Pretty printing of errors

[magicant]

• We want to pretty-format error messages by using https://github.com/rust-lang/annotate-snippets-rs.
• Yash error types (such as yash_syntax::parser::Error and yash_semantics::expansion::Error) should be convertible to annotate_snippets::snippet::Snippet via the From trait.
  • Pretty formatting of syntax error #83 Pretty formatting of syntax error #84 Move some error locations #85
  • 9f04592
  • ❔ Do we need some common functions for implementing the conversions? If so, where should they reside?
• annotate-snippets-rs supports formatting multi-line source code, but currently yash_syntax::source::Location is line-oriented.
  • What should the items in yash_syntax::source be like? → See Multi-line source code attribution #128 Multi-line source code attribution #129 Multi-line source code attribution #130
• annotate-snippets-rs supports annotating a range of characters, but currently yash_syntax::source::Location only points to a single character in the source code.
  • What should the items in yash_syntax::source be like? → Replace some Locations with Spans #135 Replace Location::index with range #136
• Color the error message if and only if the standard error is a terminal
• Show the built-in name when printing a message for a built-in error

[magicant]

Considering a new intermediate structure that can be converted to annotate_snippets::snippet::Snippet. It would be more organized and versatile than directly constructing a Snippet from an Error. It would also help owning message strings that are referenced from the Snippet.

pub struct Message {
    r#type: AnnotationType,
    title: String, // or Cow<'_, str>
    annotations: Vec<Annotation>,
}
pub struct Annotation {
    r#type: AnnotationType,
    label: String, // or Cow<'_, str>
    location: Location,
}

[magicant]

For multi-line code, the Line should be modified to:

pub struct Code {
    value: RefCell<String>,
    start_line_number: NonZeroU64,
    source: Source,
}

1. Rename the structure
2. Rename Location::line to Location::code
3. Wrap the value in RefCell
4. Rename number to start_line_number
5. Define methods to access the fields
6. Define methods to append to the value
7. Make the structure fields private
8. Share the Code between all the lines of code
   • Modify the lexer
   • Modify or remove the Lines iterator

(Update: This does not fully work. See #129)

---

For location ranges, the Location should be modified to:

pub struct Location {
    range: (usize, usize),
    code: Rc<Code>,

1. Change column: NonZeroU64 to range: (usize, usize)
2. Produce locations having the correct range in token parser