I've been working on improving the diagnostic registration system so that it can:
* Check uniqueness of error codes *across the whole compiler*. The current method using `errorck.py` is prone to failure as it relies on simple text search - I found that it breaks when referencing an error's ident within a string (e.g. `"See also E0303"`).
* Provide JSON output of error metadata, to eventually facilitate HTML output, as well as tracking of which errors need descriptions. The current schema is:
```
<error code>: {
"description": <long description>,
"use_site": {
"filename": <filename where error is used>,
"line": <line in file where error is used>
}
}
```
[Here's][metadata-dump] a pretty-printed sample dump for `librustc`.
One thing to note is that I had to move the diagnostics arrays out of the diagnostics modules. I really wanted to be able to capture error usage information, which only becomes available as a crate is compiled. Hence all invocations of `__build_diagnostics_array!` have been moved to the ends of their respective `lib.rs` files. I tried to avoid moving the array by making a plugin that expands to nothing but couldn't invoke it in item position and gave up on hackily generating a fake item. I also briefly considered using a lint, but it seemed like it would impossible to get access to the data stored in the thread-local storage.
The next step will be to generate a web page that lists each error with its rendered description and use site. Simple mapping and filtering of the metadata files also allows us to work out which error numbers are absent, which errors are unused and which need descriptions.
[metadata-dump]: https://gist.github.com/michaelsproul/3246846ff1bea71bd049
PR #24242 added the ability to the compiler to directly give suggestions about
how to modify code to fix an error. The new errors look like this:
foobar.rs:5:12: 5:25 error: expected a path on the left-hand side of `+`,
not `&'static Copy` [E0178]
foobar.rs:5 let x: &'static Copy + 'static;
^~~~~~~~~~~~~
foobar.rs:5:12: 5:35 help: try adding parentheses (per RFC 438):
foobar.rs: let x: &'static (Copy + 'static);
foobar.rs:2:13: 2:23 error: cast to unsized type: `&_` as `core::marker::Copy`
foobar.rs:2 let x = &1 as Copy;
^~~~~~~~~~
foobar.rs:2:19: 2:23 help: try casting to a reference instead:
foobar.rs: let x = &1 as &Copy;
foobar.rs:7:24: 7:25 error: expected expression, found `;`
foobar.rs:7 let x = box (1 + 1);
^
foobar.rs:7:13: 7:16 help: try using `box()` instead:
foobar.rs: let x = box() (1 + 1);
This also modifies compiletest to give the ability to directly test suggestions
given by error messages.
This commit removes the `IndexMut` impls on `HashMap` and `BTreeMap`, in
order to future-proof the API against the eventual inclusion of an
`IndexSet` trait.
Ideally, we would eventually be able to support:
```rust
map[owned_key] = val;
map[borrowed_key].mutating_method(arguments);
&mut map[borrowed_key];
```
but to keep the design space as unconstrained as possible, we do not
currently want to support `IndexMut`, in case some other strategy will
eventually be needed.
Code currently using mutating index notation can use `get_mut` instead.
[breaking-change]
Closes#23448
