Revert lazy TAIT PR #93893
Revert lazy TAIT PR #93893
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Some changes occurred in src/tools/clippy. cc @rust-lang/clippy |
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@bors r+ p=1 fixes lots recent stable to nightly regressions |
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📌 Commit d54195d has been approved by |
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⌛ Testing commit d54195d with merge 5ed0a0ad14a648aa93b3d8a18cd0b9b91d32cfca... |
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i admit i dont know anything about rust internals, |
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💥 Test timed out |
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☀️ Test successful - checks-actions |
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Finished benchmarking commit (6499c5e): comparison url. Summary: This benchmark run shows 24 relevant improvements 🎉 but 12 relevant regressions 😿 to instruction counts.
If you disagree with this performance assessment, please file an issue in rust-lang/rustc-perf. Next Steps: If you can justify the regressions found in this perf run, please indicate this with @rustbot label: +perf-regression |
…t#92007)" This reverts commit 06c8426, reversing changes made to 68630fb. The fix at rustc has been reverted in rust-lang/rust#93893 due to other problems
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We had to revert the TAIT PR, the fallout from it was too high. @rustbot label: +perf-regression-triaged |
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Revert lazy TAIT PR Revert rust-lang#92306 (sorry `@Aaron1011,` will include your changes in the fix PR) Revert rust-lang#93783 Revert rust-lang#92007 fixes rust-lang#93788 fixes rust-lang#93794 fixes rust-lang#93821 fixes rust-lang#93831 fixes rust-lang#93841
…sakis
Lazy type-alias-impl-trait take two
### user visible change 1: RPIT inference from recursive call sites
Lazy TAIT has an insta-stable change. The following snippet now compiles, because opaque types can now have their hidden type set from wherever the opaque type is mentioned.
```rust
fn bar(b: bool) -> impl std::fmt::Debug {
if b {
return 42
}
let x: u32 = bar(false); // this errors on stable
99
}
```
The return type of `bar` stays opaque, you can't do `bar(false) + 42`, you need to actually mention the hidden type.
### user visible change 2: divergence between RPIT and TAIT in return statements
Note that `return` statements and the trailing return expression are special with RPIT (but not TAIT). So
```rust
#![feature(type_alias_impl_trait)]
type Foo = impl std::fmt::Debug;
fn foo(b: bool) -> Foo {
if b {
return vec![42];
}
std::iter::empty().collect() //~ ERROR `Foo` cannot be built from an iterator
}
fn bar(b: bool) -> impl std::fmt::Debug {
if b {
return vec![42]
}
std::iter::empty().collect() // Works, magic (accidentally stabilized, not intended)
}
```
But when we are working with the return value of a recursive call, the behavior of RPIT and TAIT is the same:
```rust
type Foo = impl std::fmt::Debug;
fn foo(b: bool) -> Foo {
if b {
return vec![];
}
let mut x = foo(false);
x = std::iter::empty().collect(); //~ ERROR `Foo` cannot be built from an iterator
vec![]
}
fn bar(b: bool) -> impl std::fmt::Debug {
if b {
return vec![];
}
let mut x = bar(false);
x = std::iter::empty().collect(); //~ ERROR `impl Debug` cannot be built from an iterator
vec![]
}
```
### user visible change 3: TAIT does not merge types across branches
In contrast to RPIT, TAIT does not merge types across branches, so the following does not compile.
```rust
type Foo = impl std::fmt::Debug;
fn foo(b: bool) -> Foo {
if b {
vec![42_i32]
} else {
std::iter::empty().collect()
//~^ ERROR `Foo` cannot be built from an iterator over elements of type `_`
}
}
```
It is easy to support, but we should make an explicit decision to include the additional complexity in the implementation (it's not much, see a721052457cf513487fb4266e3ade65c29b272d2 which needs to be reverted to enable this).
### PR formalities
previous attempt: rust-lang#92007
This PR also includes rust-lang#92306 and rust-lang#93783, as they were reverted along with rust-lang#92007 in rust-lang#93893
fixes rust-lang#93411
fixes rust-lang#88236
fixes rust-lang#89312
fixes rust-lang#87340
fixes rust-lang#86800
fixes rust-lang#86719
fixes rust-lang#84073
fixes rust-lang#83919
fixes rust-lang#82139
fixes rust-lang#77987
fixes rust-lang#74282
fixes rust-lang#67830
fixes rust-lang#62742
fixes rust-lang#54895
10 participants
Revert #92306 (sorry @Aaron1011, will include your changes in the fix PR)
Revert #93783
Revert #92007
fixes #93788
fixes #93794
fixes #93821
fixes #93831
fixes #93841