctx_T *cctx);
 int compile_load_lhs_with_index(lhs_T *lhs, char_u *var_start, cctx_T *cctx);

src/testdir/test_vim9_assign.vim

@@ -248,6 +248,28 @@ def Test_assignment()
   END
 enddef
 
+" An item of a read-only v: variable can be changed in a :def function, as
+" at the script level, the variable itself cannot.
+def Test_assign_item_of_readonly_vim_var()
+  assert_equal(v:t_dict, type(v:clipproviders))
+  var lines =<< trim END
+    vim9script
+    def Define()
+      v:clipproviders['vim9_one'] = {}
+      v:clipproviders.vim9_two = {}
+    enddef
+    Define()
+    assert_equal({}, v:clipproviders.vim9_one)
+    assert_equal({}, v:clipproviders.vim9_two)
+    remove(v:clipproviders, 'vim9_one')
+    remove(v:clipproviders, 'vim9_two')
+  END
+  v9.CheckScriptSuccess(lines)
+
+  v9.CheckDefFailure(['v:clipproviders = {}'], 'E46:')
+  v9.CheckDefFailure(['v:version[0] = 1'], 'E1141:')
+enddef
+
 def Test_float_and_number()
   var lines =<< trim END
        var f: float

src/version.c

@@ -763,6 +763,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1136,
 /**/
     1135,
 /**/

src/vim9cmds.c

@@ -1151,7 +1151,7 @@ compile_for(char_u *arg_start, cctx_T *cctx)
 		    goto failed;
 	    }
 
-	    if (get_var_dest(name, &dest, CMD_for, &opt_flags,
+	    if (get_var_dest(name, &dest, CMD_for, FALSE, &opt_flags,
 					      &vimvaridx, &type, cctx) == FAIL)
 		goto failed;
 	    if (dest != dest_local)

src/vim9compile.c

@@ -1493,6 +1493,7 @@ valid_dest_reg(int name)
  * For an option "option_scope" is set.
  * For a v:var "vimvaridx" is set.
  * "type" is set to the destination type if known, unchanted otherwise.
+ * When "has_index" is TRUE an item of the variable is assigned to.
  * Return FAIL if an error message was given.
  */
     int
@@ -1500,6 +1501,7 @@ get_var_dest(
 	char_u		*name,
 	assign_dest_T	*dest,
 	cmdidx_T	cmdidx,
+	int		has_index,
 	int		*option_scope,
 	int		*vimvaridx,
 	type_T		**type,
@@ -1600,8 +1602,9 @@ get_var_dest(
 	    semsg(_(e_variable_not_found_str), name);
 	    return FAIL;
 	}
+	// An item of a read-only variable can be changed, as when not compiled.
 	// We use the current value of "sandbox" here, is that OK?
-	if (var_check_ro(di_flags, name, FALSE))
+	if (!has_index && var_check_ro(di_flags, name, FALSE))
 	    return FAIL;
 	*dest = dest_vimvar;
 	vtv = get_vim_var_tv(*vimvaridx);
@@ -1961,6 +1964,7 @@ compile_lhs_var_dest(
     int	    declare_error = FALSE;
 
     if (get_var_dest(lhs->lhs_name, &lhs->lhs_dest, cmdidx,
+				lhs->lhs_has_index,
 				&lhs->lhs_opt_flags, &lhs->lhs_vimvaridx,
 				&lhs->lhs_type, cctx) == FAIL)
 	return FAIL;