add test case to catch regression from previous commit

Once this test case is passing, previous commit can be re-added.

Closes #4560

test/stage1/behavior.zig

@@ -40,6 +40,7 @@ comptime {
     _ = @import("behavior/bugs/3384.zig");
     _ = @import("behavior/bugs/3586.zig");
     _ = @import("behavior/bugs/3742.zig");
+    _ = @import("behavior/bugs/4560.zig");
     _ = @import("behavior/bugs/394.zig");
     _ = @import("behavior/bugs/421.zig");
     _ = @import("behavior/bugs/529.zig");

test/stage1/behavior/bugs/4560.zig

@@ -0,0 +1,32 @@
+const std = @import("std");
+
+test "fixed" {
+    var s: S = .{
+        .a = 1,
+        .b = .{
+            .size = 123,
+            .max_distance_from_start_index = 456,
+        },
+    };
+    std.testing.expect(s.a == 1);
+    std.testing.expect(s.b.size == 123);
+    std.testing.expect(s.b.max_distance_from_start_index == 456);
+}
+
+const S = struct {
+    a: u32,
+    b: Map,
+
+    const Map = std.StringHashMap(*S);
+};
+
+pub fn StringHashMap(comptime V: type) type {
+    return HashMap([]const u8, V);
+}
+
+pub fn HashMap(comptime K: type, comptime V: type) type {
+    return struct {
+        size: usize,
+        max_distance_from_start_index: usize,
+    };
+}