Using serde_with to deserialize from string or struct on a vector

[colmanhumphrey]

Thanks for the crate @jonasbb!

Building off this example, which is an extension from serde's docs.

We'll assume we have the same struct Build as in the serde docs:

#[derive(Debug, Deserialize)]
struct Build {
    context: String,
    dockerfile: Option<String>,
    #[serde(default)]
    args: Map<String, String>,
}

Let's now assume we wanted to deserialize potentially many of them, e.g our target struct is:

#[derive(Deserialize, Debug)]
pub struct ManyBuilds {
    some_fields_with_overall_info: i32, // etc
    builds: Vec<Build>
}

@jonasbb's suggestion is to annotate builds like (do I have this right Jonas?):

#[derive(Deserialize, Debug)]
pub struct ManyBuilds {
    some_fields_with_overall_info: i32, // etc
    #[serde_as(as = "Vec<PickFirst<(_, DisplayFromStr)>>")]
    builds: Vec<Build>
}

This looks great, although I am currently getting the following error:

error: expected an inert attribute, found an attribute macro
  --> src/main.rs:90:5
   |
90 |     #[serde_as(as = "Vec<PickFirst<(_, DisplayFromStr)>>")]
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error: aborting due to previous error

I'm guessing there's some very simple solution, but I don't yet see it. Thanks!

[jonasbb]

That is my mistake, I was too brief in the other message. To use serde_as you need to place the proc-macro attribute #[serde_with::serde_as] before the derive. This section of the user guide explains how to setup everything and what you can do with it.

#[serde_with::serde_as]
#[derive(Deserialize, Debug)]
pub struct ManyBuilds {
    some_fields_with_overall_info: i32, // etc
    #[serde_as(as = "Vec<PickFirst<(_, DisplayFromStr)>>")]
    builds: Vec<Build>
}

Side-Note: The associated Err type on the FromStr implementations needs to implement Display for this to work.

[colmanhumphrey]

Thanks Jonas - that works! That's not your mistake at all - I had indeed previously correctly annotated the struct when trying the package a couple days ago (after reading the guide - I didn't catch onto PickFirst on that read however!), and just must have been sloppy when trying this example out, my bad.

Makes sense about the error, not currently a big constraint for my needs.

Thanks again for the prompt responses!