Here I'm trying to add some simple formatting based on the token kind,
aiming mainly to keep the implementation short for now.
This approach won't generalize to arbitrary structures (e.g., it doesn't
discern between braces for a function body and a struct literal). I
think we'll probably want to build a parse tree and associate parse
kinds with tokens in order to format, additionally doing something less
linear. But my essential goal at present is to just get a
proof-of-concept that the basics can yield something that looks okay.
In order to format comments, it's helpful if they're tracked. This
tracks them separately from tokens in order to avoid interfering with
parse; it'd be inconvenient if comment tokens could show up in arbitrary
locations, albeit possible to support.
This additionally extracts out the TokenIterator support into a template
in order to generally have it available for IndexBase types. I'm only
adding it for CommentInfo, not sure if we'll want it elsewhere, but this
structure still felt like a good fit.
This extracts out the SourceBuffer handling of `-` in order to trivially
share it.
Note this still has a number of TODOs, it's just setting up the
essential subcommand infrastructure, with some tests demonstrating that
it at least does something.
Jon Ross-Perkins