[ty] Split invalid-base error code into two error codes (#18245)

Author: AlexWaygood

crates/ty/docs/rules.md

@@ -173,7 +173,7 @@ if hasattr(DoesNotExist, "__mro__"):
 if not isinstance(DoesNotExist, type):
     reveal_type(DoesNotExist)  # revealed: Unknown & ~type
 
-    class Foo(DoesNotExist): ...  # error: [invalid-base]
+    class Foo(DoesNotExist): ...  # error: [unsupported-base]
     reveal_type(Foo.__mro__)  # revealed: tuple[<class 'Foo'>, Unknown, <class 'object'>]
 ```
 
@@ -232,11 +232,15 @@ reveal_type(AA.__mro__)  # revealed: tuple[<class 'AA'>, <class 'Z'>, Unknown, <
 
 ## `__bases__` includes a `Union`
 
+<!-- snapshot-diagnostics -->
+
 We don't support union types in a class's bases; a base must resolve to a single `ClassType`. If we
 find a union type in a class's bases, we infer the class's `__mro__` as being
 `[<class>, Unknown, object]`, the same as for MROs that cause errors at runtime.
 
 ```py
+from typing_extensions import reveal_type
+
 def returns_bool() -> bool:
     return True
 
@@ -250,7 +254,7 @@ else:
 
 reveal_type(x)  # revealed: <class 'A'> | <class 'B'>
 
-# error: 11 [invalid-base] "Invalid class base with type `<class 'A'> | <class 'B'>` (all bases must be a class, `Any`, `Unknown` or `Todo`)"
+# error: 11 [unsupported-base] "Unsupported class base with type `<class 'A'> | <class 'B'>`"
 class Foo(x): ...
 
 reveal_type(Foo.__mro__)  # revealed: tuple[<class 'Foo'>, Unknown, <class 'object'>]
@@ -259,8 +263,8 @@ reveal_type(Foo.__mro__)  # revealed: tuple[<class 'Foo'>, Unknown, <class 'obje
 ## `__bases__` is a union of a dynamic type and valid bases
 
 If a dynamic type such as `Any` or `Unknown` is one of the elements in the union, and all other
-types *would be* valid class bases, we do not emit an `invalid-base` diagnostic and use the dynamic
-type as a base to prevent further downstream errors.
+types *would be* valid class bases, we do not emit an `invalid-base` or `unsupported-base`
+diagnostic, and we use the dynamic type as a base to prevent further downstream errors.
 
 ```py
 from typing import Any
@@ -299,8 +303,8 @@ else:
 reveal_type(x)  # revealed: <class 'A'> | <class 'B'>
 reveal_type(y)  # revealed: <class 'C'> | <class 'D'>
 
-# error: 11 [invalid-base] "Invalid class base with type `<class 'A'> | <class 'B'>` (all bases must be a class, `Any`, `Unknown` or `Todo`)"
-# error: 14 [invalid-base] "Invalid class base with type `<class 'C'> | <class 'D'>` (all bases must be a class, `Any`, `Unknown` or `Todo`)"
+# error: 11 [unsupported-base] "Unsupported class base with type `<class 'A'> | <class 'B'>`"
+# error: 14 [unsupported-base] "Unsupported class base with type `<class 'C'> | <class 'D'>`"
 class Foo(x, y): ...
 
 reveal_type(Foo.__mro__)  # revealed: tuple[<class 'Foo'>, Unknown, <class 'object'>]
@@ -321,7 +325,7 @@ if returns_bool():
 else:
     foo = object
 
-# error: 21 [invalid-base] "Invalid class base with type `<class 'Y'> | <class 'object'>` (all bases must be a class, `Any`, `Unknown` or `Todo`)"
+# error: 21 [unsupported-base] "Unsupported class base with type `<class 'Y'> | <class 'object'>`"
 class PossibleError(foo, X): ...
 
 reveal_type(PossibleError.__mro__)  # revealed: tuple[<class 'PossibleError'>, Unknown, <class 'object'>]
@@ -339,12 +343,47 @@ else:
 # revealed: tuple[<class 'B'>, <class 'X'>, <class 'Y'>, <class 'O'>, <class 'object'>] | tuple[<class 'B'>, <class 'Y'>, <class 'X'>, <class 'O'>, <class 'object'>]
 reveal_type(B.__mro__)
 
-# error: 12 [invalid-base] "Invalid class base with type `<class 'B'> | <class 'B'>` (all bases must be a class, `Any`, `Unknown` or `Todo`)"
+# error: 12 [unsupported-base] "Unsupported class base with type `<class 'B'> | <class 'B'>`"
 class Z(A, B): ...
 
 reveal_type(Z.__mro__)  # revealed: tuple[<class 'Z'>, Unknown, <class 'object'>]
 ```
 
