Add extra types to VaArgSafe

[clarfonthey]

View all comments

Option 3 as proposed by @RalfJung here: #162478 (comment)

This adds the following types to VaArgSafe:

• Reference equivalents to the same pointers (it's still unsafe to get next_arg)
• NonNull<T> (for similar reasons)
• Option<NonNull<T>> (since it's ABI-compatible)
• NonZero<T> (since it's ABI-compatible)
• Option<NonZero<T>> (since it's ABI-compatible)

Additionally, as part of implementing this in the compiler, NonZero is promoted from a diagnostic item to a lang item. I'm under the impression this is fine since we're already doing a lang FCP (and none of the lang folks have chimed in yet) but it's worth mentioning.

Also have a Zulip thread for the compiler impl: #t-compiler/help > `VaArgSafe` change + random `Ty` questions @ 💬

[clarfonthey]

@rfcbot merge libs,lang

[rust-rfcbot]

@clarfonthey has proposed to merge this. The next step is review by the rest of the tagged team members:

• @ChrisDenton
• @Mark-Simulacrum
• @cuviper
• @dtolnay
• @joshtriplett
• @nia-e
• @nikomatsakis
• @scottmcm
• @the8472
• @thomcc
• @tmandry
• @traviscross

No concerns currently listed.

Once a majority of reviewers approve (and at most 2 approvals are outstanding), this will enter its final comment period. If you spot a major issue that hasn't been raised at any point in this process, please speak up!

cc @rust-lang/lang-advisors: FCP proposed for lang, please feel free to register concerns.
cc @rust-lang/libs-ping: FCP proposed for libs, please feel free to register concerns.
See this document for info about what commands tagged team members can give me.

[rustbot]

r? @Darksonn

rustbot has assigned @Darksonn.
They will have a look at your PR within the next two weeks and either review your PR or reassign to another reviewer.

Use r? to explicitly pick a reviewer

Why was this reviewer chosen?

The reviewer was selected based on:

• Owners of files modified in this PR: libs
• libs expanded to 12 candidates
• Random selection from Darksonn, JohnTitor, Mark-Simulacrum, aapoalas, jhpratt

[nia-e]

The docs for VaArgSafe::next_arg currently say

Currently, all types implementing VaArgSafe also implement Copy, but this may change in the future.

this should also be adjusted, but otherwise yeah this makes sense.

@rfcbot reviewed

[clarfonthey]

Updated docs to remove note on everything being Copy, also added NonZero and NonNull per discussion in lang meeting.

[steffahn]

The safety comments of next_arg would also need to be updated to cover all the new types.

[folkertdev]

Can you add tests for these in tests/ui/c-variadic/roundtrip.rs?

View changes since the review

[clarfonthey]

The result is very cursed but hopefully still achieves the desired result. Would appreciate an explicit review on those.

[RalfJung]

I assume the intent is that e.g. NonNull<T> is compatible with *mut T. That will need adjustments in the docs and corresponding adjustments in the const-eval / Miri checking logic.

View changes since the review

[clarfonthey]

I thought that we already had this guarantee, but if we don't, I would rather not overcomplicate this PR and can remove it. (Note: this only needs to hold for sized pointees.)

[folkertdev]

Rust guarantees they have the same layout, so it's just the docs of next_arg that should document that this equivalence applies here.

[RalfJung]

Same layout != same ABI.
But we also guarantee that they have the same ABI.

This applies to most of your additions, e.g. NonZero<i32> vs i32.

[clarfonthey]

So, looking at the docs:

Unlike *mut T, the pointer must always be non-null, even if the pointer is never dereferenced. This is so that enums may use this forbidden value as a discriminant – Option<NonNull> has the same size as *mut T. However the pointer may still dangle if it isn’t dereferenced.

That feels pretty much like an explicit guarantee that *mut T, NonNull<T>, and Option<NonNull<T>> are layout-compatible, but I guess we should probably make it more explicit in the reference.

[folkertdev]

From my understanding, variadic arguments simply require layout compatibility, since for example i32 and u32 are interchangeable in them.

If only :)

The comment on next_arg goes into detail on what it means for types to be compatible. It is much more subtle than layout compatibility. E.g. i32 and u32 are only compatible if the runtime value is representable in both types. (so like 3 is compatible but -3 is not.

[clarfonthey]

Oh, yes, that is cursed.

[folkertdev]

Morally the same is true for the nonzero types and references (which cannot be NULL), but those requirements are already captured by the type itself in these new cases.

[RalfJung]

The docs very explicitly say

The actual type of the argument U is compatible with T (as defined below).

So without changing the docs, if the caller uses NonZeroI32 and the callee uses next_arg::<i32>(), we very clearly have UB. (NonZeroI32 is not an "integer type". That term refers to primitive types, iN and uN.)

