Make the wasm_c_abi future compat warning a hard error #133951

bjorn3 · 2024-12-06T08:53:59Z

This is the next step in getting rid of the broken C abi for wasm32-unknown-unknown.

The lint was made deny-by-default in #129534 3 months ago. This still keeps the -Zwasm-c-abi flag set to legacy by default. It will be flipped in a future PR.

cc #122532

lcnr · 2024-12-06T09:03:47Z

given #129534

r? @workingjubilee @alexcrichton

does this need a compiler FCP?

daxpedda

I should note that the changes in #129534 did not actually start showing an error to users, it was still a warning by default.
See #129534 (comment)

workingjubilee · 2024-12-06T09:37:24Z

Technically we are breaking like ~85 versions of a foundation ecosystem crate, so yeah, an FCP might be warranted, but also technically we're just fixing a bug.

If we do this, we should make sure we only do one FCP between this and #133952 though since they're the same decision: "We're killing this dead, yeah?"

workingjubilee · 2024-12-06T22:45:27Z

Nominating for T-compiler:

We already accepted the MCP to phase out this behavior, but this is the "hard break" edge. If an FCP is desired before proceeding, now is the time to decide. We are technically breaking a crate on future versions of Rust. However it is the crate and target's maintainer wish that we do so, and this is the solution to a 4 year old issue:

WebAssembly ABI mismatch between clang and rust #71871

We have heard no strong objection and this has been discussed for 4 years at this point, so any box-ticking formality is exactly that: a formality.

@rustbot label: +I-compiler-nominated

Also cc @daxpedda

apiraino · 2024-12-12T15:27:24Z

Discussed in T-compiler triage on Zulip.

Even if it's just a sign-off, we want to loop in T-lang, seems the usual procedure for them is to FCP such changes.

@rustbot label -I-compiler-nominated +I-lang-easy-decision

workingjubilee · 2024-12-12T21:04:11Z

To summarize even more summarily for T-lang:

extern "C" fn on wasm32 targets has used a creative ABI that emerged because Rust and C toolchain development were more historically contemporary to each other, as opposed to the usual "first C, then 10~40 years later, Rust". Unfortunately, wasm-bindgen needed something for a stable-ish wasm ABI to talk to JavaScript. A flawed lowering was written. It was not immediately fixed because fixing it would break wasm-bindgen. For a while the wasm32-unknown-emscripten target was an acceptable workaround, and in a nascent ecosystem which might have further growing pains, the next move was not obvious.

Things have settled and it has become clear that Rust should align the ABI of extern "C" fn with that used by C toolchains for other wasm32 targets.

Thanks to @alexcrichton and @daxpedda we have implemented a relatively-smooth migration path for wasm-bindgen. There should be no meaningful concerns going forward, and this will make code that wasn't compatible with C code be compatible again, according to the conventional understanding of extern "C" fn.

joshtriplett · 2025-01-08T16:21:12Z

If I understand correctly, people who want to use the new interoperable ABI between C and Rust on WebAssembly will need to either use some flavor of wasi target or use some hypothetical new -none target that we don't yet have?

Or is the migration plan here to wait some amount of time with this as a hard error and then change it to the new ABI?

scottmcm · 2025-01-08T16:25:11Z

I might be misunderstanding something here, but I would have expected a change in tests/ui for this? What's the code that used to emit "future compat" and now would, or that no longer mentions the "because this lint is on by default" because it's a hard error not a lint?

tmandry · 2025-01-08T16:26:44Z

We discussed in today's lang team meeting and were confused what exactly we are rubber stamping here. Specifically, we wanted to know:

Does this break any use of extern "C" on wasm32-unknown-unknown target? What action is the user expected to take when we break them?

Also echoing @scottmcm's point that a test change would be ideal.

workingjubilee · 2025-01-08T16:30:20Z

If I understand correctly, people who want to use the new interoperable ABI between C and Rust on WebAssembly will need to either use some flavor of wasi target or use some hypothetical new -none target that we don't yet have?

That is the precise opposite of the situation.

joshtriplett · 2025-01-08T16:44:40Z

@workingjubilee came to the @rust-lang/lang meeting and explained the situation in great detail.

It sounds like this hard error will happen for people using old wasm-bindgen, and people using new wasm-bindgen will have things Just Work.

traviscross · 2025-01-08T16:44:58Z

Thanks to @workingjubilee for joining the call and clarifying the situation for us.

The current situation is that extern "C" with wasm32-unknown-unknown works with old versions of wasm-bindgen, but it's broken and we lint against this. People who want this to work correctly today with new versions of wasm-bindgen have to pass the -Zwasm-c-abi flag. What this change does is to make that -Zwasm-c-abi flag the default so that users doing extern "C" with new versions of wasm-bindgen will find things to just work.

