Mark PartialEq as #[rustc_trivial_field_reads]

[GrigorenkoPV]

Closes #134588

Probably needs a crater run

[rustbot]

r? @fee1-dead

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[rustbot]

The Miri subtree was changed

cc @rust-lang/miri

[fmease]

Probably needs a crater run

I'm pretty sure you'd have to bump dead_code to deny-by-default but only for struct fields (somehow), otherwise it wouldn't get caught by crater (additional warnings don't make a run fail IINM) unless you're only interested in crates that deny/forbid dead_code.

[rustbot]

Some changes occurred in exhaustiveness checking

cc @Nadrieril

[fee1-dead]

This seems like another contentious thing. I'd recommend getting some discussion first (see also #134588 (comment)), maybe on T-lang Zulip.

I wouldn't mind if we use an allow-by-default lint for this, but at present it doesn't look like a trivial change. Maybe incorporate to clippy is another option?

[rustbot]

rust-analyzer is developed in its own repository. If possible, consider making this change to rust-lang/rust-analyzer instead.

cc @rust-lang/rust-analyzer

[rust-log-analyzer]

The job aarch64-gnu-llvm-19-1 failed! Check out the build log: (web) (plain enhanced) (plain)

Click to see the possible cause of the failure (guessed by this bot)

normalized stderr:
warning: field `0` is never read
##[warning]  --> $DIR/mutually-recursive-types.rs:16:14
   |
LL |     Children(Box<List>),
   |     -------- ^^^^^^^^^
   |     |
   |     field in this variant
   |
   = note: `Tree` has derived impls for the traits `PartialEq` and `Debug`, but these are intentionally ignored during dead code analysis
   = note: `#[warn(dead_code)]` on by default
help: consider changing the field to be of unit type to suppress this warning while preserving the field numbering, or remove the field
   |
LL -     Children(Box<List>),
LL +     Children(()),
   |

warning: field `0` is never read
##[warning]  --> $DIR/mutually-recursive-types.rs:17:10
   |
LL |     Leaf(Colour),
   |     ---- ^^^^^^
   |     |
   |     field in this variant
   |
   = note: `Tree` has derived impls for the traits `PartialEq` and `Debug`, but these are intentionally ignored during dead code analysis
help: consider changing the field to be of unit type to suppress this warning while preserving the field numbering, or remove the field
   |
LL -     Leaf(Colour),
LL +     Leaf(()),
   |

warning: fields `0` and `1` are never read
##[warning]  --> $DIR/mutually-recursive-types.rs:22:10
   |
LL |     Cons(Box<Tree>, Box<List>),
   |     ---- ^^^^^^^^^  ^^^^^^^^^
   |     |
   |     fields in this variant
   |
   = note: `List` has derived impls for the traits `PartialEq` and `Debug`, but these are intentionally ignored during dead code analysis
help: consider changing the fields to be of unit type to suppress this warning while preserving the field numbering, or remove the fields
   |
LL -     Cons(Box<Tree>, Box<List>),
LL +     Cons((), ()),
   |

warning: fields `0` and `1` are never read
##[warning]  --> $DIR/mutually-recursive-types.rs:28:10
   |
LL |     Kons(isize, Box<SmallList>),
   |     ---- ^^^^^  ^^^^^^^^^^^^^^
   |     |
   |     fields in this variant
   |
   = note: `SmallList` has derived impls for the traits `PartialEq` and `Debug`, but these are intentionally ignored during dead code analysis
help: consider changing the fields to be of unit type to suppress this warning while preserving the field numbering, or remove the fields
   |
LL -     Kons(isize, Box<SmallList>),
LL +     Kons((), ()),
   |

warning: 4 warnings emitted


---
To only update this specific test, also pass `--test-args type/mutually-recursive-types.rs`

