Fix ICE for ambiguous candidates on method probing by lsunsi · Pull Request #162904 · rust-lang/rust

lsunsi · 2026-09-17T14:12:34Z

It seems like the construction of the Pick was mixing two candidate information that were not synced:

if it is ambiguous
import ids

The two candidates were consistent, but the pick became inconsistent when they were mixed.
The fix was just to use the import_ids of the ambiguous candidate in case it exists, and keep old behavior otherwise.

ICE was introduced in #161805

Co-authored-by: Philip Sampaio <philip.sampaio@gmail.com>

rustbot · 2026-09-17T14:12:40Z

r? @folkertdev

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folkertdev · 2026-09-17T14:17:06Z

r? types

jackh726 · 2026-09-29T23:46:56Z

+        let ambiguously_imported_import_ids = probes.iter().find_map(|(p, _)| match p.kind {
+            TraitCandidate { is_ambiguously_imported, .. } => {
+                is_ambiguously_imported.then_some(p.import_ids)
+            }
+            _ => None,
        });

+        let (is_ambiguously_imported, import_ids) = match ambiguously_imported_import_ids {
+            Some(import_ids) => (true, import_ids),
+            None => (false, probes[0].0.import_ids),
+        };
+


Why not combine these into a single match?

View changes since the review

Also, this needs a comment.

Done in 13e8826

jackh726 · 2026-09-30T00:05:26Z

+        let ambiguously_imported_import_ids = probes.iter().find_map(|(p, _)| match p.kind {
+            TraitCandidate { is_ambiguously_imported, .. } => {
+                is_ambiguously_imported.then_some(p.import_ids)
+            }
+            _ => None,
        });


I would do something like:

Suggested change

let ambiguously_imported_import_ids = probes.iter().find_map(|(p, _)| match p.kind {

TraitCandidate { is_ambiguously_imported, .. } => {

is_ambiguously_imported.then_some(p.import_ids)

}

_ => None,

});

let ambiguous_candidate = probes.iter().find_map(|(p, _)| match p.kind {

TraitCandidate { is_ambiguously_imported: true, .. } => Some(p),

_ => None,

});

let (ambiguous, candidate) = ambiguous_candidate.map(|c| (true, c)).unwrap_or_else(|| (false, probes[0]));

And use this in place of probes[0] below.

View changes since the review

Done in 13e8826

rustbot · 2026-09-30T00:05:56Z

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

lsunsi · 2026-09-30T16:26:28Z

@rustbot ready

jackh726 · 2026-09-30T17:34:35Z

Please squash the last two commits into one

The ICE was caused because the code assumed the import_ids would always be the same for all candidates, but it's not true. Sometimes the candidate is ambiguous with import_ids to be logged and sometimes the candidate is not ambigous and does not have the ids. Mixing the two (flag = true, without import_ids) ICEs. Co-authored-by: Philip Sampaio <philip.sampaio@gmail.com>

lsunsi · 2026-09-30T19:32:57Z

@jackh726 Done!

jackh726 · 2026-10-01T10:51:31Z

@bors r+ rollup

rust-bors · 2026-10-01T10:51:34Z

📌 Commit 109c917 has been approved by jackh726

It is now in the queue for this repository.

Fix ICE for ambiguous candidates on method probing Fixes rust-lang#162857 It seems like the construction of the Pick was mixing two candidate information that were not synced: - if it is ambiguous - import ids The two candidates were consistent, but the pick became inconsistent when they were mixed. The fix was just to use the import_ids of the ambiguous candidate in case it exists, and keep old behavior otherwise. ICE was introduced in rust-lang#161805

Rollup of 11 pull requests Successful merges: - #163483 (Bump bootstrap compiler to 1.100.0 beta) - #161380 (only rerun const eval in next-solver if the const actually references opaques) - #162900 (Some refactorings around metadata encoding) - #163580 (Provide better doc code example for `UnixDatagram::bind_addr` and `UnixListener::bind_addr`) - #163584 ([triagebot] Ping me for debugger visualizer changes) - #162904 (Fix ICE for ambiguous candidates on method probing) - #163281 (Add `f16` inline ASM support to `spirv.rs`) - #163314 (move `#[macro_export]` on declarative macro check to `rustc_attr_parsing`) - #163405 (Remove some #[linkage] options) - #163530 (`const impl PartialEq` for `f16b`) - #163581 (do not suggest precise capturing when the opaque span is in a macro expansion)

…uwer Rollup of 20 pull requests Successful merges: - #163483 (Bump bootstrap compiler to 1.100.0 beta) - #161380 (only rerun const eval in next-solver if the const actually references opaques) - #162900 (Some refactorings around metadata encoding) - #163461 (Improve diagnostic deduplication) - #163580 (Provide better doc code example for `UnixDatagram::bind_addr` and `UnixListener::bind_addr`) - #163584 ([triagebot] Ping me for debugger visualizer changes) - #159021 (windows-gnu: enable native TLS) - #161467 (wfcheck: name the item that discards an unused type parameter) - #162618 (trait_selection: Preserve eager normalization failures) - #162904 (Fix ICE for ambiguous candidates on method probing) - #163064 (Avoid computing overflowed goal chains for crate dependencies) - #163281 (Add `f16` inline ASM support to `spirv.rs`) - #163314 (move `#[macro_export]` on declarative macro check to `rustc_attr_parsing`) - #163360 ([rustdoc] Correctly handle rustc_allow_incoherent_impl on primitive methods) - #163385 (GVN transmutes of Immediate::Uninit to Immediate::Uninit) - #163405 (Remove some #[linkage] options) - #163530 (`const impl PartialEq` for `f16b`) - #163581 (do not suggest precise capturing when the opaque span is in a macro expansion) - #163590 (Make `AllocatorNightly` less clever) - #163599 (Add union pattern reference change to relnotes)