Since there would otherwise be subtle breakage for people using old versions of wasm-bindgen, this includes a heuristic to hopefully provide a hard error in those cases.

On that basis...

@rfcbot fcp merge

bjorn3 · 2025-01-20T13:56:28Z

@rustbot ready

tests/ui/wasm/wasm-bindgen-broken-error.rs

This is the next step in getting rid of the broken C abi for wasm32-unknown-unknown.

Co-Authored-By: Alex Crichton <[email protected]>

workingjubilee · 2025-01-24T20:22:50Z

Thank you everyone!

@bors r+

bors · 2025-01-24T20:22:54Z

📌 Commit 49c3aaa has been approved by workingjubilee

It is now in the queue for this repository.

Rollup of 7 pull requests Successful merges: - rust-lang#130808 (Fix linking for symbols starting with ? on i686-pc-windows-msvc) - rust-lang#133138 (Target modifiers (special marked options) are recorded in metainfo) - rust-lang#133154 (Reword resolve errors caused by likely missing crate in dep tree) - rust-lang#135707 (Shorten linker output even more when `--verbose` is not present) - rust-lang#135764 (Fix tests on LLVM 20) - rust-lang#135785 (use `PassMode::Direct` for vector types on `s390x`) - rust-lang#135818 (tests: Port `translation` to rmake.rs) Failed merges: - rust-lang#133951 (Make the wasm_c_abi future compat warning a hard error) r? `@ghost` `@rustbot` modify labels: rollup try-job: aarch64-apple try-job: i686-mingw try-job: x86_64-gnu-llvm-19-3

… r=workingjubilee Make the wasm_c_abi future compat warning a hard error This is the next step in getting rid of the broken C abi for wasm32-unknown-unknown. The lint was made deny-by-default in rust-lang#129534 3 months ago. This still keeps the `-Zwasm-c-abi` flag set to `legacy` by default. It will be flipped in a future PR. cc rust-lang#122532

…iaskrgr Rollup of 8 pull requests Successful merges: - rust-lang#133631 (Support QNX 7.1 with `io-sock`+libstd and QNX 8.0 (`no_std` only)) - rust-lang#133951 (Make the wasm_c_abi future compat warning a hard error) - rust-lang#134283 (fix(libtest): Deprecate '--logfile') - rust-lang#134679 (Windows: remove readonly files) - rust-lang#135635 (Move `std::io::pipe` code into its own file) - rust-lang#135842 (TRPL: more backward-compatible Edition changes) - rust-lang#135953 (ci.py: check the return code in `run-local`) - rust-lang#136031 (Expand polonius MIR dump) r? `@ghost` `@rustbot` modify labels: rollup

… r=workingjubilee Make the wasm_c_abi future compat warning a hard error This is the next step in getting rid of the broken C abi for wasm32-unknown-unknown. The lint was made deny-by-default in rust-lang#129534 3 months ago. This still keeps the `-Zwasm-c-abi` flag set to `legacy` by default. It will be flipped in a future PR. cc rust-lang#122532

Rollup of 7 pull requests Successful merges: - rust-lang#133951 (Make the wasm_c_abi future compat warning a hard error) - rust-lang#134283 (fix(libtest): Deprecate '--logfile') - rust-lang#135785 (use `PassMode::Direct` for vector types on `s390x`) - rust-lang#135948 (Update emscripten std tests) - rust-lang#135951 (Use `fmt::from_fn` in more places in the compiler) - rust-lang#136031 (Expand polonius MIR dump) - rust-lang#136032 (Account for mutable borrow in argument suggestion) Failed merges: - rust-lang#135635 (Move `std::io::pipe` code into its own file) r? `@ghost` `@rustbot` modify labels: rollup

Rollup merge of rust-lang#133951 - bjorn3:wasm_c_abi_lint_hard_error, r=workingjubilee Make the wasm_c_abi future compat warning a hard error This is the next step in getting rid of the broken C abi for wasm32-unknown-unknown. The lint was made deny-by-default in rust-lang#129534 3 months ago. This still keeps the `-Zwasm-c-abi` flag set to `legacy` by default. It will be flipped in a future PR. cc rust-lang#122532

RalfJung · 2025-03-17T07:44:03Z

compiler/rustc_lint_defs/src/builtin.rs

@@ -143,7 +143,6 @@ declare_lint_pass! {
        UNUSED_VARIABLES,
        USELESS_DEPRECATED,
        WARNINGS,
-        WASM_C_ABI,


FYI whenever removing something from this list, it must be added to the removed lint list. There is a comment above the list explaining that.

