New lint: [derive_partial_eq_without_eq]

tests/ui/absurd-extreme-comparisons.rs

@@ -37,7 +37,7 @@ fn main() {
 
 use std::cmp::{Ordering, PartialEq, PartialOrd};
 
-#[derive(PartialEq, PartialOrd)]
+#[derive(PartialEq, Eq, PartialOrd)]
 pub struct U(u64);
 
 impl PartialEq<u32> for U {

tests/ui/assign_ops2.rs

@@ -24,7 +24,7 @@ fn main() {
 
 use std::ops::{Mul, MulAssign};
 
-#[derive(Copy, Clone, Debug, PartialEq)]
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
 pub struct Wrap(i64);
 
 impl Mul<i64> for Wrap {

tests/ui/cmp_owned/asymmetric_partial_eq.fixed

@@ -1,5 +1,5 @@
 // run-rustfix
-#![allow(unused, clippy::redundant_clone)] // See #5700
+#![allow(unused, clippy::redundant_clone, clippy::derive_partial_eq_without_eq)] // See #5700
 
 // Define the types in each module to avoid trait impls leaking between modules.
 macro_rules! impl_types {

tests/ui/cmp_owned/asymmetric_partial_eq.rs

@@ -1,5 +1,5 @@
 // run-rustfix
-#![allow(unused, clippy::redundant_clone)] // See #5700
+#![allow(unused, clippy::redundant_clone, clippy::derive_partial_eq_without_eq)] // See #5700
 
 // Define the types in each module to avoid trait impls leaking between modules.
 macro_rules! impl_types {

tests/ui/cmp_owned/with_suggestion.fixed

@@ -45,7 +45,7 @@ impl ToOwned for Foo {
     }
 }
 
-#[derive(PartialEq)]
+#[derive(PartialEq, Eq)]
 struct Bar;
 
 impl PartialEq<Foo> for Bar {
@@ -61,7 +61,7 @@ impl std::borrow::Borrow<Foo> for Bar {
     }
 }
 
-#[derive(PartialEq)]
+#[derive(PartialEq, Eq)]
 struct Baz;
 
 impl ToOwned for Baz {

tests/ui/cmp_owned/with_suggestion.rs

@@ -45,7 +45,7 @@ impl ToOwned for Foo {
     }
 }
 
-#[derive(PartialEq)]
+#[derive(PartialEq, Eq)]
 struct Bar;
 
 impl PartialEq<Foo> for Bar {
@@ -61,7 +61,7 @@ impl std::borrow::Borrow<Foo> for Bar {
     }
 }
 
-#[derive(PartialEq)]
+#[derive(PartialEq, Eq)]
 struct Baz;
 
 impl ToOwned for Baz {

tests/ui/cmp_owned/without_suggestion.rs

@@ -26,7 +26,7 @@ impl ToOwned for Foo {
     }
 }
 
-#[derive(PartialEq)]
+#[derive(PartialEq, Eq)]
 struct Baz;
 
 impl ToOwned for Baz {
@@ -36,7 +36,7 @@ impl ToOwned for Baz {
     }
 }
 
-#[derive(PartialEq)]
+#[derive(PartialEq, Eq)]
 struct Bar;
 
 impl PartialEq<Foo> for Bar {

tests/ui/crashes/ice-6254.rs

@@ -2,6 +2,7 @@
 // panicked at 'assertion failed: rows.iter().all(|r| r.len() == v.len())',
 // compiler/rustc_mir_build/src/thir/pattern/_match.rs:2030:5
 
+#[allow(clippy::derive_partial_eq_without_eq)]
 #[derive(PartialEq)]
 struct Foo(i32);
 const FOO_REF_REF: &&Foo = &&Foo(42);

tests/ui/crashes/ice-6254.stderr

@@ -1,5 +1,5 @@
 error: to use a constant of type `Foo` in a pattern, `Foo` must be annotated with `#[derive(PartialEq, Eq)]`
-  --> $DIR/ice-6254.rs:12:9
+  --> $DIR/ice-6254.rs:13:9
    |
 LL |         FOO_REF_REF => {},
    |         ^^^^^^^^^^^

tests/ui/derive_hash_xor_eq.rs

@@ -1,3 +1,5 @@
+#![allow(clippy::derive_partial_eq_without_eq)]
+
 #[derive(PartialEq, Hash)]
 struct Foo;
 

