BoundaryML/baml · error · minijinja::Error (UnknownMethod)

BamlImage has no callable attribute '{args:#?}'

Error message

BamlImage has no callable attribute '{args:#?}'

What it means

MinijinjaBamlMedia implements minijinja::value::Object, and its call method is intentionally unimplemented: BamlImage/BAML media values are data, not callable. Attempting to invoke a BAML media object like a function inside a Jinja template raises UnknownMethod with this message.

Source

Thrown at engine/baml-lib/baml-types/src/minijinja.rs:85

        )
    }
}

// Necessary for nested instances of MinijinjaBamlImage to get rendered correctly in prompts
// See https://github.com/BoundaryML/baml/pull/855 for explanation
impl std::fmt::Debug for MinijinjaBamlMedia {
    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
        std::fmt::Display::fmt(self, f)
    }
}

impl minijinja::value::Object for MinijinjaBamlMedia {
    fn call(
        self: &Arc<Self>,
        _state: &minijinja::State<'_, '_>,
        args: &[minijinja::value::Value],
    ) -> Result<minijinja::value::Value, minijinja::Error> {
        Err(minijinja::Error::new(
            minijinja::ErrorKind::UnknownMethod,
            format!("BamlImage has no callable attribute '{args:#?}'"),
        ))
    }

    fn render(self: &Arc<Self>, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        std::fmt::Display::fmt(self, f)
    }
}

View on GitHub (pinned to bd85ce9dee)

Solutions

1. Remove the call — pass the media value directly to the parameter (e.g. {{ myImage }} or just bind it as the argument).
2. Access properties instead of invoking: use fields like url, media_type, base64 as applicable.
3. Check the template for typos where a helper function name was replaced by the media variable.

Example fix

// before (in .baml prompt)
{{ image.resize(512) }}
// after
{{ image }}

{# Jinja: never call media objects #}
{{ image }}

When it happens

Trigger: Calling a BamlImage/BamlMedia value in a prompt template, e.g. {{ myImage(...) }} or {{ myImage.myMethod() }} where the attribute resolves to the media object itself being invoked.

Common situations: Prompt templates written as if media objects exposed methods (resize, url(), etc.); typo'd property access that Jinja interprets as a call; copy-pasted template code from object-returning helpers.

Understand the failure class

Background: UnsupportedOperationException and "is not supported" errors: when a library deliberately refuses a call — this error's family across 30 libraries.

Related errors

• Encountered impossible jinja expression during parsing
• Failed to parse template '{}': {}
• Failed to get template '{}': {}
• Jinja expressions cannot be resolved without a template cont
• Template string call '{}' cannot be resolved without IR cont

AI-assisted analysis of BoundaryML/baml@bd85ce9dee (2026-09-12). Data as JSON: /api/errors/9df10a64fdced334. Report an issue: GitHub.