bevyengine/bevy · error · MissingAssetWriterError

Asset Source '{0}' does not have an AssetWriter.

Error message

Asset Source '{0}' does not have an AssetWriter.

What it means

MissingAssetWriterError: a writer was requested for an asset source id that exists but has no AssetWriter configured (e.g. a read-only source, or writer omitted when building the source). Writing/importing to that source is impossible.

Source

Thrown at crates/bevy_asset/src/io/source.rs:657

    }

    /// This will cause processed [`AssetReader`](crate::io::AssetReader) futures (such as [`AssetReader::read`](crate::io::AssetReader::read)) to wait until
    /// the [`AssetProcessor`](crate::AssetProcessor) has finished processing the requested asset.
    pub(crate) fn gate_on_processor(&mut self, processing_state: Arc<ProcessingState>) {
        for source in self.iter_processed_mut() {
            source.gate_on_processor(processing_state.clone());
        }
    }
}

/// An error returned when an [`AssetSource`] does not exist for a given id.
#[derive(Error, Debug, Clone, PartialEq, Eq)]
#[error("Asset Source '{0}' does not exist")]
pub struct MissingAssetSourceError(AssetSourceId<'static>);

/// An error returned when an [`AssetWriter`](crate::io::AssetWriter) does not exist for a given id.
#[derive(Error, Debug, Clone)]
#[error("Asset Source '{0}' does not have an AssetWriter.")]
pub struct MissingAssetWriterError(AssetSourceId<'static>);

/// An error returned when a processed [`AssetReader`](crate::io::AssetReader) does not exist for a given id.
#[derive(Error, Debug, Clone, PartialEq, Eq)]
#[error("Asset Source '{0}' does not have a processed AssetReader.")]
pub struct MissingProcessedAssetReaderError(AssetSourceId<'static>);

/// An error returned when a processed [`AssetWriter`](crate::io::AssetWriter) does not exist for a given id.
#[derive(Error, Debug, Clone)]
#[error("Asset Source '{0}' does not have a processed AssetWriter.")]
pub struct MissingProcessedAssetWriterError(AssetSourceId<'static>);

const MISSING_DEFAULT_SOURCE: &str =
    "A default AssetSource is required. Add one to `AssetSourceBuilders`";

View on GitHub (pinned to 396ca72708)

Solutions

1. Provide a writer (with_writer / processed_writer) when building the asset source
2. Only read from sources that are intentionally read-only
3. Verify you are targeting the intended source id with the write operation

When it happens

Trigger: Thrown at crates/bevy_asset/src/io/source.rs:657 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of bevyengine/bevy@396ca72708 (2026-08-20). Data as JSON: /api/errors/a8afa5af7e822241. Report an issue: GitHub.