parsed_string_literals: new lint

[samueltardieu]

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

changelog: [parsed_string_literals]: 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).

@rustbot author

[rustbot]

Reminder, once the PR becomes ready for a review, use @rustbot ready.

[samueltardieu]

Rebased to take advantage of the new diagnostic items.

What about clippy::parsed_string_literals as a name?

[Jarcho]

That sounds like a good name.

[Jarcho]

FCP started here: https://rust-lang.zulipchat.com/#narrow/channel/257328-clippy/topic/FCP.3A.20parsed_string_literals/with/519705970

[samueltardieu]

Amended to avoid a useless string allocation during diagnostic production (and version number).

[samueltardieu]

Added numerical/boolean types as well.

[samueltardieu]

I've leveraged the existing clippy_utils::source::str_literal_to_char_literal to ensure that the original representation of a character literal is preserved when possible.

[Jarcho]

A snippet isn't needed here and it's the slowest available option. The fastest thing to do is match the type down to a single segment path and compare the symbol.

[samueltardieu]

Done, and .with_source_text() is used whenever possible at lint emission type to limit the number of copies.

[rustbot]

This PR was rebased onto a different master commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

[samueltardieu]

Anything needs to be modified?

[samueltardieu]

(second push was to update a test comment now that we don't use type from let)

[samueltardieu]

Changes in the recent push:

• Special inf and nan (with any case, and with an optional leading + or -) are now properly handled through the type's associated constants, thanks to @y21 for noticing this.
• Parsing f16 has been added as well – only f128 doesn't support scanning and formatting by default.
• Category has been set to complexity as it looks this is the way the Zulip poll is trending.
• Clippy version has been set to "1.93.0" as today was the last sync before the "1.92.0" Rust version is cut from the master branch on next week.