Disallow methods from traits that are not in scope
This PR only allows a trait method to be used if the trait is in scope (fixes#31379).
This is a [breaking-change]. For example, the following would break:
```rust
mod foo {
pub trait T { fn f(&self) {} }
impl T for () {}
}
mod bar { pub use foo::T; }
fn main() {
pub use bar::*;
struct T; // This shadows the trait `T`,
().f() // making this an error.
}
```
r? @nikomatsakis
Scopes in mir
This PR adds scopes to MIR. There is a tree of scopes (each represented by a `ScopeId`). Every statement, variable, and terminator now has an associated scope and span. It also adds a `-Z dump-mir` switch one can use to conveniently examine the MIR as optimizations proceed.
The intention is two-fold. First, to support MIR debug-info. This PR does not attempt to modify trans to make use of the scope information, however.
Second, in a more temporary capacity, to support the goal of moving regionck and borowck into the MIR. To that end, the PR also constructs a "scope auxiliary" table storing the extent of each span (this is kept separate from the main MIR, since it contains node-ids) and the dom/post-dom of the region in the graph where the scope occurs. When we move to non-lexical lifetimes, I expect this auxiliary information to be discarded, but that is still some ways in the future (requires, at minimum, an RFC, and there are some thorny details to work out -- though I've got an in-progress draft).
Right now, I'm just dropping this auxiliary information after it is constructed. I was debating for some time whether to add some sort of sanity tests, but decided to just open this PR instead, because I couldn't figure out what such a test would look like (and we don't have independent tests for this today beyond the regionck and borrowck tests).
I'd prefer not to store the auxiliary data into any kind of "per-fn" map. Rather, I'd prefer that we do regionck/borrowck/whatever-else immediately after construction -- that is, we build the MIR for fn X and immediately thereafter do extended correctness checking on it. This will reduce peak memory usage and also ensure that the auxiliary data doesn't exist once optimizations begin. It also clarifies the transition point where static checks are complete and MIR can be more freely optimized.
cc @rust-lang/compiler @nagisa
Remove `ErasedRegions` from substs
This commit removes the `ErasedRegions` enum from `Substs`. Instead, in trans, we just generate a vector of `ReStatic` of suitable length. The goal is both general cleanup and to help pave the way for a glorious future where erasure is used in type check.
r? @eddyb
One concern: might be nice to do some profiling. Not sure the best way to do that. Perhaps I'll investigate running nrc's test suite locally.
This hack has long since outlived its usefulness; the transition to
trans passing around full substitutions is basically done. Instead of
`ErasedRegions`, just supply substitutions with a suitable number of
`'static` entries, and invoke `erase_regions` when needed (the latter of
which we already do).
Make warnings of renamed and removed lints themselves lints
This adds the `renamed_and_removed_lints` warning, defaulting
to the warning level.
Fixes#31141
while I'm at it, remove the "extra caching" that I was doing for no good
reason except laziness. Basically before I was caching at each scope in
the chain, but there's not really a reason to do that, since the cached
entry point at level N is always equal to the last cached exit point
from level N-1.
It's nice to be able to index with a scope-id,
but coherence rules prevent us from implementing
`Index<ScopeId>` for `Vec<ScopeAuxiliary>`, and I'd
prefer that `ScopeAuxiliary` remain in librustc_mir,
just for compilation time reasons.
This was triggered by me wanting to address a use of DUMMY_SP, but
actually I'm not sure what would be a better span -- I guess the span
for the function as a whole.
Docs: Change "statements" to "expressions" on `match`
I apt to use `expressions` over `statements`, because `match` is a expression in essence, though it can become a statement when followed a semicolon.
