On demandify region mapping
This is an adaptation of @cramertj's PR. I am sort of tempted to keep simplifying it, but also tempted to land it so and we can refactor more in follow-up PRs. As is, it does the following things:
- makes the region-maps an on-demand query, per function `tcx.region_maps(def_id)`
- interns code extents instead of of having them be integers
- remove the "root region extent" and (to some extent) item extents; instead we use `Option<CodeExtent<'tcx>>` in a few places (no space inefficiency since `CodeExtent<'tcx>` is now a pointer).
I'm not entirely happy with the way I have it setup though. Here are some of the changes I was considering (I'm not sure if they would work out well):
1. Removing `item_extents` entirely -- they are rarely used now, because most of the relevant places now accept an `Option<Region<'tcx>>` or an `Option<CodeExtent<'tcx>>`, but I think still used in a few places.
2. Merging `RegionMaps` into the typeck tables, instead of having it be its own query.
3. Change `CodeExtent<'tcx>` to store the parent pointer. This would mean that fewer places in the code actually *need* a `RegionMaps` anyhow, since most of them just want to be able to walk "up the tree". On the other hand, you wouldn't be able to intern a `CodeExtent<'tcx>` for some random node-id, you'd need to look it up in the table (since there'd be more information).
Most of this code is semi-temporary -- I expect it to largely go away as we move to NLL -- so I'm also not *that* concerned with making it perfect.
r? @eddyb
The data can't be looked up from the region variable directly, because
the region variable might have been destroyed at the end of a snapshot.
Fixes#40000.
Fixes#40743.
rustdoc: link to cross-crate sources directly.
Fixes#37684 by implementing proper support for getting the `Span` of definitions across crates.
In rustdoc this is used to generate direct links to the original source instead of fragile redirects.
This functionality could be expanded further for making error reporting code more uniform and seamless across crates, although at the moment there is no actual source to print, only file/line/column information.
Closes#37870 which is also "fixes" #37684 by throwing away the builtin macro docs from libcore.
After this lands, #37727 could be reverted, although it doesn't matter much either way.
When a type parameter shadows a primitive type, the error message
was non obvious. For example, given the file `file.rs`:
```rust
trait Parser<T> {
fn parse(text: &str) -> Option<T>;
}
impl<bool> Parser<bool> for bool {
fn parse(text: &str) -> Option<bool> {
Some(true)
}
}
fn main() {
println!("{}", bool::parse("ok").unwrap_or(false));
}
```
The output was:
```bash
% rustc file.rs
error[E0308]: mismatched types
--> file.rs:7:14
|
7 | Some(true)
| ^^^^ expected type parameter, found bool
|
= note: expected type `bool`
= note: found type `bool`
error: aborting due to previous error
```
We now show extra information about the type:
```bash
% rustc file.rs
error[E0308]: mismatched types
--> file.rs:7:14
|
7 | Some(true)
| ^^^^ expected type parameter, found bool
|
= note: expected type `bool` (type parameter)
= note: found type `bool` (bool)
error: aborting due to previous error
```
Fixes#35030
