DioxusLabs/dioxus · error

writer checked

Error message

writer checked

What it means

Internal diffing invariant: the writer-presence flag was checked earlier in the call, so a writer must exist here. Firing indicates control-flow drift between has_writer checks and writer use in create_children_at_site_with_mounts.

Source

Thrown at packages/core/src/diff/iterator.rs:548

        parent: Option<MountId>,
        site: impl FnOnce(&mut Self) -> InsertionSite,
        children: FragmentMountWriter,
    ) -> usize {
        self.create_children_at_site_with_mounts(new, parent, site, |dom, idx, mount| {
            dom.set_mounted_fragment_child(children, idx, mount)
        })
    }

    fn create_children_at_site_with_mounts(
        &mut self,
        new: &[VNode],
        parent: Option<MountId>,
        site: impl FnOnce(&mut Self) -> InsertionSite,
        mut created_mount: impl FnMut(&mut VirtualDom, usize, MountId),
    ) -> usize {
        if self.has_writer() {
            let site = site(self);
            let to = self.to.as_deref_mut().expect("writer checked");
            site.create_and_place_with_result(to, self.dom.runtime.clone(), |to| {
                let nodes = self.dom.create_children_with_mounts(
                    Some(to),
                    new,
                    parent,
                    |dom, idx, mount| {
                        created_mount(dom, idx, mount);
                    },
                );
                (nodes, nodes)
            })
        } else {
            self.dom
                .create_children_with_mounts(self.to.as_deref_mut(), new, parent, created_mount)
        }
    }
}

View on GitHub (pinned to 24f6a829df)

Solutions

1. This is an internal diffing invariant (writer state). Report it with a minimal reproduction to the Dioxus issue tracker.

When it happens

Trigger: Thrown at packages/core/src/diff/iterator.rs:548 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of DioxusLabs/dioxus@24f6a829df (2026-08-23). Data as JSON: /api/errors/270dc56de49f2aa3. Report an issue: GitHub.