[red-knot] Fallback to attributes on types.ModuleType if a symbol can't be found in locals or globals

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

@@ -0,0 +1,141 @@
+# Implicit globals from `types.ModuleType`
+
+## Implicit `ModuleType` globals
+
+All modules are instances of `types.ModuleType`.
+If a name can't be found in any local or global scope, we look it up
+as an attribute on `types.ModuleType` in typeshed
+before deciding that the name is unbound.
+
+```py
+reveal_type(__name__)  # revealed: str
+reveal_type(__file__)  # revealed: str | None
+reveal_type(__loader__)  # revealed: LoaderProtocol | None
+reveal_type(__package__)  # revealed: str | None
+reveal_type(__spec__)  # revealed: ModuleSpec | None
+
+# TODO: generics
+reveal_type(__path__)  # revealed: @Todo
+
+# TODO: this should probably be added to typeshed; not sure why it isn't?
+# error: [unresolved-reference]
+# revealed: Unbound
+reveal_type(__doc__)
+
+class X:
+    reveal_type(__name__)  # revealed: str
+
+def foo():
+    reveal_type(__name__)  # revealed: str
+```
+
+However, three attributes on `types.ModuleType` are not present as implicit
+module globals; these are excluded:
+
+```py path=unbound_dunders.py
+# error: [unresolved-reference]
+# revealed: Unbound
+reveal_type(__getattr__)
+
+# error: [unresolved-reference]
+# revealed: Unbound
+reveal_type(__dict__)
+
+# error: [unresolved-reference]
+# revealed: Unbound
+reveal_type(__init__)
+```
+
+## Accessed as attributes
+
+`ModuleType` attributes can also be accessed as attributes on module-literal types.
+The special attributes `__dict__` and `__init__`, and all attributes on
+`builtins.object`, can also be accessed as attributes on module-literal types,
+despite the fact that these are inaccessible as globals from inside the module:
+
+```py
+import typing
+
+reveal_type(typing.__name__)  # revealed: str
+reveal_type(typing.__init__)  # revealed: Literal[__init__]
+
+# These come from `builtins.object`, not `types.ModuleType`:
+# TODO: we don't currently understand `types.ModuleType` as inheriting from `object`;
+# these should not reveal `Unbound`:
+reveal_type(typing.__eq__)  # revealed: Unbound
+reveal_type(typing.__class__)  # revealed: Unbound
+reveal_type(typing.__module__)  # revealed: Unbound
+
+# TODO: needs support for attribute access on instances, properties and generics;
+# should be `dict[str, Any]`
+reveal_type(typing.__dict__)  # revealed: @Todo
+```
+
+Typeshed includes a fake `__getattr__` method in the stub for `types.ModuleType`
+to help out with dynamic imports; but we ignore that for module-literal types
+where we know exactly which module we're dealing with:
+
+```py path=__getattr__.py
+import typing
+
+reveal_type(typing.__getattr__)  # revealed: Unbound
+```
+
+## `types.ModuleType.__dict__` takes precedence over global variable `__dict__`
+
+It's impossible to override the `__dict__` attribute of `types.ModuleType`
+instances from inside the module; we should prioritise the attribute in
+the `types.ModuleType` stub over a variable named `__dict__` in the module's
+global namespace:
+
+```py path=foo.py
+__dict__ = "foo"
+
+reveal_type(__dict__)  # revealed: Literal["foo"]
+```
+
+```py path=bar.py
+import foo
+from foo import __dict__ as foo_dict
+
+# TODO: needs support for attribute access on instances, properties, and generics;
+# should be `dict[str, Any]` for both of these:
+reveal_type(foo.__dict__)  # revealed: @Todo
+reveal_type(foo_dict)  # revealed: @Todo
+```
+
+## Conditionally global or `ModuleType` attribute
+
+Attributes overridden in the module namespace take priority.
+If a builtin name is conditionally defined as a global, however,
+a name lookup should union the `ModuleType` type with the conditionally defined type:
+
+```py
+__file__ = 42
+
+def returns_bool() -> bool:
+    return True
+
+if returns_bool():
+    __name__ = 1
+
+reveal_type(__file__)  # revealed: Literal[42]
+reveal_type(__name__)  # revealed: str | Literal[1]
+```
+
+## Conditionally global or `ModuleType` attribute, with annotation
+
+The same is true if the name is annotated:
+
+```py
+__file__: int = 42
+
+def returns_bool() -> bool:
+    return True
+
+if returns_bool():
+    __name__: int = 1
+
+reveal_type(__file__)  # revealed: Literal[42]
+reveal_type(__name__)  # revealed: str | Literal[1]
+```

