https://github.com/ruby/prism/commit/6e69a81737

https://github.com/ruby/prism/commit/5f70b32b02

A lot of tools use Ripper/RubyVM::AbstractSyntaxTree to determine
if a source is valid. These tools both create an AST instead of
providing an API that will return a boolean only.

This new API only creates the C structs, but doesn't bother
reifying them into Ruby/the serialization API. Instead it only
returns true/false, which is significantly more efficient.

https://github.com/ruby/prism/commit/7014740118

https://github.com/ruby/prism/commit/e148e8fe6a

Previously numbered parameters were a field on blocks and lambdas
that indicated the maximum number of numbered parameters in either
the block or lambda, respectively. However they also had a
parameters field that would always be nil in these cases.

This changes it so that we introduce a NumberedParametersNode that
goes in place of parameters, which has a single uint8_t maximum
field on it. That field contains the maximum numbered parameter in
either the block or lambda.

As a part of the PR, I'm introducing a new UInt8Field type that
can be used on nodes, which is just to make it a little more
explicit what the maximum values can be (the maximum is actually 9,
since it only goes up to _9). Plus we can do a couple of nice
things in serialization like just read a single byte.

https://github.com/ruby/prism/commit/2d87303903

The problem was deeper than just looking back a single token.
You can push the heredoc_end token way back into the list.
We need to save the last location of a heredoc end to see if
it's the last token in the file.

Fixes https://github.com/ruby/prism/pull/1954

https://github.com/ruby/prism/commit/91dfd4eecd