Emit ForbiddenBound fatally if meeting complex bound

[mu001999]

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Fixes #149695

---

Bounds in binders are denied, hir items won't contain and index them. But nested items in the bounds will still be lowered to hir. And their parents, i.e., the block in bounds is not in hir. So that ICE happens when error handling requires visiting hir parents.

This PR collects hirless def ids and skips them when iterating parents.

This PR checks such bounds used in higher ranked binders and emit error ForbiddenBound when parsing. And make sure no such bounds appear in hir.

This PR emits this error fatally if meeting complex bound.

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[mu001999]

@rustbot reroll

[jdonszelmann]

@rustbot author

[rustbot]

Reminder, once the PR becomes ready for a review, use @rustbot ready.

[mu001999]

@rustbot review

[jdonszelmann]

@rusbot author

[jdonszelmann]

@rustbot blocked on #149728 (comment)

[mu001999]

Hi @jdonszelmann, in the lastest rough change, I tried to filter nested items in the bound, and not lower them to hir.

dbg! shows it works:

[compiler/rustc_ast_lowering/src/lib.rs:527:17] "skipping lowering of {:?}" = "skipping lowering of {:?}"
[compiler/rustc_ast_lowering/src/lib.rs:527:17] def_id = DefId(0:6 ~ bad_bounds[bee6]::produce::{constant#0}::A)
[compiler/rustc_ast_lowering/src/lib.rs:527:17] "skipping lowering of {:?}" = "skipping lowering of {:?}"
[compiler/rustc_ast_lowering/src/lib.rs:527:17] def_id = DefId(0:7 ~ bad_bounds[bee6]::produce::{constant#0}::A::{constructor#0})
[compiler/rustc_ast_lowering/src/lib.rs:527:17] "skipping lowering of {:?}" = "skipping lowering of {:?}"
[compiler/rustc_ast_lowering/src/lib.rs:527:17] def_id = DefId(0:8 ~ bad_bounds[bee6]::produce::{constant#0}::A::A)
[compiler/rustc_ast_lowering/src/lib.rs:527:17] "skipping lowering of {:?}" = "skipping lowering of {:?}"
[compiler/rustc_ast_lowering/src/lib.rs:527:17] def_id = DefId(0:10 ~ bad_bounds[bee6]::produce::{constant#0}::A#1)
[compiler/rustc_ast_lowering/src/lib.rs:527:17] "skipping lowering of {:?}" = "skipping lowering of {:?}"
[compiler/rustc_ast_lowering/src/lib.rs:527:17] def_id = DefId(0:11 ~ bad_bounds[bee6]::produce::{constant#0}::{impl#0})

But there still be errors, because they still have LocalDefId, so that they can be result of many other queries. For example, after the change, a new ICE appears because type_of(bad_bounds[bee6]::produce::{constant#0}::{impl#0}).

Concrete content of the new ICE is:

error: internal compiler error: compiler/rustc_middle/src/hir/mod.rs:385:32: No HirId for DefId(0:11 ~ bad_bounds[bee6]::produce::{constant#0}::{impl#0})


