borrowck: avoid ICE describing fields on generic params by pbkx · Pull Request #157230 · rust-lang/rust

pbkx · 2026-06-01T04:17:07Z

describe_field_from_ty is used while building borrowck diagnostics. When the
base type is a generic parameter, there is no concrete ADT or tuple field name
to recover. So, fall back to the field index instead of ICEing

This avoids crashing while reporting the original borrowck error. Does not
change borrow-checking semantics.

rustbot · 2026-06-01T04:17:12Z

r? @TaKO8Ki

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cjgillot

This happens for a generic parameter here, but it could also happen for any non-described type here, depending on what is in the box. Should we completely remove the ICE and add a fallback in all cases?

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cjgillot · 2026-06-02T22:32:57Z

                ty::Array(ty, _) | ty::Slice(ty) => {
                    self.describe_field_from_ty(ty, field, variant_index, including_tuple_field)
                }
+                ty::Param(_) => Some(field.index().to_string()),


Do you mind adding a comment to explain this surprising case?

pbkx · 2026-06-05T16:21:36Z

@rustbot ready

cjgillot · 2026-06-10T18:36:33Z

@bors r+ rollup

rust-bors · 2026-06-10T18:36:36Z

📌 Commit 5a7ca04 has been approved by cjgillot

It is now in the queue for this repository.

…aram, r=cjgillot borrowck: avoid ICE describing fields on generic params Fixes rust-lang#155344. `describe_field_from_ty` is used while building borrowck diagnostics. When the base type is a generic parameter, there is no concrete ADT or tuple field name to recover. So, fall back to the field index instead of ICEing This avoids crashing while reporting the original borrowck error. Does not change borrow-checking semantics.

Rollup of 23 pull requests Successful merges: - #157280 (traits: Allow escaping self types in ExistentialTraitRef::with_self_ty) - #157282 (Fix post-monomorphization error note race in the parallel frontend) - #157352 (Make the retained dep graph deterministic under the parallel frontend) - #157601 (Emit error for unused target expression in glob and list delegations) - #157611 (Update `browser-ui-test` version to `0.24.0`) - #157620 (Add a strategy FnMut to inject behavior into the flush cycle) - #157645 (Windows TLS - Only register the `atexit` hook when `cleanup` can be unloaded) - #157647 (Start using comptime for reflection intrinsics and their wrapper functions) - #157719 (resolve: Partially revert "Remove a special case for dummy imports") - #156497 (fix-155516: Don't suggest wrong unwrap expect) - #156583 (Support defaults for static EIIs) - #157013 (Ensure inferred let pattern types are well-formed) - #157230 (borrowck: avoid ICE describing fields on generic params) - #157288 (platform support: add SNaN erratum to MIPS targets) - #157350 (compiletest: ignore SVG `y` offset in by-lines comparison) - #157355 (Add `or_try_*` variants for `HashMap` and `BTreeMap` Entry APIs) - #157384 (Add `#[rustc_dump_generics]` attribute) - #157577 (Fix parser error recovery treating 'dyn' as a strict keyword in Rust 2015 when used in `dyn + dyn`) - #157670 (Rename `errors.rs` file to `diagnostics.rs` (4/N)) - #157691 (Move symbol hiding code to a new file) - #157697 (Add more tests that exercise the well-formedness checking of lazy type aliases) - #157700 (Rename `errors.rs` file to `diagnostics.rs` (5/N)) - #157703 (Fix doc link to Instant sub in saturating caveat) Failed merges: - #157699 (Arg splat experiment - hir FnDecl impl)

…aram, r=cjgillot borrowck: avoid ICE describing fields on generic params Fixes rust-lang#155344. `describe_field_from_ty` is used while building borrowck diagnostics. When the base type is a generic parameter, there is no concrete ADT or tuple field name to recover. So, fall back to the field index instead of ICEing This avoids crashing while reporting the original borrowck error. Does not change borrow-checking semantics.

Rollup of 31 pull requests Successful merges: - #141030 (Expand free alias types during variance computation) - #154853 (mgca: Register `ConstArgHasType` when normalizing projection consts) - #155527 (Replace printables table with `unicode_data.rs` tables) - #156629 (Stabilize `core::range::{legacy, RangeFull, RangeTo}`) - #157280 (traits: Allow escaping self types in ExistentialTraitRef::with_self_ty) - #157282 (Fix post-monomorphization error note race in the parallel frontend) - #157352 (Make the retained dep graph deterministic under the parallel frontend) - #157601 (Emit error for unused target expression in glob and list delegations) - #157611 (Update `browser-ui-test` version to `0.24.0`) - #157620 (Add a strategy FnMut to inject behavior into the flush cycle) - #157645 (Windows TLS - Only register the `atexit` hook when `cleanup` can be unloaded) - #157646 (Keep rename-imported main alive in dead-code analysis under `--test`) - #157647 (Start using comptime for reflection intrinsics and their wrapper functions) - #157719 (resolve: Partially revert "Remove a special case for dummy imports") - #155153 (Ensure Send/Sync is not implemented for std::env::Vars{,Os}) - #155198 (fix(mgca): Allow specifying generic args (of enum) on enum itself in unit & tuple variant constructions in (direct) const args) - #155323 (refactor `TypeRelativePath::AssocItem` to use `AliasTerm`) - #156497 (fix-155516: Don't suggest wrong unwrap expect) - #156583 (Support defaults for static EIIs) - #157013 (Ensure inferred let pattern types are well-formed) - #157196 (Only suggest reborrowing a moved value where the reborrow is valid) - #157230 (borrowck: avoid ICE describing fields on generic params) - #157288 (platform support: add SNaN erratum to MIPS targets) - #157330 (remove `IsTypeConst` from `hir::TraitItemKind`) - #157350 (compiletest: ignore SVG `y` offset in by-lines comparison) - #157355 (Add `or_try_*` variants for `HashMap` and `BTreeMap` Entry APIs) - #157577 (Fix parser error recovery treating 'dyn' as a strict keyword in Rust 2015 when used in `dyn + dyn`) - #157670 (Rename `errors.rs` file to `diagnostics.rs` (4/N)) - #157691 (Move symbol hiding code to a new file) - #157700 (Rename `errors.rs` file to `diagnostics.rs` (5/N)) - #157703 (Fix doc link to Instant sub in saturating caveat) Failed merges: - #157699 (Arg splat experiment - hir FnDecl impl)

