[ty] Simplify signature types, use them in CallableType (#18344)

There were many fields in `Signature` and friends that really had more
to do with how a signature was being _used_ — how it was looked up,
details about an individual call site, etc. Those fields more properly
belong in `Bindings` and friends.

This is a pure refactoring, and should not affect any tests or ecosystem
projects.

I started on this journey in support of
https://github.com/astral-sh/ty/issues/462. It seemed worth pulling out
as a separate PR.

One major concrete benefit of this refactoring is that we can now use
`CallableSignature` directly in `CallableType`. (We can't use
`CallableSignature` directly in that `Type` variant because signatures
are not currently interned.)

crates/ty_python_semantic/src/types/call.rs

@@ -1,11 +1,11 @@
 use super::context::InferContext;
-use super::{CallableSignature, Signature, Signatures, Type};
+use super::{Signature, Type};
 use crate::Db;
 
 mod arguments;
 mod bind;
 pub(super) use arguments::{Argument, CallArgumentTypes, CallArguments};
-pub(super) use bind::{Bindings, CallableBinding};
+pub(super) use bind::{Binding, Bindings, CallableBinding};
 
 /// Wraps a [`Bindings`] for an unsuccessful call with information about why the call was
 /// unsuccessful.

crates/ty_python_semantic/src/types/call/bind.rs

@@ -3,11 +3,11 @@
 //! [signatures][crate::types::signatures], we have to handle the fact that the callable might be a
 //! union of types, each of which might contain multiple overloads.
 
-use smallvec::SmallVec;
+use smallvec::{SmallVec, smallvec};
 
 use super::{
-    Argument, CallArgumentTypes, CallArguments, CallError, CallErrorKind, CallableSignature,
-    InferContext, Signature, Signatures, Type,
+    Argument, CallArgumentTypes, CallArguments, CallError, CallErrorKind, InferContext, Signature,
+    Type,
 };
 use crate::db::Db;
 use crate::dunder_all::dunder_all_names;
@@ -33,7 +33,9 @@ use ruff_python_ast as ast;
 /// It's guaranteed that the wrapped bindings have no errors.
 #[derive(Debug)]
 pub(crate) struct Bindings<'db> {
-    signatures: Signatures<'db>,
+    /// The type that is (hopefully) callable.
+    callable_type: Type<'db>,
+
     /// By using `SmallVec`, we avoid an extra heap allocation for the common case of a non-union
     /// type.
     elements: SmallVec<[CallableBinding<'db>; 1]>,
@@ -45,6 +47,40 @@ pub(crate) struct Bindings<'db> {
 }
 
 impl<'db> Bindings<'db> {
+    /// Creates a new `Bindings` from an iterator of [`Bindings`]s. Panics if the iterator is
+    /// empty.
+    pub(crate) fn from_union<I>(callable_type: Type<'db>, elements: I) -> Self
+    where
+        I: IntoIterator<Item = Bindings<'db>>,
+    {
+        let elements: SmallVec<_> = elements
+            .into_iter()
+            .flat_map(|s| s.elements.into_iter())
+            .collect();
+        assert!(!elements.is_empty());
+        Self {
+            callable_type,
+            elements,
+            argument_forms: Box::from([]),
+            conflicting_forms: Box::from([]),
+        }
+    }
+
+    pub(crate) fn replace_callable_type(&mut self, before: Type<'db>, after: Type<'db>) {
+        if self.callable_type == before {
+            self.callable_type = after;
+        }
+        for binding in &mut self.elements {
+            binding.replace_callable_type(before, after);
+        }
+    }
+
+    pub(crate) fn set_dunder_call_is_possibly_unbound(&mut self) {
+        for binding in &mut self.elements {
+            binding.dunder_call_is_possibly_unbound = true;
+        }
+    }
+
     /// Match the arguments of a call site against the parameters of a collection of possibly
     /// unioned, possibly overloaded signatures.
     ///
@@ -55,30 +91,15 @@ impl<'db> Bindings<'db> {
     ///
     /// Once you have argument types available, you can call [`check_types`][Self::check_types] to
     /// verify that each argument type is assignable to the corresponding parameter type.
-    pub(crate) fn match_parameters(
-        signatures: Signatures<'db>,
-        arguments: &CallArguments<'_>,
-    ) -> Self {
+    pub(crate) fn match_parameters(mut self, arguments: &CallArguments<'_>) -> Self {
         let mut argument_forms = vec![None; arguments.len()];
         let mut conflicting_forms = vec![false; arguments.len()];
-        let elements: SmallVec<[CallableBinding<'db>; 1]> = signatures
-            .iter()
-            .map(|signature| {
-                CallableBinding::match_parameters(
-                    signature,
-                    arguments,
-                    &mut argument_forms,
-                    &mut conflicting_forms,
-                )
-            })
-            .collect();
-
-        Bindings {
-            signatures,
-            elements,
-            argument_forms: argument_forms.into(),
-            conflicting_forms: conflicting_forms.into(),
+        for binding in &mut self.elements {
+            binding.match_parameters(arguments, &mut argument_forms, &mut conflicting_forms);
         }
+        self.argument_forms = argument_forms.into();
+        self.conflicting_forms = conflicting_forms.into();
+        self
     }
 
