TypeRelating emit WellFormed, not generalize

[lcnr]

fixes rust-lang/trait-system-refactor-initiative#250

r? BoxyUwU

[rustbot]

changes to the core type system

cc @compiler-errors, @lcnr

[rustbot]

BoxyUwU is currently at their maximum review capacity.
They may take a while to respond.

[lcnr]

@bors try @rust-timer queue

[rust-bors]

☀️ Try build successful (CI)
Build commit: 20a081a (20a081aa36c390f34fa701ef245698110b60e282, parent: 9312cd6d38396a13a08be73bb589fb1cf3dd32e6)

[rust-timer]

Finished benchmarking commit (20a081a): comparison URL.

Overall result: ❌✅ regressions and improvements - 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)	2.3%	[2.0%, 2.8%]	6
Regressions ❌ (secondary)	5.7%	[0.1%, 15.2%]	6
Improvements ✅ (primary)	-1.3%	[-1.3%, -1.3%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	1.8%	[-1.3%, 2.8%]	7

Max RSS (memory usage)

Results (secondary 1.2%)

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)	3.9%	[3.9%, 3.9%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-1.4%	[-1.4%, -1.4%]	1
All ❌✅ (primary)	-	-	0

Cycles

Results (primary 2.3%, secondary 10.1%)

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

	mean	range	count
Regressions ❌ (primary)	2.3%	[2.2%, 2.5%]	3
Regressions ❌ (secondary)	10.1%	[2.6%, 14.9%]	3
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	2.3%	[2.2%, 2.5%]	3

Binary size

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

Bootstrap: 477.625s -> 479.621s (0.42%)
Artifact size: 391.41 MiB -> 391.37 MiB (-0.01%)

[lcnr]

@bors try @rust-timer queue

[rust-bors]

☀️ Try build successful (CI)
Build commit: 3d1dd7d (3d1dd7d76f85165ff58987a09d383f7d3e8fbb59, parent: 95aeb4696545eb4c9cbb68516f2912770e3846ea)

[rust-timer]

Finished benchmarking commit (3d1dd7d): comparison URL.

Overall result: ❌✅ regressions and improvements - 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)	4.0%	[3.4%, 4.8%]	6
Regressions ❌ (secondary)	10.3%	[1.4%, 26.9%]	6
Improvements ✅ (primary)	-0.7%	[-1.4%, -0.0%]	2
Improvements ✅ (secondary)	-0.3%	[-0.3%, -0.2%]	6
All ❌✅ (primary)	2.8%	[-1.4%, 4.8%]	8

Max RSS (memory usage)

Results (primary 1.5%, 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)	1.5%	[1.5%, 1.5%]	1
Regressions ❌ (secondary)	1.8%	[1.5%, 2.0%]	2
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.3%	[-2.3%, -2.3%]	1
All ❌✅ (primary)	1.5%	[1.5%, 1.5%]	1

Cycles

Results (primary 2.8%, secondary 3.6%)

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

	mean	range	count
Regressions ❌ (primary)	2.8%	[2.6%, 3.1%]	3
Regressions ❌ (secondary)	9.6%	[3.3%, 23.4%]	6
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.4%	[-3.1%, -1.8%]	6
All ❌✅ (primary)	2.8%	[2.6%, 3.1%]	3

Binary size

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

Bootstrap: 474.976s -> 475.327s (0.07%)
Artifact size: 391.06 MiB -> 391.12 MiB (0.02%)

[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.

[lcnr]

@bors r=BoxyUwU rollup=never

[bors]

📌 Commit e1be0d2 has been approved by BoxyUwU

It is now in the queue for this repository.

[bors]

⌛ Testing commit e1be0d2 with merge 22e80cc...

