This commit refactors `SourceMap` and most importantly `RealFileName` to
make it self-contained in order to achieve cross-compiler consistency.
This is achieved:
- by making `RealFileName` immutable
- by only having `SourceMap::to_real_filename` create `RealFileName`
- by also making `RealFileName` holds it's working directory,
it's embeddable name and the remapped scopes
- by making most `FileName` and `RealFileName` methods take a scope as
an argument
In order for `SourceMap::to_real_filename` to know which scopes to apply
`FilePathMapping` now takes the current remapping scopes to apply, which
makes `FileNameDisplayPreference` and company useless and are removed.
The scopes type `RemapPathScopeComponents` was moved from
`rustc_session::config` to `rustc_span`.
The previous system for scoping the local/remapped filenames
`RemapFileNameExt::for_scope` is no longer useful as it's replaced by
methods on `FileName` and `RealFileName`.
This is useful when you have two dependencies that use different trait for
the same thing and with the same name. The user can accidentally implement
the bad one which might be confusing. This commits refactorizes existing
diagnostics about multiple different crates with the same version and adds
a note when similarly named traits are found. All diagnostics are merged
into a single one.
If a user does e.g.
impl From<Bar> for foo::Foo
and get a compilation error about that `From<Bar>` is not implemented
for `Foo`, check if multiple versions of the crate with `Foo` is present
in the dependency graph. If so, give a hint about it.
I encountered this case in the wild and didn't realize I had multiple
versions of a crate in my dependency graph. So I was a bit confused at
first. This fix will make life easier for others.
Urgau