checker: disallow static maps: mut static x := map[string]int{} (#20596)

vlib/v/checker/assign.v

@@ -597,6 +597,13 @@ or use an explicit `unsafe{ a[..] }`, if you do not want a copy of the slice.',
 				}
 			}
 		}
+		if mut left is ast.Ident {
+			if mut left.info is ast.IdentVar {
+				if left.info.is_static && right_sym.kind == .map {
+					c.error('maps cannot be static', left.pos)
+				}
+			}
+		}
 		// Single side check
 		match node.op {
 			.assign {} // No need to do single side check for =. But here put it first for speed.

vlib/v/checker/tests/static_maps_err.out

@@ -0,0 +1,7 @@
+vlib/v/checker/tests/static_maps_err.vv:3:13: error: maps cannot be static
+    1 | @[unsafe]
+    2 | fn foo() map[string]int {
+    3 |     mut static x := map[string]int{}
+      |                ^
+    4 |     return x
+    5 | }

vlib/v/checker/tests/static_maps_err.vv

@@ -0,0 +1,11 @@
+@[unsafe]
+fn foo() map[string]int {
+	mut static x := map[string]int{}
+	return x
+}
+
+fn main() {
+	unsafe {
+		foo()
+	}
+}