Refactor and categorize lowering wrt. items / exprs
Split lowering into more files along the lines of "expression related" and "item related".
Also refactor huge methods into smaller ones.
A next step might be to introduce "type related" and merge patterns and statements combined with expressions into "value related". There's still more work to do but the PR was getting too big :)
r? @oli-obk
diagnostics: Describe crate root modules in `DefKind::Mod` as "crate"
Or we can use "extern crate" like resolve previously did sometimes, not sure.
r? @davidtwco
.gitignore: Readd `/tmp/`
Specifically, `/tmp/partitioning-tests/` it is generated by the incremental tests, https://github.com/rust-lang/rust/search?p=2&q=partitioning-tests&unscoped_q=partitioning-tests. These are cleaned up by compiletest but not if you kill testing prematurely (which I just did to test out a rollup, and it is annoying to `rm -rf tmp/`).
r? @Mark-Simulacrum
cc @RalfJung
Try to break resolve into more isolated parts
Some small step towards resolve librarification.
"Late resolution" is the pass that resolves most of names in a crate beside imports and macros.
It runs when the crate is fully expanded and its module structure is fully built.
So we just walk through the crate and resolve all the expressions, types, etc.
This pass is pretty self-contained, but it was previously done by implementing `Visitor` on the whole `Resolver` (which is used for many other tasks), and fields specific to this pass were indiscernible from the global `Resolver` state.
This PR moves the late resolution pass into a separate visitor and a separate file, fields specific to this visitor are moved from `Resolver` as well.
I'm especially happy about `current_module` being removed from `Resolver`.
It was used even for operations not related to visiting and changing the `current_module` position in process.
It was also used as an implicit argument for some functions used in this style
```rust
let orig_current_module = mem::replace(&mut self.current_module, module);
self.resolve_ident_somewhere();
self.current_module = orig_current_module;
```
and having effects on e.g. privacy checking somewhere deeply inside `resolve_ident_somewhere`.
Now we explicitly pass a `ParentScope` to those functions instead, which includes the module and some other data describing our position in the crate relatively to which we resolve names.
Rustdoc was one of the users of `current_module`, it set it for resolving intra-doc links.
Now it passes it explicitly as an argument as well (I also supported resolving paths from rustdoc in unnamed blocks as a drive-by fix).
Visibility resolution is also changed to use early resolution (which is correct because it's used during the work of `BuildReducedGraphVisitor`, i.e. integration of a new AST fragment into the existing partially built module structures.) instead of untimely late resolution (which worked only due to restrictions on paths in visibilities like inability to refer to anything except ancestor modules).
This slightly regresses its diagnostics because late resolution has a more systematic error detection and recovery currently.
Due to changes in `current_module` and visibilities `BuildReducedGraphVisitor` ended up almost as heavily affected by this refactoring as late resolution.
Fixes https://github.com/rust-lang/rust/issues/63223 (due to visibility resolution changes).
Adam