patch 9.0.0444: trying to declare g:variable gives confusing error

Problem:    Trying to declare g:variable gives confusing error.
Solution:   Give a better error message. (closes #11108)

src/errors.h

@@ -3335,4 +3335,6 @@ EXTERN char e_script_variable_was_deleted[]
 	INIT(= N_("E1302: Script variable was deleted"));
 EXTERN char e_custom_list_completion_function_does_not_return_list_but_str[]
 	INIT(= N_("E1303: Custom list completion function does not return a List but a %s"));
+EXTERN char e_cannot_use_type_with_this_variable_str[]
+	INIT(= N_("E1304: Cannot use type with this variable: %s"));
 #endif

src/eval.c

@@ -1031,12 +1031,16 @@ get_lval(
 	    {
 		char_u	    *tp = skipwhite(p + 1);
 
+		if (is_scoped_variable(name))
+		{
+		    semsg(_(e_cannot_use_type_with_this_variable_str), name);
+		    return NULL;
+		}
 		if (tp == p + 1 && !quiet)
 		{
 		    semsg(_(e_white_space_required_after_str_str), ":", p);
 		    return NULL;
 		}
-
 		if (!SCRIPT_ID_VALID(current_sctx.sc_sid))
 		{
 		    semsg(_(e_using_type_not_in_script_context_str), p);

src/evalvars.c

@@ -602,6 +602,18 @@ list_script_vars(int *first)
 							   "s:", FALSE, first);
 }
 
+/*
+ * Return TRUE if "name" starts with "g:", "w:", "t:" or "b:".
+ * But only when an identifier character follows.
+ */
+    int
+is_scoped_variable(char_u *name)
+{
+    return vim_strchr((char_u *)"gwbt", name[0]) != NULL
+	&& name[1] == ':'
+	&& eval_isnamec(name[2]);
+}
+
 /*
  * Evaluate one Vim expression {expr} in string "p" and append the
  * resulting string to "gap".  "p" points to the opening "{".
@@ -3679,8 +3691,7 @@ set_var_const(
 	vim9_declare_error(name);
 	goto failed;
     }
-    if ((flags & ASSIGN_FOR_LOOP) && name[1] == ':'
+    if ((flags & ASSIGN_FOR_LOOP) && is_scoped_variable(name))
-			      && vim_strchr((char_u *)"gwbt", name[0]) != NULL)
 	// Do not make g:var, w:var, b:var or t:var final.
 	flags &= ~ASSIGN_FINAL;
 

src/ex_docmd.c

@@ -3761,11 +3761,11 @@ find_ex_command(
 		}
 	    }
 
-	    // Recognize using a type for a w:, b:, t: or g: variable:
+	    // Recognize trying to use a type for a w:, b:, t: or g: variable:
 	    // "w:varname: number = 123".
 	    if (eap->cmd[1] == ':' && *p == ':')
 	    {
-		eap->cmdidx = CMD_eval;
+		eap->cmdidx = CMD_var;
 		return eap->cmd;
 	    }
 	}

src/proto/evalvars.pro

@@ -13,6 +13,7 @@ list_T *eval_spell_expr(char_u *badword, char_u *expr);
 int get_spellword(list_T *list, char_u **pp);
 void prepare_vimvar(int idx, typval_T *save_tv);
 void restore_vimvar(int idx, typval_T *save_tv);
+int is_scoped_variable(char_u *name);
 char_u *eval_one_expr_in_str(char_u *p, garray_T *gap, int evaluate);
 list_T *heredoc_get(exarg_T *eap, char_u *cmd, int script_get, int vim9compile);
 void ex_var(exarg_T *eap);

src/testdir/test_vim9_assign.vim

@@ -1597,13 +1597,31 @@ def Test_assignment_failure()
   v9.CheckDefFailure(['var name: dict<number'], 'E1009:')
 