[rust-log-analyzer]

The job i686-msvc-2 failed! Check out the build log: (web) (plain enhanced) (plain)

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

[RUSTC-TIMING] rustc_passes test:false 100.195
   Compiling rustc_mir_transform v0.0.0 (D:\a\rust\rust\compiler\rustc_mir_transform)
[RUSTC-TIMING] rustc_const_eval test:false 178.630
   Compiling rustc_borrowck v0.0.0 (D:\a\rust\rust\compiler\rustc_borrowck)
Assertion failed: !KeyInfoT::isEqual(Val, EmptyKey) && !KeyInfoT::isEqual(Val, TombstoneKey) && "Empty/Tombstone value shouldn't be inserted into map!", file D:\a\rust\rust\src\llvm-project\llvm\include\llvm/ADT/DenseMap.h, line 698
[RUSTC-TIMING] rustc_mir_transform test:false 174.045
error: could not compile `rustc_mir_transform` (lib)

Caused by:
  process didn't exit successfully: `D:\a\rust\rust\build\bootstrap\debug\rustc 'D:\a\rust\rust\build\bootstrap\debug\rustc' --crate-name rustc_mir_transform --edition=2024 'compiler\rustc_mir_transform\src\lib.rs' --error-format=json --json=diagnostic-rendered-ansi,artifacts,future-incompat --crate-type lib --emit=dep-info,metadata,link -C opt-level=3 -C embed-bitcode=no -C debug-assertions=on --check-cfg 'cfg(docsrs,test)' --check-cfg 'cfg(feature, values())' -C metadata=a9f927dde36e14a8 -C extra-filename=-eeaa9a753632719f --out-dir 'D:\a\rust\rust\build\i686-pc-windows-msvc\stage2-rustc\i686-pc-windows-msvc\release\deps' --target i686-pc-windows-msvc -L 'dependency=D:\a\rust\rust\build\i686-pc-windows-msvc\stage2-rustc\i686-pc-windows-msvc\release\deps' -L 'dependency=D:\a\rust\rust\build\i686-pc-windows-msvc\stage2-rustc\release\deps' --extern 'either=D:\a\rust\rust\build\i686-pc-windows-msvc\stage2-rustc\i686-pc-windows-msvc\release\deps\libeither-b0623807329748f8.rmeta' --extern 'hashbrown=D:\a\rust\rust\build\i686-pc-windows-msvc\stage2-rustc\i686-pc-windows-msvc\release\deps\libhashbrown-3306f33a93800293.rmeta' --extern 'itertools=D:\a\rust\rust\build\i686-pc-windows-msvc\stage2-rustc\i686-pc-windows-msvc\release\deps\libitertools-ed4edbd05d8567ee.rmeta' --extern 'rustc_abi=D:\a\rust\rust\build\i686-pc-windows-msvc\stage2-rustc\i686-pc-windows-msvc\release\deps\librustc_abi-e66663da941c303b.rmeta' --extern 'rustc_arena=D:\a\rust\rust\build\i686-pc-windows-msvc\stage2-rustc\i686-pc-windows-msvc\release\deps\librustc_arena-918b9a62bef49ff8.rmeta' --extern 'rustc_ast=D:\a\rust\rust\build\i686-pc-windows-msvc\stage2-rustc\i686-pc-windows-msvc\release\deps\librustc_ast-922b8fdc4b28d87b.rmeta' --extern 'rustc_const_eval=D:\a\rust\rust\build\i686-pc-windows-msvc\stage2-rustc\i686-pc-windows-msvc\release\deps\librustc_const_eval-fc9f291cfce222e0.rmeta' --extern 'rustc_data_structures=D:\a\rust\rust\build\i686-pc-windows-msvc\stage2-rustc\i686-pc-windows-msvc\release\deps\librustc_data_structures-bd9eb33a171cc133.rmeta' --extern 'rustc_errors=D:\a\rust\rust\build\i686-pc-windows-msvc\stage2-rustc\i686-pc-windows-msvc\release\deps\librustc_errors-0c7803c4f09a611f.rmeta' --extern 'rustc_fluent_macro=D:\a\rust\rust\build\i686-pc-windows-msvc\stage2-rustc\release\deps\rustc_fluent_macro-6a9b9571f00ec1ae.dll' --extern 'rustc_hir=D:\a\rust\rust\build\i686-pc-windows-msvc\stage2-rustc\i686-pc-windows-msvc\release\deps\librustc_hir-f8fee4b85c66f261.rmeta' --extern 'rustc_index=D:\a\rust\rust\build\i686-pc-windows-msvc\stage2-rustc\i686-pc-windows-msvc\release\deps\librustc_index-993abffa400d95b0.rmeta' --extern 