Recently I've been pulling a lot of grammars into GitHub's highlighting backend,
replacing legacy language support with tree-sitter highlighting queries.
Our backend systems have a standard set of highlight captures we expect, very
similar to the standard tagging captures we expect. Though end-user applications
are free to choose whatever tagging nomenclature they want, I think it's nice to
include a checking stage that will help us ensure that we know whether a capture
might be recognized or not. It will also help us figure out where we need to
expand our standard set of captures (see #1539).
This patch updates the CLI to use anyhow and thiserror for error
management. The main feature that our custom `Error` type was providing
was a _list_ of messages, which would allow us to annotate "lower-level"
errors with more contextual information. This is exactly what's
provided by anyhow's `Context` trait.
(This is setup work for a future PR that will pull the `config` and
`loader` modules out into separate crates; by using `anyhow` we wouldn't
have to deal with a circular dependency between with the new crates.)
This lets you indicate, when matching a variable definition, that
another later syntax node represents the value of the variable definition,
and so any references to the same variable name within that value node
must be referring to some earlier definition.
Right now this is just used for two things:
* Specifying folders for locarting parsers to use with `tree-sitter
parse` and `tree-sitter highlight`
* Specifying colors to use for `tree-sitter-highlight`
When there are embedded documents, multiple scopes can start or
end at the same position. Previously, there was no guarantee that
the ScopeEnd events would always occur in the reverse order of the
ScopeStart events. The easiest way to avoid exposing inconsistency
is to not surface the scopes being ended.
