Revise never type fallback algorithm
This is a rebase of https://github.com/rust-lang/rust/pull/84573, but dropping the stabilization of never type (and the accompanying large test diff).
Each commit builds & has tests updated alongside it, and could be reviewed in a more or less standalone fashion. But it may make more sense to review the PR as a whole, I'm not sure. It should be noted that tests being updated isn't really a good indicator of final behavior -- never_type_fallback is not enabled by default in this PR, so we can't really see the full effects of the commits here.
This combines the work by Niko, which is [documented in this gist](https://gist.github.com/nikomatsakis/7a07b265dc12f5c3b3bd0422018fa660), with some additional rules largely derived to target specific known patterns that regress with the algorithm solely derived by Niko. We build these from an intuition that:
* In general, fallback to `()` is *sound* in all cases
* But, in general, we *prefer* fallback to `!` as it accepts more code, particularly that written to intentionally use `!` (e.g., Result's with a Infallible/! variant).
When evaluating Niko's proposed algorithm, we find that there are certain cases where fallback to `!` leads to compilation failures in real-world code, and fallback to `()` fixes those errors. In order to allow for stabilization, we need to fix a good portion of these patterns.
The final rule set this PR proposes is that, by default, we fallback from `?T` to `!`, with the following exceptions:
1. `?T: Foo` and `Bar::Baz = ?T` and `(): Foo`, then fallback to `()`
2. Per [Niko's algorithm](https://gist.github.com/nikomatsakis/7a07b265dc12f5c3b3bd0422018fa660#proposal-fallback-chooses-between--and--based-on-the-coercion-graph), the "live" `?T` also fallback to `()`.
The first rule is necessary to address a fairly common pattern which boils down to something like the snippet below. Without rule 1, we do not see the closure's return type as needing a () fallback, which leads to compilation failure.
```rust
#![feature(never_type_fallback)]
trait Bar { }
impl Bar for () { }
impl Bar for u32 { }
fn foo<R: Bar>(_: impl Fn() -> R) {}
fn main() {
foo(|| panic!());
}
```
r? `@jackh726`
Lazy TAIT preparation cleanups
Check that TAIT generics are fully generic in mir typeck instead of wf-check, as wf-check can by definition only check TAIT in return position and not account for TAITs defined in the body of the function
r? `@spastorino` `@nikomatsakis`
fix non_blanket_impls iteration order
We sometimes iterate over all `non_blanket_impls`, not sure if this is observable outside
of error messages (i.e. as incremental bugs). This should fix the underlying issue of #86986.
second attempt of #88718
r? `@nikomatsakis`
Support `#[track_caller]` on closures and generators
## Lang team summary
This PR adds support for placing the `#[track_caller]` attribute on closure and generator expressions. This attribute's addition behaves identically (from a users perspective) to the attribute being placed on the method in impl Fn/FnOnce/FnMut for ... generated by compiler.
The attribute is currently "double" feature gated -- both `stmt_expr_attributes` (preexisting) and `closure_track_caller` (newly added) must be enabled in order to place these attributes on closures.
As the Fn* traits lack a `#[track_caller]` attribute in their definition, caller information does not propagate when invoking closures through dyn Fn*. There is no limitation that this PR adds in supporting this; it can be added in the future.
# Implementation details
This is implemented in the same way as for functions - an extra
location argument is appended to the end of the ABI. For closures,
this argument is *not* part of the 'tupled' argument storing the
parameters - the final closure argument for `#[track_caller]` closures
is no longer a tuple.
For direct (monomorphized) calls, the necessary support was already
implemented - we just needeed to adjust some assertions around checking
the ABI and argument count to take closures into account.
For calls through a trait object, more work was needed.
When creating a `ReifyShim`, we need to create a shim
for the trait method (e.g. `FnOnce::call_mut`) - unlike normal
functions, closures are never invoked directly, and always go through a
trait method.
Additional handling was needed for `InstanceDef::ClosureOnceShim`. In
order to pass location information throgh a direct (monomorphized) call
to `FnOnce::call_once` on an `FnMut` closure, we need to make
`ClosureOnceShim` aware of `#[tracked_caller]`. A new field
`track_caller` is added to `ClosureOnceShim` - this is used by
`InstanceDef::requires_caller` location, allowing codegen to
pass through the extra location argument.
Since `ClosureOnceShim.track_caller` is only used by codegen,
we end up generating two identical MIR shims - one for
`track_caller == true`, and one for `track_caller == false`. However,
these two shims are used by the entire crate (i.e. it's two shims total,
not two shims per unique closure), so this shouldn't a big deal.
Fix WinUWP std compilation errors due to I/O safety
I/O safety for Windows has landed in #87329. However, it does not cover UWP specific parts and prevents all UWP targets from building. See https://github.com/YtFlow/Maple/issues/18. This PR fixes these compile errors when building std for UWP targets.
This PR allows applying a `#[track_caller]` attribute to a
closure/generator expression. The attribute as interpreted as applying
to the compiler-generated implementation of the corresponding trait
method (`FnOnce::call_once`, `FnMut::call_mut`, `Fn::call`, or
`Generator::resume`).