     /// Verify that the type of each argument is assignable to type of the parameter that it was
@@ -95,8 +116,8 @@ impl<'db> Bindings<'db> {
         db: &'db dyn Db,
         argument_types: &CallArgumentTypes<'_, 'db>,
     ) -> Result<Self, CallError<'db>> {
-        for (signature, element) in self.signatures.iter().zip(&mut self.elements) {
-            element.check_types(db, signature, argument_types);
+        for element in &mut self.elements {
+            element.check_types(db, argument_types);
         }
 
         self.evaluate_known_cases(db);
@@ -157,7 +178,7 @@ impl<'db> Bindings<'db> {
     }
 
     pub(crate) fn callable_type(&self) -> Type<'db> {
-        self.signatures.callable_type
+        self.callable_type
     }
 
     /// Returns the return type of the call. For successful calls, this is the actual return type.
@@ -228,7 +249,7 @@ impl<'db> Bindings<'db> {
         };
 
         // Each special case listed here should have a corresponding clause in `Type::signatures`.
-        for (binding, callable_signature) in self.elements.iter_mut().zip(self.signatures.iter()) {
+        for binding in &mut self.elements {
             let binding_type = binding.callable_type;
             for (overload_index, overload) in binding.matching_overloads_mut() {
                 match binding_type {
@@ -848,15 +869,12 @@ impl<'db> Bindings<'db> {
 
                                         let mut dataclass_params = DataclassParams::from(params);
 
-                                        if let Some(Some(Type::BooleanLiteral(order))) =
-                                            callable_signature.iter().nth(overload_index).and_then(
-                                                |signature| {
-                                                    let (idx, _) = signature
-                                                        .parameters()
-                                                        .keyword_by_name("order")?;
-                                                    overload.parameter_types().get(idx)
-                                                },
-                                            )
+                                        if let Some(Some(Type::BooleanLiteral(order))) = overload
+                                            .signature
+                                            .parameters()
+                                            .keyword_by_name("order")
+                                            .map(|(idx, _)| idx)
+                                            .and_then(|idx| overload.parameter_types().get(idx))
                                         {
                                             dataclass_params.set(DataclassParams::ORDER, *order);
                                         }
@@ -945,6 +963,37 @@ impl<'a, 'db> IntoIterator for &'a mut Bindings<'db> {
     }
 }
 
+impl<'db> From<CallableBinding<'db>> for Bindings<'db> {
+    fn from(from: CallableBinding<'db>) -> Bindings<'db> {
+        Bindings {
+            callable_type: from.callable_type,
+            elements: smallvec![from],
+            argument_forms: Box::from([]),
+            conflicting_forms: Box::from([]),
+        }
+    }
+}
+
+impl<'db> From<Binding<'db>> for Bindings<'db> {
+    fn from(from: Binding<'db>) -> Bindings<'db> {
+        let callable_type = from.callable_type;
+        let signature_type = from.signature_type;
+        let callable_binding = CallableBinding {
+            callable_type,
+            signature_type,
+            dunder_call_is_possibly_unbound: false,
+            bound_type: None,
+            overloads: smallvec![from],
+        };
+        Bindings {
+            callable_type,
+            elements: smallvec![callable_binding],
+            argument_forms: Box::from([]),
+            conflicting_forms: Box::from([]),
+        }
+    }
+}
+
 /// Binding information for a single callable. If the callable is overloaded, there is a separate
 /// [`Binding`] for each overload.
 ///
@@ -962,10 +1011,21 @@ impl<'a, 'db> IntoIterator for &'a mut Bindings<'db> {
 /// [overloads]: https://github.com/python/typing/pull/1839
 #[derive(Debug)]
 pub(crate) struct CallableBinding<'db> {
+    /// The type that is (hopefully) callable.
     pub(crate) callable_type: Type<'db>,
+
+    /// The type we'll use for error messages referring to details of the called signature. For
+    /// calls to functions this will be the same as `callable_type`; for other callable instances
+    /// it may be a `__call__` method.
     pub(crate) signature_type: Type<'db>,
+
+    /// If this is a callable object (i.e. called via a `__call__` method), the boundness of
+    /// that call method.
     pub(crate) dunder_call_is_possibly_unbound: bool,
 
+    /// The type of the bound `self` or `cls` parameter if this signature is for a bound method.
+    pub(crate) bound_type: Option<Type<'db>>,
+
     /// The bindings of each overload of this callable. Will be empty if the type is not callable.
     ///
     /// By using `SmallVec`, we avoid an extra heap allocation for the common case of a
@@ -974,15 +1034,56 @@ pub(crate) struct CallableBinding<'db> {
 }
 
 impl<'db> CallableBinding<'db> {
+    pub(crate) fn from_overloads(
+        signature_type: Type<'db>,
+        overloads: impl IntoIterator<Item = Signature<'db>>,
+    ) -> Self {
+        let overloads = overloads
+            .into_iter()
+            .map(|signature| Binding::single(signature_type, signature))
+            .collect();
+        Self {
+            callable_type: signature_type,
+            signature_type,
+            dunder_call_is_possibly_unbound: false,
+            bound_type: None,
+            overloads,
+        }
+    }
+
+    pub(crate) fn not_callable(signature_type: Type<'db>) -> Self {
+        Self {
+            callable_type: signature_type,
+            signature_type,
+            dunder_call_is_possibly_unbound: false,
+            bound_type: None,
+            overloads: smallvec![],
+        }
+    }
+
+    pub(crate) fn with_bound_type(mut self, bound_type: Type<'db>) -> Self {
+        self.bound_type = Some(bound_type);
+        self
+    }
+
+    fn replace_callable_type(&mut self, before: Type<'db>, after: Type<'db>) {
+        if self.callable_type == before {
+            self.callable_type = after;
+        }
+        for binding in &mut self.overloads {
+            binding.replace_callable_type(before, after);
+        }
+    }
+
     fn match_parameters(
-        signature: &CallableSignature<'db>,
+        &mut self,
         arguments: &CallArguments<'_>,
         argument_forms: &mut [Option<ParameterForm>],
         conflicting_forms: &mut [bool],
-    ) -> Self {
+    ) {
         // If this callable is a bound method, prepend the self instance onto the arguments list
         // before checking.
-        let arguments = arguments.with_self(signature.bound_type);
+        let arguments = arguments.with_self(self.bound_type);
 
