Get the `ItemId` based on a given ast-path about marker HOT 2 CLOSED

I'll start looking into this issue slowly. For reference, Clippy has clippy_utils::def_path_res. The documentation notes, that a path like std::vec could resolve to the module and macro which is a good thing to keep in mind. I'm considering, if it might be good to restrict the resolve function to TyDefIds, as that should be the main usage of it anyways.

Further things found during research:

• https://github.com/rust-lang/rust/blob/e9dd59131bc02986ec17f88307e1b0ae252dc5ad/compiler/rustc_ast_lowering/src/path.rs
• https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/ty/context/struct.TyCtxt.html#method.def_path_str
• https://doc.rust-lang.org/nightly/nightly-rustc/rustc_metadata/rmeta/decoder/struct.CrateMetadata.html
• https://rustc-dev-guide.rust-lang.org/name-resolution.html
• https://doc.rust-lang.org/nightly/nightly-rustc/rustc_resolve/late/index.html
• https://doc.rust-lang.org/nightly/nightly-rustc/rustc_resolve/struct.Resolver.html#method.resolve_path
  • https://github.com/rust-lang/rust/blob/7690fe3bc66cae219301368650317936f0d4e3a9/compiler/rustc_resolve/src/ident.rs#L1278

Notes about special cases, for extra fun:

• Crates can depend on the same crate with different versions multiple times if they rename the dependency. The name resolution will need to handle this correctly... This will be fun....
• Symbols can life in different Namespaces. This might be a problem for types, const/static variables and macros. I hope that they're all in the same namespace, but we have to test for that at some point. See Namespaces

from marker.

I'm sadly still stuck on this issue. It seems like rustc does all path resolution at once in an AST-pass. It makes sense for rustc not to expose a simple way to resolve paths outside of that, as additional usages would be a "code smell". However, this doesn't make it easy for external tools like Clippy and Marker. I see 4 ways to solve this and will need some more time to decide:

1. Create a PR allowing external tools to use rustc's path resolution. Here IDK, which method would be enough to expose and also how to create the state the solver would need
2. Use Clippy's manual path resolution
3. Write a manual path resolution for Marker, similar to Clippy's
4. Magically find a way to resolve paths with rustc that I've overlooked so far.

from marker.