Allow proper subclasses of strings (#706)

Author: adriangb

Cargo.lock

@@ -1,6 +1,6 @@
 [package]
 name = "pydantic-core"
-version = "0.41.0"
+version = "0.42.0"
 edition = "2021"
 license = "MIT"
 homepage = "https://github.com/pydantic/pydantic-core"

Cargo.toml

@@ -186,15 +186,21 @@ impl<'a> Input<'a> for PyAny {
     }
 
     fn strict_str(&'a self) -> ValResult<EitherString<'a>> {
-        if let Ok(py_str) = <PyString as PyTryFrom>::try_from_exact(self) {
+        if let Ok(py_str) = <PyString as PyTryFrom>::try_from(self) {
             Ok(py_str.into())
-        } else if PyString::is_type_of(self) {
-            Err(ValError::new(ErrorType::StringSubType, self))
         } else {
             Err(ValError::new(ErrorType::StringType, self))
         }
     }
 
+    fn exact_str(&'a self) -> ValResult<EitherString<'a>> {
+        if let Ok(py_str) = <PyString as PyTryFrom>::try_from_exact(self) {
+            Ok(EitherString::Py(py_str))
+        } else {
+            Err(ValError::new(ErrorType::IntType, self))
+        }
+    }
+
     fn exact_int(&'a self) -> ValResult<EitherInt<'a>> {
         if PyInt::is_exact_type_of(self) {
             Ok(EitherInt::Py(self))

src/input/input_python.rs

@@ -199,23 +199,15 @@ class FruitEnum(str, Enum):
     return FruitEnum
 
 
-@pytest.mark.parametrize('kwargs', [{}, {'to_lower': True}], ids=repr)
-def test_strict_subclass(FruitEnum, kwargs):
-    v = SchemaValidator(core_schema.str_schema(strict=True, **kwargs))
-    assert v.validate_python('foobar') == 'foobar'
-    with pytest.raises(ValidationError, match='type=string_type,'):
-        v.validate_python(b'foobar')
-    with pytest.raises(ValidationError, match='type=string_sub_type,') as exc_info:
-        v.validate_python(FruitEnum.pear)
-    # insert_assert(exc_info.value.errors(include_url=False))
-    assert exc_info.value.errors(include_url=False) == [
-        {
-            'type': 'string_sub_type',
-            'loc': (),
-            'msg': 'Input should be a string, not an instance of a subclass of str',
-            'input': FruitEnum.pear,
-        }
-    ]
+@pytest.mark.parametrize('to_lower', [False, True], ids=repr)
+def test_strict_subclass(to_lower: bool):
+    v = SchemaValidator(core_schema.str_schema(strict=True, to_lower=to_lower))
+
+    class StrSubclass(str):
+        pass
+
+    res = v.validate_python(StrSubclass('ABC'))
+    assert res == 'abc' if to_lower else 'ABC'
 
 
 @pytest.mark.parametrize('kwargs', [{}, {'to_lower': True}], ids=repr)