[ty] Avoid diagnostic when `typing_extensions.ParamSpec` uses `default` parameter (#21839)

## Summary

fixes: https://github.com/astral-sh/ty/issues/1798

## Test Plan

Add mdtest.

crates/ty_python_semantic/resources/mdtest/generics/legacy/paramspec.md

@@ -102,6 +102,38 @@ Other values are invalid.
 P4 = ParamSpec("P4", default=int)
 ```
 
+### `default` parameter in `typing_extensions.ParamSpec`
+
+```toml
+[environment]
+python-version = "3.12"
+```
+
+The `default` parameter to `ParamSpec` is available from `typing_extensions` in Python 3.12 and
+earlier.
+
+```py
+from typing import ParamSpec
+from typing_extensions import ParamSpec as ExtParamSpec
+
+# This shouldn't emit a diagnostic
+P1 = ExtParamSpec("P1", default=[int, str])
+
+# But, this should
+# error: [invalid-paramspec] "The `default` parameter of `typing.ParamSpec` was added in Python 3.13"
+P2 = ParamSpec("P2", default=[int, str])
+```
+
+And, it allows the same set of values as `typing.ParamSpec`.
+
+```py
+P3 = ExtParamSpec("P3", default=...)
+P4 = ExtParamSpec("P4", default=P3)
+
+# error: [invalid-paramspec]
+P5 = ExtParamSpec("P5", default=int)
+```
+
 ### Forward references in stub files
 
 Stubs natively support forward references, so patterns that would raise `NameError` at runtime are

crates/ty_python_semantic/resources/mdtest/regression/paramspec_on_python39.md

@@ -0,0 +1,19 @@
+# `ParamSpec` regression on 3.9
+
+```toml
+[environment]
+python-version = "3.9"
+```
+
+This used to panic when run on Python 3.9 because `ParamSpec` was introduced in Python 3.10 and the
+diagnostic message for `invalid-exception-caught` expects to construct `typing.ParamSpec`.
+
+```py
+# error: [invalid-syntax]
+def foo[**P]() -> None:
+    try:
+        pass
+    # error: [invalid-exception-caught] "Invalid object caught in an exception handler: Object has type `typing.ParamSpec`"
+    except P:
+        pass
+```

crates/ty_python_semantic/src/types/class.rs

@@ -4168,6 +4168,8 @@ pub enum KnownClass {
     SpecialForm,
     TypeVar,
     ParamSpec,
+    // typing_extensions.ParamSpec
+    ExtensionsParamSpec, // must be distinct from typing.ParamSpec, backports new features
     ParamSpecArgs,
     ParamSpecKwargs,
     ProtocolMeta,
@@ -4239,6 +4241,7 @@ impl KnownClass {
             | Self::TypeVar
             | Self::ExtensionsTypeVar
             | Self::ParamSpec
+            | Self::ExtensionsParamSpec
             | Self::ParamSpecArgs
             | Self::ParamSpecKwargs
             | Self::TypeVarTuple
@@ -4371,6 +4374,7 @@ impl KnownClass {
             | KnownClass::TypeVar
             | KnownClass::ExtensionsTypeVar
             | KnownClass::ParamSpec
+            | KnownClass::ExtensionsParamSpec
             | KnownClass::ParamSpecArgs
             | KnownClass::ParamSpecKwargs
             | KnownClass::TypeVarTuple
@@ -4457,6 +4461,7 @@ impl KnownClass {
             | KnownClass::TypeVar
             | KnownClass::ExtensionsTypeVar
             | KnownClass::ParamSpec
+            | KnownClass::ExtensionsParamSpec
             | KnownClass::ParamSpecArgs
             | KnownClass::ParamSpecKwargs
             | KnownClass::TypeVarTuple
@@ -4543,6 +4548,7 @@ impl KnownClass {
             | KnownClass::TypeVar
             | KnownClass::ExtensionsTypeVar
             | KnownClass::ParamSpec
+            | KnownClass::ExtensionsParamSpec
             | KnownClass::ParamSpecArgs
             | KnownClass::ParamSpecKwargs
             | KnownClass::TypeVarTuple
@@ -4634,6 +4640,7 @@ impl KnownClass {
             | Self::TypeVar
             | Self::ExtensionsTypeVar
             | Self::ParamSpec
+            | Self::ExtensionsParamSpec
             | Self::ParamSpecArgs
             | Self::ParamSpecKwargs
             | Self::TypeVarTuple
@@ -4733,6 +4740,7 @@ impl KnownClass {
             | KnownClass::TypeVar
             | KnownClass::ExtensionsTypeVar
             | KnownClass::ParamSpec
+            | KnownClass::ExtensionsParamSpec
             | KnownClass::ParamSpecArgs
             | KnownClass::ParamSpecKwargs
             | KnownClass::ProtocolMeta
@@ -4806,6 +4814,7 @@ impl KnownClass {
             Self::TypeVar => "TypeVar",
             Self::ExtensionsTypeVar => "TypeVar",
             Self::ParamSpec => "ParamSpec",
+            Self::ExtensionsParamSpec => "ParamSpec",
             Self::ParamSpecArgs => "ParamSpecArgs",
             Self::ParamSpecKwargs => "ParamSpecKwargs",
             Self::TypeVarTuple => "TypeVarTuple",
@@ -5139,11 +5148,18 @@ impl KnownClass {
             Self::TypeAliasType
             | Self::ExtensionsTypeVar
             | Self::TypeVarTuple
-            | Self::ParamSpec
+            | Self::ExtensionsParamSpec
             | Self::ParamSpecArgs
             | Self::ParamSpecKwargs
             | Self::Deprecated
             | Self::NewType => KnownModule::TypingExtensions,
+            Self::ParamSpec => {
+                if Program::get(db).python_version(db) >= PythonVersion::PY310 {
+                    KnownModule::Typing
+                } else {
+                    KnownModule::TypingExtensions
+                }
+            }