//! When removing a lint, make sure to also add a call to `register_removed` in //! compiler/rustc_lint/src/lib.rs.

Upstream changes relative to 1.85.1: Version 1.86.0 (2025-04-03) ========================== Language -------- - [Stabilize upcasting trait objects to supertraits.] (rust-lang/rust#134367) - [Allow safe functions to be marked with the `#[target_feature]` attribute.] (rust-lang/rust#134090) - [The `missing_abi` lint now warns-by-default.] (rust-lang/rust#132397) - Rust now lints about double negations, to catch cases that might have intended to be a prefix decrement operator (`--x`) as written in other languages. This was previously a clippy lint, `clippy::double_neg`, and is [now available directly in Rust as `double_negations`.] (rust-lang/rust#126604) - [More pointers are now detected as definitely not-null based on their alignment in const eval.] (rust-lang/rust#133700) - [Empty `repr()` attribute applied to invalid items are now correctly rejected.] (rust-lang/rust#133925) - [Inner attributes `#![test]` and `#![rustfmt::skip]` are no longer accepted in more places than intended.] (rust-lang/rust#134276) Compiler -------- - [Debug-assert that raw pointers are non-null on access.] (rust-lang/rust#134424) - [Change `-O` to mean `-C opt-level=3` instead of `-C opt-level=2` to match Cargo's defaults.] (rust-lang/rust#135439) - [Fix emission of `overflowing_literals` under certain macro environments.] (rust-lang/rust#136393) Platform Support ---------------- - [Replace `i686-unknown-redox` target with `i586-unknown-redox`.] (rust-lang/rust#136698) - [Increase baseline CPU of `i686-unknown-hurd-gnu` to Pentium 4.] (rust-lang/rust#136700) - New tier 3 targets: - [`{aarch64-unknown,x86_64-pc}-nto-qnx710_iosock`] (rust-lang/rust#133631). For supporting Neutrino QNX 7.1 with `io-socket` network stack. - [`{aarch64-unknown,x86_64-pc}-nto-qnx800`] (rust-lang/rust#133631). For supporting Neutrino QNX 8.0 (`no_std`-only). - [`{x86_64,i686}-win7-windows-gnu`] (rust-lang/rust#134609). Intended for backwards compatibility with Windows 7. `{x86_64,i686}-win7-windows-msvc` are the Windows MSVC counterparts that already exist as Tier 3 targets. - [`amdgcn-amd-amdhsa`](rust-lang/rust#134740). - [`x86_64-pc-cygwin`](rust-lang/rust#134999). - [`{mips,mipsel}-mti-none-elf`] (rust-lang/rust#135074). Initial bare-metal support. - [`m68k-unknown-none-elf`](rust-lang/rust#135085). - [`armv7a-nuttx-{eabi,eabihf}`, `aarch64-unknown-nuttx`, and `thumbv7a-nuttx-{eabi,eabihf}`] (rust-lang/rust#135757). Refer to Rust's [platform support page][platform-support-doc] for more information on Rust's tiered platform support. Libraries --------- - The type of `FromBytesWithNulError` in `CStr::from_bytes_with_nul(bytes: &[u8]) -> Result<&Self, FromBytesWithNulError>` was [changed from an opaque struct to an enum] (rust-lang/rust#134143), allowing users to examine why the conversion failed. - [Remove `RustcDecodable` and `RustcEncodable`.] (rust-lang/rust#134272) - [Deprecate libtest's `--logfile` option.] (rust-lang/rust#134283) - [On recent versions of Windows, `std::fs::remove_file` will now remove read-only files.] (rust-lang/rust#134679) Stabilized APIs --------------- - [`{float}::next_down`] (https://doc.rust-lang.org/stable/std/primitive.f64.html#method.next_down) - [`{float}::next_up`] (https://doc.rust-lang.org/stable/std/primitive.f64.html#method.next_up) - [`<[_]>::get_disjoint_mut`] (https://doc.rust-lang.org/stable/std/primitive.slice.html#method.get_disjoint_mut) - [`<[_]>::get_disjoint_unchecked_mut`] (https://doc.rust-lang.org/stable/std/primitive.slice.html#method.get_disjoint_unchecked_mut) - [`slice::GetDisjointMutError`] (https://doc.rust-lang.org/stable/std/slice/enum.GetDisjointMutError.html) - [`HashMap::get_disjoint_mut`] (https://doc.rust-lang.org/std/collections/hash_map/struct.HashMap.html#method.get_disjoint_mut) - [`HashMap::get_disjoint_unchecked_mut`] (https://doc.rust-lang.org/std/collections/hash_map/struct.HashMap.html#method.get_disjoint_unchecked_mut) - [`NonZero::count_ones`] (https://doc.rust-lang.org/stable/std/num/struct.NonZero.html#method.count_ones) - [`Vec::pop_if`] (https://doc.rust-lang.org/std/vec/struct.Vec.html#method.pop_if) - [`sync::Once::wait`] (https://doc.rust-lang.org/stable/std/sync/struct.Once.html#method.wait) - [`sync::Once::wait_force`] (https://doc.rust-lang.org/stable/std/sync/struct.Once.html#method.wait_force) - [`sync::OnceLock::wait`] (https://doc.rust-lang.org/stable/std/sync/struct.OnceLock.html#method.wait) These