[ty] Add autocomplete suggestions for function arguments

This adds autocomplete suggestions for function arguments. For example,
`okay` in:

```python
def foo(okay=None):

foo(o<CURSOR>
```

This also ensures that we don't suggest a keyword argument if it has
already been used.

Closes astral-sh/issues#1550

crates/ty_python_semantic/src/types.rs

@@ -30,6 +30,7 @@ pub(crate) use self::infer::{
     TypeContext, infer_deferred_types, infer_definition_types, infer_expression_type,
     infer_expression_types, infer_scope_types, static_expression_truthiness,
 };
+pub use self::signatures::ParameterKind;
 pub(crate) use self::signatures::{CallableSignature, Signature};
 pub(crate) use self::subclass_of::{SubclassOfInner, SubclassOfType};
 pub use crate::diagnostic::add_inferred_python_version_hint_to_diagnostic;

crates/ty_python_semantic/src/types/ide_support.rs

@@ -6,7 +6,7 @@ use crate::semantic_index::definition::Definition;
 use crate::semantic_index::definition::DefinitionKind;
 use crate::semantic_index::{attribute_scopes, global_scope, semantic_index, use_def_map};
 use crate::types::call::{CallArguments, MatchedArgument};
-use crate::types::signatures::Signature;
+use crate::types::signatures::{ParameterKind, Signature};
 use crate::types::{CallDunderError, UnionType};
 use crate::types::{CallableTypes, ClassBase, KnownClass, Type, TypeContext};
 use crate::{Db, DisplaySettings, HasType, SemanticModel};
@@ -459,6 +459,9 @@ pub struct CallSignatureDetails<'db> {
     /// This provides easy access to parameter names for documentation lookup.
     pub parameter_names: Vec<String>,
 
+    /// Parameter kinds, useful to determine correct autocomplete suggestions.
+    pub parameter_kinds: Vec<ParameterKind<'db>>,
+
     /// The definition where this callable was originally defined (useful for
     /// extracting docstrings).
     pub definition: Option<Definition<'db>>,
@@ -517,6 +520,11 @@ pub fn call_signature_details<'db>(
                 let display_details = signature.display(model.db()).to_string_parts();
                 let parameter_label_offsets = display_details.parameter_ranges;
                 let parameter_names = display_details.parameter_names;
+                let parameter_kinds = signature
+                    .parameters()
+                    .iter()
+                    .map(|param| param.kind().clone())
+                    .collect();
 
                 CallSignatureDetails {
                     definition: signature.definition(),
@@ -524,6 +532,7 @@ pub fn call_signature_details<'db>(
                     label: display_details.label,
                     parameter_label_offsets,
                     parameter_names,
+                    parameter_kinds,
                     argument_to_parameter_mapping,
                 }
             })

crates/ty_python_semantic/src/types/signatures.rs

@@ -2292,7 +2292,7 @@ impl<'db> Parameter<'db> {
 }
 
 #[derive(Clone, Debug, PartialEq, Eq, Hash, salsa::Update, get_size2::GetSize)]
-pub(crate) enum ParameterKind<'db> {
+pub enum ParameterKind<'db> {
     /// Positional-only parameter, e.g. `def f(x, /): ...`
     PositionalOnly {
         /// Parameter name.