patch 8.2.1286: Vim9: No error when using a type to a window variable

Problem:    Vim9: No error when using a type to a window variable
Solution:   Recognize the syntax and give an error. (closes #6521)

src/ex_docmd.c

@@ -3324,6 +3324,14 @@ find_ex_command(
 		return eap->cmd;
 	    }
 	}
+
+	// Recognize using a type for a w:, b:, t: or g: variable:
+	// "w:varname: number = 123".
+	if (eap->cmd[1] == ':' && *p == ':')
+	{
+	    eap->cmdidx = CMD_eval;
+	    return eap->cmd;
+	}
     }
 #endif
 

src/testdir/test_vim9_script.vim

@@ -376,6 +376,15 @@ def Test_assignment_failure()
 
   call assert_fails('s/^/\=Mess()/n', 'E794:')
   call CheckDefFailure(['let var: dict<number'], 'E1009:')
+
+  call CheckDefFailure(['w:foo: number = 10'],
+                       'E488: Trailing characters: : number = 1')
+  call CheckDefFailure(['t:foo: bool = true'],
+                       'E488: Trailing characters: : bool = true')
+  call CheckDefFailure(['b:foo: string = "x"'],
+                       'E488: Trailing characters: : string = "x"')
+  call CheckDefFailure(['g:foo: number = 123'],
+                       'E488: Trailing characters: : number = 123')
 enddef
 
 def Test_unlet()

src/version.c

@@ -754,6 +754,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1286,
 /**/
     1285,
 /**/