+## `__bases__` lists that include objects that are not instances of `type`
+
+<!-- snapshot-diagnostics -->
+
+```py
+class Foo(2): ...  # error: [invalid-base]
+```
+
+A base that is not an instance of `type` but does have an `__mro_entries__` method will not raise an
+exception at runtime, so we issue `unsupported-base` rather than `invalid-base`:
+
+```py
+class Foo:
+    def __mro_entries__(self, bases: tuple[type, ...]) -> tuple[type, ...]:
+        return ()
+
+class Bar(Foo()): ...  # error: [unsupported-base]
+```
+
+But for objects that have badly defined `__mro_entries__`, `invalid-base` is emitted rather than
+`unsupported-base`:
+
+```py
+class Bad1:
+    def __mro_entries__(self, bases, extra_arg):
+        return ()
+
+class Bad2:
+    def __mro_entries__(self, bases) -> int:
+        return 42
+
+class BadSub1(Bad1()): ...  # error: [invalid-base]
+class BadSub2(Bad2()): ...  # error: [invalid-base]
+```
+
 ## `__bases__` lists with duplicate bases
 
 <!-- snapshot-diagnostics -->

crates/ty_python_semantic/resources/mdtest/mro.md

@@ -0,0 +1,78 @@
+---
+source: crates/ty_test/src/lib.rs
+expression: snapshot
+---
+---
+mdtest name: mro.md - Method Resolution Order tests - `__bases__` includes a `Union`
+mdtest path: crates/ty_python_semantic/resources/mdtest/mro.md
+---
+
+# Python source files
+
+## mdtest_snippet.py
+
+```
+ 1 | from typing_extensions import reveal_type
+ 2 | 
+ 3 | def returns_bool() -> bool:
+ 4 |     return True
+ 5 | 
+ 6 | class A: ...
+ 7 | class B: ...
+ 8 | 
+ 9 | if returns_bool():
+10 |     x = A
+11 | else:
+12 |     x = B
+13 | 
+14 | reveal_type(x)  # revealed: <class 'A'> | <class 'B'>
+15 | 
+16 | # error: 11 [unsupported-base] "Unsupported class base with type `<class 'A'> | <class 'B'>`"
+17 | class Foo(x): ...
+18 | 
+19 | reveal_type(Foo.__mro__)  # revealed: tuple[<class 'Foo'>, Unknown, <class 'object'>]
+```
+
+# Diagnostics
+
+```
+info[revealed-type]: Revealed type
+  --> src/mdtest_snippet.py:14:13
+   |
+12 |     x = B
+13 |
+14 | reveal_type(x)  # revealed: <class 'A'> | <class 'B'>
+   |             ^ `<class 'A'> | <class 'B'>`
+15 |
+16 | # error: 11 [unsupported-base] "Unsupported class base with type `<class 'A'> | <class 'B'>`"
+   |
+
+```
+
+```
+warning[unsupported-base]: Unsupported class base with type `<class 'A'> | <class 'B'>`
+  --> src/mdtest_snippet.py:17:11
+   |
+16 | # error: 11 [unsupported-base] "Unsupported class base with type `<class 'A'> | <class 'B'>`"
+17 | class Foo(x): ...
+   |           ^
+18 |
+19 | reveal_type(Foo.__mro__)  # revealed: tuple[<class 'Foo'>, Unknown, <class 'object'>]
+   |
+info: ty cannot resolve a consistent MRO for class `Foo` due to this base
+info: Only class objects or `Any` are supported as class bases
+info: rule `unsupported-base` is enabled by default
+
+```
+
+```
+info[revealed-type]: Revealed type
+  --> src/mdtest_snippet.py:19:13
+   |
+17 | class Foo(x): ...
+18 |
+19 | reveal_type(Foo.__mro__)  # revealed: tuple[<class 'Foo'>, Unknown, <class 'object'>]
+   |             ^^^^^^^^^^^ `tuple[<class 'Foo'>, Unknown, <class 'object'>]`
+   |
+
+```

crates/ty_python_semantic/resources/mdtest/snapshots/mro.md_-_Method_Resolution_Or…_-_`__bases__`_includes…_(d2532518c44112c8).snap

