Externally implementable items

[jdonszelmann]

Supersedes #140010
Tracking issue: #125418

Getting started:

#![feature(eii)]

#[eii(eii1)]
pub fn decl1(x: u64) 
// body optional (it's the default)
{
    println!("default {x}");
}

// in another crate, maybe
#[eii1]
pub fn decl2(x: u64) {
    println!("explicit {x}");
}

fn main() {
    decl1(4);
}

• tiny perf regression, underlying issue makes multiple things in the compiler slow, not just EII, planning to solve those separately.
• No codegen_gcc support, they don't have bindings for weak symbols yet but could
• No windows support yet for weak definitions

This PR merges the implementation of EII for just llvm + not windows, doesn't yet contain like a new panic handler implementation or alloc handler. With this implementation, it would support implementing the panic handler in terms of EII already since it requires no default implementation so no weak symbols

The PR has been open in various forms for about a year now, but I feel that having some implementation merged to build upon

[jdonszelmann]

@bors2 try @rust-timer queue

[rust-bors]

☀️ Try build successful (CI)
Build commit: d5a6633 (d5a66337e06d3b77a1ab8f6793055535195c3ae9, parent: 364da5d88d772fa40fb20353443595385443ac25)

[rust-timer]

Finished benchmarking commit (d5a6633): comparison URL.

Overall result: ❌ regressions - please read the text below

Benchmarking this pull request means it may be perf-sensitive – we'll automatically label it not fit for rolling up. You can override this, but we strongly advise not to, due to possible changes in compiler perf.

Next Steps: If you can justify the regressions found in this try perf run, please do so in sufficient writing along with @rustbot label: +perf-regression-triaged. If not, please fix the regressions and do another perf run. If its results are neutral or positive, the label will be automatically removed.

@bors rollup=never
@rustbot label: -S-waiting-on-perf +perf-regression

Instruction count

Our most reliable metric. Used to determine the overall result above. However, even this metric can be noisy.

	mean	range	count
Regressions ❌ (primary)	0.3%	[0.1%, 1.5%]	19
Regressions ❌ (secondary)	0.4%	[0.1%, 1.0%]	44
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-0.0%	[-0.1%, -0.0%]	4
All ❌✅ (primary)	0.3%	[0.1%, 1.5%]	19

Max RSS (memory usage)

Results (primary 1.7%, secondary 3.9%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	1.7%	[0.6%, 2.3%]	6
Regressions ❌ (secondary)	4.7%	[1.1%, 11.2%]	16
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.1%	[-2.9%, -1.2%]	2
All ❌✅ (primary)	1.7%	[0.6%, 2.3%]	6

Cycles

Results (primary 3.1%, secondary -1.3%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	3.1%	[3.1%, 3.1%]	1
Regressions ❌ (secondary)	3.2%	[2.5%, 3.6%]	3
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.8%	[-4.1%, -2.0%]	9
All ❌✅ (primary)	3.1%	[3.1%, 3.1%]	1

Binary size

Results (primary 0.0%, secondary 0.1%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	0.0%	[0.0%, 0.1%]	93
Regressions ❌ (secondary)	0.1%	[0.0%, 0.3%]	61
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.0%	[0.0%, 0.1%]	93

Bootstrap: 468.052s -> 471.14s (0.66%)
Artifact size: 387.52 MiB -> 390.25 MiB (0.71%)

[jdonszelmann]

Well, shit. I think I know some fixes but I hoped this wouldn't happen

[jdonszelmann]

nope, still not. well let's at least test mingw

@bors try jobs=x86_64-mingw-1

[rust-bors]

☀️ Try build successful (CI)
Build commit: ac3a540 (ac3a540eefa022a9ca61a06b34b6511a694457c8, parent: eb171a227f9e5de5d376b6edb56b174bc8235fb3)

[jdonszelmann]

Well, fixed mingw, just a warning remaining...

[jdonszelmann]

ah forgot to bless a test

[jdonszelmann]

@rustbot review
let's try once more... nothing really changed except that I now explicitly exclude windows targets. I knew windows didn't work, but somehow I never actually remembered to exclude windows from running tests...

windows now passes (see try build). I guess it's time for another attempt at big ci

[jdonszelmann]

@bors r=lcnr,oli-obk

[bors]

📌 Commit 065e4c1 has been approved by lcnr,oli-obk

It is now in the queue for this repository.

