feat: Diagnose some incorrect usages of the question mark operator
Trying to figure out how the type stuff in r-a works some more, I think I am doing this correct here but I am not quite sure :)
Two breaking changes:
- `TypeFolder` has been split into `TypeFolder` and `FallibleTypeFolder`
- `ProjectionTy::self_type_parameter()` has been removed
This hir expression isn't needed and only existed as it was simpler to
deal with at first as it gave us a direct mapping for the ast version of
the same construct. This PR removes it, properly handling the statements
that are introduced by macro call expressions.
feat: implement destructuring assignment
This is an attempt to implement destructuring assignments, or more specifically, type inference for [assignee expressions](https://doc.rust-lang.org/reference/expressions.html#place-expressions-and-value-expressions).
I'm not sure if this is the right approach, so I don't even expect this to be merged (hence the branch name 😉) but rather want to propose one direction we could choose. I don't mind getting merged if this is good enough though!
Some notes on the implementation choices:
- Assignee expressions are **not** desugared on HIR level unlike rustc, but are inferred directly along with other expressions. This matches the processing of other syntaxes that are desugared in rustc but not in r-a. I find this reasonable because r-a only needs to infer types and it's easier to relate AST nodes and HIR nodes, so I followed it.
- Assignee expressions obviously resemble patterns, so type inference for each kind of pattern and its corresponding assignee expressions share a significant amount of logic. I tried to reuse the type inference functions for patterns by introducing `PatLike` trait which generalizes assignee expressions and patterns.
- This is not the most elegant solution I suspect (and I really don't like the name of the trait!), but it's cleaner and the change is smaller than other ways I experimented, like making the functions generic without such trait, or making them take `Either<ExprId, PatId>` in place of `PatId`.
in case this is merged:
Closes#11532Closes#11839Closes#12322
