Added explanation for E0391

[soon]

Part of #24407

[rust-highfive]

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[nrc]

nit: "contains a circular"

[nrc]

Thanks for the PR, looks like an improvement. I suggested a few minor grammar improvements. I wonder if you could find an example that has a straightforward solution? That is often informative for readers when they get an error like this. (I'm not exactly sure when this error gets triggers, otherwise I'd suggest something myself).

[soon]

@nrc There is an issue related to the same error. What do you think, are code samples from that issue easy enough to be presented in the documentation (maybe, with small fixes)?

[nrc]

Hmm, I don't think that is too useful. In fact, I don't think there is going to be a really informative example here. Looks good as is.

[nrc]

@bors: r+

[bors]

📌 Commit 9125400 has been approved by nrc

[bors]

⌛ Testing commit 9125400 with merge ba32469...

[bors]

☀️ Test successful - auto-linux-32-nopt-t, auto-linux-32-opt, auto-linux-64-nopt-t, auto-linux-64-opt, auto-linux-64-x-android-t, auto-mac-32-opt, auto-mac-64-nopt-t, auto-mac-64-opt, auto-win-gnu-32-nopt-t, auto-win-gnu-32-opt, auto-win-gnu-64-nopt-t, auto-win-gnu-64-opt, auto-win-msvc-32-opt, auto-win-msvc-64-opt