{"record":{"id":"f886e112a1a93b22","repo":"huggingface/candle","slug":"compile-with-features-flash-attn-f886e1","errorCode":null,"errorMessage":"compile with '--features flash-attn'","messagePattern":"compile with '--features flash-attn'","errorType":"panic","errorClass":null,"httpStatus":null,"severity":"error","filePath":"candle-transformers/src/models/mimi/transformer.rs","lineNumber":776,"sourceCode":"            }\n        })\n    }\n}\n\n#[cfg(feature = \"flash-attn\")]\nfn flash_attn(\n    q: &Tensor,\n    k: &Tensor,\n    v: &Tensor,\n    softmax_scale: f32,\n    causal: bool,\n) -> Result<Tensor> {\n    candle_flash_attn::flash_attn(q, k, v, softmax_scale, causal)\n}\n\n#[cfg(not(feature = \"flash-attn\"))]\nfn flash_attn(_: &Tensor, _: &Tensor, _: &Tensor, _: f32, _: bool) -> Result<Tensor> {\n    unimplemented!(\"compile with '--features flash-attn'\")\n}\n","sourceCodeStart":758,"sourceCodeEnd":778,"githubUrl":"https://github.com/huggingface/candle/blob/d5fee525bfde3273eb7c9b75fd2bc4937be867ca/candle-transformers/src/models/mimi/transformer.rs#L758-L778","documentation":"In mimi/transformer.rs the `flash_attn` helper's fallback (no `flash-attn` feature) panics with `unimplemented!`. The Mimi transformer attention calls this helper when flash attention is selected, so the missing feature turns into a runtime panic.","triggerScenarios":"Running the Mimi audio codec model with flash attention enabled in its transformer config while compiled without `--features flash-attn`.","commonSituations":"Weights/config enabling flash attention; default cargo builds; running on CPU/macOS hosts where the CUDA-only flash-attn kernel is unavailable.","solutions":["Rebuild with `cargo build --release --features candle-transformers/flash-attn` (CUDA required).","Disable flash attention in the Mimi config so the standard attention path is used.","If not applicable (Mimi defaults may not set it), check code that toggles the flash flag before constructing the transformer."],"exampleFix":"// before\ncargo run --release --example mimi-demo\n// after\ncargo run --release --features candle-transformers/flash-attn --example mimi-demo","handlingStrategy":"validation","validationCode":"#[cfg(not(feature = \"flash-attn\"))]\nfn ensure_no_flash(cfg_use_flash: bool) {\n    assert!(!cfg_use_flash, \"mimi: flash-attn requires --features candle-transformers/flash-attn\");\n}","typeGuard":"fn can_flash(use_flash: bool) -> bool {\n    !use_flash || cfg!(feature = \"flash-attn\")\n}","tryCatchPattern":"if !can_flash(config.transformer.use_flash_attn) {\n    config.transformer.use_flash_attn = false;\n}","preventionTips":["Validate nested config sections (transformer) for flash flags too","Enable the feature only on CUDA-capable CI runners","Keep audio codec examples buildable without the feature","Log when silently downgrading to standard attention"],"tags":["rust","candle","feature-flag","flash-attention","panic"],"backgroundTag":"missing-cargo-feature","analyzedSha":"d5fee525bfde3273eb7c9b75fd2bc4937be867ca","analyzedAt":"2026-09-02T00:15:47.023Z","contentChangedAt":null,"schemaVersion":2},"datasetVersion":"2026-09-09T06:17:21.866Z"}