         // TODO: This checks every overload. In the proposed more detailed call checking spec [1],
         // arguments are checked for arity first, and are only checked for type assignability against
@@ -990,37 +1091,17 @@ impl<'db> CallableBinding<'db> {
         // two phases.
         //
         // [1] https://typing.python.org/en/latest/spec/overload.html#overload-call-evaluation
-        let overloads = signature
-            .into_iter()
-            .map(|signature| {
-                Binding::match_parameters(
-                    signature,
-                    arguments.as_ref(),
-                    argument_forms,
-                    conflicting_forms,
-                )
-            })
-            .collect();
-
-        CallableBinding {
-            callable_type: signature.callable_type,
-            signature_type: signature.signature_type,
-            dunder_call_is_possibly_unbound: signature.dunder_call_is_possibly_unbound,
-            overloads,
+        for overload in &mut self.overloads {
+            overload.match_parameters(arguments.as_ref(), argument_forms, conflicting_forms);
         }
     }
 
-    fn check_types(
-        &mut self,
-        db: &'db dyn Db,
-        signature: &CallableSignature<'db>,
-        argument_types: &CallArgumentTypes<'_, 'db>,
-    ) {
+    fn check_types(&mut self, db: &'db dyn Db, argument_types: &CallArgumentTypes<'_, 'db>) {
         // If this callable is a bound method, prepend the self instance onto the arguments list
         // before checking.
-        let argument_types = argument_types.with_self(signature.bound_type);
-        for (signature, overload) in signature.iter().zip(&mut self.overloads) {
-            overload.check_types(db, signature, argument_types.as_ref());
+        let argument_types = argument_types.with_self(self.bound_type);
+        for overload in &mut self.overloads {
+            overload.check_types(db, argument_types.as_ref());
         }
     }
 
@@ -1215,9 +1296,28 @@ impl<'db> CallableBinding<'db> {
     }
 }
 
+impl<'a, 'db> IntoIterator for &'a CallableBinding<'db> {
+    type Item = &'a Binding<'db>;
+    type IntoIter = std::slice::Iter<'a, Binding<'db>>;
+
+    fn into_iter(self) -> Self::IntoIter {
+        self.overloads.iter()
+    }
+}
+
 /// Binding information for one of the overloads of a callable.
 #[derive(Debug)]
 pub(crate) struct Binding<'db> {
+    pub(crate) signature: Signature<'db>,
+
+    /// The type that is (hopefully) callable.
+    pub(crate) callable_type: Type<'db>,
+
+    /// The type we'll use for error messages referring to details of the called signature. For
+    /// calls to functions this will be the same as `callable_type`; for other callable instances
+    /// it may be a `__call__` method.
+    pub(crate) signature_type: Type<'db>,
+
     /// Return type of the call.
     return_ty: Type<'db>,
 
@@ -1241,18 +1341,37 @@ pub(crate) struct Binding<'db> {
 }
 
 impl<'db> Binding<'db> {
+    pub(crate) fn single(signature_type: Type<'db>, signature: Signature<'db>) -> Binding<'db> {
+        Binding {
+            signature,
+            callable_type: signature_type,
+            signature_type,
+            return_ty: Type::unknown(),
+            specialization: None,
+            inherited_specialization: None,
+            argument_parameters: Box::from([]),
+            parameter_tys: Box::from([]),
+            errors: vec![],
+        }
+    }
+
+    fn replace_callable_type(&mut self, before: Type<'db>, after: Type<'db>) {
+        if self.callable_type == before {
+            self.callable_type = after;
+        }
+    }
+
     fn match_parameters(
-        signature: &Signature<'db>,
+        &mut self,
         arguments: &CallArguments<'_>,
         argument_forms: &mut [Option<ParameterForm>],
         conflicting_forms: &mut [bool],
-    ) -> Self {
-        let parameters = signature.parameters();
+    ) {
+        let parameters = self.signature.parameters();
         // The parameter that each argument is matched with.
         let mut argument_parameters = vec![None; arguments.len()];
         // Whether each parameter has been matched with an argument.
         let mut parameter_matched = vec![false; parameters.len()];
-        let mut errors = vec![];
         let mut next_positional = 0;
         let mut first_excess_positional = None;
         let mut num_synthetic_args = 0;
@@ -1290,7 +1409,7 @@ impl<'db> Binding<'db> {
                         .keyword_by_name(name)
                         .or_else(|| parameters.keyword_variadic())
                     else {
-                        errors.push(BindingError::UnknownArgument {
+                        self.errors.push(BindingError::UnknownArgument {
                             argument_name: ast::name::Name::new(name),
                             argument_index: get_argument_index(argument_index, num_synthetic_args),
                         });
@@ -1315,7 +1434,7 @@ impl<'db> Binding<'db> {
             }
             if parameter_matched[index] {
                 if !parameter.is_variadic() && !parameter.is_keyword_variadic() {
-                    errors.push(BindingError::ParameterAlreadyAssigned {
+                    self.errors.push(BindingError::ParameterAlreadyAssigned {
                         argument_index: get_argument_index(argument_index, num_synthetic_args),
                         parameter: ParameterContext::new(parameter, index, positional),
                     });
@@ -1325,7 +1444,7 @@ impl<'db> Binding<'db> {
             parameter_matched[index] = true;
         }
         if let Some(first_excess_argument_index) = first_excess_positional {
-            errors.push(BindingError::TooManyPositionalArguments {
+            self.errors.push(BindingError::TooManyPositionalArguments {
                 first_excess_argument_index: get_argument_index(
                     first_excess_argument_index,
                     num_synthetic_args,
@@ -1350,27 +1469,17 @@ impl<'db> Binding<'db> {
         }
 
         if !missing.is_empty() {
-            errors.push(BindingError::MissingArguments {
+            self.errors.push(BindingError::MissingArguments {
                 parameters: ParameterContexts(missing),
             });
         }
 