[clarfonthey]

Yes, I did explicitly go through and update the docs for those cases: the general rule for those is that if not all bit patterns are valid, you are guaranteeing that you have passed a valid bit pattern, at risk of UB.

[Mark-Simulacrum]

We should probably expand this with the new types we guarantee impls for.

View changes since the review

[Darksonn]

Please add tests for the cases with breakage shared in #162858 (comment) and #162858 (comment).

View changes since the review

[traviscross]

Thanks @clarfonthey.

@rfcbot reviewed

And thanks to @theemathas for catching that this would be breaking if VaArgSafe stabilized with Rust 1.99 so we could destabilize it to give us time in #162909.

[tmandry]

@rfcbot reviewed

+1, thanks @theemathas for the catch and @maxdexh for buying us time with #162909!

[rust-rfcbot]

🔔 This is now entering its final comment period, as per the review above. 🔔

[clarfonthey]

Took a bit to get back to it, but I've also managed to replicate the test failures on aarch64 locally via qemu, so, I will try and get those fixed up before the FCP is over.

[rustbot]

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

[clarfonthey]

This line is returning 0xFFFF_FFFFu32 instead of 0xAAAA_AAAAu32 and I genuinely have no idea. This isn't even the hard part of the code, and it works in const context, just not at runtime, so, definitely some ABI shenanigans.

View changes since the review

[folkertdev]

For which input type?

[clarfonthey]

On Zulip: #t-compiler/help > `VaArgSafe` change + random `Ty` questions @ 💬

This is definitely the -1 for NonZero<i32>, but, the previous argument was supposed to be that type, and it's 0, which is definitely not right.

[folkertdev]

On x86_64 I hit this assert

rust/compiler/rustc_codegen_llvm/src/va_arg.rs

Line 779 in 837b18a

assert!(layout.ty.is_integral());

Because of std::option::Option<std::num::NonZero<i128>>. It's fine to remove that assert really. But, there might be similar asserts on targets that we don't run CI for, so this'll need some validation.

With that assert removed the roundtrip test passes.

I assume you're running on aarch64 where I get that same error, still looking into it

[rust-rfcbot]

The final comment period, with a disposition to merge, as per the review above, is now complete.

As the automated representative of the governance process, I would like to thank the author for their work and everyone else who contributed.

[rust-log-analyzer]

The job test-aarch64-gnu-llvm-22-1 failed! Check out the build log: (web) (plain enhanced) (plain)

Click to see the possible cause of the failure (guessed by this bot)

failures:

---- [ui] tests/ui/c-variadic/roundtrip.rs stdout ----

error: test did not exit with success! code=None so test would pass with `run-crash`
status: signal: 6 (SIGABRT) (core dumped)
command: cd "/checkout/obj/build/aarch64-unknown-linux-gnu/test/ui/c-variadic/roundtrip" && RUSTC="/checkout/obj/build/aarch64-unknown-linux-gnu/stage2/bin/rustc" RUST_TEST_THREADS="4" "/checkout/obj/build/aarch64-unknown-linux-gnu/test/ui/c-variadic/roundtrip/a"
stdout: none
--- stderr -------------------------------

thread 'main' (39801) panicked at /checkout/tests/ui/c-variadic/roundtrip.rs:48:5:
assertion `left == right` failed: -432476160 4294967295 0
---
panic in a function that cannot unwind
stack backtrace:
   0:     0xff8a5fa0fdf4 - <<std[e255f19bdb4cfb7]::sys::backtrace::BacktraceLock>::print::DisplayBacktrace as core[334adfad61266349]::fmt::Display>::fmt
   1:     0xff8a5fa610dc - core[334adfad61266349]::fmt::write
   2:     0xff8a5fa254bc - <std[e255f19bdb4cfb7]::sys::stdio::unix::Stderr as core[334adfad61266349]::io::write::Write>::write_fmt
   3:     0xff8a5f9d4a58 - std[e255f19bdb4cfb7]::panicking::default_hook::{closure#0}
   4:     0xff8a5f9fedf8 - std[e255f19bdb4cfb7]::panicking::default_hook
   5:     0xff8a5f9ff278 - std[e255f19bdb4cfb7]::panicking::panic_with_hook
   6:     0xff8a5f9d4b50 - std[e255f19bdb4cfb7]::panicking::panic_handler::{closure#0}
   7:     0xff8a5f9c5364 - std[e255f19bdb4cfb7]::sys::backtrace::__rust_end_short_backtrace::<std[e255f19bdb4cfb7]::panicking::panic_handler::{closure#0}, !>
   8:     0xff8a5f9d691c - __rustc[9ccf4299e9c9c915]::rust_begin_unwind
   9:     0xff8a5f9b9244 - core[334adfad61266349]::panicking::panic_nounwind_fmt
  10:     0xff8a5f9b915c - core[334adfad61266349]::panicking::panic_nounwind
  11:     0xff8a5f9b9324 - core[334adfad61266349]::panicking::panic_cannot_unwind
  12:     0xaab4130439c4 - roundtrip[2ae0f7d716a9c1b5]::non_const_variadic::<core[334adfad61266349]::num::nonzero::NonZero<i32>>
  13:     0xaab413045304 - roundtrip[2ae0f7d716a9c1b5]::main
  14:     0xaab413045270 - std[e255f19bdb4cfb7]::sys::backtrace::__rust_begin_short_backtrace::<fn(), ()>
  15:     0xaab413045288 - std[e255f19bdb4cfb7]::rt::lang_start::<()>::{closure#0}
  16:     0xff8a5f9fd4f4 - std[e255f19bdb4cfb7]::rt::lang_start_internal
  17:     0xaab4130479ec - main
  18:     0xff8a5f7b2f1c - <unknown>
  19:     0xff8a5f7b305c - __libc_start_main
  20:     0xaab413042530 - _start
  21:                0x0 - <unknown>
thread caused non-unwinding panic. aborting.
---