This feature does not have its own feature gate - however, it requires
`#![feature(stmt_expr_attributes)]` in order to actually apply
an attribute to a closure or generator.
This is implemented in the same way as for functions - an extra
location argument is appended to the end of the ABI. For closures,
this argument is *not* part of the 'tupled' argument storing the
parameters - the final closure argument for `#[track_caller]` closures
is no longer a tuple.
For direct (monomorphized) calls, the necessary support was already
implemented - we just needeed to adjust some assertions around checking
the ABI and argument count to take closures into account.
For calls through a trait object, more work was needed.
When creating a `ReifyShim`, we need to create a shim
for the trait method (e.g. `FnOnce::call_mut`) - unlike normal
functions, closures are never invoked directly, and always go through a
trait method.
Additional handling was needed for `InstanceDef::ClosureOnceShim`. In
order to pass location information throgh a direct (monomorphized) call
to `FnOnce::call_once` on an `FnMut` closure, we need to make
`ClosureOnceShim` aware of `#[tracked_caller]`. A new field
`track_caller` is added to `ClosureOnceShim` - this is used by
`InstanceDef::requires_caller` location, allowing codegen to
pass through the extra location argument.
Since `ClosureOnceShim.track_caller` is only used by codegen,
we end up generating two identical MIR shims - one for
`track_caller == true`, and one for `track_caller == false`. However,
these two shims are used by the entire crate (i.e. it's two shims total,
not two shims per unique closure), so this shouldn't a big deal.
Rollup of 8 pull requests
Successful merges:
- #89036 (Fix missing `no_global_oom_handling` cfg-gating)
- #89041 (Work around invalid DWARF bugs for fat LTO)
- #89046 ("Fix" an overflow in byte position math)
- #89127 (Re-enable the `src/test/debuginfo/mutex.rs` test on Windows)
- #89133 (Fix ICE with `--cap-lints=allow` and `-Zfuel=...=0`)
- #89162 (rustc_index: Add some map-like APIs to `IndexVec`)
- #89164 (Document `--show-type-layout` in the rustdoc book)
- #89170 (Disable the leak sanitizer on Macos aarch64 for now)
Failed merges:
r? `@ghost`
`@rustbot` modify labels: rollup
rustc_index: Add some map-like APIs to `IndexVec`
`IndexVec` is often used as a map, but its map APIs are lacking.
This PR adds a couple of useful methods.
Re-enable the `src/test/debuginfo/mutex.rs` test on Windows
This test required a newer version of cdb than was previously enabled in
CI thus leading to some bitrot in the test since the time it was
originally created. With the update to the `windows-latest` image last
week, we're now running this test in CI and thus uncovered the
regression.
I've updated the test and it now passes.
r? `@ehuss`
"Fix" an overflow in byte position math
r? `@estebank`
help! I fixed the ICE only to brick the diagnostic.
I mean, it was wrong previously (using an already expanded macro span), but it is really bad now XD
Fix missing `no_global_oom_handling` cfg-gating
Cfg-gate these trait impls that are neglected.
These functions compile now because they use `box` syntax which depends on `exchange_malloc` during codegen only; as a result they compiles with cfg `no_global_oom_handling` but shouldn't.
Discovered in #89030 because that PR makes `box` syntax depend on `exchange_malloc` lang item during MIR construction.
Implement `#[must_not_suspend]`
implements #83310
Some notes on the impl:
1. The code that searches for the attribute on the ADT is basically copied from the `must_use` lint. It's not shared, as the logic did diverge
2. The RFC does specify that the attribute can be placed on fn's (and fn-like objects), like `must_use`. I think this is a direct copy from the `must_use` reference definition. This implementation does NOT support this, as I felt that ADT's (+ `impl Trait` + `dyn Trait`) cover the usecase's people actually want on the RFC, and adding an imp for the fn call case would be significantly harder. The `must_use` impl can do a single check at fn call stmt time, but `must_not_suspend` would need to answer the question: "for some value X with type T, find any fn call that COULD have produced this value". That would require significant changes to `generator_interior.rs`, and I would need mentorship on that. `@eholk` and I are discussing it.
3. `@estebank` do you know a way I can make the user-provided `reason` note pop out? right now it seems quite hidden
Also, I am not sure if we should run perf on this
r? `@nikomatsakis`
In suggest_missing_return_type, erase late bound regions after normalizing
Fixes#88360
There might be some hardening that could be done to not error or avoid erroring with LUBing `ReErased` with `ReEmpty`, but this was the most simple fix for this particular case.
r? `@nikomatsakis`
Fix debuginfo for parameters passed via the ScalarPair abi on Windows
Mark all of these as locals so the debugger does not try to interpret
them as being a pointer to the value. This extends the approach used
in #81898.