-        Self {
-            return_ty: signature.return_ty.unwrap_or(Type::unknown()),
-            specialization: None,
-            inherited_specialization: None,
-            argument_parameters: argument_parameters.into_boxed_slice(),
-            parameter_tys: vec![None; parameters.len()].into_boxed_slice(),
-            errors,
-        }
+        self.return_ty = self.signature.return_ty.unwrap_or(Type::unknown());
+        self.argument_parameters = argument_parameters.into_boxed_slice();
+        self.parameter_tys = vec![None; parameters.len()].into_boxed_slice();
     }
 
-    fn check_types(
-        &mut self,
-        db: &'db dyn Db,
-        signature: &Signature<'db>,
-        argument_types: &CallArgumentTypes<'_, 'db>,
-    ) {
+    fn check_types(&mut self, db: &'db dyn Db, argument_types: &CallArgumentTypes<'_, 'db>) {
         let mut num_synthetic_args = 0;
         let get_argument_index = |argument_index: usize, num_synthetic_args: usize| {
             if argument_index >= num_synthetic_args {
@@ -1386,6 +1495,7 @@ impl<'db> Binding<'db> {
 
         // If this overload is generic, first see if we can infer a specialization of the function
         // from the arguments that were passed in.
+        let signature = &self.signature;
         let parameters = signature.parameters();
         if signature.generic_context.is_some() || signature.inherited_generic_context.is_some() {
             let mut builder = SpecializationBuilder::new(db);

crates/ty_python_semantic/src/types/class.rs

@@ -9,10 +9,10 @@ use super::{
 use crate::semantic_index::DeclarationWithConstraint;
 use crate::semantic_index::definition::Definition;
 use crate::types::generics::{GenericContext, Specialization};
-use crate::types::signatures::{Parameter, Parameters};
+use crate::types::signatures::{Parameter, Parameters, Signature};
 use crate::types::{
-    CallableType, DataclassParams, DataclassTransformerParams, KnownInstanceType, Signature,
-    TypeMapping, TypeVarInstance,
+    CallableType, DataclassParams, DataclassTransformerParams, KnownInstanceType, TypeMapping,
+    TypeVarInstance,
 };
 use crate::{
     Db, FxOrderSet, KnownModule, Program,
@@ -1229,13 +1229,15 @@ impl<'db> ClassLiteral<'db> {
                         // the `__set__` method can be called. We build a union of all possible options
                         // to account for possible overloads.
                         let mut value_types = UnionBuilder::new(db);
-                        for signature in &dunder_set.signatures(db) {
-                            for overload in signature {
-                                if let Some(value_param) = overload.parameters().get_positional(2) {
+                        for binding in &dunder_set.bindings(db) {
+                            for overload in binding {
+                                if let Some(value_param) =
+                                    overload.signature.parameters().get_positional(2)
+                                {
                                     value_types = value_types.add(
                                         value_param.annotated_type().unwrap_or_else(Type::unknown),
                                     );
-                                } else if overload.parameters().is_gradual() {
+                                } else if overload.signature.parameters().is_gradual() {
                                     value_types = value_types.add(Type::unknown());
                                 }
                             }
@@ -1267,7 +1269,7 @@ impl<'db> ClassLiteral<'db> {
             }
 
             let signature = Signature::new(Parameters::new(parameters), Some(Type::none(db)));
-            Some(Type::Callable(CallableType::function_like(db, signature)))
+            Some(CallableType::function_like(db, signature))
         };
 
         match (field_policy, name) {
@@ -1317,7 +1319,7 @@ impl<'db> ClassLiteral<'db> {
                     Some(KnownClass::Bool.to_instance(db)),
                 );
 
-                Some(Type::Callable(CallableType::function_like(db, signature)))
+                Some(CallableType::function_like(db, signature))
             }
             (CodeGeneratorKind::NamedTuple, name) if name != "__init__" => {
                 KnownClass::NamedTupleFallback

crates/ty_python_semantic/src/types/display.rs

@@ -8,7 +8,7 @@ use ruff_python_literal::escape::AsciiEscape;
 
 use crate::types::class::{ClassLiteral, ClassType, GenericAlias};
 use crate::types::generics::{GenericContext, Specialization};
-use crate::types::signatures::{Parameter, Parameters, Signature};
+use crate::types::signatures::{CallableSignature, Parameter, Parameters, Signature};
 use crate::types::{
     CallableType, IntersectionType, KnownClass, MethodWrapperKind, Protocol, StringLiteralType,
     SubclassOfInner, Type, TypeVarBoundOrConstraints, TypeVarInstance, UnionType,
@@ -413,13 +413,13 @@ impl<'db> CallableType<'db> {
 }
 
 pub(crate) struct DisplayCallableType<'db> {
-    signatures: &'db [Signature<'db>],
+    signatures: &'db CallableSignature<'db>,
     db: &'db dyn Db,
 }
 
 impl Display for DisplayCallableType<'_> {
     fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
-        match self.signatures {
+        match self.signatures.overloads.as_slice() {
             [signature] => signature.display(self.db).fmt(f),
             signatures => {
                 // TODO: How to display overloads?