tests/ui/derive_hash_xor_eq.stderr

@@ -1,12 +1,12 @@
 error: you are deriving `Hash` but have implemented `PartialEq` explicitly
-  --> $DIR/derive_hash_xor_eq.rs:10:10
+  --> $DIR/derive_hash_xor_eq.rs:12:10
    |
 LL | #[derive(Hash)]
    |          ^^^^
    |
    = note: `#[deny(clippy::derive_hash_xor_eq)]` on by default
 note: `PartialEq` implemented here
-  --> $DIR/derive_hash_xor_eq.rs:13:1
+  --> $DIR/derive_hash_xor_eq.rs:15:1
    |
 LL | / impl PartialEq for Bar {
 LL | |     fn eq(&self, _: &Bar) -> bool {
@@ -17,13 +17,13 @@ LL | | }
    = note: this error originates in the derive macro `Hash` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: you are deriving `Hash` but have implemented `PartialEq` explicitly
-  --> $DIR/derive_hash_xor_eq.rs:19:10
+  --> $DIR/derive_hash_xor_eq.rs:21:10
    |
 LL | #[derive(Hash)]
    |          ^^^^
    |
 note: `PartialEq` implemented here
-  --> $DIR/derive_hash_xor_eq.rs:22:1
+  --> $DIR/derive_hash_xor_eq.rs:24:1
    |
 LL | / impl PartialEq<Baz> for Baz {
 LL | |     fn eq(&self, _: &Baz) -> bool {
@@ -34,7 +34,7 @@ LL | | }
    = note: this error originates in the derive macro `Hash` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: you are implementing `Hash` explicitly but have derived `PartialEq`
-  --> $DIR/derive_hash_xor_eq.rs:31:1
+  --> $DIR/derive_hash_xor_eq.rs:33:1
    |
 LL | / impl std::hash::Hash for Bah {
 LL | |     fn hash<H: std::hash::Hasher>(&self, _: &mut H) {}
@@ -42,14 +42,14 @@ LL | | }
    | |_^
    |
 note: `PartialEq` implemented here
-  --> $DIR/derive_hash_xor_eq.rs:28:10
+  --> $DIR/derive_hash_xor_eq.rs:30:10
    |
 LL | #[derive(PartialEq)]
    |          ^^^^^^^^^
    = note: this error originates in the derive macro `PartialEq` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: you are implementing `Hash` explicitly but have derived `PartialEq`
-  --> $DIR/derive_hash_xor_eq.rs:49:5
+  --> $DIR/derive_hash_xor_eq.rs:51:5
    |
 LL | /     impl Hash for Foo3 {
 LL | |         fn hash<H: std::hash::Hasher>(&self, _: &mut H) {}
@@ -57,7 +57,7 @@ LL | |     }
    | |_____^
    |
 note: `PartialEq` implemented here
-  --> $DIR/derive_hash_xor_eq.rs:46:14
+  --> $DIR/derive_hash_xor_eq.rs:48:14
    |
 LL |     #[derive(PartialEq)]
    |              ^^^^^^^^^

tests/ui/derive_partial_eq_without_eq.fixed

@@ -0,0 +1,98 @@
+// run-rustfix
+
+#![allow(unused)]
+#![warn(clippy::derive_partial_eq_without_eq)]
+
+// Don't warn on structs that aren't PartialEq
+struct NotPartialEq {
+    foo: u32,
+    bar: String,
+}
+
+// Eq can be derived but is missing
+#[derive(Debug, PartialEq, Eq)]
+struct MissingEq {
+    foo: u32,
+    bar: String,
+}
+
+// Eq is derived
+#[derive(PartialEq, Eq)]
+struct NotMissingEq {
+    foo: u32,
+    bar: String,
+}
+
+// Eq is manually implemented
+#[derive(PartialEq)]
+struct ManualEqImpl {
+    foo: u32,
+    bar: String,
+}
+
+impl Eq for ManualEqImpl {}
+
+// Cannot be Eq because f32 isn't Eq
+#[derive(PartialEq)]
+struct CannotBeEq {
+    foo: u32,
+    bar: f32,
+}
+
+// Don't warn if PartialEq is manually implemented
+struct ManualPartialEqImpl {
+    foo: u32,
+    bar: String,
+}
+
+impl PartialEq for ManualPartialEqImpl {
+    fn eq(&self, other: &Self) -> bool {
+        self.foo == other.foo && self.bar == other.bar
+    }
+}
+
+// Generic fields should be properly checked for Eq-ness
+#[derive(PartialEq)]
+struct GenericNotEq<T: Eq, U: PartialEq> {
+    foo: T,
+    bar: U,
+}
+
+#[derive(PartialEq, Eq)]
+struct GenericEq<T: Eq, U: Eq> {
+    foo: T,
+    bar: U,
+}
+
+#[derive(PartialEq, Eq)]
+struct TupleStruct(u32);
+
+#[derive(PartialEq, Eq)]
+struct GenericTupleStruct<T: Eq>(T);
+
+#[derive(PartialEq)]
+struct TupleStructNotEq(f32);
+
+#[derive(PartialEq, Eq)]
+enum Enum {
+    Foo(u32),
+    Bar { a: String, b: () },
+}
+
+#[derive(PartialEq, Eq)]
+enum GenericEnum<T: Eq, U: Eq, V: Eq> {
+    Foo(T),
+    Bar { a: U, b: V },
+}
+
+#[derive(PartialEq)]
+enum EnumNotEq {
+    Foo(u32),
+    Bar { a: String, b: f32 },
+}
+
+// Ensure that rustfix works properly when `PartialEq` has other derives on either side
+#[derive(Debug, PartialEq, Eq, Clone)]
+struct RustFixWithOtherDerives;
+
+fn main() {}

