v: allow none for not first values on map initialization (#18821)

vlib/v/checker/containers.v

@@ -409,6 +409,11 @@ fn (mut c Checker) map_init(mut node ast.MapInit) ast.Type {
 		expecting_interface_map := map_value_sym.kind == .interface_
 		//
 		mut same_key_type := true
+
+		if node.keys.len == 1 && val0_type == ast.none_type {
+			c.error('map value cannot be only `none`', node.vals[0].pos())
+		}
+
 		for i, mut key in node.keys {
 			if i == 0 && !use_expected_type {
 				continue
@@ -445,6 +450,9 @@ fn (mut c Checker) map_init(mut node ast.MapInit) ast.Type {
 					c.error('invalid map value: ${msg}', val.pos())
 				}
 			}
+			if val_type == ast.none_type && val0_type.has_flag(.option) {
+				continue
+			}
 			if !c.check_types(val_type, val0_type)
 				|| val0_type.has_flag(.option) != val_type.has_flag(.option)
 				|| (i == 0 && val_type.is_number() && val0_type.is_number()

vlib/v/checker/tests/map_with_none_err.out

@@ -0,0 +1,34 @@
+vlib/v/checker/tests/map_with_none_err.vv:2:6: warning: unused variable: `a`
+    1 | fn main() {
+    2 |     mut a := {
+      |         ^
+    3 |         'bar': none
+    4 |     }
+vlib/v/checker/tests/map_with_none_err.vv:6:6: warning: unused variable: `b`
+    4 |     }
+    5 | 
+    6 |     mut b := {
+      |         ^
+    7 |         'foo': 1,
+    8 |         'bar': none
+vlib/v/checker/tests/map_with_none_err.vv:11:6: warning: unused variable: `c`
+    9 |     }
+   10 | 
+   11 |     mut c := {
+      |         ^
+   12 |         'foo': ?int(none),
+   13 |         'bar': none
+vlib/v/checker/tests/map_with_none_err.vv:3:10: error: map value cannot be only `none`
+    1 | fn main() {
+    2 |     mut a := {
+    3 |         'bar': none
+      |                ~~~~
+    4 |     }
+    5 |
+vlib/v/checker/tests/map_with_none_err.vv:8:10: error: invalid map value: expected `int`, not `none`
+    6 |     mut b := {
+    7 |         'foo': 1,
+    8 |         'bar': none
+      |                ~~~~
+    9 |     }
+   10 |

vlib/v/checker/tests/map_with_none_err.vv

@@ -0,0 +1,15 @@
+fn main() {
+	mut a := {
+		'bar': none
+	}
+
+	mut b := {
+		'foo': 1,
+		'bar': none
+	}
+
+	mut c := {
+		'foo': ?int(none),
+		'bar': none
+	}
+}

vlib/v/gen/c/cgen.v

@@ -4018,7 +4018,7 @@ fn (mut g Gen) map_init(node ast.MapInit) {
 			}
 			if value_sym.kind == .sum_type {
 				g.expr_with_cast(expr, node.val_types[i], unwrap_val_typ)
-			} else if node.val_types[i].has_flag(.option) {
+			} else if node.val_types[i].has_flag(.option) || node.val_types[i] == ast.none_type {
 				g.expr_with_opt(expr, node.val_types[i], unwrap_val_typ)
 			} else {
 				g.expr(expr)

vlib/v/tests/option_map_none_test.v

@@ -0,0 +1,17 @@
+fn test_main() {
+	mut a := {
+		'foo': ?int(1)
+		'bar': none
+	}
+	a['foo'] = 1
+	assert dump(a) == a
+}
+
+fn test_none() {
+	mut a := {
+		'foo': ?int(1)
+		'bar': none
+	}
+	a['foo'] = none
+	assert dump(a) == a
+}