crates/ty_python_semantic/src/types/infer.rs

@@ -64,7 +64,9 @@ use crate::symbol::{
     global_symbol, module_type_implicit_global_declaration, module_type_implicit_global_symbol,
     symbol, symbol_from_bindings, symbol_from_declarations, typing_extensions_symbol,
 };
-use crate::types::call::{Argument, Bindings, CallArgumentTypes, CallArguments, CallError};
+use crate::types::call::{
+    Argument, Binding, Bindings, CallArgumentTypes, CallArguments, CallError,
+};
 use crate::types::class::{MetaclassErrorKind, SliceLiteral};
 use crate::types::diagnostic::{
     self, CALL_NON_CALLABLE, CONFLICTING_DECLARATIONS, CONFLICTING_METACLASS,
@@ -81,16 +83,17 @@ use crate::types::diagnostic::{
 };
 use crate::types::generics::GenericContext;
 use crate::types::mro::MroErrorKind;
+use crate::types::signatures::{CallableSignature, Signature};
 use crate::types::unpacker::{UnpackResult, Unpacker};
 use crate::types::{
-    BareTypeAliasType, CallDunderError, CallableSignature, CallableType, ClassLiteral, ClassType,
-    DataclassParams, DynamicType, FunctionDecorators, FunctionType, GenericAlias,
-    IntersectionBuilder, IntersectionType, KnownClass, KnownFunction, KnownInstanceType,
-    MemberLookupPolicy, MetaclassCandidate, PEP695TypeAliasType, Parameter, ParameterForm,
-    Parameters, Signature, Signatures, StringLiteralType, SubclassOfType, Symbol,
-    SymbolAndQualifiers, Truthiness, TupleType, Type, TypeAliasType, TypeAndQualifiers,
-    TypeArrayDisplay, TypeQualifiers, TypeVarBoundOrConstraints, TypeVarInstance, TypeVarKind,
-    TypeVarVariance, UnionBuilder, UnionType, binding_type, todo_type,
+    BareTypeAliasType, CallDunderError, CallableType, ClassLiteral, ClassType, DataclassParams,
+    DynamicType, FunctionDecorators, FunctionType, GenericAlias, IntersectionBuilder,
+    IntersectionType, KnownClass, KnownFunction, KnownInstanceType, MemberLookupPolicy,
+    MetaclassCandidate, PEP695TypeAliasType, Parameter, ParameterForm, Parameters,
+    StringLiteralType, SubclassOfType, Symbol, SymbolAndQualifiers, Truthiness, TupleType, Type,
+    TypeAliasType, TypeAndQualifiers, TypeArrayDisplay, TypeQualifiers, TypeVarBoundOrConstraints,
+    TypeVarInstance, TypeVarKind, TypeVarVariance, UnionBuilder, UnionType, binding_type,
+    todo_type,
 };
 use crate::unpack::{Unpack, UnpackPosition};
 use crate::util::subscript::{PyIndex, PySlice};
@@ -4847,10 +4850,7 @@ impl<'db> TypeInferenceBuilder<'db> {
         // TODO: Useful inference of a lambda's return type will require a different approach,
         // which does the inference of the body expression based on arguments at each call site,
         // rather than eagerly computing a return type without knowing the argument types.
-        Type::Callable(CallableType::single(
-            self.db(),
-            Signature::new(parameters, Some(Type::unknown())),
-        ))
+        CallableType::single(self.db(), Signature::new(parameters, Some(Type::unknown())))
     }
 
     /// Returns the type of the first parameter if the given scope is function-like (i.e. function or lambda).
@@ -4964,8 +4964,9 @@ impl<'db> TypeInferenceBuilder<'db> {
             }
         }
 
-        let signatures = callable_type.signatures(self.db());
-        let bindings = Bindings::match_parameters(signatures, &call_arguments);
+        let bindings = callable_type
+            .bindings(self.db())
+            .match_parameters(&call_arguments);
         let call_argument_types =
             self.infer_argument_types(arguments, call_arguments, &bindings.argument_forms);
 
@@ -7282,11 +7283,9 @@ impl<'db> TypeInferenceBuilder<'db> {
             }
             _ => CallArgumentTypes::positional([self.infer_type_expression(slice_node)]),
         };
-        let signatures = Signatures::single(CallableSignature::single(
-            value_ty,
-            generic_context.signature(self.db()),
-        ));
-        let bindings = match Bindings::match_parameters(signatures, &call_argument_types)
+        let binding = Binding::single(value_ty, generic_context.signature(self.db()));
+        let bindings = match Bindings::from(binding)
+            .match_parameters(&call_argument_types)
             .check_types(self.db(), &call_argument_types)
         {
             Ok(bindings) => bindings,
@@ -8628,8 +8627,6 @@ impl<'db> TypeInferenceBuilder<'db> {
                     CallableType::unknown(db)
                 };
 
-                let callable_type = Type::Callable(callable_type);
-
                 // `Signature` / `Parameters` are not a `Type` variant, so we're storing
                 // the outer callable type on these expressions instead.
                 self.store_expression_type(arguments_slice, callable_type);
@@ -8701,20 +8698,20 @@ impl<'db> TypeInferenceBuilder<'db> {
                 }
                 _ => {
                     let argument_type = self.infer_expression(arguments_slice);
-                    let signatures = argument_type.signatures(db);
+                    let bindings = argument_type.bindings(db);
 
