[red-knot] Fix callable subtyping for standard parameters

crates/red_knot_python_semantic/resources/mdtest/type_properties/is_subtype_of.md

@@ -858,6 +858,52 @@ static_assert(not is_subtype_of(CallableTypeOf[variadic], CallableTypeOf[keyword
 static_assert(not is_subtype_of(CallableTypeOf[variadic], CallableTypeOf[keyword_variadic]))
 ```
 
+But, there are special cases when matching against standard parameters. This is due to the fact that
+a standard parameter can be passed as a positional or keyword parameter. This means that the
+subtyping relation needs to consider both cases.
+
+```py
+def variadic_keyword(*args: int, **kwargs: int) -> None: ...
+def standard_int(a: int) -> None: ...
+def standard_float(a: float) -> None: ...
+
+static_assert(is_subtype_of(CallableTypeOf[variadic_keyword], CallableTypeOf[standard_int]))
+static_assert(not is_subtype_of(CallableTypeOf[variadic_keyword], CallableTypeOf[standard_float]))
+```
+
+If the type of either the variadic or keyword-variadic parameter is not a supertype of the standard
+parameter, then the subtyping relation is invalid.
+
+```py
+def variadic_bool(*args: bool, **kwargs: int) -> None: ...
+def keyword_variadic_bool(*args: int, **kwargs: bool) -> None: ...
+
+static_assert(not is_subtype_of(CallableTypeOf[variadic_bool], CallableTypeOf[standard_int]))
+static_assert(not is_subtype_of(CallableTypeOf[keyword_variadic_bool], CallableTypeOf[standard_int]))
+```
+
+The standard parameter can follow a variadic parameter in the subtype.
+
+```py
+def standard_variadic_int(a: int, *args: int) -> None: ...
+def standard_variadic_float(a: int, *args: float) -> None: ...
+
+static_assert(is_subtype_of(CallableTypeOf[variadic_keyword], CallableTypeOf[standard_variadic_int]))
+static_assert(not is_subtype_of(CallableTypeOf[variadic_keyword], CallableTypeOf[standard_variadic_float]))
+```
+
+The keyword part of the standard parameter can be matched against keyword-only parameter with the
+same name if the keyword-variadic parameter is absent.
+
+```py
+def variadic_a(*args: int, a: int) -> None: ...
+def variadic_b(*args: int, b: int) -> None: ...
+
+static_assert(is_subtype_of(CallableTypeOf[variadic_a], CallableTypeOf[standard_int]))
+# The parameter name is different
+static_assert(not is_subtype_of(CallableTypeOf[variadic_b], CallableTypeOf[standard_int]))
+```
+
 #### Keyword-only
 
 For keyword-only parameters, the name should be the same:

crates/red_knot_python_semantic/src/types.rs

@@ -4569,6 +4569,10 @@ impl<'db> GeneralCallableType<'db> {
             iter_other: other_signature.parameters().iter(),
         };
 
+        // Collect all the standard parameters that have only been matched against a variadic
+        // parameter which means that the keyword variant is still unmatched.
+        let mut other_keywords = Vec::new();
+
         loop {
             let Some(next_parameter) = parameters.next() else {
                 // All parameters have been checked or both the parameter lists were empty. In
@@ -4578,6 +4582,14 @@ impl<'db> GeneralCallableType<'db> {
 
             match next_parameter {
                 EitherOrBoth::Left(self_parameter) => match self_parameter.kind() {
+                    ParameterKind::KeywordOnly { .. } | ParameterKind::KeywordVariadic { .. }
+                        if !other_keywords.is_empty() =>
+                    {
+                        // If there are any unmatched keyword parameters in `other`, they need to
+                        // be checked against the keyword-only / keyword-variadic parameters that
+                        // will be done after this loop.
+                        break;
+                    }
                     ParameterKind::PositionalOnly { default_type, .. }
                     | ParameterKind::PositionalOrKeyword { default_type, .. }
                     | ParameterKind::KeywordOnly { default_type, .. } => {
@@ -4652,14 +4664,25 @@ impl<'db> GeneralCallableType<'db> {
                             }
                         }
 
-                        (ParameterKind::Variadic { .. }, ParameterKind::PositionalOnly { .. }) => {
+                        (
+                            ParameterKind::Variadic { .. },
+                            ParameterKind::PositionalOnly { .. }
+                            | ParameterKind::PositionalOrKeyword { .. },
+                        ) => {
                             if !check_types(
                                 other_parameter.annotated_type(),
                                 self_parameter.annotated_type(),
                             ) {
                                 return false;
                             }
 
+                            if matches!(
+                                other_parameter.kind(),
+                                ParameterKind::PositionalOrKeyword { .. }
+                            ) {
+                                other_keywords.push(other_parameter);
+                            }
+
                             // We've reached a variadic parameter in `self` which means there can
                             // be no more positional parameters after this in a valid AST. But, the
                             // current parameter in `other` is a positional-only which means there
@@ -4674,14 +4697,17 @@ impl<'db> GeneralCallableType<'db> {
                                 let Some(other_parameter) = parameters.peek_other() else {
                                     break;
                                 };
-                                if !matches!(
-                                    other_parameter.kind(),
+                                match other_parameter.kind() {
+                                    ParameterKind::PositionalOrKeyword { .. } => {
+                                        other_keywords.push(other_parameter);
+                                    }
                                     ParameterKind::PositionalOnly { .. }
-                                        | ParameterKind::Variadic { .. }
-                                ) {
-                                    // Any other parameter kind cannot be checked against a
-                                    // variadic parameter and is deferred to the next iteration.
-                                    break;
+                                    | ParameterKind::Variadic { .. } => {}
+                                    _ => {
+                                        // Any other parameter kind cannot be checked against a
+                                        // variadic parameter and is deferred to the next iteration.
+                                        break;
+                                    }
                                 }
                                 if !check_types(
                                     other_parameter.annotated_type(),
@@ -4753,11 +4779,15 @@ impl<'db> GeneralCallableType<'db> {
             }
         }
 
-        for other_parameter in other_parameters {
+        for other_parameter in other_keywords.into_iter().chain(other_parameters) {
             match other_parameter.kind() {
                 ParameterKind::KeywordOnly {
                     name: other_name,
                     default_type: other_default,
+                }
+                | ParameterKind::PositionalOrKeyword {
+                    name: other_name,
+                    default_type: other_default,
                 } => {
                     if let Some(self_parameter) = self_keywords.remove(other_name) {
                         match self_parameter.kind() {