Fix ICE for ambiguous candidates on method probing - #162904

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)

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

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