1046    |
1047    = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
1048 
- error[E0080]: constructing invalid value of type [u8; 24]: at [8], encountered a pointer, but expected an integer
+ error[E0080]: constructing invalid value of type [u8; 32]: at [0], encountered a pointer, but expected an integer
1050   --> $DIR/c-variadic-fail.rs:202:22
1051    |
1052 LL | fn use_after_free() {


The actual stderr differed from the expected stderr
To update references, rerun the tests and pass the `--bless` flag
To only update this specific test, also pass `--test-args consts/const-eval/c-variadic-fail.rs`

error: 1 errors occurred comparing output.
status: exit status: 1
command: env -u RUSTC_LOG_COLOR RUSTC_ICE="0" RUST_BACKTRACE="short" "/checkout/obj/build/aarch64-unknown-linux-gnu/stage2/bin/rustc" "/checkout/tests/ui/consts/const-eval/c-variadic-fail.rs" "-Zsimulate-remapped-rust-src-base=/rustc/FAKE_PREFIX" "-Ztranslate-remapped-path-to-local-path=no" "-Z" "ignore-directory-in-diagnostics-source-blocks=/cargo" "-Z" "ignore-directory-in-diagnostics-source-blocks=/checkout/vendor" "--sysroot" "/checkout/obj/build/aarch64-unknown-linux-gnu/stage2" "--target=aarch64-unknown-linux-gnu" "--check-cfg" "cfg(test,FALSE)" "--error-format" "json" "--json" "future-incompat" "-Ccodegen-units=1" "-Zui-testing" "-Zdeduplicate-diagnostics=no" "-Zwrite-long-types-to-disk=no" "-Cstrip=debuginfo" "-C" "prefer-dynamic" "--out-dir" "/checkout/obj/build/aarch64-unknown-linux-gnu/test/ui/consts/const-eval/c-variadic-fail" "-Znext-solver=coherence" "-A" "unused" "-W" "unused_attributes" "-A" "internal_features" "-A" "incomplete_features" "-A" "unused_parens" "-A" "unused_braces" "-Crpath" "-Cdebuginfo=0" "-Lnative=/checkout/obj/build/aarch64-unknown-linux-gnu/native/rust-test-helpers" "--edition=2015" "-Zextra-const-ub-checks"
stdout: none
--- stderr -------------------------------
error[E0080]: more C-variadic arguments read than were passed
##[error]  --> /checkout/tests/ui/consts/const-eval/c-variadic-fail.rs:30:13
   |
LL | unsafe fn read_too_many() {
...
LL |     const { read_n::<1>() }
   |             ^^^^^^^^^^^^^ evaluation of `read_too_many::{constant#2}` failed inside this call
   |
note: inside `read_n::<1>`
  --> /checkout/tests/ui/consts/const-eval/c-variadic-fail.rs:18:17
   |
LL |         let _ = ap.next_arg::<i32>();
   |                 ^^^^^^^^^^^^^^^^^^^^
note: inside `VaList::<'_>::next_arg::<i32>`
  --> /rustc/FAKE_PREFIX/library/core/src/ffi/va_list.rs:509:0

note: erroneous constant encountered
  --> /checkout/tests/ui/consts/const-eval/c-variadic-fail.rs:30:5
   |
LL |     const { read_n::<1>() }
   |     ^^^^^^^^^^^^^^^^^^^^^^^

