fix(npm): memoize peer cache hit checks to prevent combinatorial explosion#32609
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bartlomieju merged 3 commits intomainfrom Mar 10, 2026
Merged
fix(npm): memoize peer cache hit checks to prevent combinatorial explosion#32609bartlomieju merged 3 commits intomainfrom
bartlomieju merged 3 commits intomainfrom
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…osion When resolving peer dependencies for packages with many mutual peer deps (e.g. AWS CDK v1), `find_peers_cache_hit_inner` was called recursively millions of times. Since `parent_pkgs` is constant within a single `find_peers_cache_hit` call, the result for any given `nv` is always the same. Adding a memo HashMap eliminates redundant recursive checks, turning `deno add npm:@aws-cdk/aws-ecs` from hanging indefinitely to completing in seconds. Closes #26430 Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
kajukitli
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Mar 9, 2026
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lgtm, classic memoization fix for exponential blowup
the key insight is correct: parent_pkgs is constant for the entire call tree, so once you know whether nv X has a matching cache entry, that answer won't change. memoizing it collapses O(2^n) back to O(n).
good that you don't memoize the cycle-detection early return (checking.insert returns false) — that result is path-dependent.
2.5M calls → memoized lookups is a nice win 👍
dsherret
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Mar 10, 2026
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We should get a test for this before merging. Ideally this would be a test in deno_npm.
Adds a test with 25 mutually peer-dependent packages that hangs indefinitely without the memoization fix but completes in <1s with it. Regression test for #26430 Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
bartlomieju
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Mar 10, 2026
| /// millions of redundant recursive calls and hangs indefinitely. | ||
| /// Regression test for https://github.com/denoland/deno/issues/26430 | ||
| #[tokio::test] | ||
| async fn peer_deps_mutual_many_packages_no_hang() { |
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I confirmed this test hangs on main and burns 100% CPU. It passes fine in this PR.
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Summary
deno add npm:@aws-cdk/aws-ecs(and similar large peer dep trees) hanging indefinitelyfind_peers_cache_hit_innerinlibs/npm/resolution/graph.rsrecursively checks whether cached peer resolutions match the current context. For packages with many mutual peer dependencies (like AWS CDK v1 with ~33 packages and 1200+ cache entries), this causes combinatorial explosion — a single cache lookup for@aws-cdk/aws-kmstriggered 2.5 million recursive calls taking 17+ secondsparent_pkgsis constant within a singlefind_peers_cache_hitcall, the answer for any givennvnever changes. AHashMapmemo eliminates all redundant recursive workBefore/After
deno add npm:@aws-cdk/aws-ecsTest plan
deno_npmunit tests passdeno add npm:@aws-cdk/aws-ecscompletes successfullyCloses #26430
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