   v9.CheckDefFailure(['w:foo: number = 10'],
-                  'E488: Trailing characters: : number = 1')
+                  'E1016: Cannot declare a window variable: w:foo')
   v9.CheckDefFailure(['t:foo: bool = true'],
-                  'E488: Trailing characters: : bool = true')
+                  'E1016: Cannot declare a tab variable: t:foo')
   v9.CheckDefFailure(['b:foo: string = "x"'],
-                  'E488: Trailing characters: : string = "x"')
+                  'E1016: Cannot declare a buffer variable: b:foo')
   v9.CheckDefFailure(['g:foo: number = 123'],
-                  'E488: Trailing characters: : number = 123')
+                  'E1016: Cannot declare a global variable: g:foo')
+
+  v9.CheckScriptFailure(['vim9script', 'w:foo: number = 123'],
+                  'E1304: Cannot use type with this variable: w:foo:')
+  v9.CheckScriptFailure(['vim9script', 't:foo: number = 123'],
+                  'E1304: Cannot use type with this variable: t:foo:')
+  v9.CheckScriptFailure(['vim9script', 'b:foo: number = 123'],
+                  'E1304: Cannot use type with this variable: b:foo:')
+  v9.CheckScriptFailure(['vim9script', 'g:foo: number = 123'],
+                  'E1304: Cannot use type with this variable: g:foo:')
+
+  v9.CheckScriptFailure(['vim9script', 'const w:FOO: number = 123'],
+                  'E1304: Cannot use type with this variable: w:FOO:')
+  v9.CheckScriptFailure(['vim9script', 'const t:FOO: number = 123'],
+                  'E1304: Cannot use type with this variable: t:FOO:')
+  v9.CheckScriptFailure(['vim9script', 'const b:FOO: number = 123'],
+                  'E1304: Cannot use type with this variable: b:FOO:')
+  v9.CheckScriptFailure(['vim9script', 'const g:FOO: number = 123'],
+                  'E1304: Cannot use type with this variable: g:FOO:')
 enddef
 
 def Test_assign_list()
@@ -1959,8 +1977,6 @@ def Test_var_declaration()
     FLIST[0] = 11
     assert_equal([11], FLIST)
 
-    const g:FOO: number = 321
-    assert_equal(321, g:FOO)
     const g:FOOS = 'gfoos'
     assert_equal('gfoos', g:FOOS)
     final g:FLIST = [2]
@@ -1975,8 +1991,6 @@ def Test_var_declaration()
     assert_equal(123, g:globConst)
     assert_true(islocked('g:globConst'))
 
-    const w:FOO: number = 46
-    assert_equal(46, w:FOO)
     const w:FOOS = 'wfoos'
     assert_equal('wfoos', w:FOOS)
     final w:FLIST = [3]
@@ -2015,10 +2029,8 @@ def Test_var_declaration()
   unlet g:var_prefixed
   unlet g:other_var
   unlet g:globConst
-  unlet g:FOO
   unlet g:FOOS
   unlet g:FLIST
-  unlet w:FOO
   unlet w:FOOS
   unlet w:FLIST
 enddef

src/testdir/test_vim9_cmd.vim

@@ -1936,7 +1936,7 @@ def Test_var_not_cmd()
   var lines =<< trim END
       g:notexist:cmd
   END
-  v9.CheckDefAndScriptFailure(lines, ['E488: Trailing characters: :cmd', 'E121: Undefined variable: g:notexist'], 1)
+  v9.CheckDefAndScriptFailure(lines, ['E1016: Cannot declare a global variable: g:notexist', "E1069: White space required after ':'"], 1)
 
   lines =<< trim END
       g-pat-cmd
@@ -1950,7 +1950,7 @@ def Test_var_not_cmd()
   lines =<< trim END
       s:notexist:repl
   END
-  v9.CheckDefAndScriptFailure(lines, ['E488: Trailing characters: :repl', 'E1268:'], 1)
+  v9.CheckDefAndScriptFailure(lines, ['E1101: Cannot declare a script variable in a function: s:notexist', "E1069: White space required after ':'"], 1)
 
   lines =<< trim END
       notexist:repl

src/testdir/test_vim9_script.vim

@@ -4241,13 +4241,12 @@ func Test_misplaced_type()
 endfunc
 
 def Run_Test_misplaced_type()
-  writefile(['let g:somevar = "asdf"'], 'XTest_misplaced_type')
+  writefile(['let g:somevar = "asdf"'], 'XTest_misplaced_type', 'D')
   var buf = g:RunVimInTerminal('-S XTest_misplaced_type', {'rows': 6})
-  term_sendkeys(buf, ":vim9cmd echo islocked('g:somevar: string')\<CR>")
+  term_sendkeys(buf, ":vim9cmd echo islocked('somevar: string')\<CR>")
   g:VerifyScreenDump(buf, 'Test_misplaced_type', {})
 
   g:StopVimInTerminal(buf)
-  delete('XTest_misplaced_type')
 enddef
 
 " Ensure echo doesn't crash when stringifying empty variables.

src/version.c

@@ -703,6 +703,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    444,
 /**/
     443,
 /**/