[red-knot] Dataclasses: support order=True (#17406)

## Summary

Support dataclasses with `order=True`:

```py
@DataClass(order=True)
class WithOrder:
    x: int

WithOrder(1) < WithOrder(2)  # no error
```

Also adds some additional tests to `dataclasses.md`.

ticket: #16651

## Test Plan

New Markdown tests

Author: sharkdp

.github/workflows/mypy_primer.yaml

@@ -68,7 +68,7 @@ jobs:
             --type-checker knot \
             --old base_commit \
             --new "$GITHUB_SHA" \
-            --project-selector '/(mypy_primer|black|pyp|git-revise|zipp|arrow|isort|itsdangerous|rich|packaging|pybind11|pyinstrument|typeshed-stats|scrapy|werkzeug|bidict|async-utils)$' \
+            --project-selector '/(mypy_primer|black|pyp|git-revise|zipp|arrow|isort|itsdangerous|rich|packaging|pybind11|pyinstrument|typeshed-stats|scrapy|werkzeug|bidict|async-utils|python-chess|dacite|python-htmlgen|paroxython|porcupine|psycopg)$' \
             --output concise \
             --debug > mypy_primer.diff || [ $? -eq 1 ]
 

crates/red_knot_python_semantic/resources/mdtest/dataclasses.md

@@ -91,6 +91,125 @@ repr(C())
 C() == C()
 ```
 
+## Other dataclass parameters
+
+### `repr`
+
+A custom `__repr__` method is generated by default. It can be disabled by passing `repr=False`, but
+in that case `__repr__` is still available via `object.__repr__`:
+
+```py
+from dataclasses import dataclass
+
+@dataclass(repr=False)
+class WithoutRepr:
+    x: int
+
+reveal_type(WithoutRepr(1).__repr__)  # revealed: bound method WithoutRepr.__repr__() -> str
+```
+
+### `eq`
+
+The same is true for `__eq__`. Setting `eq=False` disables the generated `__eq__` method, but
+`__eq__` is still available via `object.__eq__`:
+
+```py
+from dataclasses import dataclass
+
+@dataclass(eq=False)
+class WithoutEq:
+    x: int
+
+reveal_type(WithoutEq(1) == WithoutEq(2))  # revealed: bool
+```
+
+### `order`
+
+`order` is set to `False` by default. If `order=True`, `__lt__`, `__le__`, `__gt__`, and `__ge__`
+methods will be generated:
+
+```py
+from dataclasses import dataclass
+
+@dataclass
+class WithoutOrder:
+    x: int
+
+WithoutOrder(1) < WithoutOrder(2)  # error: [unsupported-operator]
+WithoutOrder(1) <= WithoutOrder(2)  # error: [unsupported-operator]
+WithoutOrder(1) > WithoutOrder(2)  # error: [unsupported-operator]
+WithoutOrder(1) >= WithoutOrder(2)  # error: [unsupported-operator]
+
+@dataclass(order=True)
+class WithOrder:
+    x: int
+
+WithOrder(1) < WithOrder(2)
+WithOrder(1) <= WithOrder(2)
+WithOrder(1) > WithOrder(2)
+WithOrder(1) >= WithOrder(2)
+```
+
+Comparisons are only allowed for `WithOrder` instances:
+
+```py
+WithOrder(1) < 2  # error: [unsupported-operator]
+WithOrder(1) <= 2  # error: [unsupported-operator]
+WithOrder(1) > 2  # error: [unsupported-operator]
+WithOrder(1) >= 2  # error: [unsupported-operator]
+```
+
+This also works for generic dataclasses:
+
+```py
+from dataclasses import dataclass
+
+@dataclass(order=True)
+class GenericWithOrder[T]:
+    x: T
+
+GenericWithOrder[int](1) < GenericWithOrder[int](1)
+
+GenericWithOrder[int](1) < GenericWithOrder[str]("a")  # error: [unsupported-operator]
+```
+
+If a class already defines one of the comparison methods, a `TypeError` is raised at runtime.
+Ideally, we would emit a diagnostic in that case:
+
+```py
+@dataclass(order=True)
+class AlreadyHasCustomDunderLt:
+    x: int
+
+    # TODO: Ideally, we would emit a diagnostic here
+    def __lt__(self, other: object) -> bool:
+        return False
+```
+
+### `unsafe_hash`
+
+To do
+
+### `frozen`
+
+To do
+
+### `match_args`
+
+To do
+
+### `kw_only`
+
+To do
+
+### `slots`
+
+To do
+
+### `weakref_slot`
+
+To do
+
 ## Inheritance
 
 ### Normal class inheriting from a dataclass
@@ -168,13 +287,30 @@ reveal_type(d_int.description)  # revealed: str
 DataWithDescription[int](None, "description")
 ```
 