note: erroneous constant encountered
  --> /checkout/tests/ui/consts/const-eval/c-variadic-fail.rs:30:5
   |
LL |     const { read_n::<1>() }
   |     ^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`

error[E0080]: more C-variadic arguments read than were passed
##[error]  --> /checkout/tests/ui/consts/const-eval/c-variadic-fail.rs:34:13
   |
LL | unsafe fn read_too_many() {
...
LL |     const { read_n::<2>(1) }
   |             ^^^^^^^^^^^^^^ evaluation of `read_too_many::{constant#3}` failed inside this call
   |
note: inside `read_n::<2>`
  --> /checkout/tests/ui/consts/const-eval/c-variadic-fail.rs:18:17
   |
LL |         let _ = ap.next_arg::<i32>();
   |                 ^^^^^^^^^^^^^^^^^^^^
note: inside `VaList::<'_>::next_arg::<i32>`
  --> /rustc/FAKE_PREFIX/library/core/src/ffi/va_list.rs:509:0

note: erroneous constant encountered
  --> /checkout/tests/ui/consts/const-eval/c-variadic-fail.rs:34:5
   |
LL |     const { read_n::<2>(1) }
   |     ^^^^^^^^^^^^^^^^^^^^^^^^

note: erroneous constant encountered
  --> /checkout/tests/ui/consts/const-eval/c-variadic-fail.rs:34:5
   |
LL |     const { read_n::<2>(1) }
   |     ^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`

error[E0080]: va_arg value mismatch: value `-1_i32` cannot be represented by type `u32`
##[error]  --> /checkout/tests/ui/consts/const-eval/c-variadic-fail.rs:74:13
   |
LL | unsafe fn read_cast_numeric() {
...
LL |     const { read_as::<u32>(-1i32) };
   |             ^^^^^^^^^^^^^^^^^^^^^ evaluation of `read_cast_numeric::{constant#12}` failed inside this call
   |
note: inside `read_as::<u32>`
  --> /checkout/tests/ui/consts/const-eval/c-variadic-fail.rs:39:5
   |
LL |     ap.next_arg::<T>()
   |     ^^^^^^^^^^^^^^^^^^
note: inside `VaList::<'_>::next_arg::<u32>`
  --> /rustc/FAKE_PREFIX/library/core/src/ffi/va_list.rs:509:0

note: erroneous constant encountered
  --> /checkout/tests/ui/consts/const-eval/c-variadic-fail.rs:74:5
   |
LL |     const { read_as::<u32>(-1i32) };
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

note: erroneous constant encountered
  --> /checkout/tests/ui/consts/const-eval/c-variadic-fail.rs:74:5
   |
LL |     const { read_as::<u32>(-1i32) };
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`

error[E0080]: va_arg value mismatch: value `-2147483648_i32` cannot be represented by type `u32`
##[error]  --> /checkout/tests/ui/consts/const-eval/c-variadic-fail.rs:76:13
   |
LL | unsafe fn read_cast_numeric() {
...
LL |     const { read_as::<u32>(i32::MIN) };
   |             ^^^^^^^^^^^^^^^^^^^^^^^^ evaluation of `read_cast_numeric::{constant#13}` failed inside this call
   |
note: inside `read_as::<u32>`
  --> /checkout/tests/ui/consts/const-eval/c-variadic-fail.rs:39:5
   |
LL |     ap.next_arg::<T>()
   |     ^^^^^^^^^^^^^^^^^^
note: inside `VaList::<'_>::next_arg::<u32>`
  --> /rustc/FAKE_PREFIX/library/core/src/ffi/va_list.rs:509:0

note: erroneous constant encountered
  --> /checkout/tests/ui/consts/const-eval/c-variadic-fail.rs:76:5
   |
LL |     const { read_as::<u32>(i32::MIN) };
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

note: erroneous constant encountered
  --> /checkout/tests/ui/consts/const-eval/c-variadic-fail.rs:76:5
   |
LL |     const { read_as::<u32>(i32::MIN) };
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`

error[E0080]: va_arg value mismatch: value `4294967295_u32` cannot be represented by type `i32`
##[error]  --> /checkout/tests/ui/consts/const-eval/c-variadic-fail.rs:78:13
   |
LL | unsafe fn read_cast_numeric() {
...
LL |     const { read_as::<i32>(u32::MAX) };
   |             ^^^^^^^^^^^^^^^^^^^^^^^^ evaluation of `read_cast_numeric::{constant#14}` failed inside this call
   |
note: inside `read_as::<i32>`
  --> /checkout/tests/ui/consts/const-eval/c-variadic-fail.rs:39:5
   |
LL |     ap.next_arg::<T>()
   |     ^^^^^^^^^^^^^^^^^^
note: inside `VaList::<'_>::next_arg::<i32>`
  --> /rustc/FAKE_PREFIX/library/core/src/ffi/va_list.rs:509:0

