Avoid recursive blanket impl checks by chenyukang · Pull Request #155765 · rust-lang/rust

chenyukang · 2026-04-25T04:50:19Z

Avoid recursively re-checking rustdoc blanket impl candidates while synthesizing impls.

Also record the polarity of synthesized auto-trait impls and reuses that result when checking blanket impl predicates.

If we want to assert the test of rustdoc must finished in specific time, we need to add a run-make test instead?

I tests it now runs about 2.2s for 60 variants on my local machine.

rustbot · 2026-04-25T04:50:23Z

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chenyukang · 2026-04-25T06:07:41Z

The job aarch64-gnu-llvm-21-1 failed! Check out the build log: (web) (plain enhanced) (plain)

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

Executing "/scripts/stage_2_test_set1.sh"
+ /scripts/stage_2_test_set1.sh
PR_CI_JOB set; skipping tidy
+ '[' 1 == 1 ']'
+ echo 'PR_CI_JOB set; skipping tidy'
+ SKIP_TIDY='--skip tidy'
+ ../x.py --stage 2 test --skip tidy --skip compiler --skip src
##[group]Building bootstrap
    Finished `dev` profile [unoptimized] target(s) in 0.04s
##[endgroup]
downloading https://static.rust-lang.org/dist/2026-04-14/rustfmt-nightly-aarch64-unknown-linux-gnu.tar.xz
---

---- [rustdoc-js] tests/rustdoc-js/never-search.rs stdout ----
------node stdout------------------------------
Testing /checkout/tests/rustdoc-js/never-search.js ... FAILED
[ query `! ->`]==> Expected exactly 2 results but found 3 in 'others'
[ query `! ->`]==> Exact check failed at position 0: expected '{"path":"never_search","name":"impossible"}' but found '{"crate":"never_search","name":"from","path":"never_search","exactPath":"never_search","ty":13,"parent":{"path":"never_search","exactPath":"never_search","name":"never","ty":5},"type":{"inputs":[{"id":11,"name":"never","ty":1,"path":"","exactPath":"","generics":[],"bindings":{},"unboxFlag":false}],"output":[{"id":-1,"name":"","ty":26,"path":null,"exactPath":null,"generics":[],"bindings":{},"unboxFlag":true}],"where_clause":[[]]},"paramNames":["T"],"dist":2,"path_dist":0,"index":-1,"desc":"","item":{"id":7,"crate":"never_search","ty":13,"name":"from","normalizedName":"from","modulePath":"never_search","exactModulePath":"never_search","entry":{"krate":27,"ty":13,"modulePath":27,"exactModulePath":27,"parent":12,"traitParent":4,"deprecated":false,"unstable":false,"associatedItemDisambiguatorOrExternCrateUrl":null},"path":null,"functionData":{"functionSignature":{"inputs":[{"id":11,"name":"never","ty":1,"path":"","exactPath":"","generics":[],"bindings":{},"unboxFlag":false}],"output":[{"id":-1,"name":"","ty":26,"path":null,"exactPath":null,"generics":[],"bindings