-                    // SAFETY: This is enforced by the constructor methods on `Signatures` even in
+                    // SAFETY: This is enforced by the constructor methods on `Bindings` even in
                     // the case of a non-callable union.
-                    let callable_signature = signatures
-                        .iter()
+                    let callable_binding = bindings
+                        .into_iter()
                         .next()
-                        .expect("`Signatures` should have at least one `CallableSignature`");
+                        .expect("`Bindings` should have at least one `CallableBinding`");
 
-                    let mut signature_iter = callable_signature.iter().map(|signature| {
+                    let mut signature_iter = callable_binding.into_iter().map(|binding| {
                         if argument_type.is_bound_method() {
-                            signature.bind_self()
+                            binding.signature.bind_self()
                         } else {
-                            signature.clone()
+                            binding.signature.clone()
                         }
                     });
 
@@ -8734,11 +8731,10 @@ impl<'db> TypeInferenceBuilder<'db> {
                         return Type::unknown();
                     };
 
-                    Type::Callable(CallableType::from_overloads(
-                        db,
+                    let signature = CallableSignature::from_overloads(
                         std::iter::once(signature).chain(signature_iter),
-                        false,
-                    ))
+                    );
+                    Type::Callable(CallableType::new(db, signature, false))
                 }
             },
 

crates/ty_python_semantic/src/types/property_tests/type_generation.rs

@@ -188,13 +188,13 @@ impl Ty {
 
                 create_bound_method(db, function, builtins_class)
             }
-            Ty::Callable { params, returns } => Type::Callable(CallableType::single(
+            Ty::Callable { params, returns } => CallableType::single(
                 db,
                 Signature::new(
                     params.into_parameters(db),
                     returns.map(|ty| ty.into_type(db)),
                 ),
-            )),
+            ),
         }
     }
 }

crates/ty_python_semantic/src/types/signatures.rs

@@ -22,175 +22,33 @@ use crate::types::{ClassLiteral, TypeMapping, TypeVarInstance, todo_type};
 use crate::{Db, FxOrderSet};
 use ruff_python_ast::{self as ast, name::Name};
 
-/// The signature of a possible union of callables.
-#[derive(Clone, Debug, PartialEq, Eq, Hash, salsa::Update)]
-pub(crate) struct Signatures<'db> {
-    /// The type that is (hopefully) callable.
-    pub(crate) callable_type: Type<'db>,
-    /// The type we'll use for error messages referring to details of the called signature. For calls to functions this
-    /// will be the same as `callable_type`; for other callable instances it may be a `__call__` method.
-    pub(crate) signature_type: Type<'db>,
-    /// By using `SmallVec`, we avoid an extra heap allocation for the common case of a non-union
-    /// type.
-    elements: SmallVec<[CallableSignature<'db>; 1]>,
-}
-
-impl<'db> Signatures<'db> {
-    pub(crate) fn not_callable(signature_type: Type<'db>) -> Self {
-        Self {
-            callable_type: signature_type,
-            signature_type,
-            elements: smallvec![CallableSignature::not_callable(signature_type)],
-        }
-    }
-
-    pub(crate) fn single(signature: CallableSignature<'db>) -> Self {
-        Self {
-            callable_type: signature.callable_type,
-            signature_type: signature.signature_type,
-            elements: smallvec![signature],
-        }
-    }
-
-    /// Creates a new `Signatures` from an iterator of [`Signature`]s. Panics if the iterator is
-    /// empty.
-    pub(crate) fn from_union<I>(signature_type: Type<'db>, elements: I) -> Self
-    where
-        I: IntoIterator<Item = Signatures<'db>>,
-    {
-        let elements: SmallVec<_> = elements
-            .into_iter()
-            .flat_map(|s| s.elements.into_iter())
-            .collect();
-        assert!(!elements.is_empty());
-        Self {
-            callable_type: signature_type,
-            signature_type,
-            elements,
-        }
-    }
-
-    pub(crate) fn iter(&self) -> std::slice::Iter<'_, CallableSignature<'db>> {
-        self.elements.iter()
-    }
-
-    pub(crate) fn replace_callable_type(&mut self, before: Type<'db>, after: Type<'db>) {
-        if self.callable_type == before {
-            self.callable_type = after;
-        }
-        for signature in &mut self.elements {
-            signature.replace_callable_type(before, after);
-        }
-    }
-
-    pub(crate) fn set_dunder_call_is_possibly_unbound(&mut self) {
-        for signature in &mut self.elements {
-            signature.dunder_call_is_possibly_unbound = true;
-        }
-    }
-}
-
-impl<'a, 'db> IntoIterator for &'a Signatures<'db> {
-    type Item = &'a CallableSignature<'db>;
-    type IntoIter = std::slice::Iter<'a, CallableSignature<'db>>;
-
-    fn into_iter(self) -> Self::IntoIter {
-        self.iter()
-    }
-}
-
 /// The signature of a single callable. If the callable is overloaded, there is a separate
 /// [`Signature`] for each overload.
 #[derive(Clone, Debug, PartialEq, Eq, Hash, salsa::Update)]
-pub(crate) struct CallableSignature<'db> {
-    /// The type that is (hopefully) callable.
-    pub(crate) callable_type: Type<'db>,
-
-    /// The type we'll use for error messages referring to details of the called signature. For
-    /// calls to functions this will be the same as `callable_type`; for other callable instances
-    /// it may be a `__call__` method.
-    pub(crate) signature_type: Type<'db>,
-
-    /// If this is a callable object (i.e. called via a `__call__` method), the boundness of
-    /// that call method.
-    pub(crate) dunder_call_is_possibly_unbound: bool,
-
-    /// The type of the bound `self` or `cls` parameter if this signature is for a bound method.
-    pub(crate) bound_type: Option<Type<'db>>,
-
+pub struct CallableSignature<'db> {
     /// The signatures of each overload of this callable. Will be empty if the type is not
     /// callable.
-    ///
-    /// By using `SmallVec`, we avoid an extra heap allocation for the common case of a
-    /// non-overloaded callable.
     pub(crate) overloads: SmallVec<[Signature<'db>; 1]>,
 }
 