crates/red_knot_python_semantic/src/semantic_index/builder.rs

@@ -195,6 +195,10 @@ impl<'db> SemanticIndexBuilder<'db> {
         self.current_symbol_table().mark_symbol_bound(id);
     }
 
+    fn mark_symbol_declared(&mut self, id: ScopedSymbolId) {
+        self.current_symbol_table().mark_symbol_declared(id);
+    }
+
     fn mark_symbol_used(&mut self, id: ScopedSymbolId) {
         self.current_symbol_table().mark_symbol_used(id);
     }
@@ -226,6 +230,9 @@ impl<'db> SemanticIndexBuilder<'db> {
         if category.is_binding() {
             self.mark_symbol_bound(symbol);
         }
+        if category.is_declaration() {
+            self.mark_symbol_declared(symbol);
+        }
 
         let use_def = self.current_use_def_map_mut();
         match category {
@@ -359,6 +366,7 @@ impl<'db> SemanticIndexBuilder<'db> {
                 // note that the "bound" on the typevar is a totally different thing than whether
                 // or not a name is "bound" by a typevar declaration; the latter is always true.
                 self.mark_symbol_bound(symbol);
+                self.mark_symbol_declared(symbol);
                 if let Some(bounds) = bound {
                     self.visit_expr(bounds);
                 }

crates/red_knot_python_semantic/src/semantic_index/symbol.rs

@@ -47,17 +47,27 @@ impl Symbol {
     pub fn is_bound(&self) -> bool {
         self.flags.contains(SymbolFlags::IS_BOUND)
     }
+
+    /// Is the symbol declared in its containing scope?
+    pub fn is_declared(&self) -> bool {
+        self.flags.contains(SymbolFlags::IS_DECLARED)
+    }
 }
 
 bitflags! {
+    /// Flags that can be queried to obtain information about a symbol in a given scope.
+    ///
+    /// See the doc-comment at the top of [`super::use_def`] for explanations of what it
+    /// means for a symbol to be *bound* as opposed to *declared*.
     #[derive(Copy, Clone, Debug, Eq, PartialEq)]
     struct SymbolFlags: u8 {
         const IS_USED         = 1 << 0;
-        const IS_BOUND      = 1 << 1;
+        const IS_BOUND        = 1 << 1;
+        const IS_DECLARED     = 1 << 2;
         /// TODO: This flag is not yet set by anything
-        const MARKED_GLOBAL   = 1 << 2;
+        const MARKED_GLOBAL   = 1 << 3;
         /// TODO: This flag is not yet set by anything
-        const MARKED_NONLOCAL = 1 << 3;
+        const MARKED_NONLOCAL = 1 << 4;
     }
 }
 
@@ -298,6 +308,10 @@ impl SymbolTableBuilder {
         self.table.symbols[id].insert_flags(SymbolFlags::IS_BOUND);
     }
 