tests/ui/derive_partial_eq_without_eq.rs

@@ -0,0 +1,98 @@
+// run-rustfix
+
+#![allow(unused)]
+#![warn(clippy::derive_partial_eq_without_eq)]
+
+// Don't warn on structs that aren't PartialEq
+struct NotPartialEq {
+    foo: u32,
+    bar: String,
+}
+
+// Eq can be derived but is missing
+#[derive(Debug, PartialEq)]
+struct MissingEq {
+    foo: u32,
+    bar: String,
+}
+
+// Eq is derived
+#[derive(PartialEq, Eq)]
+struct NotMissingEq {
+    foo: u32,
+    bar: String,
+}
+
+// Eq is manually implemented
+#[derive(PartialEq)]
+struct ManualEqImpl {
+    foo: u32,
+    bar: String,
+}
+
+impl Eq for ManualEqImpl {}
+
+// Cannot be Eq because f32 isn't Eq
+#[derive(PartialEq)]
+struct CannotBeEq {
+    foo: u32,
+    bar: f32,
+}
+
+// Don't warn if PartialEq is manually implemented
+struct ManualPartialEqImpl {
+    foo: u32,
+    bar: String,
+}
+
+impl PartialEq for ManualPartialEqImpl {
+    fn eq(&self, other: &Self) -> bool {
+        self.foo == other.foo && self.bar == other.bar
+    }
+}
+
+// Generic fields should be properly checked for Eq-ness
+#[derive(PartialEq)]
+struct GenericNotEq<T: Eq, U: PartialEq> {
+    foo: T,
+    bar: U,
+}
+
+#[derive(PartialEq)]
+struct GenericEq<T: Eq, U: Eq> {
+    foo: T,
+    bar: U,
+}
+
+#[derive(PartialEq)]
+struct TupleStruct(u32);
+
+#[derive(PartialEq)]
+struct GenericTupleStruct<T: Eq>(T);
+
+#[derive(PartialEq)]
+struct TupleStructNotEq(f32);
+
+#[derive(PartialEq)]
+enum Enum {
+    Foo(u32),
+    Bar { a: String, b: () },
+}
+
+#[derive(PartialEq)]
+enum GenericEnum<T: Eq, U: Eq, V: Eq> {
+    Foo(T),
+    Bar { a: U, b: V },
+}
+
+#[derive(PartialEq)]
+enum EnumNotEq {
+    Foo(u32),
+    Bar { a: String, b: f32 },
+}
+
+// Ensure that rustfix works properly when `PartialEq` has other derives on either side
+#[derive(Debug, PartialEq, Clone)]
+struct RustFixWithOtherDerives;
+
+fn main() {}

