add a FCW for overflow errors with the next solver

[adwinwhite]

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The old solver doesn't check cache entry's depth requirement when looking up cache while the next solver correctly does so. It's necessary to behave correctly with respect to incremental compilation.
As a result, the next solver is more likely to run into overflow errors.

We try to catch such breakages by rerun the evaluation with doubled recursion limit and if that succeeds we emit a FCW.

This PR is being discussed on zulip

The lint issue is #159228

r? @lcnr

[adwinwhite]

@bors try @rust-timer queue

[rust-bors]

☀️ Try build successful (CI)
Build commit: 6eb68d9 (6eb68d9057fb9a60e047c7c7dcc9b67b9cedc1a7)
Base parent: 5503df8 (5503df87342a73d0c29126a7e08dc9c1255c46ad)

[rust-timer]

Finished benchmarking commit (6eb68d9): comparison URL.

Overall result: ❌ regressions - please read:

Benchmarking means the PR may be perf-sensitive. It's automatically marked not fit for rolling up. Overriding is possible but disadvised: it risks changing compiler perf.

Next, please: If you can, justify the regressions found in this try perf run in writing along with @rustbot label: +perf-regression-triaged. If not, fix the regressions and do another perf run. Neutral or positive results will clear the label automatically.

@bors rollup=never rustc-perf
@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
Regressions ❌ (secondary)	2.3%	[0.3%, 4.5%]	9
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Max RSS (memory usage)

Results (primary -2.1%, secondary -0.9%)

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)	1.4%	[0.8%, 2.5%]	3
Improvements ✅ (primary)	-2.1%	[-2.1%, -2.1%]	1
Improvements ✅ (secondary)	-4.5%	[-4.7%, -4.3%]	2
All ❌✅ (primary)	-2.1%	[-2.1%, -2.1%]	1

Cycles

Results (secondary -4.2%)

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
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-4.2%	[-5.7%, -2.7%]	2
All ❌✅ (primary)	-	-	0

Binary size

This perf run didn't have relevant results for this metric.

Bootstrap: 487.42s -> 490.943s (0.72%)
Artifact size: 389.91 MiB -> 389.35 MiB (-0.15%)

[rust-bors]

💔 Test for 6ad9bb2 failed: CI. Failed job:

• auto - x86_64-gnu-next-trait-solver-polonius (web logs, enhanced plaintext logs)

[rust-log-analyzer]

A job failed! Check out the build log: (web) (plain enhanced) (plain)

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

[jieyouxu]

@bors retry

[rust-bors]

💔 Test for 1344a90 failed: CI. Failed job:

• auto - dist-x86_64-mingw (web logs, enhanced plaintext logs)

[JonathanBrouwer]

@bors retry

[rust-log-analyzer]

A job failed! Check out the build log: (web) (plain enhanced) (plain)

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

[jieyouxu]

@bors retry

[JonathanBrouwer]

@bors p=101
Scheduling

[rust-bors]

☀️ Test successful - CI
Approved by: lcnr
Duration: 3h 15m 48s
Pushing dc3f851 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 5e2e873 (parent) -> dc3f851 (this PR)

Test differences

Show 640 test diffs

Stage 1

• [ui (polonius)] tests/ui/traits/next-solver/overflow/fcw-on-auto-trait.rs#next: [missing] -> pass (J1)
• [ui (polonius)] tests/ui/traits/next-solver/overflow/fcw-on-auto-trait.rs#old: [missing] -> pass (J1)
• [ui (polonius)] tests/ui/traits/next-solver/overflow/fcw-on-normalization.rs#next: [missing] -> pass (J1)
• [ui (polonius)] tests/ui/traits/next-solver/overflow/fcw-on-normalization.rs#old: [missing] -> pass (J1)
• [ui] tests/ui/traits/next-solver/overflow/fcw-on-auto-trait.rs#next: [missing] -> pass (J2)
• [ui] tests/ui/traits/next-solver/overflow/fcw-on-auto-trait.rs#old: [missing] -> pass (J2)
• [ui] tests/ui/traits/next-solver/overflow/fcw-on-normalization.rs#next: [missing] -> pass (J2)
• [ui] tests/ui/traits/next-solver/overflow/fcw-on-normalization.rs#old: [missing] -> pass (J2)

Stage 2

• [ui] tests/ui/traits/next-solver/overflow/fcw-on-auto-trait.rs#next: [missing] -> pass (J0)
• [ui] tests/ui/traits/next-solver/overflow/fcw-on-auto-trait.rs#old: [missing] -> pass (J0)
• [ui] tests/ui/traits/next-solver/overflow/fcw-on-normalization.rs#next: [missing] -> pass (J0)
• [ui] tests/ui/traits/next-solver/overflow/fcw-on-normalization.rs#old: [missing] -> pass (J0)

Additionally, 628 doctest diffs were found. These are ignored, as they are noisy.

Job group index

• J0: aarch64-apple, aarch64-apple-macos-26, aarch64-gnu, aarch64-gnu-llvm-21-1, aarch64-msvc-1, arm-android, armhf-gnu, dist-i586-gnu-i586-i686-musl, i686-gnu-1, i686-gnu-nopt-1, i686-msvc-1, optional-x86_64-gnu-parallel-frontend, test-various, x86_64-gnu, x86_64-gnu-debug, x86_64-gnu-gcc, x86_64-gnu-llvm-21, x86_64-gnu-llvm-21-2, x86_64-gnu-llvm-22-2, x86_64-gnu-nopt, x86_64-gnu-stable, x86_64-mingw-1, x86_64-msvc-1
• J1: x86_64-gnu-next-trait-solver-polonius
• J2: x86_64-gnu-llvm-21-3, x86_64-gnu-llvm-22-3, x86_64-gnu-next-trait-solver-polonius

Test dashboard

Run

cargo run --manifest-path src/ci/citool/Cargo.toml -- \
    test-dashboard dc3f85158a955a87a6e4363af1fbe9cf2d063cce --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. x86_64-gnu-gcc-core-tests: 6m 16s -> 15m 36s (+148.9%)
2. dist-i686-linux: 1h 25m -> 1h 57m (+38.5%)
3. x86_64-gnu-distcheck: 1h 42m -> 2h 20m (+36.6%)
4. i686-msvc-1: 2h 15m -> 3h 4m (+36.1%)
5. x86_64-msvc-ext2: 2h -> 1h 17m (-35.6%)
6. dist-android: 23m 21s -> 31m 4s (+33.1%)
7. dist-powerpc64-linux-gnu: 1h 10m -> 1h 31m (+29.7%)
8. dist-powerpc64-linux-musl: 1h 17m -> 1h 39m (+28.7%)
9. test-various: 2h 4m -> 1h 29m (-28.1%)
10. tidy: 2m 3s -> 2m 37s (+27.2%)

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 (dc3f851): comparison URL.

Overall result: no relevant changes - no action needed

@rustbot label: -perf-regression

Instruction count

This perf run didn't have relevant results for this metric.

Max RSS (memory usage)

Results (primary -2.2%)

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
Improvements ✅ (primary)	-2.2%	[-2.2%, -2.2%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-2.2%	[-2.2%, -2.2%]	1

Cycles

Results (secondary 2.7%)

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)	2.7%	[2.7%, 2.7%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Binary size

This perf run didn't have relevant results for this metric.

Bootstrap: 487.552s -> 489.277s (0.35%)
Artifact size: 387.70 MiB -> 387.73 MiB (0.01%)