[ty] Improve `@override`, `@final` and Liskov checks in cases where there are multiple reachable definitions (#21767)

crates/ty_ide/src/importer.rs

@@ -327,9 +327,7 @@ impl<'ast> MembersInScope<'ast> {
             .members_in_scope_at(node)
             .into_iter()
             .map(|(name, memberdef)| {
-                let Some(def) = memberdef.definition else {
+                let def = memberdef.first_reachable_definition;
-                    return (name, MemberInScope::other(memberdef.ty));
-                };
                 let kind = match *def.kind(db) {
                     DefinitionKind::Import(ref kind) => {
                         MemberImportKind::Imported(AstImportKind::Import(kind.import(parsed)))
@@ -1891,13 +1889,13 @@ else:
         "#);
         assert_snapshot!(
             test.import_from("foo", "MAGIC"), @r#"
-        import foo
+        from foo import MAGIC
         if os.getenv("WHATEVER"):
             from foo import MAGIC
         else:
             from bar import MAGIC
 
-        (foo.MAGIC)
+        (MAGIC)
         "#);
     }
 
@@ -2108,13 +2106,13 @@ except ImportError:
         ");
         assert_snapshot!(
             test.import_from("foo", "MAGIC"), @r"
-        import foo
+        from foo import MAGIC
         try:
             from foo import MAGIC
         except ImportError:
             from bar import MAGIC
 
-        (foo.MAGIC)
+        (MAGIC)
         ");
     }
 

crates/ty_python_semantic/resources/mdtest/final.md

@@ -488,11 +488,110 @@ class C(A):
         pass
 
     if coinflip():
-        def method2(self) -> None: ...  # TODO: should emit [override-of-final-method]
+        def method2(self) -> None: ...  # error: [override-of-final-method]
     else:
-        def method2(self) -> None: ...  # TODO: should emit [override-of-final-method]
+        def method2(self) -> None: ...
 
     if coinflip():
         def method3(self) -> None: ...  # error: [override-of-final-method]
-        def method4(self) -> None: ...  # error: [override-of-final-method]
+
+    # TODO: we should emit Liskov violations here too:
+    if coinflip():
+        method4 = 42  # error: [override-of-final-method]
+    else:
+        method4 = 56
+```
+
+## Definitions in statically known branches
+
+```toml
+[environment]
+python-version = "3.10"
+```
+
+```py
+import sys
+from typing_extensions import final
+
+class Parent:
+    if sys.version_info >= (3, 10):
+        @final
+        def foo(self) -> None: ...
+        @final
+        def foooo(self) -> None: ...
+        @final
+        def baaaaar(self) -> None: ...
+    else:
+        @final
+        def bar(self) -> None: ...
+        @final
+        def baz(self) -> None: ...
+        @final
+        def spam(self) -> None: ...
+
+class Child(Parent):
+    def foo(self) -> None: ...  # error: [override-of-final-method]
+
+    # The declaration on `Parent` is not reachable,
+    # so this is fine
+    def bar(self) -> None: ...
+
+    if sys.version_info >= (3, 10):
+        def foooo(self) -> None: ...  # error: [override-of-final-method]
+        def baz(self) -> None: ...
+    else:
+        # Fine because this doesn't override any reachable definitions
+        def foooo(self) -> None: ...
+        # There are `@final` definitions being overridden here,
+        # but the definitions that override them are unreachable
+        def spam(self) -> None: ...
+        def baaaaar(self) -> None: ...
+```
+
+## Overloads in statically-known branches in stub files
+
+<!-- snapshot-diagnostics -->
+
+```toml
+[environment]
+python-version = "3.10"
+```
+
+```pyi
+import sys
+from typing_extensions import overload, final
+
+class Foo:
+    if sys.version_info >= (3, 10):
+        @overload
+        @final
+        def method(self, x: int) -> int: ...
+    else:
+        @overload
+        def method(self, x: int) -> int: ...
+    @overload
+    def method(self, x: str) -> str: ...
+
+    if sys.version_info >= (3, 10):
+        @overload
+        def method2(self, x: int) -> int: ...
+    else:
+        @overload
+        @final
+        def method2(self, x: int) -> int: ...
+    @overload
+    def method2(self, x: str) -> str: ...
+
+class Bar(Foo):
+    @overload
+    def method(self, x: int) -> int: ...
+    @overload
+    def method(self, x: str) -> str: ...  # error: [override-of-final-method]
+
+    # This is fine: the only overload that is marked `@final`
+    # is in a statically-unreachable branch
+    @overload
+    def method2(self, x: int) -> int: ...
+    @overload
+    def method2(self, x: str) -> str: ...
 ```

crates/ty_python_semantic/resources/mdtest/liskov.md

@@ -583,3 +583,17 @@ class GoodChild2(Parent):
     @staticmethod
     def static_method(x: object) -> bool: ...
 ```
+
+## Definitely bound members with no reachable definitions(!)
+
+We don't emit a Liskov-violation diagnostic here, but if you're writing code like this, you probably
+have bigger problems:
+
+```py
+from __future__ import annotations
+
+class MaybeEqWhile:
+    while ...:
+        def __eq__(self, other: MaybeEqWhile) -> bool:
+            return True
+```