 impl<'db> CallableSignature<'db> {
-    pub(crate) fn not_callable(signature_type: Type<'db>) -> Self {
+    pub(crate) fn single(signature: Signature<'db>) -> Self {
         Self {
-            callable_type: signature_type,
-            signature_type,
-            dunder_call_is_possibly_unbound: false,
-            bound_type: None,
-            overloads: smallvec![],
-        }
-    }
-
-    pub(crate) fn single(signature_type: Type<'db>, signature: Signature<'db>) -> Self {
-        Self {
-            callable_type: signature_type,
-            signature_type,
-            dunder_call_is_possibly_unbound: false,
-            bound_type: None,
             overloads: smallvec![signature],
         }
     }
 
     /// Creates a new `CallableSignature` from an iterator of [`Signature`]s. Returns a
     /// non-callable signature if the iterator is empty.
-    pub(crate) fn from_overloads<I>(signature_type: Type<'db>, overloads: I) -> Self
+    pub(crate) fn from_overloads<I>(overloads: I) -> Self
     where
         I: IntoIterator<Item = Signature<'db>>,
     {
         Self {
-            callable_type: signature_type,
-            signature_type,
-            dunder_call_is_possibly_unbound: false,
-            bound_type: None,
             overloads: overloads.into_iter().collect(),
         }
     }
 
-    /// Return a signature for a dynamic callable
-    pub(crate) fn dynamic(signature_type: Type<'db>) -> Self {
-        let signature = Signature {
-            generic_context: None,
-            inherited_generic_context: None,
-            parameters: Parameters::gradual_form(),
-            return_ty: Some(signature_type),
-        };
-        Self::single(signature_type, signature)
-    }
-
-    /// Return a todo signature: (*args: Todo, **kwargs: Todo) -> Todo
-    #[allow(unused_variables)] // 'reason' only unused in debug builds
-    pub(crate) fn todo(reason: &'static str) -> Self {
-        let signature_type = todo_type!(reason);
-        let signature = Signature {
-            generic_context: None,
-            inherited_generic_context: None,
-            parameters: Parameters::todo(),
-            return_ty: Some(signature_type),
-        };
-        Self::single(signature_type, signature)
-    }
-
-    pub(crate) fn with_bound_type(mut self, bound_type: Type<'db>) -> Self {
-        self.bound_type = Some(bound_type);
-        self
-    }
-
     pub(crate) fn iter(&self) -> std::slice::Iter<'_, Signature<'db>> {
         self.overloads.iter()
     }
@@ -199,9 +57,169 @@ impl<'db> CallableSignature<'db> {
         self.overloads.as_slice()
     }
 
