[WIP] Rewrite handling of universe-leaking placeholder regions into outlives constraints

[amandasystems]

This commit prepares for Polonius by moving handling of leak check/universe errors out of the inference step by rewriting any universe error into an outlives-static constraint.

This variant is a work in progress but seems to pass most tests.

Note that a few debug assertions no longer hold; a few extra eyes on those changes are appreciated!

[rustbot]

r? @davidtwco

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[amandasystems]

?r @nikomatsakis

(it's not 100% ready for review yet probably maybe, but I figured I might as well start the PR now)

[compiler-errors]

the syntax is r? nikomatsakis 😆

[amandasystems]

the syntax is r? nikomatsakis 😆

That’s funny because I tried that first, thought I made a mistake, and went back to “fix” it

[amandasystems]

Update: I had a brainwave during my investigations of the failing UI tests (there's 20-ish of them if you enable the new logic everywhere, depending on whether you count duplicates). I tried adding a new constraint category so that I could easily not blame it (ever, actually), and that reduces the errors down to one, tiny span diff:

---- [ui] tests/ui/higher-ranked/trait-bounds/due-to-where-clause.rs stdout ----
diff of stderr:

2         --> $DIR/due-to-where-clause.rs:2:5
3          |
4       LL |     test::<FooS>(&mut 42);
-          |     ^^^^^^^^^^^^ implementation of `Foo` is not general enough
+          |     ^^^^^^^^^^^^^^^^^^^^^ implementation of `Foo` is not general enough
6          |
7          = note: `FooS<'_>` must implement `Foo<'0>`, for any lifetime `'0`...
8          = note: ...but `FooS<'_>` actually implements `Foo<'1>`, for some specific lifetime `'1`

I'm pretty confident this works now. Removing the WIP label!

[nikomatsakis]

Efficiency nit

[amandasystems]

I think it's ready for a perf run, @lqd!

[lqd]

@bors try @rust-timer queue

[bors]

⌛ Trying commit 5a1c148 with merge 1b9e1e6...

[nikomatsakis]

OK, so, I reviewed and left a (tiny) nit. I don't know that a perf run is really needed, this is pretty clearly grossly inefficient. That's precisely what I expected, of course.

r=me but I'd like to hand this off to somebody else to drive over the finish line

[bors]

☀️ Try build successful - checks-actions
Build commit: 1b9e1e6 (1b9e1e65acb35d4d1d734c6461ace5c4e50a9fd0)

[rust-timer]

Finished benchmarking commit (1b9e1e6): comparison URL.

Overall result: ❌ regressions - ACTION NEEDED

Benchmarking this pull request likely means that it is perf-sensitive, so we're automatically marking it as not fit for rolling up. While you can manually mark this PR as fit for rollup, we strongly recommend not doing so since this PR may lead to changes in compiler perf.

Next Steps: If you can justify the regressions found in this try perf run, please indicate this with @rustbot label: +perf-regression-triaged along with sufficient written justification. If you cannot justify the regressions please fix the regressions and do another perf run. If the next run shows neutral or positive results, the label will be automatically removed.

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

Warning ⚠: The following benchmark(s) failed to build:

• rustc
• wg-grammar
• webrender-2022

Instruction count

This is a highly reliable metric that was used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	113.9%	[0.3%, 3862.1%]	236
Regressions ❌ (secondary)	393.2%	[0.1%, 7855.4%]	184
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	113.9%	[0.3%, 3862.1%]	236

Max RSS (memory usage)

Results

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-3.7%	[-10.5%, -0.7%]	57
Improvements ✅ (secondary)	-5.6%	[-7.4%, -3.5%]	21
All ❌✅ (primary)	-3.7%	[-10.5%, -0.7%]	57

Cycles

Results

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	215.7%	[0.9%, 3636.4%]	98
Regressions ❌ (secondary)	1147.6%	[1.0%, 7887.5%]	61
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	215.7%	[0.9%, 3636.4%]	98

Binary size

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

Bootstrap: missing data
Artifact size: 315.97 MiB -> 305.14 MiB (-3.43%)

[bors]

☔ The latest upstream changes (presumably #124015) made this pull request unmergeable. Please resolve the merge conflicts.

