flxzt/rnote · error

BrushStyle try_from:: () for value failed

Error message

BrushStyle try_from::<u32>() for value {} failed

What it means

BrushStyle::try_from(u32) failed because num_traits::FromPrimitive::from_u32 returned None: the u32 does not correspond to any BrushStyle variant (marker, etc.). The library throws this whenever a numeric pen-style value, typically restored from persisted settings or received from the UI layer, is outside the valid discriminant range.

Solutions

1. Check the u32 value being converted and map it to a valid BrushStyle discriminant (see the enum in brushconfig.rs).
2. If the value comes from persisted settings, migrate or reset it: fall back to BrushStyle::default() when conversion fails.
3. If you added/removed enum variants, re-save settings so stored numeric values match the new layout.

Example fix

// before
let style = BrushStyle::try_from(stored_u32)?;
// after
let style = BrushStyle::try_from(stored_u32)
    .unwrap_or_else(|_| BrushStyle::default());

// Rust: validate before conversion
fn is_valid_brush_style(v: u32) -> bool {
    BrushStyle::try_from(v).is_ok()
}

fn as_brush_style(v: u32) -> Option<BrushStyle> {
    num_traits::FromPrimitive::from_u32(v)
}

let style = BrushStyle::try_from(raw)
    .map_err(|e| log::warn!("{e}; using default"))
    .unwrap_or(BrushStyle::default());

When it happens

Trigger: Calling `BrushStyle::try_from(value)` with a u32 that is not a valid variant discriminant, e.g. a value loaded from an old or hand-edited settings file after the enum gained/removed/reordered variants, or a value >= the number of variants.

Common situations: Restoring brush pen configuration from an old rnote settings file whose stored u32 no longer matches the current enum layout; a UI toggle button emitting an out-of-range index; schema drift between app versions.

Understand the failure class

Background: Invalid enum value errors: "Unknown type", "Invalid scope", "must be one of" — when a string is not on the library's allowed list — this error's family across 23 libraries.

Related errors

• EraserStyle try_from
• SelectorStyle try_from
• ShaperStyle try_from
• ToolStyle try_from:: () for value failed
• ShortcutMode try_from

AI-assisted analysis of flxzt/rnote@bbc5354502 (2026-09-08). Data as JSON: /api/errors/e2c7ee3f46b3cda7. Report an issue: GitHub.

Appendix: source

Thrown at crates/rnote-engine/src/pens/pensconfig/brushconfig.rs:43

    Marker = 0,
    #[serde(rename = "solid")]
    Solid,
    #[serde(rename = "textured")]
    Textured,
}

impl Default for BrushStyle {
    fn default() -> Self {
        Self::Solid
    }
}

impl TryFrom<u32> for BrushStyle {
    type Error = anyhow::Error;

    fn try_from(value: u32) -> Result<Self, Self::Error> {
        num_traits::FromPrimitive::from_u32(value).ok_or_else(|| {
            anyhow::anyhow!("BrushStyle try_from::<u32>() for value {} failed", value)
        })
    }
}

#[derive(Debug, Clone, Serialize, Deserialize)]
#[serde(rename = "marker_options")]
pub struct MarkerOptions(SmoothOptions);

impl Default for MarkerOptions {
    fn default() -> Self {
        let mut options = SmoothOptions::default();
        options.pressure_curve = PressureCurve::Const;
        options.stroke_width = 12.0;

        Self(options)
    }
}

View on GitHub (pinned to bbc5354502)