-## Frozen instances
+## Descriptor-typed fields
 
-To do
+```py
+from dataclasses import dataclass
 
-## Descriptor-typed fields
+class Descriptor:
+    _value: int = 0
 
-To do
+    def __get__(self, instance, owner) -> str:
+        return str(self._value)
+
+    def __set__(self, instance, value: int) -> None:
+        self._value = value
+
+@dataclass
+class C:
+    d: Descriptor = Descriptor()
+
+c = C(1)
+reveal_type(c.d)  # revealed: str
+
+# TODO: should be an error
+C("a")
+```
 
 ## `dataclasses.field`
 
@@ -197,18 +333,61 @@ class C:
 reveal_type(C.__init__)  # revealed: (*args: Any, **kwargs: Any) -> None
 ```
 
-### Dataclass with `init=False`
+### Dataclass with custom `__init__` method
 
-To do
+If a class already defines `__init__`, it is not replaced by the `dataclass` decorator.
 
-### Dataclass with custom `__init__` method
+```py
+from dataclasses import dataclass
 
-To do
+@dataclass(init=True)
+class C:
+    x: str
+
+    def __init__(self, x: int) -> None:
+        self.x = str(x)
+
+C(1)  # OK
+
+# TODO: should be an error
+C("a")
+```
+
+Similarly, if we set `init=False`, we still recognize the custom `__init__` method:
+
+```py
+@dataclass(init=False)
+class D:
+    def __init__(self, x: int) -> None:
+        self.x = str(x)
+
+D(1)  # OK
+D()  # error: [missing-argument]
+```
 
 ### Dataclass with `ClassVar`s
 
 To do
 
+### Return type of `dataclass(...)`
+
+A call like `dataclass(order=True)` returns a callable itself, which is then used as the decorator.
+We can store the callable in a variable and later use it as a decorator:
+
+```py
+from dataclasses import dataclass
+
+dataclass_with_order = dataclass(order=True)
+
+reveal_type(dataclass_with_order)  # revealed: <decorator produced by dataclasses.dataclass>
+
+@dataclass_with_order
+class C:
+    x: int
+
+C(1) < C(2)  # ok
+```
+
 ### Using `dataclass` as a function
 
 To do

crates/red_knot_python_semantic/src/types/class.rs

@@ -823,21 +823,31 @@ impl<'db> ClassLiteralType<'db> {
         name: &str,
     ) -> SymbolAndQualifiers<'db> {
         if let Some(metadata) = self.dataclass_metadata(db) {
-            if name == "__init__" {
-                if metadata.contains(DataclassMetadata::INIT) {
-                    // TODO: Generate the signature from the attributes on the class
-                    let init_signature = Signature::new(
-                        Parameters::new([
-                            Parameter::variadic(Name::new_static("args"))
-                                .with_annotated_type(Type::any()),
-                            Parameter::keyword_variadic(Name::new_static("kwargs"))
-                                .with_annotated_type(Type::any()),
-                        ]),
-                        Some(Type::none(db)),
+            if name == "__init__" && metadata.contains(DataclassMetadata::INIT) {
+                // TODO: Generate the signature from the attributes on the class
+                let init_signature = Signature::new(
+                    Parameters::new([
+                        Parameter::variadic(Name::new_static("args"))
+                            .with_annotated_type(Type::any()),
+                        Parameter::keyword_variadic(Name::new_static("kwargs"))
+                            .with_annotated_type(Type::any()),
+                    ]),
+                    Some(Type::none(db)),
+                );
+
+                return Symbol::bound(Type::Callable(CallableType::new(db, init_signature))).into();
