[ty] Detect illegal multiple inheritance with NamedTuple

Author: AlexWaygood

crates/ty/docs/rules.md

@@ -115,15 +115,28 @@ class Location(NamedTuple):
 
 ### Multiple Inheritance
 
-Multiple inheritance is not supported for `NamedTuple` classes:
+<!-- snapshot-diagnostics -->
+
+Multiple inheritance is not supported for `NamedTuple` classes except with `Generic`:
 
 ```py
-from typing import NamedTuple
+from typing import NamedTuple, Protocol
 
-# This should ideally emit a diagnostic
+# error: [invalid-named-tuple] "NamedTuple class `C` cannot use multiple inheritance except with `Generic[]`"
 class C(NamedTuple, object):
     id: int
-    name: str
+
+# fmt: off
+
+class D(
+    int,  # error: [invalid-named-tuple]
+    NamedTuple
+): ...
+
+# fmt: on
+
+# error: [invalid-named-tuple]
+class E(NamedTuple, Protocol): ...
 ```
 
 ### Inheriting from a `NamedTuple`

crates/ty_python_semantic/resources/mdtest/named_tuple.md

@@ -0,0 +1,73 @@
+---
+source: crates/ty_test/src/lib.rs
+expression: snapshot
+---
+---
+mdtest name: named_tuple.md - `NamedTuple` - `typing.NamedTuple` - Multiple Inheritance
+mdtest path: crates/ty_python_semantic/resources/mdtest/named_tuple.md
+---
+
+# Python source files
+
+## mdtest_snippet.py
+
+```
+ 1 | from typing import NamedTuple, Protocol
+ 2 | 
+ 3 | # error: [invalid-named-tuple] "NamedTuple class `C` cannot use multiple inheritance except with `Generic[]`"
+ 4 | class C(NamedTuple, object):
+ 5 |     id: int
+ 6 | 
+ 7 | # fmt: off
+ 8 | 
+ 9 | class D(
+10 |     int,  # error: [invalid-named-tuple]
+11 |     NamedTuple
+12 | ): ...
+13 | 
+14 | # fmt: on
+15 | 
+16 | # error: [invalid-named-tuple]
+17 | class E(NamedTuple, Protocol): ...
+```
+
+# Diagnostics
+
+```
+error[invalid-named-tuple]: NamedTuple class `C` cannot use multiple inheritance except with `Generic[]`
+ --> src/mdtest_snippet.py:4:21
+  |
+3 | # error: [invalid-named-tuple] "NamedTuple class `C` cannot use multiple inheritance except with `Generic[]`"
+4 | class C(NamedTuple, object):
+  |                     ^^^^^^
+5 |     id: int
+  |
+info: rule `invalid-named-tuple` is enabled by default
+
+```
+
+```
+error[invalid-named-tuple]: NamedTuple class `D` cannot use multiple inheritance except with `Generic[]`
+  --> src/mdtest_snippet.py:10:5
+   |
+ 9 | class D(
+10 |     int,  # error: [invalid-named-tuple]
+   |     ^^^
+11 |     NamedTuple
+12 | ): ...
+   |
+info: rule `invalid-named-tuple` is enabled by default
+
+```
+
+```
+error[invalid-named-tuple]: NamedTuple class `E` cannot use multiple inheritance except with `Generic[]`
+  --> src/mdtest_snippet.py:17:21
+   |
+16 | # error: [invalid-named-tuple]
+17 | class E(NamedTuple, Protocol): ...
+   |                     ^^^^^^^^
+   |
+info: rule `invalid-named-tuple` is enabled by default
+
+```

crates/ty_python_semantic/resources/mdtest/snapshots/named_tuple.md_-_`NamedTuple`_-_`typing.NamedTuple`_-_Multiple_Inheritance_(82ed33d1b3b433d8).snap

@@ -227,7 +227,7 @@ impl CodeGeneratorKind {
         code_generator_of_class(db, class)
     }
 
-    fn matches(self, db: &dyn Db, class: ClassLiteral<'_>) -> bool {
+    pub(super) fn matches(self, db: &dyn Db, class: ClassLiteral<'_>) -> bool {
         CodeGeneratorKind::from_class(db, class) == Some(self)
     }
 }

crates/ty_python_semantic/src/types/class.rs

@@ -57,6 +57,7 @@ pub(crate) fn register_lints(registry: &mut LintRegistryBuilder) {
     registry.register_lint(&INVALID_OVERLOAD);
     registry.register_lint(&INVALID_PARAMETER_DEFAULT);
     registry.register_lint(&INVALID_PROTOCOL);
+    registry.register_lint(&INVALID_NAMED_TUPLE);
     registry.register_lint(&INVALID_RAISE);
     registry.register_lint(&INVALID_SUPER_ARGUMENT);
     registry.register_lint(&INVALID_TYPE_CHECKING_CONSTANT);
@@ -448,6 +449,39 @@ declare_lint! {
     }
 }
 
