patch 8.2.4589: cannot index the g: dictionary

Problem:    Cannot index the g: dictionary.
Solution:   Recognize using "g:[key]". (closes #9969)

src/eval.c

@@ -929,7 +929,8 @@ get_lval(
 	if (vim9script)
 	{
 	    // "a: type" is declaring variable "a" with a type, not "a:".
-	    if (p == name + 2 && p[-1] == ':')
+	    // However, "g:[key]" is indexing a dictionary.
+	    if (p == name + 2 && p[-1] == ':' && *p != '[')
 	    {
 		--p;
 		lp->ll_name_end = p;

src/ex_docmd.c

@@ -3523,12 +3523,14 @@ find_ex_command(
 		return eap->cmd;
 	    }
 
-	    if (p != eap->cmd && (
+	    if ((p != eap->cmd && (
 			    // "varname[]" is an expression.
 			    *p == '['
 			    // "varname.key" is an expression.
-			 || (*p == '.' && (ASCII_ISALPHA(p[1])
-							     || p[1] == '_'))))
+			 || (*p == '.'
+				     && (ASCII_ISALPHA(p[1]) || p[1] == '_'))))
+			// g:[key] is an expression
+		    || STRNCMP(eap->cmd, "g:[", 3) == 0)
 	    {
 		char_u	*after = eap->cmd;
 

src/testdir/test_vim9_assign.vim

@@ -1116,6 +1116,14 @@ def Test_assignment_dict()
   END
   v9.CheckDefAndScriptSuccess(lines)
 
+  lines =<< trim END
+    var key = 'foo'
+    g:[key] = 'value'
+    assert_equal('value', g:foo)
+    unlet g:foo
+  END
+  v9.CheckDefAndScriptSuccess(lines)
+
   lines =<< trim END
     var dd = {one: 1}
     dd.one) = 2

src/version.c

@@ -750,6 +750,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    4589,
 /**/
     4588,
 /**/

src/vim9compile.c

@@ -1000,7 +1000,12 @@ generate_loadvar(
 	    break;
 	case dest_global:
 	    if (vim_strchr(name, AUTOLOAD_CHAR) == NULL)
-		generate_LOAD(cctx, ISN_LOADG, 0, name + 2, type);
+	    {
+		if (name[2] == NUL)
+		    generate_instr_type(cctx, ISN_LOADGDICT, &t_dict_any);
+		else
+		    generate_LOAD(cctx, ISN_LOADG, 0, name + 2, type);
+	    }
 	    else
 		generate_LOAD(cctx, ISN_LOADAUTO, 0, name, type);
 	    break;
@@ -2413,17 +2418,19 @@ may_compile_assignment(exarg_T *eap, char_u **line, cctx_T *cctx)
 
 	    // Recognize an assignment if we recognize the variable
 	    // name:
+	    // "&opt = expr"
+	    // "$ENV = expr"
+	    // "@r = expr"
 	    // "g:var = expr"
+	    // "g:[key] = expr"
 	    // "local = expr"  where "local" is a local var.
 	    // "script = expr"  where "script" is a script-local var.
 	    // "import = expr"  where "import" is an imported var
-	    // "&opt = expr"
-	    // "$ENV = expr"
-	    // "@r = expr"
 	    if (*eap->cmd == '&'
 		    || *eap->cmd == '$'
 		    || *eap->cmd == '@'
 		    || ((len) > 2 && eap->cmd[1] == ':')
+		    || STRNCMP(eap->cmd, "g:[", 3) == 0
 		    || variable_exists(eap->cmd, len, cctx))
 	    {
 		*line = compile_assignment(eap->cmd, eap, CMD_SIZE, cctx);