Clippy is incompatible with serde 1.0.107

[kornelski]

Summary

Re #7606

The version of serde specified in Cargo.toml is too low, and incompatible with this crate.

test compile_test ... FAILED

failures:

---- compile_test stdout ----
diff of stderr:

 error[E0412]: cannot find type `PhantomData` in this scope
   --> $DIR/ice-6252.rs:8:9
    |
 LL |     _n: PhantomData,
    |         ^^^^^^^^^^^ not found in this scope
    |
 help: consider importing one of these items
    |
 LL | use core::marker::PhantomData;
    |
-LL | use serde::__private::PhantomData;
+LL | use serde::export::PhantomData;
    |
 LL | use std::marker::PhantomData;
    |

 error[E0412]: cannot find type `VAL` in this scope
   --> $DIR/ice-6252.rs:10:63

Reproducer

Clippy asks for serde 1.0.0, which is even lower, but currently the lowest possible version is 1.0.107, because that's what cargo_metadata crate specifies, and this forces this version for the whole project (Cargo doesn't duplicate dependencies with the same semver-major version).

cargo update -p serde --precise 1.0.107
cargo test --all

The same tests pass if you do:

cargo update -p serde

to bump serde to 1.0.136. Somewhere between 107 and 136 serde has changed its behavior, and the tests rely on the later serde version.

Version

rustc 1.60.0-nightly (6abb6385b 2022-01-26)
binary: rustc
commit-hash: 6abb6385b2cb7249f67b9b3ce7522527767dd907
commit-date: 2022-01-26
host: aarch64-apple-darwin
release: 1.60.0-nightly
LLVM version: 13.0.0

Additional Labels

No response

[flip1995]

Continuing the conversation of #7606: I mean, Clippy doesn't have a Cargo.lock file, so running cargo update if something weird breaks with dependencies is usually the solution. This probably did break for you, because you had an outdated Cargo.lock file in your checkout.

We could set serde to 1.0.125, so that it at least uses that version. This is the version that is currently in rust-lang/rusts Cargo.lock file. Since we don't really care that much about the serde version in Clippy (as long as tests pass), I'd say we don't cause a serde version update in rust-lang/rust. We can set the minimum version to whatever works in the range of 1.0.108 and 1.0.125 though.