":{},"unboxFlag":true}],"where_clause":[[]]},"paramNames":["T"],"elemCount":2},"deprecated":false,"unstable":false,"parent":{"name":"never","path":{"ty":5,"modulePath":"never_search","exactModulePath":"never_search"}},"traitParent":{"name":"From","path":{"ty":10,"modulePath":"core::convert","exactModulePath":"core::convert"}}},"displayPath":"<span>never_search::</span><span>never::</span>","fullPath":"never_search::never::from|13","traitPath":"core::convert::From::from|13","href":"../never_search/struct.never.html#method.from","displayTypeSignature":{"type":["","!"," -> T"],"mappedNames":{},"whereClause":{}},"id":7,"elems":[{"name":"never","id":11,"typeFilter":1,"generics":[],"bindings":{},"fullPath":["never"],"pathLast":"never","normalizedPathLast":"never","pathWithoutLast":[]}],"returned":[],"is_alias":false,"displayType":"`!` -> T","displayMappedNames":"","displayWhereClause":""}'
[ query `! ->`]==> Exact check failed at position 0: expected '{"path":"never_search","name":"box_impossible"}' but found '{"crate":"never_search","name":"impossible","path":"never_search","exactPath":"never_search","ty":7,"type":{"inputs":[{"id":11,"name":"never","ty":1,"path":"","exactPath":"","generics":[],"bindings":{},"unboxFlag":false}],"output":[{"id":9,"name":"unit","ty":1,"path":"","exactPath":"","generics":[],"bindings":{},"unboxFlag":false}],"where_clause":[]},"paramNames":[],"dist":2,"path_dist":0,"index":-1,"desc":"","item":{"id":26,"crate":"never_search","ty":7,"name":"impossible","normalizedName":"impossible","modulePath":"never_search","exactModulePath":"never_search","entry":{"krate":27,"ty":7,"modulePath":27,"exactModulePath":null,"parent":null,"traitParent":null,"deprecated":false,"unstable":false,"associatedItemDisambiguatorOrExternCrateUrl":null},"path":null,"functionData":{"functionSignature":{"inputs":[{"id":11,"name":"never","ty":1,"path":"","exactPath":"","generics":[],"bindings":{},"unboxFlag":false}],"output":[{"id":9,"name":"unit","ty":1,"path":"","exactPath":"","generics":[],"bindings":{},"unboxFlag":false}],"where_clause":[]},"paramNames":[],"elemCount":2},"deprecated":false,"unstable":false,"parent":null,"traitParent":null},"displayPath":"<span>never_search::</span>","fullPath":"never_search::impossible|7","traitPath":null,"href":"../never_search/fn.impossible.html","displayTypeSignature":{"type":["","!"," -> ()"],"mappedNames":{},"whereClause":{}},"id":26,"elems":[{"name":"never","id":11,"typeFilter":1,"generics":[],"bindings":{},"fullPath":["never"],"pathLast":"never","normalizedPathLast":"never","pathWithoutLast":[]}],"returned":[],"is_alias":false,"displayType":"`!` -> ()","displayMappedNames":"","displayWhereClause":""}'

