abacus 0.2.1

The mathemagical programming language
Documentation 
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#![allow(unused_assignments)] // False positive from miette Diagnostic derive (rust-lang/rust#147648)

use miette::{Diagnostic, SourceSpan};
use thiserror::Error;

use crate::lexer::token::Span;

#[derive(Debug, Error, Diagnostic)]
pub enum EvalError {
    #[error("undefined variable: {name}")]
    UndefinedVar {
        name: String,
        #[label("not defined here")]
        span: Option<SourceSpan>,
    },

    #[error("undefined function: {name}")]
    UndefinedFunc {
        name: String,
        #[label("not defined here")]
        span: Option<SourceSpan>,
    },

    #[error("no matching arm for function: {name}")]
    NoMatchingArm {
        name: String,
        #[label("no matching arm")]
        span: Option<SourceSpan>,
    },

    #[error("type error: {message}")]
    TypeError {
        message: &'static str,
        #[label("type error")]
        span: Option<SourceSpan>,
    },

    #[error("division by zero")]
    DivideByZero {
        #[label("division by zero")]
        span: Option<SourceSpan>,
    },

    #[error("integer overflow")]
    Overflow {
        #[label("overflow")]
        span: Option<SourceSpan>,
    },

    #[error("recursion limit ({limit}) exceeded in {name}")]
    RecursionLimit {
        name: String,
        limit: usize,
        #[label("too many recursive calls")]
        span: Option<SourceSpan>,
    },
}

impl EvalError {
    pub fn undefined_var(name: String, span: Span) -> Self {
        Self::UndefinedVar {
            name,
            span: Some(span.into_source_span()),
        }
    }

    pub fn undefined_func(name: String, span: Span) -> Self {
        Self::UndefinedFunc {
            name,
            span: Some(span.into_source_span()),
        }
    }

    pub fn no_matching_arm(name: String, span: Span) -> Self {
        Self::NoMatchingArm {
            name,
            span: Some(span.into_source_span()),
        }
    }

    pub fn type_error(message: &'static str, span: Span) -> Self {
        Self::TypeError {
            message,
            span: Some(span.into_source_span()),
        }
    }

    pub fn divide_by_zero(span: Span) -> Self {
        Self::DivideByZero {
            span: Some(span.into_source_span()),
        }
    }

    pub fn overflow(span: Span) -> Self {
        Self::Overflow {
            span: Some(span.into_source_span()),
        }
    }

    pub fn recursion_limit(name: String, limit: usize, span: Span) -> Self {
        Self::RecursionLimit {
            name,
            limit,
            span: Some(span.into_source_span()),
        }
    }

    pub fn with_span(self, span: Span) -> Self {
        let span = Some(span.into_source_span());
        match self {
            EvalError::UndefinedVar { name, .. } => EvalError::UndefinedVar { name, span },
            EvalError::UndefinedFunc { name, .. } => EvalError::UndefinedFunc { name, span },
            EvalError::NoMatchingArm { name, .. } => EvalError::NoMatchingArm { name, span },
            EvalError::TypeError { message, .. } => EvalError::TypeError { message, span },
            EvalError::DivideByZero { .. } => EvalError::DivideByZero { span },
            EvalError::Overflow { .. } => EvalError::Overflow { span },
            EvalError::RecursionLimit { name, limit, .. } => {
                EvalError::RecursionLimit { name, limit, span }
            }
        }
    }
}

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

    fn span() -> Span {
        Span::new(1, 4)
    }

    #[test]
    fn with_span_overrides_span_for_all_variants() {
        let src = span().into_source_span();

        match EvalError::undefined_var("x".into(), Span::new(0, 1)).with_span(span()) {
            EvalError::UndefinedVar { span: Some(s), .. } => assert_eq!(s, src),
            _ => panic!("unexpected variant"),
        }

        match EvalError::undefined_func("f".into(), Span::new(0, 1)).with_span(span()) {
            EvalError::UndefinedFunc { span: Some(s), .. } => assert_eq!(s, src),
            _ => panic!("unexpected variant"),
        }

        match EvalError::no_matching_arm("f".into(), Span::new(0, 1)).with_span(span()) {
            EvalError::NoMatchingArm { span: Some(s), .. } => assert_eq!(s, src),
            _ => panic!("unexpected variant"),
        }

        match EvalError::type_error("bad", Span::new(0, 1)).with_span(span()) {
            EvalError::TypeError { span: Some(s), .. } => assert_eq!(s, src),
            _ => panic!("unexpected variant"),
        }

        match EvalError::divide_by_zero(Span::new(0, 1)).with_span(span()) {
            EvalError::DivideByZero { span: Some(s) } => assert_eq!(s, src),
            _ => panic!("unexpected variant"),
        }
    }
}