'rustc_infer=D:\a\rust\rust\build\i686-pc-windows-msvc\stage2-rustc\i686-pc-windows-msvc\release\deps\librustc_infer-fbc26e608d4146b8.rmeta' --extern 'rustc_macros=D:\a\rust\rust\build\i686-pc-windows-msvc\stage2-rustc\release\deps\rustc_macros-644bb58810d8b30c.dll' --extern 'rustc_middle=D:\a\rust\rust\build\i686-pc-windows-msvc\stage2-rustc\i686-pc-windows-msvc\release\deps\librustc_middle-8fe8c0823e133b89.rmeta' --extern 'rustc_mir_build=D:\a\rust\rust\build\i686-pc-windows-msvc\stage2-rustc\i686-pc-windows-msvc\release\deps\librustc_mir_build-f23036b1867a3c63.rmeta' --extern 'rustc_mir_dataflow=D:\a\rust\rust\build\i686-pc-windows-msvc\stage2-rustc\i686-pc-windows-msvc\release\deps\librustc_mir_dataflow-7d5c2a7c2130cc57.rmeta' --extern 'rustc_session=D:\a\rust\rust\build\i686-pc-windows-msvc\stage2-rustc\i686-pc-windows-msvc\release\deps\librustc_session-c9df7d4cd7c4ddaf.rmeta' --extern 'rustc_span=D:\a\rust\rust\build\i686-pc-windows-msvc\stage2-rustc\i686-pc-windows-msvc\release\deps\librustc_span-1b2351166f5be056.rmeta' --extern 'rustc_target=D:\a\rust\rust\build\i686-pc-windows-msvc\stage2-rustc\i686-pc-windows-msvc\release\deps\librustc_target-8229e6e2ebbea7f6.rmeta' --extern 'rustc_trait_selection=D:\a\rust\rust\build\i686-pc-windows-msvc\stage2-rustc\i686-pc-windows-msvc\release\deps\librustc_trait_selection-f4e8c378481f834d.rmeta' --extern 'smallvec=D:\a\rust\rust\build\i686-pc-windows-msvc\stage2-rustc\i686-pc-windows-msvc\release\deps\libsmallvec-f6c7aff23145fe9c.rmeta' --extern 'tracing=D:\a\rust\rust\build\i686-pc-windows-msvc\stage2-rustc\i686-pc-windows-msvc\release\deps\libtracing-66dbc3f06e5547cc.rmeta' --cfg=windows_raw_dylib -Csymbol-mangling-version=v0 -Zannotate-moves -Zunstable-options '--check-cfg=cfg(bootstrap)' -Zmacro-backtrace -Csplit-debuginfo=packed -Ctarget-feature=+crt-static -Alinker-messages -Zon-broken-pipe=kill -Z binary-dep-depinfo -L 'native=D:\a\rust\rust\build\i686-pc-windows-msvc\stage2-rustc\i686-pc-windows-msvc\release\build\stacker-98d534daedc1c708\out' -L 'native=D:\a\rust\rust\build\i686-pc-windows-msvc\stage2-rustc\i686-pc-windows-msvc\release\build\psm-0886f750a5c4fe93\out' -L 'native=D:\a\rust\rust\build\i686-pc-windows-msvc\stage2-rustc\i686-pc-windows-msvc\release\build\blake3-fbfb16860e30e178\out' -L 'native=C:\Program Files\Microsoft Visual Studio\2022\Enterprise\VC\Tools\MSVC\14.44.35207\atlmfc\lib\x86' -L 'native=C:\Program Files\Microsoft Visual Studio\2022\Enterprise\VC\Tools\MSVC\14.44.35207\atlmfc\lib\x86' -L 'native=C:\Program Files\Microsoft Visual Studio\2022\Enterprise\VC\Tools\MSVC\14.44.35207\atlmfc\lib\x86'` (exit code: 0xc000001d, STATUS_ILLEGAL_INSTRUCTION)
warning: build failed, waiting for other jobs to finish...
[RUSTC-TIMING] rustc_hir_analysis test:false 359.355
[RUSTC-TIMING] rustc_hir_typeck test:false 313.835
[RUSTC-TIMING] rustc_borrowck test:false 297.168
Bootstrap failed while executing `test --stage 2 --skip=tests --skip=coverage-map --skip=coverage-run --skip=library --skip=tidyselftest`
Build completed unsuccessfully in 1:13:12
make: *** [Makefile:114: ci-msvc-ps1] Error 1
  local time: Fri Dec  5 16:18:36 CUT 2025
  network time: Fri, 05 Dec 2025 16:18:36 GMT
##[error]Process completed with exit code 2.
##[group]Run echo "disk usage:"
echo "disk usage:"

[bors]

💔 Test failed - checks-actions

[matthiaskrgr]

@bors retry

[bors]

⌛ Testing commit e1be0d2 with merge b4f1098...