note: erroneous constant encountered
  --> /checkout/tests/ui/consts/const-eval/c-variadic-fail.rs:78:5
   |
LL |     const { read_as::<i32>(u32::MAX) };
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

note: erroneous constant encountered
  --> /checkout/tests/ui/consts/const-eval/c-variadic-fail.rs:78:5
   |
LL |     const { read_as::<i32>(u32::MAX) };
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`

error[E0080]: va_arg value mismatch: value `2147483648_u32` cannot be represented by type `i32`
##[error]  --> /checkout/tests/ui/consts/const-eval/c-variadic-fail.rs:80:13
   |
LL | unsafe fn read_cast_numeric() {
...
LL |     const { read_as::<i32>(i32::MAX as u32 + 1) };
   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ evaluation of `read_cast_numeric::{constant#15}` failed inside this call
   |
note: inside `read_as::<i32>`
  --> /checkout/tests/ui/consts/const-eval/c-variadic-fail.rs:39:5
   |
LL |     ap.next_arg::<T>()
   |     ^^^^^^^^^^^^^^^^^^
note: inside `VaList::<'_>::next_arg::<i32>`
  --> /rustc/FAKE_PREFIX/library/core/src/ffi/va_list.rs:509:0

note: erroneous constant encountered
  --> /checkout/tests/ui/consts/const-eval/c-variadic-fail.rs:80:5
   |
LL |     const { read_as::<i32>(i32::MAX as u32 + 1) };
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

note: erroneous constant encountered
  --> /checkout/tests/ui/consts/const-eval/c-variadic-fail.rs:80:5
   |
LL |     const { read_as::<i32>(i32::MAX as u32 + 1) };
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`

error[E0080]: va_arg value mismatch: value `18446744073709551615_u64` cannot be represented by type `i64`
##[error]  --> /checkout/tests/ui/consts/const-eval/c-variadic-fail.rs:82:13
   |
LL | unsafe fn read_cast_numeric() {
...
LL |     const { read_as::<i64>(u64::MAX) };
   |             ^^^^^^^^^^^^^^^^^^^^^^^^ evaluation of `read_cast_numeric::{constant#16}` failed inside this call
   |
note: inside `read_as::<i64>`
  --> /checkout/tests/ui/consts/const-eval/c-variadic-fail.rs:39:5
   |
LL |     ap.next_arg::<T>()
   |     ^^^^^^^^^^^^^^^^^^
note: inside `VaList::<'_>::next_arg::<i64>`
  --> /rustc/FAKE_PREFIX/library/core/src/ffi/va_list.rs:509:0

note: erroneous constant encountered
  --> /checkout/tests/ui/consts/const-eval/c-variadic-fail.rs:82:5
   |
LL |     const { read_as::<i64>(u64::MAX) };
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

note: erroneous constant encountered
  --> /checkout/tests/ui/consts/const-eval/c-variadic-fail.rs:82:5
   |
LL |     const { read_as::<i64>(u64::MAX) };
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`

error[E0080]: va_arg value mismatch: value `9223372036854775808_u64` cannot be represented by type `i64`
##[error]  --> /checkout/tests/ui/consts/const-eval/c-variadic-fail.rs:84:13
   |
LL | unsafe fn read_cast_numeric() {
...
LL |     const { read_as::<i64>(i64::MAX as u64 + 1) };
   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ evaluation of `read_cast_numeric::{constant#17}` failed inside this call
   |
note: inside `read_as::<i64>`
  --> /checkout/tests/ui/consts/const-eval/c-variadic-fail.rs:39:5
   |
LL |     ap.next_arg::<T>()
   |     ^^^^^^^^^^^^^^^^^^
note: inside `VaList::<'_>::next_arg::<i64>`
  --> /rustc/FAKE_PREFIX/library/core/src/ffi/va_list.rs:509:0

note: erroneous constant encountered
  --> /checkout/tests/ui/consts/const-eval/c-variadic-fail.rs:84:5
   |
LL |     const { read_as::<i64>(i64::MAX as u64 + 1) };
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

note: erroneous constant encountered
  --> /checkout/tests/ui/consts/const-eval/c-variadic-fail.rs:84:5
   |
LL |     const { read_as::<i64>(i64::MAX as u64 + 1) };
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`