tests/ui/derive_partial_eq_without_eq.stderr

@@ -0,0 +1,46 @@
+error: you are deriving `PartialEq` and can implement `Eq`
+  --> $DIR/derive_partial_eq_without_eq.rs:13:17
+   |
+LL | #[derive(Debug, PartialEq)]
+   |                 ^^^^^^^^^ help: consider deriving `Eq` as well: `PartialEq, Eq`
+   |
+   = note: `-D clippy::derive-partial-eq-without-eq` implied by `-D warnings`
+
+error: you are deriving `PartialEq` and can implement `Eq`
+  --> $DIR/derive_partial_eq_without_eq.rs:61:10
+   |
+LL | #[derive(PartialEq)]
+   |          ^^^^^^^^^ help: consider deriving `Eq` as well: `PartialEq, Eq`
+
+error: you are deriving `PartialEq` and can implement `Eq`
+  --> $DIR/derive_partial_eq_without_eq.rs:67:10
+   |
+LL | #[derive(PartialEq)]
+   |          ^^^^^^^^^ help: consider deriving `Eq` as well: `PartialEq, Eq`
+
+error: you are deriving `PartialEq` and can implement `Eq`
+  --> $DIR/derive_partial_eq_without_eq.rs:70:10
+   |
+LL | #[derive(PartialEq)]
+   |          ^^^^^^^^^ help: consider deriving `Eq` as well: `PartialEq, Eq`
+
+error: you are deriving `PartialEq` and can implement `Eq`
+  --> $DIR/derive_partial_eq_without_eq.rs:76:10
+   |
+LL | #[derive(PartialEq)]
+   |          ^^^^^^^^^ help: consider deriving `Eq` as well: `PartialEq, Eq`
+
+error: you are deriving `PartialEq` and can implement `Eq`
+  --> $DIR/derive_partial_eq_without_eq.rs:82:10
+   |
+LL | #[derive(PartialEq)]
+   |          ^^^^^^^^^ help: consider deriving `Eq` as well: `PartialEq, Eq`
+
+error: you are deriving `PartialEq` and can implement `Eq`
+  --> $DIR/derive_partial_eq_without_eq.rs:95:17
+   |
+LL | #[derive(Debug, PartialEq, Clone)]
+   |                 ^^^^^^^^^ help: consider deriving `Eq` as well: `PartialEq, Eq`
+
+error: aborting due to 7 previous errors
+

tests/ui/equatable_if_let.fixed

@@ -1,6 +1,6 @@
 // run-rustfix
 
-#![allow(unused_variables, dead_code)]
+#![allow(unused_variables, dead_code, clippy::derive_partial_eq_without_eq)]
 #![warn(clippy::equatable_if_let)]
 
 use std::cmp::Ordering;

tests/ui/equatable_if_let.rs

@@ -1,6 +1,6 @@
 // run-rustfix
 
-#![allow(unused_variables, dead_code)]
+#![allow(unused_variables, dead_code, clippy::derive_partial_eq_without_eq)]
 #![warn(clippy::equatable_if_let)]
 
 use std::cmp::Ordering;

tests/ui/unit_cmp.rs

@@ -1,5 +1,9 @@
 #![warn(clippy::unit_cmp)]
-#![allow(clippy::no_effect, clippy::unnecessary_operation)]
+#![allow(
+    clippy::no_effect,
+    clippy::unnecessary_operation,
+    clippy::derive_partial_eq_without_eq
+)]
 
 #[derive(PartialEq)]
 pub struct ContainsUnit(()); // should be fine

tests/ui/unit_cmp.stderr

@@ -1,5 +1,5 @@
 error: ==-comparison of unit values detected. This will always be true
-  --> $DIR/unit_cmp.rs:12:8
+  --> $DIR/unit_cmp.rs:16:8
    |
 LL |       if {
    |  ________^
@@ -12,7 +12,7 @@ LL | |     } {}
    = note: `-D clippy::unit-cmp` implied by `-D warnings`
 
 error: >-comparison of unit values detected. This will always be false
-  --> $DIR/unit_cmp.rs:18:8
+  --> $DIR/unit_cmp.rs:22:8
    |
 LL |       if {
    |  ________^
@@ -23,7 +23,7 @@ LL | |     } {}
    | |_____^
 
 error: `assert_eq` of unit values detected. This will always succeed
-  --> $DIR/unit_cmp.rs:24:5
+  --> $DIR/unit_cmp.rs:28:5
    |
 LL | /     assert_eq!(
 LL | |         {
@@ -35,7 +35,7 @@ LL | |     );
    | |_____^
 
 error: `debug_assert_eq` of unit values detected. This will always succeed
-  --> $DIR/unit_cmp.rs:32:5
+  --> $DIR/unit_cmp.rs:36:5
    |
 LL | /     debug_assert_eq!(
 LL | |         {
@@ -47,7 +47,7 @@ LL | |     );
    | |_____^
 
 error: `assert_ne` of unit values detected. This will always fail
-  --> $DIR/unit_cmp.rs:41:5
+  --> $DIR/unit_cmp.rs:45:5
    |
 LL | /     assert_ne!(
 LL | |         {
@@ -59,7 +59,7 @@ LL | |     );
    | |_____^
 
 error: `debug_assert_ne` of unit values detected. This will always fail
-  --> $DIR/unit_cmp.rs:49:5
+  --> $DIR/unit_cmp.rs:53:5
    |
 LL | /     debug_assert_ne!(
 LL | |         {