It should be considered by the edition of the caller, not the callee.
Technically we still don't do it correctly - we need the span of the method name (if it comes from a macro), but we don't keep it and this is good enough for now.
There are few things to note in the implementation:
First, this is a best-effort implementation. Mainly, type aliases may not be shown (due to their eager nature it's harder) and partial pathes (aka. hovering over `Struct` in `Struct::method`) are not supported at all.
Second, we only need to show substitutions in expression and pattern position, because in type position all generic arguments always have to be written explicitly.
We add union fields access (in both expressions and patterns) and inline assembly.
That completes the unsafe check (there are some other unsafe things but they are unstable), and so also opens the door to reporting unused unsafe without annoying people about their not-unused unsafe blocks.
So that given a `TypeRef` we will be able to trace it back to source code.
This is necessary to be able to provide diagnostics for lowering to chalk tys, since the input to that is `TypeRef`.
This means that `TypeRef`s now have an identity, which means storing them in arena and not interning them, which is an unfortunate (but necessary) loss but also a pretty massive change. Luckily, because of the separation layer we have for IDE and HIR, this change never crosses the IDE boundary.
Or macro_rules hygiene, or mixed site hygiene. In other words, hygiene for variables and labels but not items.
The realization that made me implement this was that while "full" hygiene (aka. def site hygiene) is really hard for us to implement, and will likely involve intrusive changes and performance losses, since every `Name` will have to carry hygiene, mixed site hygiene is very local: it applies only to bodies, and we very well can save it in a side map with minor losses.
This fixes one diagnostic in r-a that was about `izip!()` using hygiene (yay!) but it introduces a huge number of others, because of #18262. Up until now this issue wasn't a major problem because it only affected few cases, but with hygiene identifiers referred by macros like that are not resolved at all. The next commit will fix that.
And few more fixups.
I was worried this will lead to more memory usage since `ExprOrPatId` is double the size of `ExprId`, but this does not regress `analysis-stats .`. If this turns out to be a problem, we can easily use the high bit to encode this information.
Add public function for resolving callable AST exprs to their HIR equivalents
(the PR is motivated by an outside use of the `ra_ap_hir` crate that would benefit from being able to walk a `hir::Function`'s AST, resolving callable exprs within to their HIR equivalents)