+            } else if matches!(name, "__lt__" | "__le__" | "__gt__" | "__ge__") {
+                if metadata.contains(DataclassMetadata::ORDER) {
+                    let signature = Signature::new(
+                        Parameters::new([Parameter::positional_or_keyword(Name::new_static(
+                            "other",
+                        ))
+                        .with_annotated_type(Type::instance(
+                            self.apply_optional_specialization(db, specialization),
+                        ))]),
+                        Some(KnownClass::Bool.to_instance(db)),
                     );
-
-                    return Symbol::bound(Type::Callable(CallableType::new(db, init_signature)))
-                        .into();
+                    return Symbol::bound(Type::Callable(CallableType::new(db, signature))).into();
                 }
             }
         }

crates/red_knot_python_semantic/src/types/generics.rs

@@ -13,7 +13,7 @@ use crate::Db;
 ///
 /// TODO: Handle nested generic contexts better, with actual parent links to the lexically
 /// containing context.
-#[salsa::tracked(debug)]
+#[salsa::interned(debug)]
 pub struct GenericContext<'db> {
     #[return_ref]
     pub(crate) variables: Box<[TypeVarInstance<'db>]>,
@@ -25,7 +25,7 @@ impl<'db> GenericContext<'db> {
         index: &'db SemanticIndex<'db>,
         type_params_node: &ast::TypeParams,
     ) -> Self {
-        let variables = type_params_node
+        let variables: Box<[_]> = type_params_node
             .iter()
             .filter_map(|type_param| Self::variable_from_type_param(db, index, type_param))
             .collect();
@@ -116,7 +116,7 @@ impl<'db> GenericContext<'db> {
 ///
 /// TODO: Handle nested specializations better, with actual parent links to the specialization of
 /// the lexically containing context.
-#[salsa::tracked(debug)]
+#[salsa::interned(debug)]
 pub struct Specialization<'db> {
     pub(crate) generic_context: GenericContext<'db>,
     #[return_ref]
@@ -138,7 +138,7 @@ impl<'db> Specialization<'db> {
     /// That lets us produce the generic alias `A[int]`, which is the corresponding entry in the
     /// MRO of `B[int]`.
     pub(crate) fn apply_specialization(self, db: &'db dyn Db, other: Specialization<'db>) -> Self {
-        let types = self
+        let types: Box<[_]> = self
             .types(db)
             .into_iter()
             .map(|ty| ty.apply_specialization(db, other))
@@ -154,7 +154,7 @@ impl<'db> Specialization<'db> {
     pub(crate) fn combine(self, db: &'db dyn Db, other: Self) -> Self {
         let generic_context = self.generic_context(db);
         assert!(other.generic_context(db) == generic_context);
-        let types = self
+        let types: Box<[_]> = self
             .types(db)
             .into_iter()
             .zip(other.types(db))
@@ -167,7 +167,7 @@ impl<'db> Specialization<'db> {
     }
 
     pub(crate) fn normalized(self, db: &'db dyn Db) -> Self {
-        let types = self.types(db).iter().map(|ty| ty.normalized(db)).collect();
+        let types: Box<[_]> = self.types(db).iter().map(|ty| ty.normalized(db)).collect();
         Self::new(db, self.generic_context(db), types)
     }
 
@@ -201,7 +201,7 @@ impl<'db> SpecializationBuilder<'db> {
     }
 
     pub(crate) fn build(mut self) -> Specialization<'db> {
-        let types = self
+        let types: Box<[_]> = self
             .generic_context
             .variables(self.db)
             .iter()