[ty] Support class-arguments for dataclass transformers (#21457)

## Summary

Allow metaclass-based and baseclass-based dataclass-transformers to
overwrite the default behavior using class arguments:

```py
class Person(Model, order=True):
    # ...
```

## Conformance tests

Four new tests passing!

## Test Plan

New Markdown tests

crates/ty_python_semantic/resources/mdtest/dataclasses/dataclass_transform.md

@@ -356,13 +356,17 @@ model < model  # No error
 
 ### Overwriting of default parameters on the dataclass-like class
 
+In the following examples, we show how a model can overwrite the default parameters set by the
+`dataclass_transform` decorator. In particular, we change from `frozen=True` to `frozen=False`, and
+from `order=False` (default) to `order=True`:
+
 #### Using function-based transformers
 
 ```py
 from typing import dataclass_transform
 
 @dataclass_transform(frozen_default=True)
-def default_frozen_model(*, frozen: bool = True): ...
+def default_frozen_model(*, frozen: bool = True, order: bool = False): ...
 @default_frozen_model()
 class Frozen:
     name: str
@@ -370,12 +374,16 @@ class Frozen:
 f = Frozen(name="test")
 f.name = "new"  # error: [invalid-assignment]
 
-@default_frozen_model(frozen=False)
+Frozen(name="A") < Frozen(name="B")  # error: [unsupported-operator]
+
+@default_frozen_model(frozen=False, order=True)
 class Mutable:
     name: str
 
 m = Mutable(name="test")
 m.name = "new"  # No error
+
+reveal_type(Mutable(name="A") < Mutable(name="B"))  # revealed: bool
 ```
 
 #### Using metaclass-based transformers
@@ -392,6 +400,7 @@ class DefaultFrozenMeta(type):
         namespace,
         *,
         frozen: bool = True,
+        order: bool = False,
     ): ...
 
 class DefaultFrozenModel(metaclass=DefaultFrozenMeta): ...
@@ -402,12 +411,17 @@ class Frozen(DefaultFrozenModel):
 f = Frozen(name="test")
 f.name = "new"  # error: [invalid-assignment]
 
-class Mutable(DefaultFrozenModel, frozen=False):
+Frozen(name="A") < Frozen(name="B")  # error: [unsupported-operator]
+
+class Mutable(DefaultFrozenModel, frozen=False, order=True):
     name: str
 
 m = Mutable(name="test")
-# TODO: no error here
+# TODO: This should not be an error. In order to support this, we need to implement the precise `frozen` semantics of
+# `dataclass_transform` described here: https://typing.python.org/en/latest/spec/dataclasses.html#dataclass-semantics
 m.name = "new"  # error: [invalid-assignment]
+
+reveal_type(Mutable(name="A") < Mutable(name="B"))  # revealed: bool
 ```
 
 #### Using base-class-based transformers
@@ -421,6 +435,7 @@ class DefaultFrozenModel:
         cls,
         *,
         frozen: bool = True,
+        order: bool = False,
     ): ...
 
 class Frozen(DefaultFrozenModel):
@@ -429,12 +444,15 @@ class Frozen(DefaultFrozenModel):
 f = Frozen(name="test")
 f.name = "new"  # error: [invalid-assignment]
 
-class Mutable(DefaultFrozenModel, frozen=False):
+Frozen(name="A") < Frozen(name="B")  # error: [unsupported-operator]
+
+class Mutable(DefaultFrozenModel, frozen=False, order=True):
     name: str
 
 m = Mutable(name="test")
-# TODO: This should not be an error
+m.name = "new"  # No error
-m.name = "new"  # error: [invalid-assignment]
+
+reveal_type(Mutable(name="A") < Mutable(name="B"))  # revealed: bool
 ```
 
 ## `field_specifiers`

crates/ty_python_semantic/src/semantic_index/definition.rs

@@ -714,6 +714,13 @@ impl DefinitionKind<'_> {
         }
     }
 
+    pub(crate) const fn as_class(&self) -> Option<&AstNodeRef<ast::StmtClassDef>> {
+        match self {
+            DefinitionKind::Class(class) => Some(class),
+            _ => None,
+        }
+    }
+
     pub(crate) fn is_import(&self) -> bool {
         matches!(
             self,

crates/ty_python_semantic/src/types/class.rs

@@ -2206,7 +2206,7 @@ impl<'db> ClassLiteral<'db> {
 
         let field_policy = CodeGeneratorKind::from_class(db, self, specialization)?;
 
-        let transformer_params =
+        let mut transformer_params =
             if let CodeGeneratorKind::DataclassLike(Some(transformer_params)) = field_policy {
                 Some(DataclassParams::from_transformer_params(
                     db,
@@ -2216,6 +2216,36 @@ impl<'db> ClassLiteral<'db> {
                 None
             };
 
+        // Dataclass transformer flags can be overwritten using class arguments.
+        if let Some(transformer_params) = transformer_params.as_mut() {
+            if let Some(class_def) = self.definition(db).kind(db).as_class() {
+                let module = parsed_module(db, self.file(db)).load(db);
+
+                if let Some(arguments) = &class_def.node(&module).arguments {
+                    let mut flags = transformer_params.flags(db);
+
+                    for keyword in &arguments.keywords {
+                        if let Some(arg_name) = &keyword.arg {
+                            if let Some(is_set) =
+                                keyword.value.as_boolean_literal_expr().map(|b| b.value)
+                            {
+                                match arg_name.as_str() {
+                                    "eq" => flags.set(DataclassFlags::EQ, is_set),
+                                    "order" => flags.set(DataclassFlags::ORDER, is_set),
+                                    "kw_only" => flags.set(DataclassFlags::KW_ONLY, is_set),
+                                    "frozen" => flags.set(DataclassFlags::FROZEN, is_set),
+                                    _ => {}
+                                }
+                            }
+                        }
+                    }
+
+                    *transformer_params =
+                        DataclassParams::new(db, flags, transformer_params.field_specifiers(db));
+                }
+            }
+        }
+
         let has_dataclass_param = |param| {
             dataclass_params.is_some_and(|params| params.flags(db).contains(param))
                 || transformer_params.is_some_and(|params| params.flags(db).contains(param))