So that consumers don't unintentionally encode the fact that a
constant id is actually 1 + its index in the constants table.
Ideally this makes it so that we can change the underlying
implementation if we want to.
https://github.com/ruby/prism/commit/3a7f3cb6d5
CRuby is now hashing the contents of a file and attaching that to
iseqs in order to properly determine if a file has changed since
it was compiled. This is used in a couple places, but namely it is
used for error_highlight to make sure it isn't highlighting stale
locations.
The hashing algorithm doesn't actually matter since it's just used
to compare across parses, so as long as it is consistent it's okay.
I wanted something fast and standard, so this commit implements the
XXH3_64 algorithm from the spec. Noteably it uses the default
secret and a seed of 0 to make things even simpler. With NEON and
SSE2 implementations, this thing flies quite a bit faster than the
upstream FNV-1a implementation.
I figured this could be useful for other consumers as well, in
particular for tools that generate some kind of metadata around
files (type checkers, linters, etc). Eventually a nice extension
may be to hash a minimal version of the contents (i.e., with
context-insensitive whitespace removed) so that changes to docs or
indentation do not change the hash value.
If you're using the C API, you are only charged for this function
if you actually call it since it is computed lazily. For everyone
else it is automatically called, but truthfully it is so fast that
the difference is completely negligible.
https://github.com/ruby/prism/commit/6b7c5773eb
Kevin Newton