patch 8.2.3869: Vim9: type checking for "any" is inconsistent

Problem:    Vim9: type checking for "any" is inconsistent.
Solution:   Always use a runtime type check for using "any" for a more
            specific type.

src/testdir/test_vim9_func.vim

@@ -548,7 +548,7 @@ def Test_call_default_args()
   END
   CheckScriptFailure(lines, 'E1001: Variable not found: b')
 
-  # using script variable requires matching type or type cast
+  # using script variable requires matching type or type cast when executed
   lines =<< trim END
       vim9script
       var a: any
@@ -557,18 +557,8 @@ def Test_call_default_args()
       enddef
       defcompile
   END
-  CheckScriptFailure(lines, 'E1013: Argument 1: type mismatch, expected string but got any')
-
-  lines =<< trim END
-      vim9script
-      var a: any
-      def Func(arg: string = <string>a)
-        echo arg
-      enddef
-      a = 'works'
-      Func()
-  END
-  CheckScriptSuccess(lines)
+  CheckScriptSuccess(lines + ['a = "text"', 'Func()'])
+  CheckScriptFailure(lines + ['a = 123', 'Func()'], 'E1013: Argument 1: type mismatch, expected string but got number')
 
   # using global variable does not require type cast
   lines =<< trim END

src/version.c

@@ -749,6 +749,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    3869,
 /**/
     3868,
 /**/

src/vim9compile.c

@@ -366,8 +366,11 @@ use_typecheck(type_T *actual, type_T *expected)
 	    || (actual->tt_type == VAR_FUNC
 		&& (expected->tt_type == VAR_FUNC
 					   || expected->tt_type == VAR_PARTIAL)
-		&& (actual->tt_member == &t_any || actual->tt_argcount < 0)
-		&& ((actual->tt_member == &t_void)
+		&& (actual->tt_member == &t_any
+		    || actual->tt_member == &t_unknown
+		    || actual->tt_argcount < 0)
+		&& (actual->tt_member == &t_unknown ||
+		    (actual->tt_member == &t_void)
 					 == (expected->tt_member == &t_void))))
 	return TRUE;
     if ((actual->tt_type == VAR_LIST || actual->tt_type == VAR_DICT)
@@ -412,8 +415,7 @@ need_type_where(
 
     // If the actual type can be the expected type add a runtime check.
     // If it's a constant a runtime check makes no sense.
-    if (ret == MAYBE || ((!actual_is_const || actual == &t_any)
-					   && use_typecheck(actual, expected)))
+    if (!actual_is_const && ret == MAYBE && use_typecheck(actual, expected))
     {
 	generate_TYPECHECK(cctx, expected, offset, where.wt_index);
 	return OK;
@@ -2547,8 +2549,8 @@ compile_def_function(
 		did_set_arg_type = TRUE;
 		ufunc->uf_arg_types[arg_idx] = val_type;
 	    }
-	    else if (check_type(ufunc->uf_arg_types[arg_idx], val_type,
-							  TRUE, where) == FAIL)
+	    else if (need_type_where(val_type, ufunc->uf_arg_types[arg_idx],
+				       -1, where, &cctx, FALSE, FALSE) == FAIL)
 		goto erret;
 
 	    if (generate_STORE(&cctx, ISN_STORE, i - count - off, NULL) == FAIL)

src/vim9expr.c

@@ -415,7 +415,7 @@ compile_load(
 		// Global, Buffer-local, Window-local and Tabpage-local
 		// variables can be defined later, thus we don't check if it
 		// exists, give an error at runtime.
-		res = generate_LOAD(cctx, isn_type, 0, name, &t_unknown);
+		res = generate_LOAD(cctx, isn_type, 0, name, &t_any);
 	    }
 	}
     }
@@ -2846,6 +2846,7 @@ compile_expr1(char_u **arg, cctx_T *cctx, ppconst_T *ppconst)
 	    type_T	**typep;
 
 	    generate_ppconst(cctx, ppconst);
+	    ppconst->pp_is_const = FALSE;
 
 	    // If the types differ, the result has a more generic type.
 	    typep = ((type_T **)stack->ga_data) + stack->ga_len - 1;

src/vim9type.c

@@ -477,7 +477,19 @@ check_typval_type(type_T *expected, typval_T *actual_tv, where_T where)
     ga_init2(&type_list, sizeof(type_T *), 10);
     actual_type = typval2type(actual_tv, get_copyID(), &type_list, TRUE);
     if (actual_type != NULL)
-	res = check_type(expected, actual_type, TRUE, where);
+    {
+	res = check_type_maybe(expected, actual_type, TRUE, where);
+	if (res == MAYBE && !(actual_type->tt_type == VAR_FUNC
+				      && actual_type->tt_member == &t_unknown))
+	{
+	    // If a type check is needed that means assigning "any" or
+	    // "unknown" to a more specific type, which fails here.
+	    // Execpt when it looks like a lambda, since they have an
+	    // incomplete type.
+	    type_mismatch_where(expected, actual_type, where);
+	    res = FAIL;
+	}
+    }
     clear_type_list(&type_list);
     return res;
 }
@@ -567,9 +579,11 @@ check_type_maybe(
     {
 	// tt_type should match, except that a "partial" can be assigned to a
 	// variable with type "func".
-	// And "unknown" (using global variable) needs a runtime type check.
+	// And "unknown" (using global variable) and "any" need a runtime type
+	// check.
 	if (!(expected->tt_type == actual->tt_type
 		    || actual->tt_type == VAR_UNKNOWN
+		    || actual->tt_type == VAR_ANY
 		    || (expected->tt_type == VAR_FUNC
 					   && actual->tt_type == VAR_PARTIAL)))
 	{
@@ -585,10 +599,10 @@ check_type_maybe(
 	{
 	    // "unknown" is used for an empty list or dict
 	    if (actual->tt_member != NULL && actual->tt_member != &t_unknown)
-		ret = check_type(expected->tt_member, actual->tt_member,
+		ret = check_type_maybe(expected->tt_member, actual->tt_member,
 								 FALSE, where);
 	}
-	else if (expected->tt_type == VAR_FUNC)
+	else if (expected->tt_type == VAR_FUNC && actual != &t_any)
 	{
 	    // If the return type is unknown it can be anything, including
 	    // nothing, thus there is no point in checking.
@@ -596,8 +610,8 @@ check_type_maybe(
 	    {
 		if (actual->tt_member != NULL
 					    && actual->tt_member != &t_unknown)
-		    ret = check_type(expected->tt_member, actual->tt_member,
-								 FALSE, where);
+		    ret = check_type_maybe(expected->tt_member,
+					      actual->tt_member, FALSE, where);
 		else
 		    ret = MAYBE;
 	    }