-    fn replace_callable_type(&mut self, before: Type<'db>, after: Type<'db>) {
-        if self.callable_type == before {
-            self.callable_type = after;
+    pub(crate) fn normalized(&self, db: &'db dyn Db) -> Self {
+        Self::from_overloads(
+            self.overloads
+                .iter()
+                .map(|signature| signature.normalized(db)),
+        )
+    }
+
+    pub(crate) fn apply_type_mapping<'a>(
+        &self,
+        db: &'db dyn Db,
+        type_mapping: &TypeMapping<'a, 'db>,
+    ) -> Self {
+        Self::from_overloads(
+            self.overloads
+                .iter()
+                .map(|signature| signature.apply_type_mapping(db, type_mapping)),
+        )
+    }
+
+    pub(crate) fn find_legacy_typevars(
+        &self,
+        db: &'db dyn Db,
+        typevars: &mut FxOrderSet<TypeVarInstance<'db>>,
+    ) {
+        for signature in &self.overloads {
+            signature.find_legacy_typevars(db, typevars);
+        }
+    }
+
+    pub(crate) fn bind_self(&self) -> Self {
+        Self {
+            overloads: self.overloads.iter().map(Signature::bind_self).collect(),
+        }
+    }
+
+    /// Check whether this callable type is fully static.
+    ///
+    /// See [`Type::is_fully_static`] for more details.
+    pub(crate) fn is_fully_static(&self, db: &'db dyn Db) -> bool {
+        self.overloads
+            .iter()
+            .all(|signature| signature.is_fully_static(db))
+    }
+
+    /// Check whether this callable type is a subtype of another callable type.
+    ///
+    /// See [`Type::is_subtype_of`] for more details.
+    pub(crate) fn is_subtype_of(&self, db: &'db dyn Db, other: &Self) -> bool {
+        Self::is_assignable_to_impl(
+            &self.overloads,
+            &other.overloads,
+            &|self_signature, other_signature| self_signature.is_subtype_of(db, other_signature),
+        )
+    }
+
+    /// Check whether this callable type is assignable to another callable type.
+    ///
+    /// See [`Type::is_assignable_to`] for more details.
+    pub(crate) fn is_assignable_to(&self, db: &'db dyn Db, other: &Self) -> bool {
+        Self::is_assignable_to_impl(
+            &self.overloads,
+            &other.overloads,
+            &|self_signature, other_signature| self_signature.is_assignable_to(db, other_signature),
+        )
+    }
+
+    /// Implementation for the various relation checks between two, possible overloaded, callable
+    /// types.
+    ///
+    /// The `check_signature` closure is used to check the relation between two [`Signature`]s.
+    fn is_assignable_to_impl<F>(
+        self_signatures: &[Signature<'db>],
+        other_signatures: &[Signature<'db>],
+        check_signature: &F,
+    ) -> bool
+    where
+        F: Fn(&Signature<'db>, &Signature<'db>) -> bool,
+    {
+        match (self_signatures, other_signatures) {
+            ([self_signature], [other_signature]) => {
+                // Base case: both callable types contain a single signature.
+                check_signature(self_signature, other_signature)
+            }
+
+            // `self` is possibly overloaded while `other` is definitely not overloaded.
+            (_, [_]) => self_signatures.iter().any(|self_signature| {
+                Self::is_assignable_to_impl(
+                    std::slice::from_ref(self_signature),
+                    other_signatures,
+                    check_signature,
+                )
+            }),
+
+            // `self` is definitely not overloaded while `other` is possibly overloaded.
+            ([_], _) => other_signatures.iter().all(|other_signature| {
+                Self::is_assignable_to_impl(
+                    self_signatures,
+                    std::slice::from_ref(other_signature),
+                    check_signature,
+                )
+            }),
+
+            // `self` is definitely overloaded while `other` is possibly overloaded.
+            (_, _) => other_signatures.iter().all(|other_signature| {
+                Self::is_assignable_to_impl(
+                    self_signatures,
+                    std::slice::from_ref(other_signature),
+                    check_signature,
+                )
+            }),
+        }
+    }
+
+    /// Check whether this callable type is equivalent to another callable type.
+    ///
+    /// See [`Type::is_equivalent_to`] for more details.
+    pub(crate) fn is_equivalent_to(&self, db: &'db dyn Db, other: &Self) -> bool {
+        match (self.overloads.as_slice(), other.overloads.as_slice()) {
+            ([self_signature], [other_signature]) => {
+                // Common case: both callable types contain a single signature, use the custom
+                // equivalence check instead of delegating it to the subtype check.
+                self_signature.is_equivalent_to(db, other_signature)
+            }
+            (self_signatures, other_signatures) => {
+                if !self_signatures
+                    .iter()
+                    .chain(other_signatures.iter())
+                    .all(|signature| signature.is_fully_static(db))
+                {
+                    return false;
+                }
+                if self == other {
+                    return true;
+                }
+                self.is_subtype_of(db, other) && other.is_subtype_of(db, self)
+            }
+        }
+    }
+
+    /// Check whether this callable type is gradual equivalent to another callable type.
+    ///
+    /// See [`Type::is_gradual_equivalent_to`] for more details.
+    pub(crate) fn is_gradual_equivalent_to(&self, db: &'db dyn Db, other: &Self) -> bool {
+        match (self.overloads.as_slice(), other.overloads.as_slice()) {
+            ([self_signature], [other_signature]) => {
+                self_signature.is_gradual_equivalent_to(db, other_signature)
+            }
+            _ => {
+                // TODO: overloads
+                false
+            }
+        }
+    }
+
+    pub(crate) fn replace_self_reference(&self, db: &'db dyn Db, class: ClassLiteral<'db>) -> Self {
+        Self {
+            overloads: self
+                .overloads
+                .iter()
+                .cloned()
+                .map(|signature| signature.replace_self_reference(db, class))
+                .collect(),
         }
     }
 }
@@ -263,6 +281,28 @@ impl<'db> Signature<'db> {
         }
     }
 
+    /// Return a signature for a dynamic callable
+    pub(crate) fn dynamic(signature_type: Type<'db>) -> Self {
+        Signature {
+            generic_context: None,
+            inherited_generic_context: None,
+            parameters: Parameters::gradual_form(),
+            return_ty: Some(signature_type),
+        }
+    }
+
+    /// Return a todo signature: (*args: Todo, **kwargs: Todo) -> Todo
+    #[allow(unused_variables)] // 'reason' only unused in debug builds
+    pub(crate) fn todo(reason: &'static str) -> Self {
+        let signature_type = todo_type!(reason);
+        Signature {
+            generic_context: None,
+            inherited_generic_context: None,
+            parameters: Parameters::todo(),
+            return_ty: Some(signature_type),
+        }
+    }
+
     /// Return a typed signature from a function definition.
     pub(super) fn from_function(
         db: &'db dyn Db,
@@ -295,6 +335,11 @@ impl<'db> Signature<'db> {
         }
     }
 
+    /// Returns the signature which accepts any parameters and returns an `Unknown` type.
+    pub(crate) fn unknown() -> Self {
+        Self::new(Parameters::unknown(), Some(Type::unknown()))
+    }
+
     /// Return the "bottom" signature, subtype of all other fully-static signatures.
     pub(crate) fn bottom(db: &'db dyn Db) -> Self {
         Self::new(Parameters::object(db), Some(Type::Never))
@@ -1750,7 +1795,7 @@ mod tests {
         assert_eq!(
             func.signature(&db),
             &FunctionSignature {
-                overloads: CallableSignature::single(Type::FunctionLiteral(func), expected_sig),
+                overloads: CallableSignature::single(expected_sig),
                 implementation: None
             },
         );