Normalize opaques with late-bound vars again
We have a hack in the compiler where if an opaque has escaping late-bound vars, we skip revealing it even though we *could* reveal it from a technical perspective. First of all, this is weird, since we really should be revealing all opaques in `Reveal::All` mode. Second of all, it causes subtle bugs (linked below).
I attempted to fix this in #100980, which was unfortunately reverted due to perf regressions on codebases that used really deeply nested futures in some interesting ways. The worst of which was #103423, which caused the project to hang on build. Another one was #104842, which was just a slow-down, but not a hang. I took some time afterwards to investigate how to rework `normalize_erasing_regions` to take advantage of better caching, but that effort kinda fizzled out (#104133).
However, recently, I was made aware of more bugs whose root cause is not revealing opaques during codegen. That made me want to fix this again -- in the process, interestingly, I took the the minimized example from https://github.com/rust-lang/rust/issues/103423#issuecomment-1292947043, and it doesn't seem to hang any more...
Thinking about this harder, there have been some changes to the way we lower and typecheck async futures that may have reduced the pathologically large number of outlives obligations (see description of #103423) that we were encountering when normalizing opaques with bound vars the last time around:
* #104321 (lower `async { .. }` directly as a generator that implements `Future`, removing the `from_generator` shim)
* #104833 (removing an `identity_future` fn that was wrapping desugared future generators)
... so given that I can see:
* No significant regression on rust perf bot (https://github.com/rust-lang/rust/pull/107620#issuecomment-1600070317)
* No timeouts in crater run I did (https://github.com/rust-lang/rust/pull/107620#issuecomment-1605428952, rechecked failing crates in https://github.com/rust-lang/rust/pull/107620#issuecomment-1605973434)
... and given that this PR:
* Fixes#104601
* Fixes#107557
* Fixes#109464
* Allows us to remove a `DefiningAnchor::Bubble` from codegen (75a8f681837c70051e0200a14f58ae07dbe58e66)
I'm inclined to give this another shot at landing this. Best case, it just works -- worst case, we get more examples to study how we need to improve the compiler to make this work.
r? types
Make the `Elaboratable` trait take clauses
We only ever elaborate clauses, so make this explicit in the trait's definition rather than having a bunch of `.expect_clause()` calls everywhere.
Convert `run-make/coverage-reports` tests to use a custom compiletest mode
I was frustrated by the fact that most of the coverage tests are glued together with makefiles and shell scripts, so I tried my hand at converting most of them over to a newly-implemented `run-coverage` mode/suite in compiletest.
This ~~*mostly*~~ resolves#85009, ~~though I've left a small number of the existing tests as-is because they would require more work to fix/support~~.
---
I had time to go back and add support for the more troublesome tests that I had initially skipped over, so this PR now manages to completely get rid of `run-make/coverage-reports`.
---
The patches are arranged as follows:
- Declare the new mode/suite in bootstrap
- Small changes to compiletest that will be used by the new mode
- Implement the new mode in compiletest
- Migrate most of the tests over
- Add more code to bootstrap and compiletest to support the remaining tests
- Migrate the remaining tests (with some temporary hacks to avoid re-blessing them)
- Remove the temporary hacks and re-bless the migrated tests
- Remove the unused remnants of `run-make/coverage-reports`
Support for native WASM exceptions
### Motivation
Currently, rustc does not support native WASM exceptions. It does support JavaScript based exceptions for the wasm32-emscripten-target, but this requires back&forth with javascript for many calls, which is very slow.
Native wasm support for exceptions is quite common: Clang+LLVM implemented them years ago, and all major browsers support them by now. They enable zero-cost exceptions, at least with regard to runtime-performance-cost. They may increase startup-time and code size, though.
### Important: This PR does not change default behaviour
Exceptions usually add a lot of code in form of unwinding blocks, increasing the binary size. Most users probably do not want that, especially which regard to web development.
Therefore, wasm exceptions play a similar role as WASM-threads: rustc should support them, like clang does, but users who want to use it have to use some command-line magic like rustflags to opt in.
### What does this PR do?
As stated above, the default behaviour is not changed. It is already possible to opt-in into wasm exceptions using the command line. Unfortunately, the LLVM IR is invalid and the LLVM backend crashes.
