scarf_parser/

error.rs

// =======================================================================
// error.rs
// =======================================================================
//! Errors used in parsing

use crate::*;
use core::ops::Range;
use lexer::Token;
use scarf_syntax::*;
use std::fmt;
use std::fs;
use winnow::{
    error::{AddContext, ParserError},
    stream::Stream,
};

/// Something the parser expected to find instead of what was found,
/// in the case of an error
#[derive(Debug, Clone, PartialEq)]
pub enum Expectation<'s> {
    /// A particular lexed token
    Token(Token<'s>),
    /// A human-readable expectation
    Label(&'s str),
    /// The end of a file
    EOI,
}

/// A verbose error message describing the error location, what was
/// found, and what was expected instead
#[derive(Debug, Clone, PartialEq)]
pub struct VerboseError<'s> {
    /// The [`Span`] where the error occurred
    pub span: Span<'s>,
    /// What token was found (if any - [`None`] indicates the end of a file)
    pub found: Option<Token<'s>>,
    /// What was expected instead of what was found
    pub expected: Vec<Expectation<'s>>,
}

impl<'s> ParserError<Tokens<'s>> for VerboseError<'s> {
    type Inner = Self;
    fn from_input(input: &Tokens<'s>) -> Self {
        match input.peek_token() {
            Some(token) => VerboseError {
                span: token.1.clone(),
                found: Some(token.0),
                expected: vec![],
            },
            None => {
                // Use the last token instead, indicate EOF
                match input.previous_tokens().next() {
                    Some(token) => {
                        let mut curr_span: &Span = &token.1;
                        let root_file = loop {
                            if let Some(included_from_span) =
                                curr_span.included_from
                            {
                                curr_span = included_from_span;
                            } else {
                                break curr_span.file;
                            }
                        };
                        VerboseError {
                            span: Span {
                                file: root_file,
                                bytes: Range {
                                    start: token.1.bytes.end,
                                    end: token.1.bytes.end,
                                },
                                expanded_from: None,
                                included_from: None,
                            },
                            found: None,
                            expected: vec![],
                        }
                    }
                    None => {
                        // No tokens ever present in input - use defaults
                        VerboseError {
                            span: Span::default(),
                            found: None,
                            expected: vec![],
                        }
                    }
                }
            }
        }
    }
    fn into_inner(self) -> winnow::Result<Self::Inner, Self> {
        Ok(self)
    }
    fn or(mut self, mut other: Self) -> Self {
        // Prefer errors that got to the end of the input
        match (self.found, other.found) {
            (None, Some(_)) => self,
            (Some(_), None) => other,
            (None, None) => {
                self.expected.append(&mut other.expected);
                self
            }
            (Some(_), Some(_)) => {
                // Prefer the one with a later span (a.k.a. got farther)
                match self.span.compare(&other.span) {
                    SpanRelation::Later => self,
                    SpanRelation::Earlier => other,
                    SpanRelation::Same => {
                        self.expected.append(&mut other.expected);
                        self
                    }
                }
            }
        }
    }
}
impl<'s> AddContext<Tokens<'s>, Token<'s>> for VerboseError<'s> {
    fn add_context(
        mut self,
        _input: &Tokens<'s>,
        _token_start: &<Tokens<'s> as Stream>::Checkpoint,
        _context: Token<'s>,
    ) -> Self {
        self.expected.push(Expectation::Token(_context));
        self
    }
}
impl<'s> AddContext<Tokens<'s>, &'s str> for VerboseError<'s> {
    fn add_context(
        mut self,
        _input: &Tokens<'s>,
        _token_start: &<Tokens<'s> as Stream>::Checkpoint,
        _context: &'s str,
    ) -> Self {
        self.expected.push(Expectation::Label(_context));
        self
    }
}

fn format_expectation<'s>(pattern: &Expectation<'s>) -> String {
    match pattern {
        Expectation::Token(token) => token.to_string(),
        Expectation::Label(label) => label.to_string(),
        Expectation::EOI => "end of input".to_string(),
    }
}

fn format_reason<'s>(error: &VerboseError<'s>) -> String {
    let found_str = match error.found {
        Some(tok) => tok.to_string(),
        None => "end of input".to_owned(),
    };
    let mut dedup_expected: Vec<Expectation<'s>> = vec![];
    for expected in error.expected.iter() {
        if !dedup_expected.contains(expected) {
            dedup_expected.push(expected.clone());
        }
    }
    let expected_str = match &dedup_expected[..] {
        [] => "something else".to_owned(),
        [expected] => format_expectation(expected),
        _ => {
            let mut temp_expected_str = String::new();
            for expected in &dedup_expected[..dedup_expected.len() - 1] {
                temp_expected_str
                    .push_str(format_expectation(expected).as_str());
                temp_expected_str.push_str(", ");
            }
            temp_expected_str.push_str("or ");
            temp_expected_str.push_str(
                format_expectation(dedup_expected.last().unwrap()).as_str(),
            );
            temp_expected_str
        }
    };
    format!("found {}, expected {}", found_str, expected_str)
}

fn format_reason_short<'s>(error: &VerboseError<'s>) -> String {
    match error.found {
        Some(tok) => format!("Didn't expect {}", tok.to_string()),
        None => "Didn't expect end of input".to_owned(),
    }
}

impl<'s> VerboseError<'s> {
    /// Generate an error report for the [`VerboseError`]
    pub fn report<C>(
        &self,
        code: C,
    ) -> Report<'s, (String, std::ops::Range<usize>)>
    where
        C: fmt::Display,
    {
        let error_span = if self.found.is_none() {
            let file_len = fs::metadata(self.span.file)
                .expect("TODO: Handle file read error")
                .len();
            let byte_span = Range {
                start: file_len as usize,
                end: file_len as usize,
            };
            Span {
                file: self.span.file,
                bytes: byte_span,
                expanded_from: None,
                included_from: self.span.included_from,
            }
        } else {
            self.span.clone()
        };
        let mut report = Report::build(
            ReportKind::Error,
            (error_span.file.to_string(), error_span.bytes.clone()),
        )
        .with_code(code)
        .with_config(
            ariadne::Config::new().with_index_type(ariadne::IndexType::Byte),
        )
        .with_message(format_reason(&self));
        report = attach_span_label(
            &error_span,
            Color::Red,
            format_reason_short(&self),
            report,
        );
        report.finish()
    }
}

impl<'s> VerboseError<'s> {
    /// Similar to [`VerboseError::or`], but modifies an existing
    /// error instead of creating a new one
    pub(crate) fn or_in_place(&mut self, mut other: Self) {
        // Prefer errors that got to the end of the input
        match (self.found, other.found) {
            (None, Some(_)) => (),
            (Some(_), None) => *self = other,
            (None, None) => {
                self.expected.append(&mut other.expected);
            }
            (Some(_), Some(_)) => {
                // Prefer the one with a later span (a.k.a. got farther)
                match self.span.compare(&other.span) {
                    SpanRelation::Later => (),
                    SpanRelation::Earlier => *self = other,
                    SpanRelation::Same => {
                        self.expected.append(&mut other.expected);
                    }
                }
            }
        }
    }
}