[ty] synthesize __replace__ for dataclasses (>=3.13)

crates/ty_python_semantic/resources/mdtest/call/replace.md

@@ -0,0 +1,70 @@
+# `replace`
+
+The `replace` function and the `replace` protocol were added in Python 3.13:
+<https://docs.python.org/3/whatsnew/3.13.html#copy>
+
+```toml
+[environment]
+python-version = "3.13"
+```
+
+## Basic
+
+```py
+from copy import replace
+from datetime import time
+
+t = time(12, 0, 0)
+t = replace(t, minute=30)
+
+reveal_type(t)  # revealed: time
+```
+
+## The `__replace__` protocol
+
+### Dataclasses
+
+Dataclasses support the `__replace__` protocol:
+
+```py
+from dataclasses import dataclass
+from copy import replace
+
+@dataclass
+class Point:
+    x: int
+    y: int
+
+reveal_type(Point.__replace__)  # revealed: (self: Point, *, x: int = int, y: int = int) -> Point
+```
+
+The `__replace__` method can either be called directly or through the `replace` function:
+
+```py
+a = Point(1, 2)
+
+b = a.__replace__(x=3, y=4)
+reveal_type(b)  # revealed: Point
+
+b = replace(a, x=3, y=4)
+reveal_type(b)  # revealed: Point
+```
+
+A call to `replace` does not require all keyword arguments:
+
+```py
+c = a.__replace__(y=4)
+reveal_type(c)  # revealed: Point
+
+d = replace(a, y=4)
+reveal_type(d)  # revealed: Point
+```
+
+Invalid calls to `__replace__` or `replace` will raise an error:
+
+```py
+e = a.__replace__(x="wrong")  # error: [invalid-argument-type]
+
+# TODO: this should ideally also be emit an error
+e = replace(a, x="wrong")
+```

crates/ty_python_semantic/src/types/class.rs

@@ -1596,7 +1596,10 @@ impl<'db> ClassLiteral<'db> {
 
         let field_policy = CodeGeneratorKind::from_class(db, self)?;
 
-        let signature_from_fields = |mut parameters: Vec<_>| {
+        let instance_ty =
+            Type::instance(db, self.apply_optional_specialization(db, specialization));
+
+        let signature_from_fields = |mut parameters: Vec<_>, return_ty: Option<Type<'db>>| {
             let mut kw_only_field_seen = false;
             for (
                 field_name,
@@ -1669,21 +1672,26 @@ impl<'db> ClassLiteral<'db> {
                     }
                 }
 
-                let mut parameter = if kw_only_field_seen {
+                let mut parameter = if kw_only_field_seen || name == "__replace__" {
                     Parameter::keyword_only(field_name)
                 } else {
                     Parameter::positional_or_keyword(field_name)
                 }
                 .with_annotated_type(field_ty);
 
-                if let Some(default_ty) = default_ty {
+                if name == "__replace__" {
+                    // When replacing, we know there is a default value for the field
+                    // (the value that is currently assigned to the field)
+                    // assume this to be the declared type of the field
+                    parameter = parameter.with_default_type(field_ty);
+                } else if let Some(default_ty) = default_ty {
                     parameter = parameter.with_default_type(default_ty);
                 }
 
                 parameters.push(parameter);
             }
 
-            let mut signature = Signature::new(Parameters::new(parameters), Some(Type::none(db)));
+            let mut signature = Signature::new(Parameters::new(parameters), return_ty);
             signature.inherited_generic_context = self.generic_context(db);
             Some(CallableType::function_like(db, signature))
         };
@@ -1701,16 +1709,13 @@ impl<'db> ClassLiteral<'db> {
 
                 let self_parameter = Parameter::positional_or_keyword(Name::new_static("self"))
                     // TODO: could be `Self`.
-                    .with_annotated_type(Type::instance(
-                        db,
-                        self.apply_optional_specialization(db, specialization),
-                    ));
-                signature_from_fields(vec![self_parameter])
+                    .with_annotated_type(instance_ty);
+                signature_from_fields(vec![self_parameter], Some(Type::none(db)))
             }
             (CodeGeneratorKind::NamedTuple, "__new__") => {
                 let cls_parameter = Parameter::positional_or_keyword(Name::new_static("cls"))
                     .with_annotated_type(KnownClass::Type.to_instance(db));
-                signature_from_fields(vec![cls_parameter])
+                signature_from_fields(vec![cls_parameter], Some(Type::none(db)))
             }
             (CodeGeneratorKind::DataclassLike, "__lt__" | "__le__" | "__gt__" | "__ge__") => {
                 if !has_dataclass_param(DataclassParams::ORDER) {
@@ -1721,16 +1726,10 @@ impl<'db> ClassLiteral<'db> {
                     Parameters::new([
                         Parameter::positional_or_keyword(Name::new_static("self"))
                             // TODO: could be `Self`.
-                            .with_annotated_type(Type::instance(
-                                db,
-                                self.apply_optional_specialization(db, specialization),
-                            )),
+                            .with_annotated_type(instance_ty),
                         Parameter::positional_or_keyword(Name::new_static("other"))
                             // TODO: could be `Self`.
-                            .with_annotated_type(Type::instance(
-                                db,
-                                self.apply_optional_specialization(db, specialization),
-                            )),
+                            .with_annotated_type(instance_ty),
                     ]),
                     Some(KnownClass::Bool.to_instance(db)),
                 );
@@ -1745,15 +1744,20 @@ impl<'db> ClassLiteral<'db> {
                     .place
                     .ignore_possibly_unbound()
             }
+            (CodeGeneratorKind::DataclassLike, "__replace__")
+                if Program::get(db).python_version(db) >= PythonVersion::PY313 =>
+            {
+                let self_parameter = Parameter::positional_or_keyword(Name::new_static("self"))
+                    .with_annotated_type(instance_ty);
+
+                signature_from_fields(vec![self_parameter], Some(instance_ty))
+            }
             (CodeGeneratorKind::DataclassLike, "__setattr__") => {
                 if has_dataclass_param(DataclassParams::FROZEN) {
                     let signature = Signature::new(
                         Parameters::new([
                             Parameter::positional_or_keyword(Name::new_static("self"))
-                                .with_annotated_type(Type::instance(
-                                    db,
-                                    self.apply_optional_specialization(db, specialization),
-                                )),
+                                .with_annotated_type(instance_ty),
                             Parameter::positional_or_keyword(Name::new_static("name")),
                             Parameter::positional_or_keyword(Name::new_static("value")),
                         ]),