APIs are now stable in const contexts: - [`hint::black_box`] (https://doc.rust-lang.org/stable/std/hint/fn.black_box.html) - [`io::Cursor::get_mut`] (https://doc.rust-lang.org/stable/std/io/struct.Cursor.html#method.get_mut) - [`io::Cursor::set_position`] (https://doc.rust-lang.org/stable/std/io/struct.Cursor.html#method.set_position) - [`str::is_char_boundary`] (https://doc.rust-lang.org/stable/std/primitive.str.html#method.is_char_boundary) - [`str::split_at`] (https://doc.rust-lang.org/stable/std/primitive.str.html#method.split_at) - [`str::split_at_checked`] (https://doc.rust-lang.org/stable/std/primitive.str.html#method.split_at_checked) - [`str::split_at_mut`] (https://doc.rust-lang.org/stable/std/primitive.str.html#method.split_at_mut) - [`str::split_at_mut_checked`] (https://doc.rust-lang.org/stable/std/primitive.str.html#method.split_at_mut_checked) Cargo ----- - [When merging, replace rather than combine configuration keys that refer to a program path and its arguments.] (rust-lang/cargo#15066) - [Error if both `--package` and `--workspace` are passed but the requested package is missing.] (rust-lang/cargo#15071) This was previously silently ignored, which was considered a bug since missing packages should be reported. - [Deprecate the token argument in `cargo login` to avoid shell history leaks.] (rust-lang/cargo#15057) - [Simplify the implementation of `SourceID` comparisons.] (rust-lang/cargo#14980) This may potentially change behavior if the canonicalized URL compares differently in alternative registries. Rustdoc ----- - [Add a sans-serif font setting.] (rust-lang/rust#133636) Compatibility Notes ------------------- - [The `wasm_c_abi` future compatibility warning is now a hard error.] (rust-lang/rust#133951) Users of `wasm-bindgen` should upgrade to at least version 0.2.89, otherwise compilation will fail. - [Remove long-deprecated no-op attributes `#![no_start]` and `#![crate_id]`.] (rust-lang/rust#134300) - [The future incompatibility lint `cenum_impl_drop_cast` has been made into a hard error.] (rust-lang/rust#135964) This means it is now an error to cast a field-less enum to an integer if the enum implements `Drop`. - [SSE2 is now required for "i686" 32-bit x86 hard-float targets; disabling it causes a warning that will become a hard error eventually.] (rust-lang/rust#137037) To compile for pre-SSE2 32-bit x86, use a "i586" target instead. Internal Changes ---------------- These changes do not affect any public interfaces of Rust, but they represent significant improvements to the performance or internals of rustc and related tools. - [Build the rustc on AArch64 Linux with ThinLTO + PGO.] (rust-lang/rust#133807) The ARM 64-bit compiler (AArch64) on Linux is now optimized with ThinLTO and PGO, similar to the optimizations we have already performed for the x86-64 compiler on Linux. This should make it up to 30% faster.

bjorn3 added O-wasm Target: WASM (WebAssembly), http://webassembly.org/ A-ABI Area: Concerning the application binary interface (ABI) labels Dec 6, 2024

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Remove wasm legacy abi #133952

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bjorn3 and others added 2 commits January 23, 2025 10:22

Make the wasm_c_abi future compat warning a hard error

4d1c16c

This is the next step in getting rid of the broken C abi for wasm32-unknown-unknown.

Add test

49c3aaa

Co-Authored-By: Alex Crichton <[email protected]>

bjorn3 force-pushed the wasm_c_abi_lint_hard_error branch from b030685 to 49c3aaa Compare January 23, 2025 10:55

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Rollup of 7 pull requests #136045

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Rollup of 8 pull requests #136050

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Rollup of 7 pull requests #136081

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Rollup of 7 pull requests #136085

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Tracking Issue for perma-unstable wasm-c-abi flag #122532

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Make the wasm_c_abi future compat warning a hard error #133951

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