The 'druid' attribute has been replaced with separate…

Error message

The 'druid' attribute has been replaced with separate 'lens' and 'data' attributes.

What it means

The derive code for the `data` attribute parsing panics when it encounters the deprecated `#[druid(...)]` field attribute. The `druid` attribute namespace was split into separate `lens` and `data` attributes, and old usage is rejected outright rather than silently migrated.

Solutions

Replace `#[druid(data = ...)]` with `#[data(...)]` on the field
Replace any `#[druid(lens = ...)]` usage with `#[lens(...)]`
Consult the druid-derive changelog for the attribute split migration

Example fix

// before
#[derive(Data)]
struct S { #[druid(data = "true")] flag: bool }

// after
#[derive(Data)]
struct S { #[data(flag)] flag: bool }

Defensive patterns

Strategy: validation

Validate before calling

// grep for the deprecated attribute before compiling:
// grep -rn '#\[druid(' src/

Prevention

Migrate all `#[druid(...)]` attributes to `#[data(...)]` / `#[lens(...)]` when upgrading druid
Run the compiler/CI early after version bumps to catch deprecated attributes
Update any internal snippets/templates that reference the old attribute

When it happens

Trigger: A struct field carries `#[druid(...)]` (matched by `BASE_DRUID_DEPRECATED_ATTR_PATH`) while the macro parses attributes to build `DataAttr`, inside `parse_ast`.

Common situations: Upgrading druid from an older version where `#[druid(...)]` was the documented attribute; copied example code from old tutorials or blog posts.

Understand the failure class

Background: "is deprecated and will be removed" — deprecation warnings for old API names, keywords, and options, and how to migrate before the removal release — this error's family across 29 libraries.

Related errors

AI-assisted analysis of linebender/druid@0f8b1195e4 (2026-09-10). Data as JSON: /api/errors/ee97888ed149a72a. Report an issue: GitHub.

Appendix: source

Thrown at druid-derive/src/attr.rs:131

    pub fn iter(&self) -> impl Iterator<Item = &Field<Attrs>> {
        self.fields.iter()
    }
}

impl Field<DataAttr> {
    pub fn parse_ast(field: &syn::Field, index: usize) -> Result<Self, Error> {
        let ident = match field.ident.as_ref() {
            Some(ident) => FieldIdent::Named(ident.to_string().trim_start_matches("r#").to_owned()),
            None => FieldIdent::Unnamed(index),
        };

        let ty = field.ty.clone();

        let mut data_attr = DataAttr::Empty;
        for attr in field.attrs.iter() {
            if attr.path.is_ident(BASE_DRUID_DEPRECATED_ATTR_PATH) {
                panic!(
                    "The 'druid' attribute has been replaced with separate \
                    'lens' and 'data' attributes.",
                );
            } else if attr.path.is_ident(BASE_DATA_ATTR_PATH) {
                match attr.parse_meta()? {
                    Meta::List(meta) => {
                        assert!(
                            meta.nested.len() <= 1,
                            "only single data attribute is allowed"
                        );
                        if let Some(nested) = meta.nested.first() {
                            match nested {
                                NestedMeta::Meta(Meta::Path(path))
                                    if path.is_ident(IGNORE_ATTR_PATH) =>
                                {
                                    data_attr = DataAttr::Ignore;
                                }
                                NestedMeta::Meta(Meta::NameValue(meta))

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