error[E0080]: va_arg type mismatch: requested `i32` is incompatible with next argument of type `u64`
##[error]  --> /checkout/tests/ui/consts/const-eval/c-variadic-fail.rs:87:13
   |
LL | unsafe fn read_cast_numeric() {
...
LL |     const { read_as::<i32>(1u64) };
   |             ^^^^^^^^^^^^^^^^^^^^ evaluation of `read_cast_numeric::{constant#18}` failed inside this call
   |
note: inside `read_as::<i32>`
  --> /checkout/tests/ui/consts/const-eval/c-variadic-fail.rs:39:5
   |
LL |     ap.next_arg::<T>()
   |     ^^^^^^^^^^^^^^^^^^
note: inside `VaList::<'_>::next_arg::<i32>`
  --> /rustc/FAKE_PREFIX/library/core/src/ffi/va_list.rs:509:0

note: erroneous constant encountered
  --> /checkout/tests/ui/consts/const-eval/c-variadic-fail.rs:87:5
   |
LL |     const { read_as::<i32>(1u64) };
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

note: erroneous constant encountered
  --> /checkout/tests/ui/consts/const-eval/c-variadic-fail.rs:87:5
   |
LL |     const { read_as::<i32>(1u64) };
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`

error[E0080]: va_arg type mismatch: requested `f64` is incompatible with next argument of type `i32`
##[error]  --> /checkout/tests/ui/consts/const-eval/c-variadic-fail.rs:90:13
   |
LL | unsafe fn read_cast_numeric() {
...
LL |     const { read_as::<f64>(1i32) };
   |             ^^^^^^^^^^^^^^^^^^^^ evaluation of `read_cast_numeric::{constant#19}` failed inside this call
   |
note: inside `read_as::<f64>`
  --> /checkout/tests/ui/consts/const-eval/c-variadic-fail.rs:39:5
   |
LL |     ap.next_arg::<T>()
   |     ^^^^^^^^^^^^^^^^^^
note: inside `VaList::<'_>::next_arg::<f64>`
  --> /rustc/FAKE_PREFIX/library/core/src/ffi/va_list.rs:509:0

note: erroneous constant encountered
  --> /checkout/tests/ui/consts/const-eval/c-variadic-fail.rs:90:5
   |
LL |     const { read_as::<f64>(1i32) };
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

note: erroneous constant encountered
  --> /checkout/tests/ui/consts/const-eval/c-variadic-fail.rs:90:5
   |
LL |     const { read_as::<f64>(1i32) };
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`

error[E0080]: va_arg type mismatch: requested `*const u16` is incompatible with next argument of type `*const c_void`
##[error]  --> /checkout/tests/ui/consts/const-eval/c-variadic-fail.rs:113:13
   |
LL | unsafe fn read_cast_pointer() {
...
LL |     const { read_as::<*const u16>(ptr::dangling::<c_void>()) };
   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ evaluation of `read_cast_pointer::{constant#12}` failed inside this call
   |
note: inside `read_as::<*const u16>`
  --> /checkout/tests/ui/consts/const-eval/c-variadic-fail.rs:39:5
   |
LL |     ap.next_arg::<T>()
   |     ^^^^^^^^^^^^^^^^^^
note: inside `VaList::<'_>::next_arg::<*const u16>`
  --> /rustc/FAKE_PREFIX/library/core/src/ffi/va_list.rs:509:0

note: erroneous constant encountered
  --> /checkout/tests/ui/consts/const-eval/c-variadic-fail.rs:113:5
   |
LL |     const { read_as::<*const u16>(ptr::dangling::<c_void>()) };
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

note: erroneous constant encountered
  --> /checkout/tests/ui/consts/const-eval/c-variadic-fail.rs:113:5
   |
LL |     const { read_as::<*const u16>(ptr::dangling::<c_void>()) };
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`

error[E0080]: va_arg type mismatch: requested `*const c_void` is incompatible with next argument of type `*const u16`
##[error]  --> /checkout/tests/ui/consts/const-eval/c-variadic-fail.rs:115:13
   |
LL | unsafe fn read_cast_pointer() {
...
LL |     const { read_as::<*const c_void>(ptr::dangling::<u16>()) };
   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ evaluation of `read_cast_pointer::{constant#13}` failed inside this call
   |
note: inside `read_as::<*const c_void>`
  --> /checkout/tests/ui/consts/const-eval/c-variadic-fail.rs:39:5
   |
LL |     ap.next_arg::<T>()
   |     ^^^^^^^^^^^^^^^^^^
note: inside `VaList::<'_>::next_arg::<*const c_void>`
  --> /rustc/FAKE_PREFIX/library/core/src/ffi/va_list.rs:509:0

note: erroneous constant encountered
  --> /checkout/tests/ui/consts/const-eval/c-variadic-fail.rs:115:5
   |
LL |     const { read_as::<*const c_void>(ptr::dangling::<u16>()) };
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

