[ty] support kw_only=True for dataclasses

astral-sh/ty#111

Author: thejchap

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

@@ -465,7 +465,45 @@ To do
 
 ### `kw_only`
 
-To do
+An error is emitted if a dataclass is defined with `kw_only=True` and positional arguments are
+passed to the constructor.
+
+```toml
+[environment]
+python-version = "3.10"
+```
+
+```py
+from dataclasses import dataclass
+
+@dataclass(kw_only=True)
+class A:
+    x: int
+    y: int
+
+# error: [missing-argument] "No arguments provided for required parameters `x`, `y`"
+# error: [too-many-positional-arguments] "Too many positional arguments: expected 0, got 2"
+a = A(1, 2)
+a = A(x=1, y=2)
+```
+
+### `kw_only` - Python < 3.10
+
+For Python < 3.10, `kw_only` is not supported.
+
+```toml
+[environment]
+python-version = "3.9"
+```
+
+```py
+from dataclasses import dataclass
+
+@dataclass(kw_only=True)  # TODO: Emit a diagnostic here
+class A:
+    x: int
+    y: int
+```
 
 ### `slots`
 

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

@@ -12,6 +12,7 @@ use ruff_db::parsed::parsed_module;
 use smallvec::{SmallVec, smallvec, smallvec_inline};
 
 use super::{Argument, CallArguments, CallError, CallErrorKind, InferContext, Signature, Type};
+use crate::Program;
 use crate::db::Db;
 use crate::dunder_all::dunder_all_names;
 use crate::place::{Boundness, Place};
@@ -33,7 +34,7 @@ use crate::types::{
     WrapperDescriptorKind, enums, ide_support, todo_type,
 };
 use ruff_db::diagnostic::{Annotation, Diagnostic, SubDiagnostic, SubDiagnosticSeverity};
-use ruff_python_ast as ast;
+use ruff_python_ast::{self as ast, PythonVersion};
 
 /// Binding information for a possible union of callables. At a call site, the arguments must be
 /// compatible with _all_ of the types in the union for the call to be valid.
@@ -860,7 +861,11 @@ impl<'db> Bindings<'db> {
                                     params |= DataclassParams::MATCH_ARGS;
                                 }
                                 if to_bool(kw_only, false) {
-                                    params |= DataclassParams::KW_ONLY;
+                                    if Program::get(db).python_version(db) >= PythonVersion::PY310 {
+                                        params |= DataclassParams::KW_ONLY;
+                                    } else {
+                                        // TODO: emit diagnostic
+                                    }
                                 }
                                 if to_bool(slots, false) {
                                     params |= DataclassParams::SLOTS;

crates/ty_python_semantic/src/types/class.rs

@@ -1843,7 +1843,10 @@ impl<'db> ClassLiteral<'db> {
                     }
                 }
 
-                let mut parameter = if kw_only_field_seen || name == "__replace__" {
+                let mut parameter = if kw_only_field_seen
+                    || name == "__replace__"
+                    || has_dataclass_param(DataclassParams::KW_ONLY)
+                {
                     Parameter::keyword_only(field_name)
                 } else {
                     Parameter::positional_or_keyword(field_name)