vrl 0.32.0

Vector Remap Language
Documentation 
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use crate::compiler::prelude::*;

fn downcase(value: &Value) -> Resolved {
    Ok(value.try_bytes_utf8_lossy()?.to_lowercase().into())
}

#[derive(Clone, Copy, Debug)]
pub struct Downcase;

impl Function for Downcase {
    fn identifier(&self) -> &'static str {
        "downcase"
    }

    fn usage(&self) -> &'static str {
        "Downcases the `value` string, where downcase is defined according to the Unicode Derived Core Property Lowercase."
    }

    fn category(&self) -> &'static str {
        Category::String.as_ref()
    }

    fn return_kind(&self) -> u16 {
        kind::BYTES
    }

    fn parameters(&self) -> &'static [Parameter] {
        const PARAMETERS: &[Parameter] = &[Parameter::required(
            "value",
            kind::BYTES,
            "The string to convert to lowercase.",
        )];
        PARAMETERS
    }

    fn compile(
        &self,
        _state: &state::TypeState,
        _ctx: &mut FunctionCompileContext,
        arguments: ArgumentList,
    ) -> Compiled {
        let value = arguments.required("value");

        Ok(DowncaseFn { value }.as_expr())
    }

    fn examples(&self) -> &'static [Example] {
        &[
            example! {
                title: "Downcase a string",
                source: r#"downcase("Hello, World!")"#,
                result: Ok("hello, world!"),
            },
            example! {
                title: "Downcase with number",
                source: r#"downcase("FOO 2 BAR")"#,
                result: Ok("foo 2 bar"),
            },
        ]
    }
}

#[derive(Debug, Clone)]
struct DowncaseFn {
    value: Box<dyn Expression>,
}

impl FunctionExpression for DowncaseFn {
    fn resolve(&self, ctx: &mut Context) -> Resolved {
        let value = self.value.resolve(ctx)?;
        downcase(&value)
    }

    fn type_def(&self, _: &state::TypeState) -> TypeDef {
        TypeDef::bytes().infallible()
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::value;

    test_function![
        downcase => Downcase;

        simple {
            args: func_args![value: "FOO 2 bar"],
            want: Ok(value!("foo 2 bar")),
            tdef: TypeDef::bytes(),
        }
    ];
}