------node stderr------------------------------

------------------------------------------

error: rustdoc-js test failed!
status: exit status: 1
command: "/usr/bin/node" "/checkout/src/tools/rustdoc-js/tester.js" "--doc-folder" "/checkout/obj/build/aarch64-unknown-linux-gnu/test/rustdoc-js/never-search" "--crate-name" "never_search" "--test-file" "/checkout/tests/rustdoc-js/never-search.js" "--revision" ""
--- stdout -------------------------------
Testing /checkout/tests/rustdoc-js/never-search.js ... FAILED
[ query `! ->`]==> Expected exactly 2 results but found 3 in 'others'
[ query `! ->`]==> Exact check failed at position 0: expected '{"path":"never_search","name":"impossible"}' but found '{"crate":"never_search","name":"from","path":"never_search","exactPath":"never_search","ty":13,"parent":{"path":"never_search","exactPath":"never_search","name":"never","ty":5},"type":{"inputs":[{"id":11,"name":"never","ty":1,"path":"","exactPath":"","generics":[],"bindings":{},"unboxFlag":false}],"output":[{"id":-1,"name":"","ty":26,"path":null,"exactPath":null,"generics":[],"bindings":{},"unboxFlag":true}],"where_clause":[[]]},"paramNames":["T"],"dist":2,"path_dist":0,"index":-1,"desc":"","item":{"id":7,"crate":"never_search","ty":13,"name":"from","normalizedName":"from","modulePath":"never_search","exactModulePath":"never_search","entry":{"krate":27,"ty":13,"modulePath":27,"exactModulePath":27,"parent":12,"traitParent":4,"deprecated":false,"unstable":false,"associatedItemDisambiguatorOrExternCrateUrl":null},"path":null,"functionData":{"functionSignature":{"inputs":[{"id":11,"name":"never","ty":1,"path":"","exactPath":"","generics":[],"bindings":{},"unboxFlag":false}],"output":[{"id":-1,"name":"","ty":26,"path":null,"exactPath":null,"generics":[],"bindings":{},"unboxFlag":true}],"where_clause":[[]]},"paramNames":["T"],"elemCount":2},"deprecated":false,"unstable":false,"parent":{"name":"never","path":{"ty":5,"modulePath":"never_search","exactModulePath":"never_search"}},"traitParent":{"name":"From","path":{"ty":10,"modulePath":"core::convert","exactModulePath":"core::convert"}}},"displayPath":"<span>never_search::</span><span>never::</span>","fullPath":"never_search::never::from|13","traitPath":"core::convert::From::from|13","href":"../never_search/struct.never.html#method.from","displayTypeSignature":{"type":["","!"," -> T"],"mappedNames":{},"whereClause":{}},"id":7,"elems":[{"name":"never","id":11,"typeFilter":1,"generics":[],"bindings":{},"fullPath":["never"],"pathLast":"never","normalizedPathLast":"never","pathWithoutLast":[]}],"returned":[],"is_alias":false,"displayType":"`!` -> T","displayMappedNames":"","displayWhereClause":""}'
[ query `! ->`]==> Exact check failed at position 0: expected '{"path":"never_search","name":"box_impossible"}' but found '{"crate":"never_search","name":"impossible","path":"never_search","exactPath":"never_search","ty":7,"type":{"inputs":[{"id":11,"name":"never","ty":1,"path":"","exactPath":"","generics":[],"bindings":{},"unboxFlag":false}],"output":[{"id":9,"name":"unit","ty":1,"path":"","exactPath":"","generics":[],"bindings":{},"unboxFlag":false}],"where_clause":[]},"paramNames":[],"dist":2,"path_dist":0,"index":-1,"desc":"","item":{"id":26,"crate":"never_search","ty":7,"name":"impossible","normalizedName":"impossible","modulePath":"never_search","exactModulePath":"never_search","entry":{"krate":27,"ty":7,"modulePath":27,"exactModulePath":null,"parent":null,"traitParent":null,"deprecated":false,"unstable":false,"associatedItemDisambiguatorOrExternCrateUrl":null},"path":null,"functionData":{"functionSignature":{"inputs":[{"id":11,"name":"never","ty":1,"path":"","exactPath":"","generics":[],"bindings":{},"unboxFlag":false}],"output":[{"id":9,"name":"unit","ty":1,"path":"","exactPath":"","generics":[],"bindings":{},"unboxFlag":false}],"where_clause":[]},"paramNames":[],"elemCount":2},"deprecated":false,"unstable":false,"parent":null,"traitParent":null},"displayPath":"<span>never_search::</span>","fullPath":"never_search::impossible|7","traitPath":null,"href":"../never_search/fn.impossible.html","displayTypeSignature":{"type":["","!"," -> ()"],"mappedNames":{},"whereClause":{}},"id":26,"elems":[{"name":"never","id":11,"typeFilter":1,"generics":[],"bindings":{},"fullPath":["never"],"pathLast":"never","normalizedPathLast":"never","pathWithoutLast":[]}],"returned":[],"is_alias":false,"displayType":"`!` -> ()","displayMappedNames":"","displayWhereClause":""}'
------------------------------------------
stderr: none

---- [rustdoc-js] tests/rustdoc-js/never-search.rs stdout end ----

The CI failure is caused after this PR,
rustdoc now includes the blanket impl method from:

impl<T> From<!> for T

when searching ! ->.

