When going from the plain rowan::SyntaxNode tree to the syntax_nodes::*
elements, attach the source file and keep track of it from that point
on. That'll pave the way for proper multi-file diagnostics generated
later on from the passes, where we store syntax_nodes::* types.
Let the bulk of the push_error() calls take a Spanned trait impl, so
that we can pass node on the call sites. Then when later change the
underyling trait to pass something that can also provide the source file
and we don't have to change all call sites again.
Remove the need for PartialEq for the Diagnostics. The objective is to
introduce an enum here in the future
that may hold types that do not support
PartialEq. It turns out that we don't really need it though.
Taking &mut self makes more sense when wanting to populate from a list.
Also we should return a list of diagnostics for each file that we loaded
or an error if we couldn't load the file (for example due to permission
problems, etc.).
This way the caller can choose to show diagnostics, ignore them, etc.
Don't require the callers to hold on to the source code string until an
eventual diagnostics code path is hit. Instead it turns out it's
simpler to let the parser consume the source code as string, where
internally after tokenizing it can be moved into the diagnostics and
from there into the code map if needed.
There are a few places where we now clone the source code, but that's
only in cases where we also extract stuff separately (test code) or the
syntax updater.
Provide a ToTokens implementation of Diagnostics by moving the code from the macro.
This makes it easier later to re-use the same logic to return
with diagnostics.