thread 'rustc' (6902108) panicked at compiler/rustc_middle/src/hir/mod.rs:385:32:
Box<dyn Any>
stack backtrace:
   0: std::panicking::begin_panic::<rustc_errors::ExplicitBug>
             at /rustc/1b6e21e163baa0b20f119e17e3871910978a60b6/library/std/src/panicking.rs:761:5
   1: std::panic::panic_any::<rustc_errors::ExplicitBug>
             at /rustc/1b6e21e163baa0b20f119e17e3871910978a60b6/library/std/src/panic.rs:260:5
   2: <rustc_errors::diagnostic::BugAbort as rustc_errors::diagnostic::EmissionGuarantee>::emit_producing_guarantee
             at ./compiler/rustc_errors/src/diagnostic.rs:63:9
   3: <rustc_errors::diagnostic::Diag<rustc_errors::diagnostic::BugAbort>>::emit
             at ./compiler/rustc_errors/src/diagnostic.rs:1405:9
   4: <rustc_errors::DiagCtxtHandle>::bug::<alloc::string::String>
             at ./compiler/rustc_errors/src/lib.rs:1231:30
   5: rustc_middle::util::bug::opt_span_bug_fmt::<rustc_span::span_encoding::Span>::{closure#0}
             at ./compiler/rustc_middle/src/util/bug.rs:39:48
   6: rustc_middle::ty::context::tls::with_opt::<rustc_middle::util::bug::opt_span_bug_fmt<rustc_span::span_encoding::Span>::{closure#0}, !>::{closure#0}
             at ./compiler/rustc_middle/src/ty/context/tls.rs:136:23
   7: rustc_middle::ty::context::tls::with_context_opt::<rustc_middle::ty::context::tls::with_opt<rustc_middle::util::bug::opt_span_bug_fmt<rustc_span::span_encoding::Span>::{closure#0}, !>::{closure#0}, !>
             at ./compiler/rustc_middle/src/ty/context/tls.rs:79:18
   8: rustc_middle::ty::context::tls::with_opt::<rustc_middle::util::bug::opt_span_bug_fmt<rustc_span::span_encoding::Span>::{closure#0}, !>
             at ./compiler/rustc_middle/src/ty/context/tls.rs:134:5
   9: rustc_middle::util::bug::opt_span_bug_fmt::<rustc_span::span_encoding::Span>
             at ./compiler/rustc_middle/src/util/bug.rs:33:5
  10: rustc_middle::util::bug::bug_fmt
             at ./compiler/rustc_middle/src/util/bug.rs:16:5
  11: rustc_middle::hir::provide::{closure#0}
             at ./compiler/rustc_middle/src/macros.rs:18:9
  12: <rustc_middle::hir::provide::{closure#0} as core::ops::function::FnOnce<(rustc_middle::ty::context::TyCtxt, rustc_span::def_id::LocalDefId)>>::call_once
             at /rustc/1b6e21e163baa0b20f119e17e3871910978a60b6/library/core/src/ops/function.rs:250:5
  13: rustc_query_impl::query_impl::local_def_id_to_hir_id::dynamic_query::{closure#2}::{closure#0}
             at ./compiler/rustc_query_impl/src/plumbing.rs:298:9
      [... omitted 22 frames ...]
  14: rustc_middle::query::inner::query_get_at::<rustc_data_structures::vec_cache::VecCache<rustc_span::def_id::LocalDefId, rustc_middle::query::erase::Erased<[u8; 8]>, rustc_query_system::dep_graph::graph::DepNodeIndex>>
             at ./compiler/rustc_middle/src/query/inner.rs:33:17
  15: <rustc_middle::query::plumbing::TyCtxtAt>::local_def_id_to_hir_id::<rustc_span::def_id::LocalDefId>
             at ./compiler/rustc_middle/src/query/plumbing.rs:415:31
  16: <rustc_middle::ty::context::TyCtxt>::local_def_id_to_hir_id::<rustc_span::def_id::LocalDefId>
             at ./compiler/rustc_middle/src/query/plumbing.rs:406:35
  17: rustc_hir_analysis::collect::type_of::type_of::{closure#0}
             at ./compiler/rustc_hir_analysis/src/collect/type_of.rs:56:22
  18: rustc_hir_analysis::collect::type_of::type_of
             at ./compiler/rustc_hir_analysis/src/collect/type_of.rs:21:1
  19: rustc_query_impl::query_impl::type_of::dynamic_query::{closure#2}::{closure#0}
             at ./compiler/rustc_query_impl/src/plumbing.rs:302:13
      [... omitted 22 frames ...]
  20: rustc_middle::query::inner::query_get_at::<rustc_query_system::query::caches::DefIdCache<rustc_middle::query::erase::Erased<[u8; 8]>>>
             at ./compiler/rustc_middle/src/query/inner.rs:33:17
  21: <rustc_middle::query::plumbing::TyCtxtAt>::type_of::<rustc_span::def_id::DefId>
             at ./compiler/rustc_middle/src/query/plumbing.rs:415:31
  22: <rustc_middle::ty::context::TyCtxt>::type_of::<rustc_span::def_id::DefId>
             at ./compiler/rustc_middle/src/query/plumbing.rs:406:35
  23: rustc_middle::ty::trait_def::trait_impls_of_provider
             at ./compiler/rustc_middle/src/ty/trait_def.rs:227:32
  24: rustc_query_impl::query_impl::trait_impls_of::dynamic_query::{closure#2}::{closure#0}
             at ./compiler/rustc_query_impl/src/plumbing.rs:298:9
      [... omitted 22 frames ...]
  25: rustc_middle::query::inner::query_get_at::<rustc_query_system::query::caches::DefIdCache<rustc_middle::query::erase::Erased<[u8; 8]>>>
             at ./compiler/rustc_middle/src/query/inner.rs:33:17
  26: <rustc_middle::query::plumbing::TyCtxtAt>::trait_impls_of::<rustc_span::def_id::DefId>
             at ./compiler/rustc_middle/src/query/plumbing.rs:415:31
  27: <rustc_middle::ty::context::TyCtxt>::trait_impls_of::<rustc_span::def_id::DefId>
             at ./compiler/rustc_middle/src/query/plumbing.rs:406:35
  28: <rustc_middle::ty::context::TyCtxt>::all_impls
             at ./compiler/rustc_middle/src/ty/trait_def.rs:194:68

[mu001999]

I think at least it's more difficult than I expected. Do you have any suggestions?