+declare_lint! {
+    /// ## What it does
+    /// Checks for invalidly defined `NamedTuple` classes.
+    ///
+    /// ## Why is this bad?
+    /// An invalidly defined `NamedTuple` class may lead to the type checker
+    /// inferring unexpected things. It may also lead to `TypeError`s at runtime.
+    ///
+    /// ## Examples
+    /// A class definition cannot combine `NamedTuple` with other base classes
+    /// in multiple inheritance; doing so raises a `TypeError` at runtime. The sole
+    /// exception to this rule is `Generic[]`, which can be used alongside `NamedTuple`
+    /// in a class's bases list.
+    ///
+    /// ```pycon
+    /// >>> from typing import NamedTuple
+    /// >>> class Foo(NamedTuple, object): ...
+    /// ...
+    /// Traceback (most recent call last):
+    ///   File "<python-input-1>", line 1, in <module>
+    ///     class Foo(NamedTuple, object): ...
+    ///   File "/python3.13/typing.py", line 2998, in __new__
+    ///     raise TypeError(
+    ///         'can only inherit from a NamedTuple type and Generic')
+    /// TypeError: can only inherit from a NamedTuple type and Generic
+    /// ```
+    pub(crate) static INVALID_NAMED_TUPLE = {
+        summary: "detects invalid `NamedTuple` class definitions",
+        status: LintStatus::preview("1.0.0"),
+        default_level: Level::Error,
+    }
+}
+
 declare_lint! {
     /// ## What it does
     /// Checks for classes with an inconsistent [method resolution order] (MRO).

crates/ty_python_semantic/src/types/diagnostic.rs

@@ -95,16 +95,17 @@ use crate::types::diagnostic::{
     self, CALL_NON_CALLABLE, CONFLICTING_DECLARATIONS, CONFLICTING_METACLASS,
     CYCLIC_CLASS_DEFINITION, DIVISION_BY_ZERO, DUPLICATE_KW_ONLY, INCONSISTENT_MRO,
     INVALID_ARGUMENT_TYPE, INVALID_ASSIGNMENT, INVALID_ATTRIBUTE_ACCESS, INVALID_BASE,
-    INVALID_DECLARATION, INVALID_GENERIC_CLASS, INVALID_KEY, INVALID_PARAMETER_DEFAULT,
-    INVALID_TYPE_FORM, INVALID_TYPE_GUARD_CALL, INVALID_TYPE_VARIABLE_CONSTRAINTS,
-    IncompatibleBases, POSSIBLY_UNBOUND_IMPLICIT_CALL, POSSIBLY_UNBOUND_IMPORT,
-    TypeCheckDiagnostics, UNDEFINED_REVEAL, UNRESOLVED_ATTRIBUTE, UNRESOLVED_GLOBAL,
-    UNRESOLVED_IMPORT, UNRESOLVED_REFERENCE, UNSUPPORTED_OPERATOR, report_implicit_return_type,
-    report_instance_layout_conflict, report_invalid_argument_number_to_special_form,
-    report_invalid_arguments_to_annotated, report_invalid_arguments_to_callable,
-    report_invalid_assignment, report_invalid_attribute_assignment,
-    report_invalid_generator_function_return_type, report_invalid_key_on_typed_dict,
-    report_invalid_return_type, report_possibly_unbound_attribute,
+    INVALID_DECLARATION, INVALID_GENERIC_CLASS, INVALID_KEY, INVALID_NAMED_TUPLE,
+    INVALID_PARAMETER_DEFAULT, INVALID_TYPE_FORM, INVALID_TYPE_GUARD_CALL,
+    INVALID_TYPE_VARIABLE_CONSTRAINTS, IncompatibleBases, POSSIBLY_UNBOUND_IMPLICIT_CALL,
+    POSSIBLY_UNBOUND_IMPORT, TypeCheckDiagnostics, UNDEFINED_REVEAL, UNRESOLVED_ATTRIBUTE,
+    UNRESOLVED_GLOBAL, UNRESOLVED_IMPORT, UNRESOLVED_REFERENCE, UNSUPPORTED_OPERATOR,
+    report_implicit_return_type, report_instance_layout_conflict,
+    report_invalid_argument_number_to_special_form, report_invalid_arguments_to_annotated,
+    report_invalid_arguments_to_callable, report_invalid_assignment,
+    report_invalid_attribute_assignment, report_invalid_generator_function_return_type,
+    report_invalid_key_on_typed_dict, report_invalid_return_type,
+    report_possibly_unbound_attribute,
 };
 use crate::types::enums::is_enum_class;
 use crate::types::function::{
@@ -1110,13 +1111,33 @@ impl<'db, 'ast> TypeInferenceBuilder<'db, 'ast> {
             }
 
             let is_protocol = class.is_protocol(self.db());
+            let is_named_tuple = CodeGeneratorKind::NamedTuple.matches(self.db(), class);
             let mut solid_bases = IncompatibleBases::default();
 
             // (2) Iterate through the class's explicit bases to check for various possible errors:
             //     - Check for inheritance from plain `Generic`,
             //     - Check for inheritance from a `@final` classes
             //     - If the class is a protocol class: check for inheritance from a non-protocol class
+            //     - If the class is a NamedTuple class: check for multiple inheritance that isn't `Generic[]`
             for (i, base_class) in class.explicit_bases(self.db()).iter().enumerate() {
+                if is_named_tuple
+                    && !matches!(
+                        base_class,
+                        Type::SpecialForm(SpecialFormType::NamedTuple)
+                            | Type::KnownInstance(KnownInstanceType::SubscriptedGeneric(_))
+                    )
+                {
+                    if let Some(builder) = self
+                        .context
+                        .report_lint(&INVALID_NAMED_TUPLE, &class_node.bases()[i])
+                    {
+                        builder.into_diagnostic(format_args!(
+                            "NamedTuple class `{}` cannot use multiple inheritance except with `Generic[]`",
+                            class.name(self.db()),
+                        ));
+                    }
+                }
+
                 let base_class = match base_class {
                     Type::SpecialForm(SpecialFormType::Generic) => {
                         if let Some(builder) = self