[rust-log-analyzer]

The job x86_64-gnu-llvm-17 failed! Check out the build log: (web) (plain)

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

#17 exporting to docker image format
#17 sending tarball 29.9s done
#17 DONE 37.3s
##[endgroup]
Setting extra environment values for docker:  --env ENABLE_GCC_CODEGEN=1 --env GCC_EXEC_PREFIX=/usr/lib/gcc/
[CI_JOB_NAME=x86_64-gnu-llvm-17]
---
sccache: Starting the server...
##[group]Configure the build
configure: processing command line
configure: 
configure: build.configure-args := ['--build=x86_64-unknown-linux-gnu', '--llvm-root=/usr/lib/llvm-17', '--enable-llvm-link-shared', '--set', 'rust.thin-lto-import-instr-limit=10', '--set', 'change-id=99999999', '--enable-verbose-configure', '--enable-sccache', '--disable-manage-submodules', '--enable-locked-deps', '--enable-cargo-native-static', '--set', 'rust.codegen-units-std=1', '--set', 'dist.compression-profile=balanced', '--dist-compression-formats=xz', '--disable-dist-src', '--release-channel=nightly', '--enable-debug-assertions', '--enable-overflow-checks', '--enable-llvm-assertions', '--set', 'rust.verify-llvm-ir', '--set', 'rust.codegen-backends=llvm,cranelift,gcc', '--set', 'llvm.static-libstdcpp', '--enable-new-symbol-mangling']
configure: target.x86_64-unknown-linux-gnu.llvm-config := /usr/lib/llvm-17/bin/llvm-config
configure: llvm.link-shared     := True
configure: rust.thin-lto-import-instr-limit := 10
configure: change-id            := 99999999
---
diff of stderr:

2   --> $DIR/due-to-where-clause.rs:2:5
3    |
4 LL |     test::<FooS>(&mut 42);
-    |     ^^^^^^^^^^^^ implementation of `Foo` is not general enough
+    |     ^^^^^^^^^^^^^^^^^^^^^ implementation of `Foo` is not general enough
6    |
7    = note: `FooS<'_>` must implement `Foo<'0>`, for any lifetime `'0`...
8    = note: ...but `FooS<'_>` actually implements `Foo<'1>`, for some specific lifetime `'1`

The actual stderr differed from the expected stderr.
Actual stderr saved to /checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/higher-ranked/trait-bounds/due-to-where-clause/due-to-where-clause.stderr
To update references, rerun the tests and pass the `--bless` flag
To update references, rerun the tests and pass the `--bless` flag
To only update this specific test, also pass `--test-args higher-ranked/trait-bounds/due-to-where-clause.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/x86_64-unknown-linux-gnu/stage2/bin/rustc" "/checkout/tests/ui/higher-ranked/trait-bounds/due-to-where-clause.rs" "-Zthreads=1" "-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/x86_64-unknown-linux-gnu/stage2" "--target=x86_64-unknown-linux-gnu" "--error-format" "json" "--json" "future-incompat" "-Ccodegen-units=1" "-Zui-testing" "-Zdeduplicate-diagnostics=no" "-Zwrite-long-types-to-disk=no" "-Cstrip=debuginfo" "--emit" "metadata" "-C" "prefer-dynamic" "--out-dir" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/higher-ranked/trait-bounds/due-to-where-clause" "-A" "unused" "-A" "internal_features" "-Crpath" "-Cdebuginfo=0" "-Lnative=/checkout/obj/build/x86_64-unknown-linux-gnu/native/rust-test-helpers" "-L" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/higher-ranked/trait-bounds/due-to-where-clause/auxiliary"
--- stderr -------------------------------
error: implementation of `Foo` is not general enough
##[error]  --> /checkout/tests/ui/higher-ranked/trait-bounds/due-to-where-clause.rs:2:5
   |
   |
LL |     test::<FooS>(&mut 42); //~ ERROR implementation of `Foo` is not general enough
   |     ^^^^^^^^^^^^^^^^^^^^^ implementation of `Foo` is not general enough
   |
   = note: `FooS<'_>` must implement `Foo<'0>`, for any lifetime `'0`...
   = note: ...but `FooS<'_>` actually implements `Foo<'1>`, for some specific lifetime `'1`
error: aborting due to 1 previous error
------------------------------------------

[bors]

☔ The latest upstream changes (presumably #124558) made this pull request unmergeable. Please resolve the merge conflicts.