resolve: Split extern prelude into two scopes

[petrochenkov]

One scope for extern crate items and another for --extern options, with the former shadowing the latter.

If in a single scope some things can overwrite other things, especially with ad hoc restrictions like MacroExpandedExternCrateCannotShadowExternArguments, then it's not really a single scope.
So this PR splits Scope::ExternPrelude into two cleaner scopes.

This is similar to how #144131 splits module scope into two scopes for globs and non-globs, but simpler.

[rustbot]

r? @davidtwco

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Use r? to explicitly pick a reviewer

[rustbot]

These commits modify the Cargo.lock file. Unintentional changes to Cargo.lock can be introduced when switching branches and rebasing PRs.

If this was unintentional then you should revert the changes before this PR is merged.
Otherwise, you can ignore this comment.

[petrochenkov]

Blocked on #144746.
@rustbot blocked

[petrochenkov]

@bors2 try @rust-timer queue

[rust-bors]

⌛ Trying commit 4d377d2 with merge 7203fa8…

To cancel the try build, run the command @bors try cancel.

[rustbot]

Unknown labels: S-waiting-on-perf

[rust-bors]

☀️ Try build successful (CI)
Build commit: 7203fa8 (7203fa84a1f9a0aa515efc5f680f761ea01d95fc, parent: 4b55fe199cfe9c710555a5af7f2a49491ad38254)

[rust-timer]

Finished benchmarking commit (7203fa8): 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)	0.1%	[0.1%, 0.2%]	5
Regressions ❌ (secondary)	0.1%	[0.0%, 0.2%]	12
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.1%	[0.1%, 0.2%]	5

Max RSS (memory usage)

Results (primary 2.0%, secondary -3.3%)

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

	mean	range	count
Regressions ❌ (primary)	2.0%	[2.0%, 2.0%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-3.3%	[-4.2%, -2.4%]	2
All ❌✅ (primary)	2.0%	[2.0%, 2.0%]	1

Cycles

Results (secondary 0.7%)

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)	3.9%	[2.9%, 4.4%]	3
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-4.1%	[-5.2%, -3.0%]	2
All ❌✅ (primary)	-	-	0

Binary size

This benchmark run did not return any relevant results for this metric.

Bootstrap: 467.125s -> 467.279s (0.03%)
Artifact size: 376.83 MiB -> 376.88 MiB (0.01%)

[petrochenkov]

The error on CI is basically from this case:

// main.rs
extern crate std as something;

fn main() {
    something::println!();
}

// command line
rustc --extern something=/path/to/nowhere main.rs

Previously we didn't try to load something from --extern because it was shadowed, now we try and fail.
(Except on CI the loading succeeds and results in duplicate lang items later, but the root reason is the same.)

[petrochenkov]

The error on CI is basically from this case:

// main.rs
extern crate std as something;

fn main() {
    something::println!();
}

// command line
rustc --extern something=/path/to/nowhere main.rs

Previously we didn't try to load something from --extern because it was shadowed, now we try and fail. (Except on CI the loading succeeds and results in duplicate lang items later, but the root reason is the same.)

Addressed in #145113.
@rustbot blocked

[petrochenkov]

I've included a piece of #145113 only affecting --extern flags into this PR.
@rustbot ready

[rustbot]

Some changes occurred in src/tools/clippy

cc @rust-lang/clippy

[davidtwco]

LGTM if there aren't more changes you want to make and CI is passing

[petrochenkov]

@bors r=davidtwco

[bors]

📌 Commit 9aa6cb5 has been approved by davidtwco

It is now in the queue for this repository.

[bors]

⌛ Testing commit 9aa6cb5 with merge 8e77954...

[bors]

☀️ Test successful - checks-actions
Approved by: davidtwco
Pushing 8e77954 to master...

[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 3672a55 (parent) -> 8e77954 (this PR)

Test differences

Show 22 test diffs

Stage 1

• [ui] tests/ui/resolve/extern-prelude-speculative.rs: [missing] -> pass (J1)

Stage 2

• [ui] tests/ui/resolve/extern-prelude-speculative.rs: [missing] -> pass (J0)

Additionally, 20 doctest diffs were found. These are ignored, as they are noisy.

Job group index

• J0: aarch64-apple, aarch64-gnu, aarch64-gnu-llvm-19-1, 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-apple-2, x86_64-gnu, x86_64-gnu-llvm-19, x86_64-gnu-llvm-19-2, x86_64-gnu-llvm-20-2, x86_64-gnu-nopt, x86_64-gnu-stable, x86_64-mingw-1, x86_64-msvc-1
• J1: x86_64-gnu-llvm-19-3, x86_64-gnu-llvm-20-3

Test dashboard

Run

cargo run --manifest-path src/ci/citool/Cargo.toml -- \
    test-dashboard 8e7795415acaa9471b5eeb2301915d6996d289ec --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-x86_64-apple: 11797.7s -> 18031.9s (52.8%)
2. dist-aarch64-linux: 8640.0s -> 6005.8s (-30.5%)
3. aarch64-apple: 6841.8s -> 5245.9s (-23.3%)
4. aarch64-msvc-1: 7552.7s -> 6718.1s (-11.1%)
5. x86_64-apple-2: 7080.6s -> 7840.2s (10.7%)
6. dist-apple-various: 5541.7s -> 5039.5s (-9.1%)
7. x86_64-gnu-llvm-20-1: 3393.3s -> 3698.2s (9.0%)
8. dist-x86_64-netbsd: 5005.2s -> 4591.3s (-8.3%)
9. aarch64-gnu-debug: 4973.0s -> 4669.2s (-6.1%)
10. dist-i686-msvc: 8237.1s -> 7746.4s (-6.0%)

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 (8e77954): comparison URL.

Overall result: ❌✅ regressions and improvements - 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)	0.2%	[0.2%, 0.2%]	2
Regressions ❌ (secondary)	0.7%	[0.3%, 1.9%]	4
Improvements ✅ (primary)	-0.4%	[-0.7%, -0.2%]	5
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-0.2%	[-0.7%, 0.2%]	7

Max RSS (memory usage)

Results (primary -7.3%, secondary 2.9%)

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)	2.9%	[2.9%, 2.9%]	1
Improvements ✅ (primary)	-7.3%	[-7.3%, -7.3%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-7.3%	[-7.3%, -7.3%]	1

Cycles

Results (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)	1.6%	[1.6%, 1.6%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Binary size

Results (secondary -0.4%)

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)	0.1%	[0.1%, 0.1%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-0.4%	[-0.8%, -0.1%]	6
All ❌✅ (primary)	-	-	0

Bootstrap: 468.653s -> 469.796s (0.24%)
Artifact size: 377.36 MiB -> 377.36 MiB (-0.00%)