[bors]

⌛ Testing commit 065e4c1 with merge 3f4dc1e...

[bors]

☀️ Test successful - checks-actions
Approved by: lcnr,oli-obk
Pushing 3f4dc1e to main...

[github-actions]

What is this?

This is an experimental post-merge analysis report that shows differences in test outcomes between the merged PR and its parent PR.

Comparing 2cd4ee6 (parent) -> 3f4dc1e (this PR)

Test differences

Show 153 test diffs

Stage 0

• errors::verify_builtin_macros_eii_extern_target_expected_list_94: [missing] -> pass (J2)
• errors::verify_builtin_macros_eii_extern_target_expected_unsafe_95: [missing] -> pass (J2)
• errors::verify_builtin_macros_eii_only_once_97: [missing] -> pass (J2)
• errors::verify_builtin_macros_eii_shared_macro_expected_function_96: [missing] -> pass (J2)
• errors::verify_builtin_macros_eii_shared_macro_expected_max_one_argument_98: [missing] -> pass (J2)
• errors::verify_passes_duplicate_eii_impls_120: [missing] -> pass (J2)
• errors::verify_passes_eii_fn_with_track_caller_118: [missing] -> pass (J2)
• errors::verify_passes_eii_impl_not_function_117: [missing] -> pass (J2)
• errors::verify_passes_eii_without_impl_119: [missing] -> pass (J2)

Stage 1

• errors::verify_builtin_macros_eii_extern_target_expected_list_94: [missing] -> pass (J0)
• errors::verify_builtin_macros_eii_extern_target_expected_macro_93: [missing] -> pass (J0)
• errors::verify_builtin_macros_eii_extern_target_expected_unsafe_95: [missing] -> pass (J0)
• errors::verify_builtin_macros_eii_only_once_97: [missing] -> pass (J0)
• errors::verify_builtin_macros_eii_shared_macro_expected_function_96: [missing] -> pass (J0)
• errors::verify_builtin_macros_eii_shared_macro_expected_max_one_argument_98: [missing] -> pass (J0)
• errors::verify_passes_duplicate_eii_impls_120: [missing] -> pass (J0)
• errors::verify_passes_eii_fn_with_track_caller_118: [missing] -> pass (J0)
• errors::verify_passes_eii_without_impl_119: [missing] -> pass (J0)
• [ui] tests/ui/eii/codegen_cross_crate.rs: [missing] -> pass (J2)
• [ui] tests/ui/eii/cross_crate.rs: [missing] -> pass (J2)
• [ui] tests/ui/eii/cross_crate_wrong_ty.rs: [missing] -> pass (J2)
• [ui] tests/ui/eii/default/call_default.rs: [missing] -> pass (J2)
• [ui] tests/ui/eii/default/call_impl.rs: [missing] -> pass (J2)
• [ui] tests/ui/eii/default/local_crate.rs: [missing] -> pass (J2)
• [ui] tests/ui/eii/default/local_crate_explicit.rs: [missing] -> pass (J2)
• [ui] tests/ui/eii/duplicate/duplicate1.rs: [missing] -> pass (J2)
• [ui] tests/ui/eii/duplicate/duplicate2.rs: [missing] -> pass (J2)
• [ui] tests/ui/eii/errors.rs: [missing] -> pass (J2)
• [ui] tests/ui/eii/multiple_decls.rs: [missing] -> pass (J2)
• [ui] tests/ui/eii/multiple_impls.rs: [missing] -> pass (J2)
• [ui] tests/ui/eii/privacy1.rs: [missing] -> pass (J2)
• [ui] tests/ui/eii/privacy2.rs: [missing] -> pass (J2)
• [ui] tests/ui/eii/same-symbol.rs: [missing] -> pass (J2)
• [ui] tests/ui/eii/subtype_1.rs: [missing] -> pass (J2)
• [ui] tests/ui/eii/subtype_2.rs: [missing] -> pass (J2)
• [ui] tests/ui/eii/subtype_4.rs: [missing] -> pass (J2)
• [ui] tests/ui/eii/unsafe_impl_err.rs: [missing] -> pass (J2)
• [ui] tests/ui/eii/unsafe_impl_ok.rs: [missing] -> pass (J2)
• [ui] tests/ui/eii/wrong_ret_ty.rs: [missing] -> pass (J2)
• [ui] tests/ui/eii/wrong_target.rs: [missing] -> pass (J2)
• [ui] tests/ui/eii/wrong_ty.rs: [missing] -> pass (J2)
• [ui] tests/ui/eii/wrong_ty_2.rs: [missing] -> pass (J2)
• [ui] tests/ui/error-codes/E0806.rs: [missing] -> pass (J2)
• [ui] tests/ui/feature-gates/feature-gate-eii-internals.rs: [missing] -> pass (J2)
• [ui] tests/ui/feature-gates/feature-gate-extern-item-impls.rs: [missing] -> pass (J2)

