unnecessary_ip_addr_parse: new lint

[samueltardieu]

This lint detects parsing of string literals into IP addresses when they are known correct.

changelog: [unnecessary_ip_addr_parse]: new lint

Inspired by this Zulip comment.

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[Jarcho]

Is there any reason to limit linting this to just ip addresses? Any call to parse on a string literal has the same issue regardless of the type. The suggestion would have to be specialised per type so it could only exist for a subset of cases. Possibly a config to ignore specific types, but I'm not sure if this would be needed.

[samueltardieu]

I guess this could be extended, but at this stage I'm not sure we should make a generic lint for this. Specialized lints can be collectively renamed into a more generic one if we don't see one of them being disabled in isolation. I'd be more comfortable with a separate lint for the time being.

In any case, I'll suspend this PR until rust-lang/rust#140976 is merged and synced to Clippy (hopefully tomorrow).

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