note: erroneous constant encountered
  --> /checkout/tests/ui/consts/const-eval/c-variadic-fail.rs:115:5
   |
LL |     const { read_as::<*const c_void>(ptr::dangling::<u16>()) };
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`

error[E0080]: va_arg type mismatch: requested `*const u16` is incompatible with next argument of type `*const i32`
##[error]  --> /checkout/tests/ui/consts/const-eval/c-variadic-fail.rs:117:13
   |
LL | unsafe fn read_cast_pointer() {
...
LL |     const { read_as::<*const u16>(ptr::dangling::<i32>()) };
   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ evaluation of `read_cast_pointer::{constant#14}` failed inside this call
   |
note: inside `read_as::<*const u16>`
  --> /checkout/tests/ui/consts/const-eval/c-variadic-fail.rs:39:5
   |
LL |     ap.next_arg::<T>()
   |     ^^^^^^^^^^^^^^^^^^
note: inside `VaList::<'_>::next_arg::<*const u16>`
  --> /rustc/FAKE_PREFIX/library/core/src/ffi/va_list.rs:509:0

note: erroneous constant encountered
  --> /checkout/tests/ui/consts/const-eval/c-variadic-fail.rs:117:5
   |
LL |     const { read_as::<*const u16>(ptr::dangling::<i32>()) };
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

note: erroneous constant encountered
  --> /checkout/tests/ui/consts/const-eval/c-variadic-fail.rs:117:5
   |
LL |     const { read_as::<*const u16>(ptr::dangling::<i32>()) };
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`

error[E0080]: va_arg type mismatch: requested `*const u8` is incompatible with next argument of type `usize`
##[error]  --> /checkout/tests/ui/consts/const-eval/c-variadic-fail.rs:120:13
   |
LL | unsafe fn read_cast_pointer() {
...
LL |     const { read_as::<*const u8>(1usize) };
   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ evaluation of `read_cast_pointer::{constant#15}` failed inside this call
   |
note: inside `read_as::<*const u8>`
  --> /checkout/tests/ui/consts/const-eval/c-variadic-fail.rs:39:5
   |
LL |     ap.next_arg::<T>()
   |     ^^^^^^^^^^^^^^^^^^
note: inside `VaList::<'_>::next_arg::<*const u8>`
  --> /rustc/FAKE_PREFIX/library/core/src/ffi/va_list.rs:509:0

note: erroneous constant encountered
  --> /checkout/tests/ui/consts/const-eval/c-variadic-fail.rs:120:5
   |
LL |     const { read_as::<*const u8>(1usize) };
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

note: erroneous constant encountered
  --> /checkout/tests/ui/consts/const-eval/c-variadic-fail.rs:120:5
   |
LL |     const { read_as::<*const u8>(1usize) };
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`

error[E0080]: constructing invalid value of type NonNull<c_void>: at .pointer, encountered 0, but expected something greater or equal to 1
##[error]  --> /checkout/tests/ui/consts/const-eval/c-variadic-fail.rs:125:13
   |
LL | unsafe fn read_cast_null() {
LL |     const { read_as::<NonNull<c_void>>(ptr::null::<c_void>()) };
   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ evaluation of `read_cast_null::{constant#0}` failed inside this call
   |
note: inside `read_as::<NonNull<c_void>>`
  --> /checkout/tests/ui/consts/const-eval/c-variadic-fail.rs:39:5
   |
LL |     ap.next_arg::<T>()
   |     ^^^^^^^^^^^^^^^^^^
note: inside `VaList::<'_>::next_arg::<NonNull<c_void>>`
  --> /rustc/FAKE_PREFIX/library/core/src/ffi/va_list.rs:509:0

note: erroneous constant encountered
  --> /checkout/tests/ui/consts/const-eval/c-variadic-fail.rs:125:5
   |
LL |     const { read_as::<NonNull<c_void>>(ptr::null::<c_void>()) };
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

note: erroneous constant encountered
  --> /checkout/tests/ui/consts/const-eval/c-variadic-fail.rs:125:5
   |
LL |     const { read_as::<NonNull<c_void>>(ptr::null::<c_void>()) };
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`

error[E0080]: constructing invalid value of type NonNull<c_void>: at .pointer, encountered 0, but expected something greater or equal to 1
##[error]  --> /checkout/tests/ui/consts/const-eval/c-variadic-fail.rs:127:13
   |
LL | unsafe fn read_cast_null() {
...
LL |     const { read_as::<NonNull<c_void>>(ptr::null_mut::<c_void>()) };
   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ evaluation of `read_cast_null::{constant#1}` failed inside this call
   |
note: inside `read_as::<NonNull<c_void>>`
  --> /checkout/tests/ui/consts/const-eval/c-variadic-fail.rs:39:5
   |
LL |     ap.next_arg::<T>()
   |     ^^^^^^^^^^^^^^^^^^
note: inside `VaList::<'_>::next_arg::<NonNull<c_void>>`
  --> /rustc/FAKE_PREFIX/library/core/src/ffi/va_list.rs:509:0

