Semver incompatible change (?) landed in 1.0.153

[banool]

Note: I know that semver only applies to the "public API" of a crate so I'm not 100% sure if this qualifies as a violation of semver since I'm not sure how the public API is defined here.

This PR was released as part of 1.0.153: #2387.

In that PR @dtolnay mentioned that we'd just go for it with the change and reassess later if this happened to cause issues for anyone:

I was hopeful that somebody would look into what possibility of breakage this has for existing formats, but in the absence of anyone having been willing to do that, I think it will be all right to reassess based on any reported consequences.

I'm well and truly late to the party hahah but unfortunately this does cause some issues.

At a high level you can see the issue like this:

git clone git@github.com:aptos-labs/aptos-core.git
# Change serde version in Cargo.toml to 1.0.153
cd testsuite/generate-format
cargo run -- --corpus aptos

I'm still trying to figure out how exactly this change actually breaks our code, I just wanted to report in with an instance of a breakage. Once I know precisely what it changes for us I'll chime in again, though this looks pretty complicated. I believe the tldr is we have code that produces a yaml representation of generated code. We diff that yaml to make sure no incompatibilities arise. This code generation no longer works with 1.0.153 I believe because some of the other tooling we use (serde-reflection) breaks with this change to aliases + nesting.

If it turns out that this is part of the public API then I can make a minimally reproducible example to help debug.