```
rustc <sourcefile>
--target wasm32-unknown-unknown
-C panic=unwind
-C llvm-args=-wasm-enable-eh
-C target-feature=+exception-handling
```
As it turns out, LLVM is quite picky when it comes to IR for exception handling. If the IR does not look exactly like it should, some LLVM-assertions fail and the code generation crashes.
This PR adds the necessary modifications to the code generator to make it work. It also adds `exception-handling` as a wasm target feature.
### What this PR does not / what is missing
This PR is not a full fledges solution. It is the first step. A few parts are still missing; however, it is already useable (see next section).
Currently missing:
* The std library has to be adapted. Currently, only [no_std] crates work
* Usually, nested exceptions abort the program (i.e. a panic during the cleanup of another panic). This is currently not done yet.
- Currently, code inside cleanup handlers does not unwind
- To fix this requires a little more work: The code generator currently maintains a single terminate block per function for this. Unfortunately, WASM requires funclet based exception handling. Therefore, we need to create a terminate block per funclet. This is probably not a big problem, but I want to keep this PR simple.
### How to use the compiler given this PR?
This PR does not add any command line flags or features. It uses those which are already there. To compile with exceptions enabled, you need
* to set the panic strategy to unwind, i.e. `-C panic=unwind`
* to enable the exception-handling target feature, i.e. `-C target-feature=+exception-handling`
* to tell LLVM about the exception handling, i.e. `-C llvm-args=-wasm-enable-eh`
Since the standard library has not been adapted, you can only use it in [no_std] crates as of now. The intrinsic `core::intrinsics::r#try` works. To throw exceptions, you need the ```@llvm.wasm.throw``` intrinsic.
I created a sample application which works for me: https://github.com/mirkootter/rust-wasm-demos
This example can be run at https://webassembly.sh
suggests `is_some_and` over `map().unwrap`
changelog: Enhancement: [`option_map_unwrap_or`] now considers the [`msrv`] config when creating the suggestion.
* modified option_map_unwrap_or lint to recognise when an `Option<T>` is mapped to an `Option<bool>` with false being used when `None` is detected; suggests the use of `is_some_and` instead
* msrv is set to 1.70.0 for this lint; when `is_some_and` was stabilised
fixes#9125
Rollup of 5 pull requests
Successful merges:
- #112946 (Improve cgu naming and ordering)
- #113048 (Fix build on Solaris where fd-lock cannot be used.)
- #113100 (Fix display of long items in search results)
- #113107 (add check for ConstKind::Value(_) to in_operand())
- #113119 (rustdoc: Reduce internal function visibility.)
r? `@ghost`
`@rustbot` modify labels: rollup
Rollup of 7 pull requests
Successful merges:
- #112670 (privacy: Type privacy lints fixes and cleanups)
- #112929 (Test that we require implementing trait items whose bounds don't hold in the current impl)
- #113054 (Make `rustc_on_unimplemented` std-agnostic)
- #113137 (don't suggest `move` for borrows that aren't closures)
- #113139 (style-guide: Clarify let-else further)
- #113140 (style-guide: Add an example of formatting a multi-line attribute)
- #113143 (style-guide: Narrow guidance about references and dereferencing)
r? `@ghost`
`@rustbot` modify labels: rollup
style-guide: Narrow guidance about references and dereferencing
The style guide advises "prefer dereferencing to taking references", but
doesn't give guidance on when that "preference" should get overridden by
other considerations. Give an example of when it's fine to ignore
that advice.
style-guide: Add an example of formatting a multi-line attribute
We already say to format attributes like functions, but we didn't have
an example of formatting a multi-line attribute.
style-guide: Clarify let-else further
Give some additional examples with multi-line patterns.
Make it clearer to go on to the next case if the conditions aren't met.
Test that we require implementing trait items whose bounds don't hold in the current impl
I initially tried to make most of these pass, but that's a big can of worms, so I'm just adding them as tests, considering we have no tests for these things.
After the last commit, they contain `Option<&OperandBundleDef<'a>>` but
the values are always `Some(_)`. This commit removes the needless
`Option` wrapper. This also simplifies the type signatures of
`LLVMRustBuild{Invoke,Call}`, which were relying on the fact that the
represention of `Option<&T>` is the same as `&T` for non-`None` values.