@@ -0,0 +1,97 @@
+---
+source: crates/ty_test/src/lib.rs
+expression: snapshot
+---
+---
+mdtest name: mro.md - Method Resolution Order tests - `__bases__` lists that include objects that are not instances of `type`
+mdtest path: crates/ty_python_semantic/resources/mdtest/mro.md
+---
+
+# Python source files
+
+## mdtest_snippet.py
+
+```
+ 1 | class Foo(2): ...  # error: [invalid-base]
+ 2 | class Foo:
+ 3 |     def __mro_entries__(self, bases: tuple[type, ...]) -> tuple[type, ...]:
+ 4 |         return ()
+ 5 | 
+ 6 | class Bar(Foo()): ...  # error: [unsupported-base]
+ 7 | class Bad1:
+ 8 |     def __mro_entries__(self, bases, extra_arg):
+ 9 |         return ()
+10 | 
+11 | class Bad2:
+12 |     def __mro_entries__(self, bases) -> int:
+13 |         return 42
+14 | 
+15 | class BadSub1(Bad1()): ...  # error: [invalid-base]
+16 | class BadSub2(Bad2()): ...  # error: [invalid-base]
+```
+
+# Diagnostics
+
+```
+error[invalid-base]: Invalid class base with type `Literal[2]`
+ --> src/mdtest_snippet.py:1:11
+  |
+1 | class Foo(2): ...  # error: [invalid-base]
+  |           ^
+2 | class Foo:
+3 |     def __mro_entries__(self, bases: tuple[type, ...]) -> tuple[type, ...]:
+  |
+info: Definition of class `Foo` will raise `TypeError` at runtime
+info: rule `invalid-base` is enabled by default
+
+```
+
+```
+warning[unsupported-base]: Unsupported class base with type `Foo`
+ --> src/mdtest_snippet.py:6:11
+  |
+4 |         return ()
+5 |
+6 | class Bar(Foo()): ...  # error: [unsupported-base]
+  |           ^^^^^
+7 | class Bad1:
+8 |     def __mro_entries__(self, bases, extra_arg):
+  |
+info: ty cannot resolve a consistent MRO for class `Bar` due to this base
+info: Only class objects or `Any` are supported as class bases
+info: rule `unsupported-base` is enabled by default
+
+```
+
+```
+error[invalid-base]: Invalid class base with type `Bad1`
+  --> src/mdtest_snippet.py:15:15
+   |
+13 |         return 42
+14 |
+15 | class BadSub1(Bad1()): ...  # error: [invalid-base]
+   |               ^^^^^^
+16 | class BadSub2(Bad2()): ...  # error: [invalid-base]
+   |
+info: Definition of class `BadSub1` will raise `TypeError` at runtime
+info: An instance type is only a valid class base if it has a valid `__mro_entries__` method
+info: Type `Bad1` has an `__mro_entries__` method, but it cannot be called with the expected arguments
+info: Expected a signature at least as permissive as `def __mro_entries__(self, bases: tuple[type, ...], /) -> tuple[type, ...]`
+info: rule `invalid-base` is enabled by default
+
+```
+
+```
+error[invalid-base]: Invalid class base with type `Bad2`
+  --> src/mdtest_snippet.py:16:15
+   |
+15 | class BadSub1(Bad1()): ...  # error: [invalid-base]
+16 | class BadSub2(Bad2()): ...  # error: [invalid-base]
+   |               ^^^^^^
+   |
+info: Definition of class `BadSub2` will raise `TypeError` at runtime
+info: An instance type is only a valid class base if it has a valid `__mro_entries__` method
+info: Type `Bad2` has an `__mro_entries__` method, but it does not return a tuple of types
+info: rule `invalid-base` is enabled by default
+
+```

crates/ty_python_semantic/resources/mdtest/snapshots/mro.md_-_Method_Resolution_Or…_-_`__bases__`_lists_th…_(6f8d0bf648c4b305).snap

@@ -164,8 +164,12 @@ impl<'db> ClassBase<'db> {
                 }
             }
             Type::NominalInstance(_) => None, // TODO -- handle `__mro_entries__`?
-            Type::PropertyInstance(_) => None,
-            Type::Never
+
+            // This likely means that we're in unreachable code,
+            // in which case we want to treat `Never` in a forgiving way and silence diagnostics
+            Type::Never => Some(ClassBase::unknown()),
+
+            Type::PropertyInstance(_)
             | Type::BooleanLiteral(_)
             | Type::FunctionLiteral(_)
             | Type::Callable(..)