lini 0.7.2

Pretty diagrams from plain text, with fine-grained control. Compiles to clean, themeable SVG.
Documentation 
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use crate::span::{Span, line_col};
use std::fmt;

#[derive(Debug)]
pub struct Error {
    pub message: String,
    pub span: Span,
    /// A secondary span rendered inline as `(previously at L:C)` — used for
    /// duplicate-definition diagnostics (SPEC §16). Only shown with source.
    pub related: Option<Span>,
}

impl Error {
    pub fn at(span: Span, message: impl Into<String>) -> Self {
        Self {
            message: message.into(),
            span,
            related: None,
        }
    }

    /// Attach the span of a prior definition, shown as `(previously at L:C)`.
    pub fn with_related(mut self, span: Span) -> Self {
        self.related = Some(span);
        self
    }

    pub fn display_with_source<'a>(
        &'a self,
        source: &'a str,
        filename: &'a str,
    ) -> ErrorDisplay<'a> {
        ErrorDisplay {
            err: self,
            source,
            filename,
        }
    }
}

impl fmt::Display for Error {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "error: {}", self.message)
    }
}

impl std::error::Error for Error {}

pub struct ErrorDisplay<'a> {
    err: &'a Error,
    source: &'a str,
    filename: &'a str,
}

impl<'a> fmt::Display for ErrorDisplay<'a> {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        let (line, col) = line_col(self.source, self.err.span.start);
        write!(
            f,
            "{}:{}:{}: error: {}",
            self.filename, line, col, self.err.message
        )?;
        if let Some(related) = self.err.related {
            let (rl, rc) = line_col(self.source, related.start);
            write!(f, " (previously at {}:{})", rl, rc)?;
        }
        Ok(())
    }
}

#[derive(Debug, Clone)]
pub struct Diagnostic {
    pub level: Level,
    pub message: String,
    pub span: Span,
}

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum Level {
    Warning,
}

impl Diagnostic {
    pub fn warn(span: Span, message: impl Into<String>) -> Self {
        Self {
            level: Level::Warning,
            message: message.into(),
            span,
        }
    }

    pub fn display_with_source<'a>(
        &'a self,
        source: &'a str,
        filename: &'a str,
    ) -> DiagnosticDisplay<'a> {
        DiagnosticDisplay {
            diag: self,
            source,
            filename,
        }
    }
}

pub struct DiagnosticDisplay<'a> {
    diag: &'a Diagnostic,
    source: &'a str,
    filename: &'a str,
}

impl<'a> fmt::Display for DiagnosticDisplay<'a> {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        let (line, col) = line_col(self.source, self.diag.span.start);
        let kind = match self.diag.level {
            Level::Warning => "warning",
        };
        write!(
            f,
            "{}:{}:{}: {}: {}",
            self.filename, line, col, kind, self.diag.message
        )
    }
}