I think it's ok to update the test case.

fmease · 2026-04-25T09:17:06Z

This can just be a rustdoc UI test since we don't care about the HTML. For that move, it into tests/rustdoc-ui/, remove the #![crate_name], the htmldocck directives and add //@ check-pass

View changes since the review

fmease · 2026-04-25T09:20:02Z

@@ -0,0 +1,268 @@
+#![crate_name = "foo"]


In a source code comment at the top, can you add which initial (auto trait, ADT) pairing(s) used to cause the blowout (unless that info isn't meaningful)

View changes since the review

fmease · 2026-04-25T09:23:23Z

I'm curious, does this have any effect on issue #114891?

View changes since the review

fmease · 2026-04-25T09:29:43Z

+                let predicate = infcx.resolve_vars_if_possible(predicate);
+                if let Some(may_apply) =
+                    cached_auto_trait_predicate_result(cx, predicate, impl_ty, item_ty)


It's very odd to me that we have to special case auto traits here when synthesizing blanket impls, it feels like we're manually helping out the trait solver here when it's likely the old trait solver's fault?

Well, I don't actually know the actually fast-expanding tree of obligations in dtolnay's example. Could you enlighten me?

View changes since the review

I'm gonna rebase my dusty PR #125907, impl lcnr's final suggestion and check if that PR also fixes the issue.

fmease · 2026-04-25T09:34:43Z

    pub(crate) generated_synthetics: FxHashSet<(Ty<'tcx>, DefId)>,
+    /// Polarity of synthesized auto-trait impls processed so far.
+    pub(crate) generated_auto_trait_impls: FxHashMap<(Ty<'tcx>, DefId), ty::ImplPolarity>,


Don't try to address this now since I want to test my other PR first. I'd just like to note that it's confusing to name this generated_auto_trait_impls because generated_synthetics directly above caches both synthetic blanket and synthetic auto trait impls (which is actually problematic, they should be separate caches, see #148980) meaning we would now have "two" auto trait impl caches which are slightly different.

View changes since the review

fmease · 2026-04-25T09:40:38Z

@@ -4,6 +4,7 @@ const EXPECTED = [
    {
        'query': '! ->',


I need to ponder about this behavior change; obviously optimizations like caching shouldn't observably affect the semantics of a program and if they do that indicates a bug somewhere even if the change is 'desirable'.

I've just woken up and I've only skimmed this PR, so this is just a hunch: I see you're somehow involving ImplPolarity in your cache and the impl in question is impl<T> From<!> for T which is a reservation impl (ImplPolarity::Reservation), so you might not be handling that 'correctly'.

Again, it's possible that the change is desirable (I haven't thought about that yet) but then that should be explicitly encoded outside of the caching logic.

View changes since the review

fmease · 2026-04-25T09:46:56Z

+        E58(std::sync::Arc<E58<Span>>),
+        E59(std::sync::Arc<E59<Span>>),
+    }
+}


If we want to assert the test of rustdoc must finished in specific time, we need to add a run-make test instead?

That seems iffy to me as it can easily render the test flaky. It could lead to the test failing on slow machines or in CI if the OS is under heavy workload and suspends the process for a while.

View changes since the review

rustdoc: avoid recursive blanket impl checks

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rustbot assigned fmease Apr 25, 2026

rustbot added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Apr 25, 2026

rustbot added T-rustdoc Relevant to the rustdoc team, which will review and decide on the PR/issue. T-rustdoc-frontend Relevant to the rustdoc-frontend team, which will review and decide on the web UI/UX output. labels Apr 25, 2026

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fix tests for search never

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rustbot added A-rustdoc-js Area: Rustdoc's JS front-end A-rustdoc-search Area: Rustdoc's search feature labels Apr 25, 2026

fmease reviewed Apr 25, 2026

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Avoid recursive blanket impl checks#155765

Avoid recursive blanket impl checks#155765
chenyukang wants to merge 2 commits intorust-lang:mainfrom
chenyukang:yukang-fix-155759-rustdoc-blanket-impl

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