Lib.rs

Representation of an error in the Lark compiler.

For more information, see the main readme and internals doc.

lib.rs:

Types for tracking errors through queries.

Here is how it works:

• Queries that can themselves report errors return WithError<T>; the errors contained in that value were discovered during executing that query.
• If another query uses the result of a query that returns WithError, it can just use into_value to ignore the errors -- WithError always includes some form of sentinel value that you can use (i.e., you can just ignore the errors and try to get on with life).
• In the worst case, one can you Result<T, ErrorReported> and have Err(ErrorReported) act as a sentintel value for "failed to produce a value because of some error". This is not preferred because now downstream queries have to care whether you propagated an error or not, but sometimes it's the best/easiest thing to do.
  • To help with this, the or_sentinel! query acts as a kind of ? operator for bridging a Result<T, ErrorReported> into a U where U has a proper sentinel -- if the result is Err(ErrorReported), it creates the error-sentinel for U and returns it.
  • This relies on the ErrorSentinel trait, which defines the error-sentinel for a given type.

This scheme is not the most ergonomic and I would like to change it, but it will do for now. -nikomatsakis