Rollup merge of #162904 - lsunsi:issue162857, r=jackh726 Fix ICE for ambiguous candidates on method probing Fixes #162857 It seems like the construction of the Pick was mixing two candidate information that were not synced: - if it is ambiguous - import ids The two candidates were consistent, but the pick became inconsistent when they were mixed. The fix was just to use the import_ids of the ambiguous candidate in case it exists, and keep old behavior otherwise. ICE was introduced in #161805

…uwer Rollup of 20 pull requests Successful merges: - rust-lang/rust#163483 (Bump bootstrap compiler to 1.100.0 beta) - rust-lang/rust#161380 (only rerun const eval in next-solver if the const actually references opaques) - rust-lang/rust#162900 (Some refactorings around metadata encoding) - rust-lang/rust#163461 (Improve diagnostic deduplication) - rust-lang/rust#163580 (Provide better doc code example for `UnixDatagram::bind_addr` and `UnixListener::bind_addr`) - rust-lang/rust#163584 ([triagebot] Ping me for debugger visualizer changes) - rust-lang/rust#159021 (windows-gnu: enable native TLS) - rust-lang/rust#161467 (wfcheck: name the item that discards an unused type parameter) - rust-lang/rust#162618 (trait_selection: Preserve eager normalization failures) - rust-lang/rust#162904 (Fix ICE for ambiguous candidates on method probing) - rust-lang/rust#163064 (Avoid computing overflowed goal chains for crate dependencies) - rust-lang/rust#163281 (Add `f16` inline ASM support to `spirv.rs`) - rust-lang/rust#163314 (move `#[macro_export]` on declarative macro check to `rustc_attr_parsing`) - rust-lang/rust#163360 ([rustdoc] Correctly handle rustc_allow_incoherent_impl on primitive methods) - rust-lang/rust#163385 (GVN transmutes of Immediate::Uninit to Immediate::Uninit) - rust-lang/rust#163405 (Remove some #[linkage] options) - rust-lang/rust#163530 (`const impl PartialEq` for `f16b`) - rust-lang/rust#163581 (do not suggest precise capturing when the opaque span is in a macro expansion) - rust-lang/rust#163590 (Make `AllocatorNightly` less clever) - rust-lang/rust#163599 (Add union pattern reference change to relnotes)

rustbot · 2026-10-08T12:40:49Z

beta backport approved as per compiler team on Zulip. A backport PR will be authored by the release team at the end of the current development cycle. Backport labels are handled by them.

…uwer Rollup of 20 pull requests Successful merges: - #163483 (Bump bootstrap compiler to 1.100.0 beta) - #161380 (only rerun const eval in next-solver if the const actually references opaques) - #162900 (Some refactorings around metadata encoding) - #163461 (Improve diagnostic deduplication) - #163580 (Provide better doc code example for `UnixDatagram::bind_addr` and `UnixListener::bind_addr`) - #163584 ([triagebot] Ping me for debugger visualizer changes) - #159021 (windows-gnu: enable native TLS) - #161467 (wfcheck: name the item that discards an unused type parameter) - #162618 (trait_selection: Preserve eager normalization failures) - #162904 (Fix ICE for ambiguous candidates on method probing) - #163064 (Avoid computing overflowed goal chains for crate dependencies) - #163281 (Add `f16` inline ASM support to `spirv.rs`) - #163314 (move `#[macro_export]` on declarative macro check to `rustc_attr_parsing`) - #163360 ([rustdoc] Correctly handle rustc_allow_incoherent_impl on primitive methods) - #163385 (GVN transmutes of Immediate::Uninit to Immediate::Uninit) - #163405 (Remove some #[linkage] options) - #163530 (`const impl PartialEq` for `f16b`) - #163581 (do not suggest precise capturing when the opaque span is in a macro expansion) - #163590 (Make `AllocatorNightly` less clever) - #163599 (Add union pattern reference change to relnotes)

Add regression test for ambiguous trait with mixed import ids

e9a87d0

Co-authored-by: Philip Sampaio <philip.sampaio@gmail.com>

rustbot assigned folkertdev Sep 17, 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 Sep 17, 2026

lsunsi commented Sep 17, 2026

View reviewed changes

Comment thread compiler/rustc_hir_typeck/src/method/probe.rs Outdated

rustbot added the T-types Relevant to the types team, which will review and decide on the PR/issue. label Sep 17, 2026

rustbot assigned jackh726 and unassigned folkertdev Sep 17, 2026

jackh726 requested changes Sep 30, 2026

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rustbot 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 Sep 30, 2026

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 Sep 30, 2026

lsunsi force-pushed the issue162857 branch from 13e8826 to 109c917 Compare September 30, 2026 18:33

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 Oct 1, 2026

GuillaumeGomez mentioned this pull request Oct 1, 2026

Rollup of 10 pull requests #163600

Closed

GuillaumeGomez mentioned this pull request Oct 1, 2026

Rollup of 11 pull requests #163601

Closed

JonathanBrouwer mentioned this pull request Oct 1, 2026

Rollup of 20 pull requests #163609

Merged

rust-bors Bot merged commit e970c24 into rust-lang:main Oct 2, 2026
13 checks passed

rustbot added this to the 1.101.0 milestone Oct 2, 2026

theemathas added the beta-nominated Nominated for backporting to the compiler in the beta channel. label Oct 2, 2026

lsunsi deleted the issue162857 branch October 2, 2026 10:36

rustbot added the beta-accepted Accepted for backporting to the compiler in the beta channel. label Oct 8, 2026

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