Fixes#88625
Rollup of 12 pull requests
Successful merges:
- #88795 (Print a note if a character literal contains a variation selector)
- #89015 (core::ascii::escape_default: reduce struct size)
- #89078 (Cleanup: Remove needless reference in ParentHirIterator)
- #89086 (Stabilize `Iterator::map_while`)
- #89096 ([bootstrap] Improve the error message when `ninja` is not found to link to installation instructions)
- #89113 (dont `.ensure()` the `thir_abstract_const` query call in `mir_build`)
- #89114 (Fixes a technicality regarding the size of C's `char` type)
- #89115 (⬆️ rust-analyzer)
- #89126 (Fix ICE when `indirect_structural_match` is allowed)
- #89141 (Impl `Error` for `FromSecsError` without foreign type)
- #89142 (Fix match for placeholder region)
- #89147 (add case for checking const refs in check_const_value_eq)
Failed merges:
r? `@ghost`
`@rustbot` modify labels: rollup
Impl `Error` for `FromSecsError` without foreign type
Using it through the crate-local path in `std` means that it shouldn't make an "Implementations on Foreign Types" section in the `std::error::Error` docs.
Fix ICE when `indirect_structural_match` is allowed
Fixes#89088. The ICE is caused by `delay_good_path_bug()`, which is called (indirectly) from a `format!()` macro invocation. I have moved the macro invocation into the `decorate` closure of `struct_span_lint_hir()`, so that the macro is only invoked if the lint is not allowed (i.e., causes at least a warning, and thus prevents `delay_good_path_bug()` from firing).
Fixes a technicality regarding the size of C's `char` type
Specifically, ISO/IEC 9899:2018 — better known as "C18" — (and at least
C11, C99 and C89) do not specify the size of `byte` in bits.
Section 3.6 defines "byte" as "addressable unit of data storage" while
section 6.2.5 ("Types") only defines "char" as "large enough to store
any member of the basic execution set" giving it a lower bound of 7 bit
(since there are 96 characters in the basic execution set).
With section 6.5.3.4 paragraph 4 "When sizeof is applied to an operant
that has type char […] the result is 1" you could read this as the size
of `char` in bits being defined as exactly the same as the number of
bits in a byte but it's also valid to read that as an exception.
In general implementations take `char` as the smallest unit of
addressable memory, which for modern byte-addressed architectures is
overwhelmingly 8 bits to the point of this convention being completely
cemented into just about all of our software.
So is any of this actually relevant at all? I hope not. I sincerely hope
that this never, ever comes up.
But if for some reason a poor rustacean is having to interface with C
code running on a Cray X1 that in 2003 is still doing word-addressed
memory with 64-bit chars and they trust the docs here blindly it will
blow up in her face. And I'll be truly sorry for her to have to deal
with … all of that.
dont `.ensure()` the `thir_abstract_const` query call in `mir_build`
might fix an ICE seen in #89022 (note: this PR does not close that issue) about attempting to read stolen thir. I couldn't repro the ICE but this `.ensure` seems sus anyway.
r? `@lcnr`
[bootstrap] Improve the error message when `ninja` is not found to link to installation instructions
fixes#89091
Signed-off-by: Daira Hopwood <daira@jacaranda.org>
Migrate in-tree crates to 2021
This replaces #89075 (cherry picking some of the commits from there), and closes#88637 and fixes#89074.
It excludes a migration of the library crates for now (see tidy diff) because we have some pending bugs around macro spans to fix there.
I instrumented bootstrap during the migration to make sure all crates moved from 2018 to 2021 had the compatibility warnings applied first.
Originally, the intent was to support cargo fix --edition within bootstrap, but this proved fairly difficult to pull off. We'd need to architect the check functionality to support running cargo check and cargo fix within the same x.py invocation, and only resetting sysroots on check. Further, it was found that cargo fix doesn't behave too well with "not quite workspaces", such as Clippy which has several crates. Bootstrap runs with --manifest-path ... for all the tools, and this makes cargo fix only attempt migration for that crate. We can't use e.g. --workspace due to needing to maintain sysroots for different phases of compilation appropriately.
It is recommended to skip the mass migration of Cargo.toml's to 2021 for review purposes; you can also use `git diff d6cd2c6c87 -I'^edition = .20...$'` to ignore the edition = 2018/21 lines in the diff.
rustc_codegen_llvm: make sse4.2 imply crc32 for LLVM 14
This fixes compiling things like the `snap` crate after
https://reviews.llvm.org/D105462. I added a test that verifies the
additional attribute gets specified, and confirmed that I can build
cargo with both LLVM 13 and 14 with this change applied.
r? `@nagisa` cc `@nikic`
This allows the format_args! macro to keep the pre-expansion code out of
the unsafe block without doing gymnastics with nested `match`
expressions. This reduces codegen.
Don't use projection cache or candidate cache in intercrate mode
Fixes#88969
It appears that *just* disabling the evaluation cache (in #88994)
leads to other issues involving intercrate mode caching. I suspect
that since we now always end up performing the full evaluation
in intercrate mode, we end up 'polluting' the candidate and projection
caches with results that depend on being in intercrate mode in some way.
Previously, we might have hit a cached evaluation (stored during
non-intercrate mode), and skipped doing this extra work in
intercrate mode.
The whole situation with intercrate mode caching is turning into
a mess. Ideally, we would remove intercrate mode entirely - however,
this might require waiting on Chalk.