             Self::NoDefaultType => {
                 let python_version = Program::get(db).python_version(db);
 
@@ -5247,6 +5263,7 @@ impl KnownClass {
             | Self::TypeVar
             | Self::ExtensionsTypeVar
             | Self::ParamSpec
+            | Self::ExtensionsParamSpec
             | Self::ParamSpecArgs
             | Self::ParamSpecKwargs
             | Self::TypeVarTuple
@@ -5337,6 +5354,7 @@ impl KnownClass {
             | Self::TypeVar
             | Self::ExtensionsTypeVar
             | Self::ParamSpec
+            | Self::ExtensionsParamSpec
             | Self::ParamSpecArgs
             | Self::ParamSpecKwargs
             | Self::TypeVarTuple
@@ -5420,7 +5438,7 @@ impl KnownClass {
             "Iterable" => &[Self::Iterable],
             "Iterator" => &[Self::Iterator],
             "Mapping" => &[Self::Mapping],
-            "ParamSpec" => &[Self::ParamSpec],
+            "ParamSpec" => &[Self::ParamSpec, Self::ExtensionsParamSpec],
             "ParamSpecArgs" => &[Self::ParamSpecArgs],
             "ParamSpecKwargs" => &[Self::ParamSpecKwargs],
             "TypeVarTuple" => &[Self::TypeVarTuple],
@@ -5542,6 +5560,8 @@ impl KnownClass {
             | Self::TypedDictFallback
             | Self::TypeVar
             | Self::ExtensionsTypeVar
+            | Self::ParamSpec
+            | Self::ExtensionsParamSpec
             | Self::NamedTupleLike
             | Self::ConstraintSet
             | Self::GenericContext
@@ -5555,7 +5575,6 @@ impl KnownClass {
             | Self::TypeAliasType
             | Self::NoDefaultType
             | Self::SupportsIndex
-            | Self::ParamSpec
             | Self::ParamSpecArgs
             | Self::ParamSpecKwargs
             | Self::TypeVarTuple
@@ -5970,6 +5989,7 @@ mod tests {
                     KnownClass::Member | KnownClass::Nonmember | KnownClass::StrEnum => {
                         PythonVersion::PY311
                     }
+                    KnownClass::ParamSpec => PythonVersion::PY310,
                     _ => PythonVersion::PY37,
                 };
                 (class, version_added)

crates/ty_python_semantic/src/types/infer/builder.rs

@@ -5033,9 +5033,15 @@ impl<'db, 'ast> TypeInferenceBuilder<'db, 'ast> {
                         ) => {
                             self.infer_legacy_typevar(target, call_expr, definition, typevar_class)
                         }
-                        Some(KnownClass::ParamSpec) => {
+                        Some(
-                            self.infer_paramspec(target, call_expr, definition)
+                            paramspec_class @ (KnownClass::ParamSpec
-                        }
+                            | KnownClass::ExtensionsParamSpec),
+                        ) => self.infer_legacy_paramspec(
+                            target,
+                            call_expr,
+                            definition,
+                            paramspec_class,
+                        ),
                         Some(KnownClass::NewType) => {
                             self.infer_newtype_expression(target, call_expr, definition)
                         }
@@ -5080,11 +5086,12 @@ impl<'db, 'ast> TypeInferenceBuilder<'db, 'ast> {
         target_ty
     }
 
-    fn infer_paramspec(
+    fn infer_legacy_paramspec(
         &mut self,
         target: &ast::Expr,
         call_expr: &ast::ExprCall,
         definition: Definition<'db>,
+        known_class: KnownClass,
     ) -> Type<'db> {
         fn error<'db>(
             context: &InferContext<'db, '_>,
@@ -5101,7 +5108,8 @@ impl<'db, 'ast> TypeInferenceBuilder<'db, 'ast> {
 
         let db = self.db();
         let arguments = &call_expr.arguments;
-        let assume_all_features = self.in_stub();
+        let is_typing_extensions = known_class == KnownClass::ExtensionsParamSpec;
+        let assume_all_features = self.in_stub() || is_typing_extensions;
         let python_version = Program::get(db).python_version(db);
         let have_features_from =
             |version: PythonVersion| assume_all_features || python_version >= version;
@@ -5594,7 +5602,10 @@ impl<'db, 'ast> TypeInferenceBuilder<'db, 'ast> {
             self.infer_type_expression(&bound.value);
         }
         if let Some(default) = arguments.find_keyword("default") {
-            if let Some(KnownClass::ParamSpec) = known_class {
+            if matches!(
+                known_class,
+                Some(KnownClass::ParamSpec | KnownClass::ExtensionsParamSpec)
+            ) {
                 self.infer_paramspec_default(&default.value);
             } else {
                 self.infer_type_expression(&default.value);
@@ -8440,7 +8451,7 @@ impl<'db, 'ast> TypeInferenceBuilder<'db, 'ast> {
                             );
                         }
                     }
-                    Some(KnownClass::ParamSpec) => {
+                    Some(KnownClass::ParamSpec | KnownClass::ExtensionsParamSpec) => {
                         if let Some(builder) = self
                             .context
                             .report_lint(&INVALID_PARAMSPEC, call_expression)