"Respectful" YAML patching in Rust

Fri, 08 May 2026 00:00:00 +0000

Patching a YAML file programmatically is straightforward in principle: parse, modify, serialize. Ideally the process should also be respectful — that is, preserve the following properties of the initial file:

Formatting. The same YAML value can be represented in multiple ways: how mappings and lists are indented, whether blank lines separate sections, how strings are quoted, and so on. For example, a list can be represented in block style
```
items:
 - 1
 - 2
 - 3
```
or in flow style

The `Sync` bound nobody asked for

Mon, 04 May 2026 00:00:00 +0000

&self as a receiver in an async method of a trait whose returned future must be Send implicitly forces Sync on the trait implementor type — even if neither the trait nor its callers ever explicitly ask for Sync.

Here’s a quick demonstration.

1.1. Future without Send bound, Send + Sync impl type — compiles:

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struct SendSync;

static_assertions::assert_impl_all!(SendSync: Send, Sync);

pub trait T {
 fn f(&self) -> impl Future<Output = ()>;
}

impl T for SendSync {
 async fn f(&self) {}
}

1.2. Future without Send bound, Send-only impl type — also compiles:

Posts on Evgeniy Terekhin

"Respectful" YAML patching in Rust

The `Sync` bound nobody asked for