error: 1 errors occurred comparing output.
status: exit status: 0
command: env -u RUSTC_LOG_COLOR RUSTC_ICE="0" RUST_BACKTRACE="short" "/checkout/obj/build/aarch64-unknown-linux-gnu/stage2/bin/rustc" "/checkout/tests/ui/type/mutually-recursive-types.rs" "-Zthreads=1" "-Zsimulate-remapped-rust-src-base=/rustc/FAKE_PREFIX" "-Ztranslate-remapped-path-to-local-path=no" "-Z" "ignore-directory-in-diagnostics-source-blocks=/cargo" "-Z" "ignore-directory-in-diagnostics-source-blocks=/checkout/vendor" "--sysroot" "/checkout/obj/build/aarch64-unknown-linux-gnu/stage2" "--target=aarch64-unknown-linux-gnu" "--check-cfg" "cfg(test,FALSE)" "-O" "--error-format" "json" "--json" "future-incompat" "-Ccodegen-units=1" "-Zui-testing" "-Zdeduplicate-diagnostics=no" "-Zwrite-long-types-to-disk=no" "-Cstrip=debuginfo" "-C" "prefer-dynamic" "-o" "/checkout/obj/build/aarch64-unknown-linux-gnu/test/ui/type/mutually-recursive-types/a" "-A" "internal_features" "-Crpath" "-Cdebuginfo=0" "-Lnative=/checkout/obj/build/aarch64-unknown-linux-gnu/native/rust-test-helpers"
stdout: none
--- stderr -------------------------------
warning: field `0` is never read
##[warning]  --> /checkout/tests/ui/type/mutually-recursive-types.rs:16:14
   |
LL |     Children(Box<List>),
   |     -------- ^^^^^^^^^
   |     |
   |     field in this variant
   |
   = note: `Tree` has derived impls for the traits `PartialEq` and `Debug`, but these are intentionally ignored during dead code analysis
   = note: `#[warn(dead_code)]` on by default
help: consider changing the field to be of unit type to suppress this warning while preserving the field numbering, or remove the field
   |
LL -     Children(Box<List>),
LL +     Children(()),
   |

warning: field `0` is never read
##[warning]  --> /checkout/tests/ui/type/mutually-recursive-types.rs:17:10
   |
LL |     Leaf(Colour),
   |     ---- ^^^^^^
   |     |
   |     field in this variant
   |
   = note: `Tree` has derived impls for the traits `PartialEq` and `Debug`, but these are intentionally ignored during dead code analysis
help: consider changing the field to be of unit type to suppress this warning while preserving the field numbering, or remove the field
   |
LL -     Leaf(Colour),
LL +     Leaf(()),
   |

warning: fields `0` and `1` are never read
##[warning]  --> /checkout/tests/ui/type/mutually-recursive-types.rs:22:10
   |
LL |     Cons(Box<Tree>, Box<List>),
   |     ---- ^^^^^^^^^  ^^^^^^^^^
   |     |
   |     fields in this variant
   |
   = note: `List` has derived impls for the traits `PartialEq` and `Debug`, but these are intentionally ignored during dead code analysis
help: consider changing the fields to be of unit type to suppress this warning while preserving the field numbering, or remove the fields
   |
LL -     Cons(Box<Tree>, Box<List>),
LL +     Cons((), ()),
   |

warning: fields `0` and `1` are never read
##[warning]  --> /checkout/tests/ui/type/mutually-recursive-types.rs:28:10
   |
LL |     Kons(isize, Box<SmallList>),
   |     ---- ^^^^^  ^^^^^^^^^^^^^^
   |     |
   |     fields in this variant
   |
   = note: `SmallList` has derived impls for the traits `PartialEq` and `Debug`, but these are intentionally ignored during dead code analysis
help: consider changing the fields to be of unit type to suppress this warning while preserving the field numbering, or remove the fields
   |
LL -     Kons(isize, Box<SmallList>),
LL +     Kons((), ()),
   |

warning: 4 warnings emitted
------------------------------------------