+    pub(super) fn mark_symbol_declared(&mut self, id: ScopedSymbolId) {
+        self.table.symbols[id].insert_flags(SymbolFlags::IS_DECLARED);
+    }
+
     pub(super) fn mark_symbol_used(&mut self, id: ScopedSymbolId) {
         self.table.symbols[id].insert_flags(SymbolFlags::IS_USED);
     }

crates/red_knot_python_semantic/src/types.rs

@@ -5,7 +5,7 @@ use ruff_python_ast as ast;
 use crate::module_resolver::file_to_module;
 use crate::semantic_index::ast_ids::HasScopedAstId;
 use crate::semantic_index::definition::{Definition, DefinitionKind};
-use crate::semantic_index::symbol::{ScopeId, ScopedSymbolId};
+use crate::semantic_index::symbol::{ScopeId, ScopedSymbolId, Symbol};
 use crate::semantic_index::{
     global_scope, semantic_index, symbol_table, use_def_map, BindingWithConstraints,
     BindingWithConstraintsIterator, DeclarationsIterator,
@@ -88,9 +88,64 @@ fn symbol_ty<'db>(db: &'db dyn Db, scope: ScopeId<'db>, name: &str) -> Type<'db>
         .unwrap_or(Type::Unbound)
 }
 
-/// Shorthand for `symbol_ty` that looks up a module-global symbol by name in a file.
+/// Return a list of the symbols that typeshed declares in the body scope of
+/// the stub for the class `types.ModuleType`.
+///
+/// Conceptually this could be a `Set` rather than a list,
+/// but the number of symbols declared in this scope is likely to be very small,
+/// so the cost of hashing the names is likely to be more expensive than it's worth.
+#[salsa::tracked(return_ref)]
+fn module_type_symbols<'db>(db: &'db dyn Db) -> smallvec::SmallVec<[ast::name::Name; 8]> {
+    let Some(module_type) = KnownClass::ModuleType
+        .to_class(db)
+        .into_class_literal_type()
+    else {
+        // The most likely way we get here is if a user specified a `--custom-typeshed-dir`
+        // without a `types.pyi` stub in the `stdlib/` directory
+        return smallvec::SmallVec::default();
+    };
+
+    let module_type_scope = module_type.body_scope(db);
+    let module_type_symbol_table = symbol_table(db, module_type_scope);
+
+    // `__dict__` and `__init__` are very special members that can be accessed as attributes
+    // on the module when imported, but cannot be accessed as globals *inside* the module.
+    //
+    // `__getattr__` is even more special: it doesn't exist at runtime, but typeshed includes it
+    // to reduce false positives associated with functions that dynamically import modules
+    // and return `Instance(types.ModuleType)`. We should ignore it for any known module-literal type.
+    module_type_symbol_table
+        .symbols()
+        .filter(|symbol| symbol.is_declared())
+        .map(Symbol::name)
+        .filter(|symbol_name| !matches!(&***symbol_name, "__dict__" | "__getattr__" | "__init__"))
+        .cloned()
+        .collect()
+}
+
+/// Looks up a module-global symbol by name in a file.
 pub(crate) fn global_symbol_ty<'db>(db: &'db dyn Db, file: File, name: &str) -> Type<'db> {
-    symbol_ty(db, global_scope(db, file), name)
+    let explicit_ty = symbol_ty(db, global_scope(db, file), name);
+    if !explicit_ty.may_be_unbound(db) {
+        return explicit_ty;
+    }
+
+    // Not defined explicitly in the global scope?
+    // All modules are instances of `types.ModuleType`;
+    // look it up there (with a few very special exceptions)
+    if module_type_symbols(db)
+        .iter()
+        .any(|module_type_member| &**module_type_member == name)
+    {
+        // TODO: this should use `.to_instance(db)`. but we don't understand attribute access
+        // on instance types yet.
+        let module_type_member = KnownClass::ModuleType.to_class(db).member(db, name);
+        if !module_type_member.is_unbound() {
+            return explicit_ty.replace_unbound_with(db, module_type_member);
+        }
+    }
+
+    explicit_ty
 }
 
