typst/crates/typst-eval/src/methods.rs

//! Handles special built-in methods on values.

use typst_library::diag::{At, SourceResult};
use typst_library::foundations::{Args, Str, Type, Value};
use typst_syntax::Span;

/// Whether a specific method is mutating.
pub(crate) fn is_mutating_method(method: &str) -> bool {
    matches!(method, "push" | "pop" | "insert" | "remove")
}

/// Whether a specific method is an accessor.
pub(crate) fn is_accessor_method(method: &str) -> bool {
    matches!(method, "first" | "last" | "at")
}

/// Call a mutating method on a value.
pub(crate) fn call_method_mut(
    value: &mut Value,
    method: &str,
    mut args: Args,
    span: Span,
) -> SourceResult<Value> {
    let ty = value.ty();
    let missing = || Err(missing_method(ty, method)).at(span);
    let mut output = Value::None;

    match value {
        Value::Array(array) => match method {
            "push" => array.push(args.expect("value")?),
            "pop" => output = array.pop().at(span)?,
            "insert" => {
                array.insert(args.expect("index")?, args.expect("value")?).at(span)?
            }
            "remove" => {
                output = array
                    .remove(args.expect("index")?, args.named("default")?)
                    .at(span)?
            }
            _ => return missing(),
        },

        Value::Dict(dict) => match method {
            "insert" => dict.insert(args.expect::<Str>("key")?, args.expect("value")?),
            "remove" => {
                output =
                    dict.remove(args.expect("key")?, args.named("default")?).at(span)?
            }
            _ => return missing(),
        },

        _ => return missing(),
    }

    args.finish()?;
    Ok(output)
}

/// Call an accessor method on a value.
pub(crate) fn call_method_access<'a>(
    value: &'a mut Value,
    method: &str,
    mut args: Args,
    span: Span,
) -> SourceResult<&'a mut Value> {
    let ty = value.ty();
    let missing = || Err(missing_method(ty, method)).at(span);

    let slot = match value {
        Value::Array(array) => match method {
            "first" => array.first_mut().at(span)?,
            "last" => array.last_mut().at(span)?,
            "at" => array.at_mut(args.expect("index")?).at(span)?,
            _ => return missing(),
        },
        Value::Dict(dict) => match method {
            "at" => dict.at_mut(&args.expect::<Str>("key")?).at(span)?,
            _ => return missing(),
        },
        _ => return missing(),
    };

    args.finish()?;
    Ok(slot)
}

/// The missing method error message.
#[cold]
fn missing_method(ty: Type, method: &str) -> String {
    format!("type {ty} has no method `{method}`")
}