There's currently a bug with empty files, in that it initializes SourceBuffer with an invalid StringRef that results in a crash. That got me looking at the std::optional TODO, but the issue is that there are really three states:
- Buffered
- mmapped (not buffered)
- Moved out of (no longer initialized)
Technically an optional could work if we initialize the buffer on move out, indicating the mmap is gone. But the mode setup felt better to me.
And then this also adds the size check. Which is really how I started looking at this.
The small size is for the 1m vs 5m time limit -- all these tests _should_ be fast so a lower limit seems consistent, and the 5m timeout was getting in my way when trying to debug *actual* timeouts.
The Carbon::Testing bit is for convenience -- test libraries are generally using it, it seems like the tests should too. Note this reduces the need for `using`.
This does push NodeMatchers into Carbon::Testing -- I don't think this was benefiting from having its own namespace; `using namespace` is discouraged [under style](https://google.github.io/styleguide/cppguide.html#Namespaces), we wouldn't support an equivalent in Carbon, and it feels like it's not helping to avoid name collisions. (also tidy was bugging about it, and while I could NOLINT that, this felt like the better approach)
This should clean up our top level directory and the build patterns.
No non-mechanical edits here. Just injecting `toolchain/` and
`TOOLCHAIN_` and then running formatting tools.
Jon Meow