[fmease]

@bors r-

[rust-bors]

This pull request was unapproved.

Auto build was cancelled due to unapproval. Cancelled workflows:

• https://github.com/rust-lang/rust/actions/runs/22864415094

[mu001999]

@jdonszelmann Hi, what's your opinion on the next step? Do a crater run and nominate it for T-lang discussion, or back to directly emitting a fatal error?

@rustbot review

[jdonszelmann]

I guess a fatal error it is. This is a wild ride, but if we might implement this at some point and given that its rare, a fatal error seems like the way to go

[jdonszelmann]

@rustbot author

[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.

[mu001999]

@rustbot review

[jdonszelmann]

@bors r+

[rust-bors]

📌 Commit 1503274 has been approved by jdonszelmann

It is now in the queue for this repository.

[rust-bors]

☀️ Test successful - CI
Approved by: jdonszelmann
Duration: 3h 12m 5s
Pushing 91021cc 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 85e19b8 (parent) -> 91021cc (this PR)

Test differences

Show 6 test diffs

Stage 1

• [ui] tests/ui/traits/non_lifetime_binders/bad-bounds.rs: [missing] -> pass (J1)

Stage 2

• [ui] tests/ui/traits/non_lifetime_binders/bad-bounds.rs: [missing] -> pass (J0)

Additionally, 4 doctest diffs were found. These are ignored, as they are noisy.

Job group index

• J0: aarch64-apple, 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-nopt, x86_64-gnu-stable, x86_64-mingw-1, x86_64-msvc-1
• J1: x86_64-gnu-llvm-21-3

Test dashboard

Run

cargo run --manifest-path src/ci/citool/Cargo.toml -- \
    test-dashboard 91021ccc790478a1a89c003e7d32b8d155ae6aae --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. pr-check-1: 33m 12s -> 24m 36s (-25.9%)
2. optional-x86_64-gnu-parallel-frontend: 2h 41m -> 2h 10m (-18.9%)
3. aarch64-apple: 2h 31m -> 2h 57m (+17.0%)
4. x86_64-rust-for-linux: 56m 38s -> 47m 28s (-16.2%)
5. i686-gnu-2: 1h 44m -> 1h 28m (-15.3%)
6. i686-gnu-1: 2h 25m -> 2h 6m (-12.7%)
7. aarch64-gnu-llvm-21-2: 51m 40s -> 45m 55s (-11.1%)
8. pr-check-2: 44m 13s -> 39m 23s (-10.9%)
9. i686-gnu-nopt-1: 2h 22m -> 2h 7m (-10.4%)
10. dist-apple-various: 1h 42m -> 1h 53m (+10.1%)

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 (91021cc): comparison URL.

Overall result: no relevant changes - no action needed

@rustbot label: -perf-regression

Instruction count

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

Max RSS (memory usage)

Results (primary 0.9%, 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)	2.0%	[1.5%, 2.2%]	4
Regressions ❌ (secondary)	2.5%	[2.1%, 2.8%]	3
Improvements ✅ (primary)	-1.3%	[-1.5%, -1.1%]	2
Improvements ✅ (secondary)	-2.6%	[-3.5%, -1.3%]	3
All ❌✅ (primary)	0.9%	[-1.5%, 2.2%]	6

Cycles

Results (primary -0.3%, secondary -4.3%)

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

	mean	range	count
Regressions ❌ (primary)	1.9%	[1.9%, 1.9%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-2.5%	[-2.5%, -2.5%]	1
Improvements ✅ (secondary)	-4.3%	[-4.3%, -4.3%]	1
All ❌✅ (primary)	-0.3%	[-2.5%, 1.9%]	2

Binary size

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

Bootstrap: 480.745s -> 479.493s (-0.26%)
Artifact size: 396.86 MiB -> 394.94 MiB (-0.48%)