Using a different partitoning in base_db::input::SourceRoot

[alibektas]

👋 I have been working on #13529 and (indirectly) on #15741 ( as a matter of fact there should have been a "toml support for rust-analyzer issue". In order for both of these features to be implemented there needs to be a map ( and its inv. ) that maps SourceFiles ( so essentially a FileId ) to its corresponding (most of the time the closest) Cargo.toml/RA.toml file. I believe that this should be handled when we get to partition a Vfs into SourceRoots. Based on my poor observation we partition with the intention to group as many files as possible into the same FileSet. I want to change that in such a way that Cargo.toml/RATOML files are used as anchors to a SourceRoot , meaning that if you encounter , say , a Cargo.toml you would know that this is a new SourceRoot. This change would enable me to map a FileId to the FileId of its corresponding SourceRoot, as in

srid = SourceDatabaseExt::file_source_root(db, file_id)
sr = SourceDatabaseExt::source_root(db, srid)
cargo_file_id = sr.cargo_toml_id()  // Option<FileId>

I cannot see any other way of doing this so I wanted to get community's opinion on this.

[Veykril]

Can't you just store the FileId of the cargo.toml inside the SourceRoot? That aside, why do you need such a mapping?

[alibektas]

Can't you just store the FileId of the cargo.toml inside the SourceRoot

That is what I am exactly trying to do. But the problem is that the current partition does not guarantee that there will be one or many Cargo.tomls in a SourceRoot. I want this to be limited to at most one

That aside, why do you need such a mapping?

Because when we introduce multiple rust-analyzer.toml files to be used to configure different parts of a project I always need to be able to ask what the nearest configuration file that applies to a certain FileId is.

[Veykril]

Can't you just store the FileId of the cargo.toml inside the SourceRoot?

Answer is yes after some discussion in DMs