[ty] Fix overload filtering to prefer more "precise" match

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

@@ -925,7 +925,7 @@ def _(t: tuple[int, str] | tuple[int, str, int]) -> None:
     f(*t)  # error: [no-matching-overload]
 ```
 
-## Filtering based on variaidic arguments
+## Filtering based on variadic arguments
 
 This is step 4 of the overload call evaluation algorithm which specifies that:
 
@@ -1469,6 +1469,79 @@ def _(arg: list[Any]):
     reveal_type(f4(*arg))  # revealed: Unknown
 ```
 
+### Varidic argument with generics
+
+`overloaded.pyi`:
+
+```pyi
+from typing import Any, TypeVar, overload
+
+T1 = TypeVar("T1")
+T2 = TypeVar("T2")
+T3 = TypeVar("T3")
+
+@overload
+def f1(x: T1, /) -> tuple[T1]: ...
+@overload
+def f1(x1: T1, x2: T2, /) -> tuple[T1, T2]: ...
+@overload
+def f1(x1: T1, x2: T2, x3: T3, /) -> tuple[T1, T2, T3]: ...
+@overload
+def f1(*args: Any) -> tuple[Any, ...]: ...
+
+@overload
+def f2(x1: T1) -> tuple[T1]: ...
+@overload
+def f2(x1: T1, x2: T2) -> tuple[T1, T2]: ...
+@overload
+def f2(*args: Any, **kwargs: Any) -> tuple[Any, ...]: ...
+
+@overload
+def f3(x: T1) -> tuple[T1]: ...
+@overload
+def f3(x1: T1, x2: T2) -> tuple[T1, T2]: ...
+@overload
+def f3(*args: Any) -> tuple[Any, ...]: ...
+@overload
+def f3(**kwargs: Any) -> dict[str, Any]: ...
+```
+
+```py
+from overloaded import f1, f2, f3
+from typing import Any
+
+# These calls only match the last overload
+reveal_type(f1())  # revealed: tuple[Any, ...]
+reveal_type(f1(1, 2, 3, 4))  # revealed: tuple[Any, ...]
+
+# While these calls match multiple overloads but step 5 filters out all the remaining overloads
+# except the most specific one in terms of the number of arguments.
+reveal_type(f1(1))  # revealed: tuple[Literal[1]]
+reveal_type(f1(1, 2))  # revealed: tuple[Literal[1], Literal[2]]
+reveal_type(f1(1, 2, 3))  # revealed: tuple[Literal[1], Literal[2], Literal[3]]
+
+def _(args1: list[int], args2: list[Any]):
+    reveal_type(f1(*args1))  # revealed: tuple[Any, ...]
+    reveal_type(f1(*args2))  # revealed: tuple[Any, ...]
+
+reveal_type(f2())  # revealed: tuple[Any, ...]
+reveal_type(f2(1, 2))  # revealed: tuple[Literal[1], Literal[2]]
+# TODO: Should be `tuple[Literal[1], Literal[2]]`
+reveal_type(f2(x1=1, x2=2))  # revealed: Unknown
+# TODO: Should be `tuple[Literal[2], Literal[1]]`
+reveal_type(f2(x2=1, x1=2))  # revealed: Unknown
+reveal_type(f2(1, 2, z=3))  # revealed: tuple[Any, ...]
+
+reveal_type(f3(1, 2))  # revealed: tuple[Literal[1], Literal[2]]
+reveal_type(f3(1, 2, 3))  # revealed: tuple[Any, ...]
+# TODO: Should be `tuple[Literal[1], Literal[2]]`
+reveal_type(f3(x1=1, x2=2))  # revealed: Unknown
+reveal_type(f3(z=1))  # revealed: dict[str, Any]
+
+# error: [no-matching-overload]
+reveal_type(f3(1, 2, x=3))  # revealed: Unknown
+```
+
 ### Non-participating fully-static parameter
 
 Ref: <https://github.com/astral-sh/ty/issues/552#issuecomment-2969052173>

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

@@ -228,7 +228,7 @@ impl<'a, 'db> CallArguments<'a, 'db> {
                 if expansion_size > MAX_EXPANSIONS {
                     tracing::debug!(
                         "Skipping argument type expansion as it would exceed the \
-                    maximum number of expansions ({MAX_EXPANSIONS})"
+                            maximum number of expansions ({MAX_EXPANSIONS})"
                     );
                     return Some(State::LimitReached(index));
                 }

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

@@ -2,6 +2,13 @@
 //! arguments against the parameters of the callable. Like with
 //! [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.
+//!
+//! ### Tracing
+//!
+//! This module is instrumented with debug-level `tracing` messages. You can set the `TY_LOG`
+//! environment variable to see this output when testing locally. `tracing` log messages typically
+//! have a `target` field, which is the name of the module the message appears in — in this case,
+//! `ty_python_semantic::types::call::bind`.
 
 use std::borrow::Cow;
 use std::collections::HashSet;
@@ -1582,6 +1589,13 @@ impl<'db> CallableBinding<'db> {
         // before checking.
         let argument_types = argument_types.with_self(self.bound_type);
 
