Use `#[automatically_derived]` in all generated code

[clechasseur]

I am using serde_with in a small project and am seeing missing line coverage in my code coverage report, pointing to my #[derive] directives. Apparently, this can be avoided by adding the #[automatically_derived] attribute to generated code.

I've done a quick search in this repository and it seems to be used already for some generated code, so I can only assume there are places it isn't used yet (I'm not very familiar with derive macro implementation so I can't be certain 🙂).

Here's an example of how I use serde_with:

https://github.com/clechasseur/aoc_leaderbot/blob/fa643db51d692821b01c9094007f2434b1ecc371/aoc_leaderboard/src/aoc.rs#L40

This is not high-priority for me as I am just poking around a toy project, but I thought I'd report it in any case. If I can be of further assistance, don't hesitate to ask.

[clechasseur]

Hmm, I just noticed that the highlighted line is the one with the #[derive], but #[serde_as] is not a derive macro. So perhaps the problem lies elsewhere. You can see the highlighted line here:

https://app.codecov.io/gh/clechasseur/aoc_leaderbot/pull/3/blob/aoc_leaderboard/src/aoc.rs#L22

It seems to highlight Deserialize, but the weird thing is that I have other structs that derive Deserialize but don't use #[serde_as] and they're not tagged as uncovered.

[jonasbb]

I don't think this is a problem with serde_with. I modified one of your other structs to use the serde(with="...") attribute, without anything from serde_with. Here is the addition of with="PuzzleCompletionInfo". I see a miss in the Deserialize derive here as well.

/// Information about the completion of a day in an [Advent of Code] event.
///
/// [Advent of Code]: https://adventofcode.com/
#[derive(Debug, Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Serialize, Deserialize)]
pub struct CompletionDayLevel {
    /// Info about the completion of the day's part 1.
    #[serde(rename = "1", with="PuzzleCompletionInfo")]
    pub part_1: PuzzleCompletionInfo,

    /// Info about the completion of the day's part 2.
    ///
    /// Can be [`None`] if user has not yet solved part 2.
    #[serde(rename = "2", default, skip_serializing_if = "Option::is_none")]
    pub part_2: Option<PuzzleCompletionInfo>,
}

As such, I think this is an issue with the normal serde derives. I took a quick look at serde, but didn't find a missing #[automatically_derived] there either, but opening an issue might be worth it.

[clechasseur]

Thank you, and sorry if I entered the issue in the wrong project; debugging code coverage in macro-generated code is non-trivial and I guess I didn't put the finger on the right problem. I'll try to come up with a more minimal repro and look at the serde crate itself. Feel free to close this issue.

[jonasbb]

No problem, such a debugging challenge is nice once in a while :) There was some recent stuff in the serde repo about the Deserialize derive and llvm-cov: serde-rs/serde#2866 and serde-rs/serde#2868. Both should be included in v1.0.216 of serde, which you seem to use.