Stage 2

• [ui] tests/ui/eii/codegen_cross_crate.rs: [missing] -> pass (J1)
• [ui] tests/ui/eii/codegen_single_crate.rs: [missing] -> pass (J1)
• [ui] tests/ui/eii/default/call_impl.rs: [missing] -> pass (J1)
• [ui] tests/ui/eii/default/local_crate.rs: [missing] -> pass (J1)
• [ui] tests/ui/eii/default/local_crate_explicit.rs: [missing] -> pass (J1)
• [ui] tests/ui/eii/duplicate/duplicate1.rs: [missing] -> pass (J1)
• [ui] tests/ui/eii/duplicate/duplicate2.rs: [missing] -> pass (J1)
• [ui] tests/ui/eii/duplicate/duplicate3.rs: [missing] -> pass (J1)
• [ui] tests/ui/eii/multiple_impls.rs: [missing] -> pass (J1)
• [ui] tests/ui/eii/privacy1.rs: [missing] -> pass (J1)
• [ui] tests/ui/eii/same-symbol.rs: [missing] -> pass (J1)
• [ui] tests/ui/eii/codegen_cross_crate.rs: [missing] -> ignore (ignored when the operating system is windows) (J3)
• [ui] tests/ui/eii/codegen_single_crate.rs: [missing] -> ignore (ignored when the operating system is windows) (J3)
• [ui] tests/ui/eii/default/call_default.rs: [missing] -> ignore (ignored when the operating system is windows) (J3)
• [ui] tests/ui/eii/default/call_impl.rs: [missing] -> ignore (ignored when the operating system is windows) (J3)
• [ui] tests/ui/eii/default/local_crate.rs: [missing] -> ignore (ignored when the operating system is windows) (J3)
• [ui] tests/ui/eii/default/local_crate_explicit.rs: [missing] -> ignore (ignored when the operating system is windows) (J3)
• [ui] tests/ui/eii/duplicate/duplicate1.rs: [missing] -> ignore (ignored when the operating system is windows) (J3)
• [ui] tests/ui/eii/duplicate/duplicate2.rs: [missing] -> ignore (ignored when the operating system is windows) (J3)
• [ui] tests/ui/eii/duplicate/duplicate3.rs: [missing] -> ignore (ignored when the operating system is windows) (J3)
• [ui] tests/ui/eii/multiple_impls.rs: [missing] -> ignore (ignored when the operating system is windows) (J3)
• [ui] tests/ui/eii/privacy1.rs: [missing] -> ignore (ignored when the operating system is windows) (J3)
• [ui] tests/ui/eii/same-symbol.rs: [missing] -> ignore (ignored when the operating system is windows) (J3)
• [ui] tests/ui/eii/codegen_cross_crate.rs: [missing] -> ignore (gcc backend is marked as ignore) (J4)
• [ui] tests/ui/eii/codegen_single_crate.rs: [missing] -> ignore (gcc backend is marked as ignore) (J4)
• [ui] tests/ui/eii/default/call_default.rs: [missing] -> ignore (gcc backend is marked as ignore) (J4)
• [ui] tests/ui/eii/default/call_impl.rs: [missing] -> ignore (gcc backend is marked as ignore) (J4)
• [ui] tests/ui/eii/default/local_crate.rs: [missing] -> ignore (gcc backend is marked as ignore) (J4)
• [ui] tests/ui/eii/default/local_crate_explicit.rs: [missing] -> ignore (gcc backend is marked as ignore) (J4)
• [ui] tests/ui/eii/duplicate/duplicate1.rs: [missing] -> ignore (gcc backend is marked as ignore) (J4)
• [ui] tests/ui/eii/duplicate/duplicate2.rs: [missing] -> ignore (gcc backend is marked as ignore) (J4)
• [ui] tests/ui/eii/duplicate/duplicate3.rs: [missing] -> ignore (gcc backend is marked as ignore) (J4)
• [ui] tests/ui/eii/multiple_impls.rs: [missing] -> ignore (gcc backend is marked as ignore) (J4)
• [ui] tests/ui/eii/privacy1.rs: [missing] -> ignore (gcc backend is marked as ignore) (J4)
• [ui] tests/ui/eii/same-symbol.rs: [missing] -> ignore (gcc backend is marked as ignore) (J4)
• [ui] tests/ui/eii/cross_crate.rs: [missing] -> pass (J5)
• [ui] tests/ui/eii/cross_crate_wrong_ty.rs: [missing] -> pass (J5)
• [ui] tests/ui/eii/errors.rs: [missing] -> pass (J5)
• [ui] tests/ui/eii/multiple_decls.rs: [missing] -> pass (J5)
• [ui] tests/ui/eii/privacy2.rs: [missing] -> pass (J5)
• [ui] tests/ui/eii/subtype_1.rs: [missing] -> pass (J5)
• [ui] tests/ui/eii/subtype_2.rs: [missing] -> pass (J5)
• [ui] tests/ui/eii/subtype_3.rs: [missing] -> pass (J5)
• [ui] tests/ui/eii/subtype_4.rs: [missing] -> pass (J5)
• [ui] tests/ui/eii/unsafe_impl_err.rs: [missing] -> pass (J5)
• [ui] tests/ui/eii/unsafe_impl_ok.rs: [missing] -> pass (J5)
• [ui] tests/ui/eii/wrong_ret_ty.rs: [missing] -> pass (J5)
• [ui] tests/ui/eii/wrong_target.rs: [missing] -> pass (J5)
• [ui] tests/ui/eii/wrong_ty.rs: [missing] -> pass (J5)
• [ui] tests/ui/eii/wrong_ty_2.rs: [missing] -> pass (J5)
• [ui] tests/ui/error-codes/E0806.rs: [missing] -> pass (J5)
• [ui] tests/ui/feature-gates/feature-gate-eii-internals.rs: [missing] -> pass (J5)
• [ui] tests/ui/feature-gates/feature-gate-extern-item-impls.rs: [missing] -> pass (J5)
• [ui] tests/ui/eii/default/call_default.rs: [missing] -> ignore (ignored when the operating system is macos) (J6)
• [ui] tests/ui/eii/default/call_default.rs: [missing] -> pass (J7)

