Either output_size or scale_factor must be provided

Error message

Either output_size or scale_factor must be provided

What it means

Interpolate1d's `calculate_output_size` requires the config to specify either an explicit output size or a scale factor; the match on the size enum has no other arms, so any other/none configuration panics. It fires when neither `Interpolate1dConfig::Output` nor `::Scale` was provided.

Source

Thrown at crates/burn-nn/src/modules/interpolate/interpolate1d.rs:160

) -> usize {
    match (output_size, scale_factor) {
        (Some(output_size), None) => {
            // Use provided
            output_size
        }
        (None, Some(scale_factor)) => {
            // Calculate output size based on scale factor
            let [_, _, l] = input_dims;

            let new_dim = (l as f64) * (scale_factor as f64);

            if new_dim > usize::MAX as f64 {
                panic!("Scale factor is too large");
            }

            new_dim as usize
        }
        _ => panic!("Either output_size or scale_factor must be provided"),
    }
}

impl ModuleDisplay for Interpolate1d {
    fn custom_settings(&self) -> Option<DisplaySettings> {
        DisplaySettings::new()
            .with_new_line_after_attribute(false)
            .optional()
    }

    fn custom_content(&self, content: Content) -> Option<Content> {
        content
            .add_debug_attribute("mode", &self.mode)
            .add("output_size", &format!("{:?}", self.output_size))
            .add("scale_factor", &self.scale_factor)
            .optional()
    }
}

View on GitHub (pinned to d16f7ba2ed)

Solutions

Construct with an explicit size: `Interpolate1d::new(Interpolate1dConfig::Output(len))` or `Interpolate1dConfig::Scale(factor)`.
Check that deserialized configs include exactly one of output_size/scale_factor before use.
Avoid `..Default::default()` overriding the size field when building the config.

Example fix

// before
let interp = Interpolate1d::new(Interpolate1dConfig::default()); // neither set
// after
let interp = Interpolate1d::new(Interpolate1dConfig::Output(256));
// or
let interp = Interpolate1d::new(Interpolate1dConfig::Scale(2.0));

Defensive patterns

Strategy: validation

Validate before calling

fn interpolate_config_is_set(config: &Interpolate1dConfig) -> bool {
    matches!(config, Interpolate1dConfig::Output(_) | Interpolate1dConfig::Scale(_))
}
assert!(interpolate_config_is_set(&config), "Interpolate1dConfig must set Output or Scale");

Type guard

fn has_size_spec(config: &Interpolate1dConfig) -> bool {
    matches!(config, Interpolate1dConfig::Output(_) | Interpolate1dConfig::Scale(_))
}

Try / catch

let result = std::panic::catch_unwind(|| interpolate.forward(input));
match result {
    Ok(out) => out,
    Err(_) => Interpolate1d::new(Interpolate1dConfig::Scale(1.0)).forward(input), // identity fallback
}

Prevention

Never construct Interpolate1d from a bare default config; always set Output or Scale.
Watch for `..Default::default()` wiping the size field in struct-update syntax.
Validate deserialized interpolate configs contain a size spec before building the module.

When it happens

Trigger: Constructing Interpolate1d with a default/empty config (neither Output nor Scale set) and calling forward, causing calculate_output_size to fall through to the catch-all panic.

Common situations: Using `Interpolate1d::default()` or `..Default::default()` in struct update syntax that wipes out the size setting; deserializing an incomplete config where the size field is missing; copying a builder pattern and forgetting the final size setter.

Understand the failure class

Background: "X is required", "must be set", "cannot be empty": the missing-required-config error family, from Vertex AI project/location to WeChat keys — this error's family across 18 libraries.

Related errors

AI-assisted analysis of tracel-ai/burn@d16f7ba2ed (2026-09-05). Data as JSON: /api/errors/de7612446a3366bc. Report an issue: GitHub.