+        tracing::debug!(
+            target: "ty_python_semantic::types::call::bind",
+            matching_overload_index = ?self.matching_overload_index(),
+            signature = %self.signature_type.display(db),
+            "after step 1",
+        );
+
         // Step 1: Check the result of the arity check which is done by `match_parameters`
         let matching_overload_indexes = match self.matching_overload_index() {
             MatchingOverloadIndex::None => {
@@ -1612,6 +1626,13 @@ impl<'db> CallableBinding<'db> {
             overload.check_types(db, argument_types.as_ref(), call_expression_tcx);
         }
 
+        tracing::debug!(
+            target: "ty_python_semantic::types::call::bind",
+            matching_overload_index = ?self.matching_overload_index(),
+            signature = %self.signature_type.display(db),
+            "after step 2",
+        );
+
         match self.matching_overload_index() {
             MatchingOverloadIndex::None => {
                 // If all overloads result in errors, proceed to step 3.
@@ -1624,6 +1645,13 @@ impl<'db> CallableBinding<'db> {
                 // If two or more candidate overloads remain, proceed to step 4.
                 self.filter_overloads_containing_variadic(&indexes);
 
+                tracing::debug!(
+                    target: "ty_python_semantic::types::call::bind",
+                    matching_overload_index = ?self.matching_overload_index(),
+                    signature = %self.signature_type.display(db),
+                    "after step 4",
+                );
+
                 match self.matching_overload_index() {
                     MatchingOverloadIndex::None => {
                         // This shouldn't be possible because step 4 can only filter out overloads
@@ -1642,6 +1670,13 @@ impl<'db> CallableBinding<'db> {
                             argument_types.as_ref(),
                             &indexes,
                         );
+
+                        tracing::debug!(
+                            target: "ty_python_semantic::types::call::bind",
+                            matching_overload_index = ?self.matching_overload_index(),
+                            signature = %self.signature_type.display(db),
+                            "after step 5",
+                        );
                     }
                 }
 
@@ -1744,12 +1779,26 @@ impl<'db> CallableBinding<'db> {
                     overload.match_parameters(db, expanded_arguments, &mut argument_forms);
                 }
 
+                tracing::debug!(
+                    target: "ty_python_semantic::types::call::bind",
+                    matching_overload_index = ?self.matching_overload_index(),
+                    signature = %self.signature_type.display(db),
+                    "after step 1",
+                );
+
                 merged_argument_forms.merge(&argument_forms);
 
                 for (_, overload) in self.matching_overloads_mut() {
                     overload.check_types(db, expanded_arguments, call_expression_tcx);
                 }
 
+                tracing::debug!(
+                    target: "ty_python_semantic::types::call::bind",
+                    matching_overload_index = ?self.matching_overload_index(),
+                    signature = %self.signature_type.display(db),
+                    "after step 2",
+                );
+
                 let return_type = match self.matching_overload_index() {
                     MatchingOverloadIndex::None => None,
                     MatchingOverloadIndex::Single(index) => {
@@ -1758,6 +1807,13 @@ impl<'db> CallableBinding<'db> {
                     MatchingOverloadIndex::Multiple(matching_overload_indexes) => {
                         self.filter_overloads_containing_variadic(&matching_overload_indexes);
 
+                        tracing::debug!(
+                            target: "ty_python_semantic::types::call::bind",
+                            matching_overload_index = ?self.matching_overload_index(),
+                            signature = %self.signature_type.display(db),
+                            "after step 4",
+                        );
+
                         match self.matching_overload_index() {
                             MatchingOverloadIndex::None => {
                                 tracing::debug!(
@@ -1772,6 +1828,14 @@ impl<'db> CallableBinding<'db> {
                                     expanded_arguments,
                                     &indexes,
                                 );
+
+                                tracing::debug!(
+                                    target: "ty_python_semantic::types::call::bind",
+                                    matching_overload_index = ?self.matching_overload_index(),
+                                    signature = %self.signature_type.display(db),
+                                    "after step 5",
+                                );
+
                                 Some(self.return_type())
                             }
                         }
@@ -1926,12 +1990,37 @@ impl<'db> CallableBinding<'db> {
             .take(max_parameter_count)
             .collect::<Vec<_>>();
 
+        // The following loop is trying to construct a tuple of argument types that correspond to
+        // the participating parameter indexes. Considering the following example:
+        //
+        // ```python
+        // @overload
+        // def f(x: Literal[1], y: Literal[2]) -> tuple[int, int]: ...
+        // @overload
+        // def f(*args: Any) -> tuple[Any, ...]: ...
+        //
+        // f(1, 2)
+        // ```
+        //
+        // Here, only the first parameter participates in the filtering process because only one
+        // overload has the second parameter. So, while going through the argument types, the
+        // second argument needs to be skipped but for the second overload both arguments map to
+        // the first parameter and that parameter is considered for the filtering process. This
+        // flag is to handle that special case of many-to-one mapping from arguments to parameters.
+        let mut variadic_parameter_handled = false;
+
         for (argument_index, argument_type) in arguments.iter_types().enumerate() {
+            if variadic_parameter_handled {
+                continue;
+            }
             for overload_index in matching_overload_indexes {
                 let overload = &self.overloads[*overload_index];
                 for (parameter_index, variadic_argument_type) in
                     overload.argument_matches[argument_index].iter()
                 {
+                    if overload.signature.parameters()[parameter_index].is_variadic() {
+                        variadic_parameter_handled = true;
+                    }
                     if !participating_parameter_indexes.contains(&parameter_index) {
                         continue;
                     }