(and 5 additional test diffs)

Additionally, 48 doctest diffs were found. These are ignored, as they are noisy.

Job group index

• J0: aarch64-apple, aarch64-gnu, aarch64-gnu-llvm-20-2, aarch64-msvc-2, i686-gnu-2, i686-gnu-nopt-2, i686-msvc-2, x86_64-gnu, x86_64-gnu-llvm-20-1, x86_64-gnu-llvm-21-1, x86_64-gnu-nopt, x86_64-gnu-stable, x86_64-mingw-2, x86_64-msvc-2
• J1: aarch64-apple, aarch64-gnu, aarch64-gnu-llvm-20-1, arm-android, armhf-gnu, dist-i586-gnu-i586-i686-musl, i686-gnu-1, i686-gnu-nopt-1, test-various, x86_64-gnu, x86_64-gnu-debug, x86_64-gnu-llvm-20, x86_64-gnu-llvm-20-2, x86_64-gnu-llvm-21-2, x86_64-gnu-nopt, x86_64-gnu-stable
• J2: x86_64-gnu-llvm-20-3, x86_64-gnu-llvm-21-3
• J3: aarch64-msvc-1, i686-msvc-1, x86_64-mingw-1, x86_64-msvc-1
• J4: x86_64-gnu-gcc
• J5: aarch64-apple, aarch64-gnu, aarch64-gnu-llvm-20-1, aarch64-msvc-1, arm-android, armhf-gnu, dist-i586-gnu-i586-i686-musl, i686-gnu-1, i686-gnu-nopt-1, i686-msvc-1, test-various, x86_64-gnu, x86_64-gnu-debug, x86_64-gnu-gcc, x86_64-gnu-llvm-20, x86_64-gnu-llvm-20-2, x86_64-gnu-llvm-21-2, x86_64-gnu-nopt, x86_64-gnu-stable, x86_64-mingw-1, x86_64-msvc-1
• J6: aarch64-apple
• J7: aarch64-gnu, aarch64-gnu-llvm-20-1, arm-android, armhf-gnu, dist-i586-gnu-i586-i686-musl, i686-gnu-1, i686-gnu-nopt-1, test-various, x86_64-gnu, x86_64-gnu-debug, x86_64-gnu-llvm-20, x86_64-gnu-llvm-20-2, x86_64-gnu-llvm-21-2, x86_64-gnu-nopt, x86_64-gnu-stable

