[ty] Make __getattr__ available for ModuleType instances (#21450)

## Summary

Typeshed has a (fake) `__getattr__` method on `types.ModuleType` with a
return type of `Any`. We ignore this method when accessing attributes on
module *literals*, but with this PR, we respect this method when dealing
with `ModuleType` itself. That is, we allow arbitrary attribute accesses
on instances of `types.ModuleType`. This is useful because dynamic
import mechanisms such as `importlib.import_module` use `ModuleType` as
a return type.

closes https://github.com/astral-sh/ty/issues/1346

## Ecosystem

Massive reduction in diagnostics. The few new diagnostics are true
positives.

## Test Plan

Added regression test.

crates/ty_python_semantic/resources/mdtest/call/dunder_import.md

@@ -49,12 +49,9 @@ def _(flag: bool):
 a = reveal_type(__import__("a.b.c"))  # revealed: ModuleType
 
 # TODO: Should be `int`, `str`, `bytes`
-# error: [unresolved-attribute]
-reveal_type(a.a)  # revealed: Unknown
-# error: [unresolved-attribute]
-reveal_type(a.b.b)  # revealed: Unknown
-# error: [unresolved-attribute]
-reveal_type(a.b.c.c)  # revealed: Unknown
+reveal_type(a.a)  # revealed: Any
+reveal_type(a.b.b)  # revealed: Any
+reveal_type(a.b.c.c)  # revealed: Any
 ```
 
 `a/__init__.py`:

crates/ty_python_semantic/resources/mdtest/scopes/moduletype_attrs.md

@@ -120,6 +120,21 @@ we're dealing with:
 reveal_type(typing.__getattr__)  # revealed: Unknown
 ```
 
+However, if we have a `ModuleType` instance, we make `__getattr__` available. This means that
+arbitrary attribute accesses are allowed (with a result type of `Any`):
+
+```py
+import types
+
+reveal_type(types.ModuleType.__getattr__)  # revealed: def __getattr__(self, name: str) -> Any
+
+def f(module: types.ModuleType):
+    reveal_type(module.__getattr__)  # revealed: bound method ModuleType.__getattr__(name: str) -> Any
+
+    reveal_type(module.__all__)  # revealed: Any
+    reveal_type(module.whatever)  # revealed: Any
+```
+
 ## `types.ModuleType.__dict__` takes precedence over global variable `__dict__`
 
 It's impossible to override the `__dict__` attribute of `types.ModuleType` instances from inside the

crates/ty_python_semantic/src/place.rs

@@ -10,9 +10,9 @@ use crate::semantic_index::{
 };
 use crate::semantic_index::{DeclarationWithConstraint, global_scope, use_def_map};
 use crate::types::{
-    ApplyTypeMappingVisitor, DynamicType, KnownClass, MaterializationKind, Truthiness, Type,
-    TypeAndQualifiers, TypeQualifiers, UnionBuilder, UnionType, binding_type, declaration_type,
-    todo_type,
+    ApplyTypeMappingVisitor, DynamicType, KnownClass, MaterializationKind, MemberLookupPolicy,
+    Truthiness, Type, TypeAndQualifiers, TypeQualifiers, UnionBuilder, UnionType, binding_type,
+    declaration_type, todo_type,
 };
 use crate::{Db, FxOrderSet, Program, resolve_module};
 
@@ -364,7 +364,9 @@ pub(crate) fn imported_symbol<'db>(
         } else if name == "__builtins__" {
             Place::bound(Type::any()).into()
         } else {
-            KnownClass::ModuleType.to_instance(db).member(db, name)
+            KnownClass::ModuleType
+                .to_instance(db)
+                .member_lookup_with_policy(db, name.into(), MemberLookupPolicy::NO_GETATTR_LOOKUP)
         }
     })
 }
@@ -1374,7 +1376,9 @@ mod implicit_globals {
     use crate::place::{Definedness, PlaceAndQualifiers, TypeOrigin};
     use crate::semantic_index::symbol::Symbol;
     use crate::semantic_index::{place_table, use_def_map};
-    use crate::types::{CallableType, KnownClass, Parameter, Parameters, Signature, Type};
+    use crate::types::{
+        CallableType, KnownClass, MemberLookupPolicy, Parameter, Parameters, Signature, Type,
+    };
     use ruff_python_ast::PythonVersion;
 
     use super::{Place, place_from_declarations};
@@ -1473,7 +1477,13 @@ mod implicit_globals {
                 .iter()
                 .any(|module_type_member| &**module_type_member == name) =>
             {
-                KnownClass::ModuleType.to_instance(db).member(db, name)
+                KnownClass::ModuleType
+                    .to_instance(db)
+                    .member_lookup_with_policy(
+                        db,
+                        name.into(),
+                        MemberLookupPolicy::NO_GETATTR_LOOKUP,
+                    )
             }
 
             _ => Place::Undefined.into(),

crates/ty_python_semantic/src/types.rs

@@ -336,6 +336,9 @@ bitflags! {
 
         /// Skip looking up attributes on the builtin `int` and `str` classes.
         const MRO_NO_INT_OR_STR_LOOKUP = 1 << 3;
+
+        /// Do not call `__getattr__` during member lookup.
+        const NO_GETATTR_LOOKUP = 1 << 4;
     }
 }
 
@@ -363,6 +366,11 @@ impl MemberLookupPolicy {
     pub(crate) const fn mro_no_int_or_str_fallback(self) -> bool {
         self.contains(Self::MRO_NO_INT_OR_STR_LOOKUP)
     }
+
+    /// Do not call `__getattr__` during member lookup.
+    pub(crate) const fn no_getattr_lookup(self) -> bool {
+        self.contains(Self::NO_GETATTR_LOOKUP)
+    }
 }
 
 impl Default for MemberLookupPolicy {
@@ -4222,7 +4230,7 @@ impl<'db> Type<'db> {
     /// Similar to [`Type::member`], but allows the caller to specify what policy should be used
     /// when looking up attributes. See [`MemberLookupPolicy`] for more information.
     #[salsa::tracked(cycle_initial=member_lookup_cycle_initial, heap_size=ruff_memory_usage::heap_size)]
-    fn member_lookup_with_policy(
+    pub(crate) fn member_lookup_with_policy(
         self,
         db: &'db dyn Db,
         name: Name,
@@ -4512,18 +4520,7 @@ impl<'db> Type<'db> {
                 );
 
                 let custom_getattr_result = || {
-                    // Typeshed has a fake `__getattr__` on `types.ModuleType` to help out with
-                    // dynamic imports. We explicitly hide it here to prevent arbitrary attributes
-                    // from being available on modules. Same for `types.GenericAlias` - its
-                    // `__getattr__` method will delegate to `__origin__` to allow looking up
-                    // attributes on the original type. But in typeshed its return type is `Any`.
-                    // It will need a special handling, so it remember the origin type to properly
-                    // resolve the attribute.
-                    if matches!(
-                        self.as_nominal_instance()
-                            .and_then(|instance| instance.known_class(db)),
-                        Some(KnownClass::ModuleType | KnownClass::GenericAlias)
-                    ) {
+                    if policy.no_getattr_lookup() {
                         return Place::Undefined.into();
                     }