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If you are saying the cycle is not detected because the real package name is not taken into account, then won't this fix the issue?

    const node = ctx.dependenciesTree.get(childNodeId)!
    graph.push([node.resolvedPackage.name, edges])
    graph.push([currentAlias, edges])

Here:
https://github.com/pnpm/pnpm/blob/0e596f60b8a1d6725463c145327d2b5a0017ef36/pkg-manager/resolve-dependencies/src/resolvePeers.ts#L847`

I tried applying the suggested change locally, but unfortunately it doesn't seem to resolve the issue. Running a reproducible case still results in the same error that was originally fixed by #8760:

diff --git a/pkg-manager/resolve-dependencies/src/resolvePeers.ts b/pkg-manager/resolve-dependencies/src/resolvePeers.ts
index 07830ddd1..77b19dddb 100644
--- a/pkg-manager/resolve-dependencies/src/resolvePeers.ts
+++ b/pkg-manager/resolve-dependencies/src/resolvePeers.ts
@@ -844,6 +844,8 @@ async function resolvePeersOfChildren<T extends PartialResolvedPackage> (
       allResolvedPeers.set(peerName, peerNodeId)
       edges.push(peerName)
     }
+    const node = ctx.dependenciesTree.get(childNodeId)!
+    graph.push([node.resolvedPackage.name, edges])
     graph.push([currentAlias, edges])
     for (const [missingPeer, range] of missingPeers.entries()) {
       allMissingPeers.set(missingPeer, range)

pnpm: Duplicate edge specification from "react-dom"
...
    at resolvePeersOfChildren (.../pnpm/pkg-manager/resolve-dependencies/src/resolvePeers.ts:855:24)
    at async resolvePeersOfNode (.../pnpm/pkg-manager/resolve-dependencies/src/resolvePeers.ts:467:7)
    at async resolvePeersOfChildren (.../pnpm/pkg-manager/resolve-dependencies/src/resolvePeers.ts:835:9)
    at async resolvePeersOfNode (.../pnpm/pkg-manager/resolve-dependencies/src/resolvePeers.ts:467:7)
    at async resolvePeersOfChildren (.../pnpm/pkg-manager/resolve-dependencies/src/resolvePeers.ts:835:9)
    at async resolvePeers (.../pnpm/pkg-manager/resolve-dependencies/src/resolvePeers.ts:123:27)

The issue seems to involve a peer layout where an alias and the actual package name depend on each other. Since only one directional edge is retained in the graph, graph-cycles doesn't detect the cycle, and both sides end up mutually waiting.

That said, I'm not deeply familiar with the overall structure of the pnpm codebase, so it's very possible I'm missing something.

Thanks for taking a look!

pnpm: Duplicate edge specification from "react-dom"

This should work then

const node = ctx.dependenciesTree.get(childNodeId)!
graph.push([node.resolvedPackage.name, edges])
if (currentAlias !== node.resolvedPackage.name) {
     graph.push([currentAlias, edges])
}

It would be really good to cover this with a test. Can you share the reproduction? If it uses private packages, we can simulate the same dependency graph with our registry mock: https://github.com/pnpm/registry-mock

That doesn't work either.

pnpm: Duplicate edge specification from "@editor-kit/plugins"
    at <anonymous> (.../.pnpm-store/v10/links/graph-cycles/1.2.1/6f2b25f857fcf85625df3e696ef321b4f88cc829daec112b0865999e9edd275c/node_modules/graph-cycles/dist/index.js:27:19)
    at Array.forEach (<anonymous>)
    at buildAndEnsureValidGraph (.../.pnpm-store/v10/links/graph-cycles/1.2.1/6f2b25f857fcf85625df3e696ef321b4f88cc829daec112b0865999e9edd275c/node_modules/graph-cycles/dist/index.js:25:11)
    at analyzeGraph2 (.../.pnpm-store/v10/links/graph-cycles/1.2.1/6f2b25f857fcf85625df3e696ef321b4f88cc829daec112b0865999e9edd275c/node_modules/graph-cycles/dist/index.js:33:22)
    at resolvePeersOfChildren (.../pnpm/pkg-manager/resolve-dependencies/src/resolvePeers.ts:857:24)
    at async resolvePeers (.../pnpm/pkg-manager/resolve-dependencies/src/resolvePeers.ts:123:27)
    at async resolveDependencies2 (.../pnpm/pkg-manager/resolve-dependencies/src/index.ts:202:7)
    at async _installInContext (.../pnpm/pkg-manager/core/src/install/index.ts:1129:7)
    at async installInContext (.../pnpm/pkg-manager/core/src/install/index.ts:1628:12)
    at async _install (.../pnpm/pkg-manager/core/src/install/index.ts:633:20)

I successfully used @pnpm/registry-mock to publish packages to the mock registry locally after removing unrelated files, and reproduced the deadlock against the local mock registry.

How should I provide this reproduction? Is there any guideline I should follow?

Here's the reproduction repo: https://github.com/reekystive/pnpm-peers-deadlock-issue

Submit your packages to the registry-mock repository, then I'll publish it and you'll be able to write a test for it in this PR.

I am adding the test

Congrats on merging your first pull request! 🎉🎉🎉

Thanks for fixing this!

Our team relies heavily on pnpm every day, thank you for all the hard work and thoughtful design that make it such a dependable tool. We’re very grateful! ❤️

Thanks for providing the reproduction packages. Without that it is really hard to fix such issues.