Test dashboard

Run

cargo run --manifest-path src/ci/citool/Cargo.toml -- \
    test-dashboard 3f4dc1e02d759aa3c3807d4efc1f7f6e293536a5 --output-dir test-dashboard

And then open test-dashboard/index.html in your browser to see an overview of all executed tests.

Job duration changes

1. dist-various-1: 6357.6s -> 4002.1s (-37.0%)
2. aarch64-apple: 8425.7s -> 10833.1s (+28.6%)
3. pr-check-1: 1689.2s -> 1977.5s (+17.1%)
4. pr-check-2: 2372.8s -> 2728.2s (+15.0%)
5. dist-x86_64-apple: 8299.8s -> 7057.8s (-15.0%)
6. x86_64-rust-for-linux: 2795.6s -> 3206.8s (+14.7%)
7. tidy: 149.0s -> 164.3s (+10.3%)
8. i686-gnu-2: 5735.3s -> 6254.3s (+9.0%)
9. x86_64-gnu-miri: 4730.6s -> 5145.0s (+8.8%)
10. x86_64-gnu-aux: 6545.2s -> 7108.9s (+8.6%)

How to interpret the job duration changes?

Job durations can vary a lot, based on the actual runner instance
that executed the job, system noise, invalidated caches, etc. The table above is provided
mostly for t-infra members, for simpler debugging of potential CI slow-downs.

[rust-timer]

Finished benchmarking commit (3f4dc1e): comparison URL.

Overall result: ❌ regressions - please read the text below

Our benchmarks found a performance regression caused by this PR.
This might be an actual regression, but it can also be just noise.

Next Steps:

• If the regression was expected or you think it can be justified,
  please write a comment with sufficient written justification, and add
  @rustbot label: +perf-regression-triaged to it, to mark the regression as triaged.
• If you think that you know of a way to resolve the regression, try to create
  a new PR with a fix for the regression.
• If you do not understand the regression or you think that it is just noise,
  you can ask the @rust-lang/wg-compiler-performance working group for help (members of this group
  were already notified of this PR).

@rustbot label: +perf-regression
cc @rust-lang/wg-compiler-performance

Instruction count

Our most reliable metric. Used to determine the overall result above. However, even this metric can be noisy.

	mean	range	count
Regressions ❌ (primary)	0.6%	[0.6%, 0.7%]	2
Regressions ❌ (secondary)	0.3%	[0.1%, 0.8%]	35
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-0.0%	[-0.1%, -0.0%]	2
All ❌✅ (primary)	0.6%	[0.6%, 0.7%]	2

Max RSS (memory usage)

Results (primary -1.8%, secondary 1.6%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	2.7%	[0.8%, 5.3%]	3
Improvements ✅ (primary)	-1.8%	[-2.4%, -1.2%]	2
Improvements ✅ (secondary)	-1.7%	[-1.7%, -1.7%]	1
All ❌✅ (primary)	-1.8%	[-2.4%, -1.2%]	2

Cycles

Results (primary 2.4%, secondary 1.4%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	2.4%	[2.4%, 2.4%]	1
Regressions ❌ (secondary)	4.4%	[2.5%, 5.2%]	7
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-5.7%	[-7.4%, -3.6%]	3
All ❌✅ (primary)	2.4%	[2.4%, 2.4%]	1

Binary size

Results (primary 0.0%, secondary 0.1%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	0.0%	[0.0%, 0.1%]	53
Regressions ❌ (secondary)	0.1%	[0.0%, 0.3%]	54
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.0%	[0.0%, 0.1%]	53

Bootstrap: 474.624s -> 478.161s (0.75%)
Artifact size: 389.52 MiB -> 390.27 MiB (0.19%)