Rollup merge of #157230 - pbkx:issue-155344-borrowck-field-param, r=cjgillot borrowck: avoid ICE describing fields on generic params Fixes #155344. `describe_field_from_ty` is used while building borrowck diagnostics. When the base type is a generic parameter, there is no concrete ADT or tuple field name to recover. So, fall back to the field index instead of ICEing This avoids crashing while reporting the original borrowck error. Does not change borrow-checking semantics.

Rollup of 31 pull requests Successful merges: - rust-lang#141030 (Expand free alias types during variance computation) - rust-lang#154853 (mgca: Register `ConstArgHasType` when normalizing projection consts) - rust-lang#155527 (Replace printables table with `unicode_data.rs` tables) - rust-lang#156629 (Stabilize `core::range::{legacy, RangeFull, RangeTo}`) - rust-lang#157280 (traits: Allow escaping self types in ExistentialTraitRef::with_self_ty) - rust-lang#157282 (Fix post-monomorphization error note race in the parallel frontend) - rust-lang#157352 (Make the retained dep graph deterministic under the parallel frontend) - rust-lang#157601 (Emit error for unused target expression in glob and list delegations) - rust-lang#157611 (Update `browser-ui-test` version to `0.24.0`) - rust-lang#157620 (Add a strategy FnMut to inject behavior into the flush cycle) - rust-lang#157645 (Windows TLS - Only register the `atexit` hook when `cleanup` can be unloaded) - rust-lang#157646 (Keep rename-imported main alive in dead-code analysis under `--test`) - rust-lang#157647 (Start using comptime for reflection intrinsics and their wrapper functions) - rust-lang#157719 (resolve: Partially revert "Remove a special case for dummy imports") - rust-lang#155153 (Ensure Send/Sync is not implemented for std::env::Vars{,Os}) - rust-lang#155198 (fix(mgca): Allow specifying generic args (of enum) on enum itself in unit & tuple variant constructions in (direct) const args) - rust-lang#155323 (refactor `TypeRelativePath::AssocItem` to use `AliasTerm`) - rust-lang#156497 (fix-155516: Don't suggest wrong unwrap expect) - rust-lang#156583 (Support defaults for static EIIs) - rust-lang#157013 (Ensure inferred let pattern types are well-formed) - rust-lang#157196 (Only suggest reborrowing a moved value where the reborrow is valid) - rust-lang#157230 (borrowck: avoid ICE describing fields on generic params) - rust-lang#157288 (platform support: add SNaN erratum to MIPS targets) - rust-lang#157330 (remove `IsTypeConst` from `hir::TraitItemKind`) - rust-lang#157350 (compiletest: ignore SVG `y` offset in by-lines comparison) - rust-lang#157355 (Add `or_try_*` variants for `HashMap` and `BTreeMap` Entry APIs) - rust-lang#157577 (Fix parser error recovery treating 'dyn' as a strict keyword in Rust 2015 when used in `dyn + dyn`) - rust-lang#157670 (Rename `errors.rs` file to `diagnostics.rs` (4/N)) - rust-lang#157691 (Move symbol hiding code to a new file) - rust-lang#157700 (Rename `errors.rs` file to `diagnostics.rs` (5/N)) - rust-lang#157703 (Fix doc link to Instant sub in saturating caveat) Failed merges: - rust-lang#157699 (Arg splat experiment - hir FnDecl impl)

borrowck: avoid ICE describing fields on generic params

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rustbot assigned TaKO8Ki Jun 1, 2026

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Jun 1, 2026

cjgillot reviewed Jun 2, 2026

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cjgillot added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Jun 2, 2026

Use field-index fallback for undescribed fields

5a7ca04

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Jun 5, 2026

rust-bors Bot added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Jun 10, 2026

jhpratt mentioned this pull request Jun 10, 2026

Rollup of 23 pull requests #157726

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jhpratt mentioned this pull request Jun 11, 2026

Rollup of 28 pull requests #157735

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jhpratt mentioned this pull request Jun 11, 2026

Rollup of 31 pull requests #157739

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rust-bors Bot merged commit 37ef6c0 into rust-lang:main Jun 11, 2026
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rustbot added this to the 1.98.0 milestone Jun 11, 2026

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borrowck: avoid ICE describing fields on generic params#157230

borrowck: avoid ICE describing fields on generic params#157230
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