Investigate adding a lint or some automated check which detects when a serde default is defined on a config setting which is of type Option<T>.

[neuronull]

As part of the postmortem to #16630 , one long(er) term idea was to automate the detection of for example

struct FooConfig {
   #[serde(default = "default_setting")]
    my_setting: Option<WhatverType>,
}

fn default_setting() -> Option<WhateverType> {
    Some(WhateverType::suits_your_fancy())
}

, since that shouldn't be an Option<T> at this point. It should just be a the type itself.

This is a code smell and can lead to the issues like in the aforementioned bug.

It looks like we are doing that in a few places already:

 grep -r "#\[serde(default =" -A 1 | grep "Option<"

./config/api.rs-    pub address: Option<SocketAddr>,
./sources/host_metrics/mod.rs-    pub collectors: Option<Vec<Collector>>,
./sources/host_metrics/mod.rs-    pub namespace: Option<String>,
./sources/host_metrics/mod.rs-    pub cgroups: Option<CGroupsConfig>,
./sources/docker_logs/mod.rs-    partial_event_marker_field: Option<String>,