#[serde(flatten)] does not compile without "std" feature: could not find Content in de

[pftbest]

error[E0433]: failed to resolve: could not find `Content` in `de`
  --> src/lib.rs:45:24
   |
45 | #[derive(Clone, Debug, Deserialize)]
   |                        ^^^^^^^^^^^ could not find `Content` in `de`
   |
   = note: this error originates in a derive macro (in Nightly builds, run with -Z macro-backtrace for more info)

error[E0412]: cannot find type `Content` in module `_serde::private::de`
  --> src/lib.rs:45:24
   |
45 | #[derive(Clone, Debug, Deserialize)]
   |                        ^^^^^^^^^^^ not found in `_serde::private::de`
   |
   = note: this error originates in a derive macro (in Nightly builds, run with -Z macro-backtrace for more info)

error[E0433]: failed to resolve: could not find `ToString` in `export`
  --> src/lib.rs:45:24
   |
45 | #[derive(Clone, Debug, Deserialize)]
   |                        ^^^^^^^^^^^ not found in `_serde::export`
   |
   = note: this error originates in a derive macro (in Nightly builds, run with -Z macro-backtrace for more info)
help: consider importing this trait
   |
5  | use std::string::ToString;
   |

error[E0433]: failed to resolve: could not find `Vec` in `export`
  --> src/lib.rs:45:24
   |
45 | #[derive(Clone, Debug, Deserialize)]
   |                        ^^^^^^^^^^^ not found in `_serde::export`
   |
   = note: this error originates in a derive macro (in Nightly builds, run with -Z macro-backtrace for more info)
help: consider importing this struct
   |
5  | use std::vec::Vec;
   |

[dtolnay]

This is intentional - it needs a heap allocated buffer which is not present unless you use std or alloc.

[t-moe]

Run into the same issue today, too bad there is no doc saying that this needs std.

https://serde.rs/attr-flatten.html