note: erroneous constant encountered
  --> /checkout/tests/ui/consts/const-eval/c-variadic-fail.rs:127:5
   |
LL |     const { read_as::<NonNull<c_void>>(ptr::null_mut::<c_void>()) };
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

note: erroneous constant encountered
  --> /checkout/tests/ui/consts/const-eval/c-variadic-fail.rs:127:5
   |
LL |     const { read_as::<NonNull<c_void>>(ptr::null_mut::<c_void>()) };
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`

error[E0080]: constructing invalid value of type NonNull<c_void>: at .pointer, encountered 0, but expected something greater or equal to 1
---

note: erroneous constant encountered
  --> /checkout/tests/ui/consts/const-eval/c-variadic-fail.rs:255:5
   |
LL |     const { unsafe { helper(1, 2, 3) } };
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

note: erroneous constant encountered
  --> /checkout/tests/ui/consts/const-eval/c-variadic-fail.rs:255:5
   |
LL |     const { unsafe { helper(1, 2, 3) } };
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`

error[E0080]: pointer not dereferenceable: pointer must point to some allocation, but got null pointer
##[error]  --> /checkout/tests/ui/consts/const-eval/c-variadic-fail.rs:263:5
   |
LL | fn drop_of_invalid() {
LL |     const {
...
LL |     }
   |     ^ evaluation of `drop_of_invalid::{constant#0}` failed inside this call
   |
note: inside `std::ptr::drop_glue::<VaList<'_>> - shim(Some(VaList<'_>))`
  --> /rustc/FAKE_PREFIX/library/core/src/ptr/mod.rs:844:0
note: inside `<VaList<'_> as Drop>::drop`
  --> /rustc/FAKE_PREFIX/library/core/src/ffi/va_list.rs:262:0

note: erroneous constant encountered
  --> /checkout/tests/ui/consts/const-eval/c-variadic-fail.rs:260:5
   |
LL | /     const {
LL | |         let mut invalid: MaybeUninit<VaList> = MaybeUninit::zeroed();
LL | |         let ap = unsafe { invalid.assume_init() };
LL | |     }
   | |_____^

note: erroneous constant encountered
  --> /checkout/tests/ui/consts/const-eval/c-variadic-fail.rs:260:5
   |
LL | /     const {
LL | |         let mut invalid: MaybeUninit<VaList> = MaybeUninit::zeroed();
LL | |         let ap = unsafe { invalid.assume_init() };
LL | |     }
   | |_____^
   |
   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`

---

---- [ui] tests/ui/consts/const-eval/c-variadic-fail.rs stdout end ----
---- [ui] tests/ui/consts/const-eval/c-variadic.rs stdout ----

error: test did not exit with success! code=None so test would pass with `run-crash`
status: signal: 11 (SIGSEGV) (core dumped)
command: cd "/checkout/obj/build/aarch64-unknown-linux-gnu/test/ui/consts/const-eval/c-variadic" && RUSTC="/checkout/obj/build/aarch64-unknown-linux-gnu/stage2/bin/rustc" RUST_TEST_THREADS="4" "/checkout/obj/build/aarch64-unknown-linux-gnu/test/ui/consts/const-eval/c-variadic/a"
stdout: none
stderr: none

---- [ui] tests/ui/consts/const-eval/c-variadic.rs stdout end ----

[theemathas]

I assume that, once this PR is merged, we can re-stabilize VaArgSafe?

[asquared31415]

I think that, per #162478 (comment) there needs to be some sort of improvement to the details of this trait as a whole. It's "obviously correct" for wrappers around c_int to implement VaArgSafe, but right now they do not have a way to do so. Stabilizing things as-is (even with this PR) means that any future mechanism for permitting a type to implement VaArgSafe becomes a new semver hazard, as implementing it is a breaking change to all consumers of that type. Stabilizing VaArgSafe right now would mean committing to "we will never automatically implement VaArgSafe for any type, and we will never implement VaArgSafe on any types in std that are stable without it".

[theemathas]

@asquared31415 The VaArgSafe trait is currently sealed. So, users can only rely on fundamental types and local user-defined types not implementing the trait.

So, by stabilizing VaArgSafe, we're committing to:

• VaArgSafe being a trait
• VaArgSafe not being implemented on Pin or Box
• Not automatically implementing VaArgSafe on user-defined types