Group labels originating from the same file into a single snippet

[brendanzab]

As mentioned in #77, Rustc does a clever job of grouping together labels:

It would be super neat if we could do something similar!

At the moment our diagnostics are all spread out:

error[E0308]: `case` clauses have incompatible types

   ┌── FizzBuzz.fun:8:12 ───
   │
 8 │     _ _ => num
   │            ^^^ expected `String`, found `Nat`
   │
   = expected type `String`
        found type `Nat`

   ┌── FizzBuzz.fun:4:13 ───
   │
 4 │   fizz₁ num = case (mod num 5) (mod num 3) of
   │ ╭─────────────'
 5 │ │     0 0 => "FizzBuzz"
 6 │ │     0 _ => "Fizz"
 7 │ │     _ 0 => "Buzz"
 8 │ │     _ _ => num
   │ ╰──────────────' `case` clauses have incompatible types
   │

   ┌── FizzBuzz.fun:3:15 ───
   │
 3 │ fizz₁ : Nat → String
   │               ------ expected type `String` found here
   │

It would be great if we could collapse things down, for example:

error[E0308]: `case` clauses have incompatible types

   ┌── FizzBuzz.fun:8:12 ───
   │
 3 │   fizz₁ : Nat → String
   │                 ------ expected type `String` found here
 4 │   fizz₁ num = case (mod num 5) (mod num 3) of
   │ ╭─────────────'
 5 │ │     0 0 => "FizzBuzz"
 6 │ │     0 _ => "Fizz"
 7 │ │     _ 0 => "Buzz"
 8 │ │     _ _ => num
   │ │            ^^^ expected `String`, found `Nat`
   │ ╰──────────────' `case` clauses have incompatible types
   │
   = expected type `String`
        found type `Nat`

Or in the case of that rustc error:

error[E0308]: match arms have incompatible types

    ┌─ codespan/src/file.rs:102:34
    :
99  │  ╭──────── match line_index.compare(self.last_line_index()) {
100 │  │             Ordering::Less => Ok(self.line_starts()[line_index.to_usize()]),
    │  │                               --------------------------------------------- this is found to be of type `std::result::Result<index::ByteIndex, file::LineIndexOutOfBoundsError>`
101 │  │             Ordering::Equal => Ok(self.source_span().end()),
    │  │                                ---------------------------- this is found to be of type `std::result::Result<index::ByteIndex, file::LineIndexOutOfBoundsError>`
102 │  │             Ordering::Greater => LineIndexOutOfBoundsError {
    │ ╭│──────────────────────────────────^
103 │ ││                 given: line_index,
104 │ ││                 max: self.last_line_index(),
105 │ ││             },
    │ ╰│─────────────^ expected enum `std::result::Result`, found struct `file::LineIndexOutOfBoundsError`
106 │  │         }
    │  ╰─────────' `match` arms have incompatible types
    :
    = note: expected type `std::result::Result<index::ByteIndex, file::LineIndexOutOfBoundsError>`
               found type `file::LineIndexOutOfBoundsError`

It might be worth studying how librustc_errors does this. There's a bunch of clever logic in emitter.rs that it might be worth understanding.

[brendanzab]

This seems like it could be a helpful library: https://crates.io/crates/nested_intervals - or at least thinking about this stuff in terms of interval sets... 🤔

[brendanzab]

Making progress on this on my overlapping-maks branch:

error[E0308]: match arms have incompatible types

   ┌── codespan/src/file.rs:1:9 ───
   │
 1 │ ╭         match line_index.compare(self.last_line_index()) {
 2 │ │             Ordering::Less => Ok(self.line_starts()[line_index.to_usize()]),
   │ │                               --------------------------------------------- this is found to be of type `Result<ByteIndex, LineIndexOutOfBoundsError>`
 3 │ │             Ordering::Equal => Ok(self.source_span().end()),
   │ │                                ---------------------------- this is found to be of type `Result<ByteIndex, LineIndexOutOfBoundsError>`
 4 │   │             Ordering::Greater => LineIndexOutOfBoundsError {
   │ ╭─│──────────────────────────────────^
 5 │ │ │                 given: line_index,
 6 │ │ │                 max: self.last_line_index(),
 7 │ │ │             },
   │ ╰─│─────────────^ expected enum `Result`, found struct `LineIndexOutOfBoundsError`
 8 │ │         }
   │ ╰─────────' `match` arms have incompatible types
   │
   = expected type `Result<ByteIndex, LineIndexOutOfBoundsError>`
        found type `LineIndexOutOfBoundsError`