[bors]

☀️ Test successful - checks-actions
Approved by: BoxyUwU
Pushing b4f1098 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 36b2369 (parent) -> b4f1098 (this PR)

Test differences

Show 15 test diffs

Stage 1

• [ui] tests/ui/traits/next-solver/generalize/subtype-obligations-bivariant-args.rs#next: [missing] -> pass (J0)
• [ui] tests/ui/traits/next-solver/generalize/subtype-obligations-bivariant-args.rs#old: [missing] -> pass (J0)

Stage 2

• [ui] tests/ui/traits/next-solver/generalize/subtype-obligations-bivariant-args.rs#next: [missing] -> pass (J1)
• [ui] tests/ui/traits/next-solver/generalize/subtype-obligations-bivariant-args.rs#old: [missing] -> pass (J1)

Additionally, 11 doctest diffs were found. These are ignored, as they are noisy.

Job group index

• J0: x86_64-gnu-llvm-20-3, x86_64-gnu-llvm-21-3
• J1: 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

Test dashboard

Run

cargo run --manifest-path src/ci/citool/Cargo.toml -- \
    test-dashboard b4f1098e10e71139bbdc08df5ea8183e68fc0955 --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-aarch64-linux: 9163.9s -> 6451.7s (-29.6%)
2. x86_64-rust-for-linux: 2619.9s -> 3209.3s (+22.5%)
3. pr-check-1: 1682.5s -> 2009.8s (+19.5%)
4. x86_64-gnu-llvm-20-2: 5143.2s -> 6022.1s (+17.1%)
5. aarch64-gnu-llvm-20-2: 2151.5s -> 2517.0s (+17.0%)
6. x86_64-gnu-llvm-20: 2382.7s -> 2758.3s (+15.8%)
7. x86_64-gnu-gcc: 3119.6s -> 3519.4s (+12.8%)
8. x86_64-gnu-tools: 3142.9s -> 3531.7s (+12.4%)
9. dist-apple-various: 4221.1s -> 3708.5s (-12.1%)
10. x86_64-gnu-llvm-20-1: 3153.0s -> 3533.7s (+12.1%)

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 (b4f1098): 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
Regressions ❌ (secondary)	0.2%	[0.0%, 0.5%]	14
Improvements ✅ (primary)	-1.3%	[-1.3%, -1.3%]	1
Improvements ✅ (secondary)	-0.2%	[-0.3%, -0.1%]	8
All ❌✅ (primary)	-1.3%	[-1.3%, -1.3%]	1

Max RSS (memory usage)

Results (primary 1.0%, secondary 1.9%)

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

	mean	range	count
Regressions ❌ (primary)	1.0%	[1.0%, 1.0%]	1
Regressions ❌ (secondary)	4.0%	[1.6%, 6.6%]	9
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-1.3%	[-2.4%, -0.8%]	6
All ❌✅ (primary)	1.0%	[1.0%, 1.0%]	1

Cycles

Results (primary 3.0%, secondary -1.2%)

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

	mean	range	count
Regressions ❌ (primary)	3.0%	[2.8%, 3.3%]	2
Regressions ❌ (secondary)	4.0%	[2.6%, 6.1%]	3
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-3.8%	[-6.6%, -1.8%]	6
All ❌✅ (primary)	3.0%	[2.8%, 3.3%]	2

Binary size

Results (primary -0.0%, secondary -0.0%)

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)	-0.0%	[-0.0%, -0.0%]	1
Improvements ✅ (secondary)	-0.0%	[-0.0%, -0.0%]	1
All ❌✅ (primary)	-0.0%	[-0.0%, -0.0%]	1

Bootstrap: 468.958s -> 471.737s (0.59%)
Artifact size: 386.84 MiB -> 388.97 MiB (0.55%)

[panstromek]

perf triage:

post-merge results look worse on secondary benchmarks, compared to pre-merge run. The final result still is positive, but only because of 1 primary bechmark. I looked through the secondary regressions and most of them returned back to previous state in next PR, so this is probably noise.

@rustbot label: +perf-regression-triaged