 /// Infer the type of a binding.
@@ -801,7 +856,46 @@ impl<'db> Type<'db> {
                 // TODO: attribute lookup on function type
                 Type::Todo
             }
-            Type::ModuleLiteral(file) => global_symbol_ty(db, *file, name),
+            Type::ModuleLiteral(file) => {
+                // `__dict__` is a very special member that is never overridden by module globals;
+                // we should always look it up directly as an attribute on `types.ModuleType`,
+                // never in the global scope of the module.
+                if name == "__dict__" {
+                    return KnownClass::ModuleType
+                        .to_instance(db)
+                        .member(db, "__dict__");
+                }
+
+                let global_lookup = symbol_ty(db, global_scope(db, *file), name);
+
+                // If it's unbound, check if it's present as an instance on `types.ModuleType`
+                // or `builtins.object`.
+                //
+                // We do a more limited version of this in `global_symbol_ty`,
+                // but there are two crucial differences here:
+                // - If a member is looked up as an attribute, `__init__` is also available
+                //   on the module, but it isn't available as a global from inside the module
+                // - If a member is looked up as an attribute, members on `builtins.object`
+                //   are also available (because `types.ModuleType` inherits from `object`);
+                //   these attributes are also not available as globals from inside the module.
+                //
+                // The same way as in `global_symbol_ty`, however, we need to be careful to
+                // ignore `__getattr__`. Typeshed has a fake `__getattr__` on `types.ModuleType`
+                // to help out with dynamic imports; we shouldn't use it for `ModuleLiteral` types
+                // where we know exactly which module we're dealing with.
+                if name != "__getattr__" && global_lookup.may_be_unbound(db) {
+                    // TODO: this should use `.to_instance()`, but we don't understand instance attribute yet
+                    let module_type_instance_member =
+                        KnownClass::ModuleType.to_class(db).member(db, name);
+                    if module_type_instance_member.is_unbound() {
+                        global_lookup
+                    } else {
+                        global_lookup.replace_unbound_with(db, module_type_instance_member)
+                    }
+                } else {
+                    global_lookup
+                }
+            }
             Type::ClassLiteral(class) => class.class_member(db, name),
             Type::Instance(_) => {
                 // TODO MRO? get_own_instance_member, get_instance_member
@@ -1848,15 +1942,13 @@ impl<'db> TupleType<'db> {
 
 #[cfg(test)]
 mod tests {
-    use super::{
-        builtins_symbol_ty, BytesLiteralType, IntersectionBuilder, StringLiteralType, Truthiness,
-        TupleType, Type, UnionType,
-    };
+    use super::*;
     use crate::db::tests::TestDb;
     use crate::program::{Program, SearchPathSettings};
     use crate::python_version::PythonVersion;
     use crate::ProgramSettings;
     use ruff_db::system::{DbWithTestSystem, SystemPathBuf};
+    use ruff_python_ast as ast;
     use test_case::test_case;
 
     fn setup_db() -> TestDb {
@@ -2223,4 +2315,16 @@ mod tests {
 
         assert_eq!(ty.into_type(&db).repr(&db), expected.into_type(&db));
     }
+
+    #[test]
+    fn module_type_symbols_includes_declared_types_but_not_referenced_types() {
+        let db = setup_db();
+        let symbol_names = module_type_symbols(&db);
+
+        let dunder_name_symbol_name = ast::name::Name::new_static("__name__");
+        assert!(symbol_names.contains(&dunder_name_symbol_name));
+
+        let property_symbol_name = ast::name::Name::new_static("property");
+        assert!(!symbol_names.contains(&property_symbol_name));
+    }
 }

crates/ruff_benchmark/benches/red_knot.rs

@@ -23,8 +23,6 @@ struct Case {
 const TOMLLIB_312_URL: &str = "https://raw.githubusercontent.com/python/cpython/8e8a4baf652f6e1cee7acde9d78c4b6154539748/Lib/tomllib";
 
 static EXPECTED_DIAGNOSTICS: &[&str] = &[
-    // We don't support `ModuleType`-attributes as globals yet:
-    "/src/tomllib/__init__.py:10:30: Name `__name__` used when not defined",
     // We don't support `*` imports yet:
     "/src/tomllib/_parser.py:7:29: Module `collections.abc` has no member `Iterable`",
     // We don't support terminal statements in control flow yet: