Example
---
```rust
macro_rules! foo {
($($x:$0)*) => ();
}
```
**Completion items**:
```text
ba block
ba expr
ba expr_2021
ba ident
ba item
ba lifetime
ba literal
ba meta
ba pat
ba pat_param
ba path
ba stmt
ba tt
ba ty
ba vis
```
It sees them as regular impls; the details are abstracted. It's beautiful for the IDE layer, and less beautiful for `hir`, so this is a big change.
Some small differences still exist:
- We show builtin derives impl (to the IDE layer) as if they have had no generic parameters. It is possible to show the parameters, but that means also having to handle fake impls in `TypeParam` etc., and the benefit is questionable.
- Getting the fn *def* type of a method of a builtin derive impl is not supported, as there is no real `FunctionId`, therefore no `CallableDefId`. The trait method is returned instead. Note: getting the fn *ptr* type of the method is supported well.
- Builtin derive impls and their methods do not fully support `HasSource`, because, well, they have no source (at least, not in the form of `ast::Impl` and `ast::Fn`). To support them, we use the derive's `TextRange` where possible, and the trait method's source when not.
It's important to note that the def map still records the `MacroCallId`. I have doubts over this, as this means it's very easy to create the queries we don't want to create, but it does make things more convenient. In particular, a nicety of this setup is that even "Expand macro recursively" works (it creates the macro input/output query, but given that they will only be created when the user invokes the command, that does not seem to be a problem).
Example
---
```rust
fn main() {
let bar = Some(true);
bar.i$0
}
```
**Before this PR**
```rust
fn main() {
let bar = Some(true);
if let Some($1) = bar {
$0
}
}
```
**After this PR**
```rust
fn main() {
let bar = Some(true);
if let Some(${1:bar}) = bar {
$0
}
}
```
Basically, we switch to expanding cfg_attr in AST form, filter irrelevant attributes from the item tree, and move hir-def attributes (non-item-tree) to be flag-based.
The main motivation is memory usage, although this also simplifies the code, and fixes some bugs around handling of `cfg_attr`s.
- Discussed in https://github.com/rust-lang/rust-analyzer/issues/21107
- Avoids activating an `attributes` feature to crates that do not use it
- Updates the 6 crates that use attributes feature to specify it in
their Cargo.toml: {hir,hir-def,hir-ty,ide-assists,ide-db,project-model}
It cannot be exactly the same, because we have needs rustc doesn't have (namely, accurate enumeration of all methods, not just with a specific name, for completions etc., while rustc also needs a best-effort implementation for diagnostics) but it is closer than the previous impl.
In addition we rewrite the closely related handling of operator inference and impl collection.
This in turn necessitate changing some other parts of inference in order to retain behavior. As a result, the behavior more closely matches rustc and is also more correct.
This fixes 2 type mismatches on self (1 remains) and 4 diagnostics (1 remains), plus some unknown types.
Basically, we switch to expanding cfg_attr in AST form, filter irrelevant attributes from the item tree, and move hir-def attributes (non-item-tree) to be flag-based.
The main motivation is memory usage, although this also simplifies the code, and fixes some bugs around handling of `cfg_attr`s.