crates/ty_python_semantic/resources/mdtest/named_tuple.md

@@ -610,3 +610,24 @@ class Child(Base):
     # This is fine - Child is not directly a NamedTuple
     _asdict = 42
 ```
+
+## Edge case: multiple reachable definitions with distinct issues
+
+<!-- snapshot-diagnostics -->
+
+```py
+from typing import NamedTuple
+
+def coinflip() -> bool:
+    return True
+
+class Foo(NamedTuple):
+    if coinflip():
+        _asdict: bool  # error: [invalid-named-tuple] "NamedTuple field `_asdict` cannot start with an underscore"
+    else:
+        # TODO: there should only be one diagnostic here...
+        #
+        # error: [invalid-named-tuple] "Cannot overwrite NamedTuple attribute `_asdict`"
+        # error: [invalid-named-tuple] "Cannot overwrite NamedTuple attribute `_asdict`"
+        _asdict = True
+```

crates/ty_python_semantic/resources/mdtest/override.md

@@ -220,6 +220,178 @@ class Foo:
     def bar(self): ...  # error: [invalid-explicit-override]
 ```
 
+## Possibly-unbound definitions
+
+```py
+from typing_extensions import override
+
+def coinflip() -> bool:
+    return False
+
+class Parent:
+    if coinflip():
+        def method1(self) -> None: ...
+        def method2(self) -> None: ...
+
+    if coinflip():
+        def method3(self) -> None: ...
+        def method4(self) -> None: ...
+    else:
+        def method3(self) -> None: ...
+        def method4(self) -> None: ...
+
+    def method5(self) -> None: ...
+    def method6(self) -> None: ...
+
+class Child(Parent):
+    @override
+    def method1(self) -> None: ...
+    @override
+    def method2(self) -> None: ...
+
+    if coinflip():
+        @override
+        def method3(self) -> None: ...
+
+    if coinflip():
+        @override
+        def method4(self) -> None: ...
+    else:
+        @override
+        def method4(self) -> None: ...
+
+    if coinflip():
+        @override
+        def method5(self) -> None: ...
+
+    if coinflip():
+        @override
+        def method6(self) -> None: ...
+    else:
+        @override
+        def method6(self) -> None: ...
+
+    if coinflip():
+        @override
+        def method7(self) -> None: ...  # error: [invalid-explicit-override]
+
+    if coinflip():
+        @override
+        def method8(self) -> None: ...  # error: [invalid-explicit-override]
+    else:
+        @override
+        def method8(self) -> None: ...
+```
+
+## Multiple reachable definitions, only one of which is decorated with `@override`
+
+The diagnostic should point to the first definition decorated with `@override`, which may not
+necessarily be the first definition of the symbol overall:
+
+`runtime.py`:
+
+```py
+from typing_extensions import override, overload
+
+def coinflip() -> bool:
+    return True
+
+class Foo:
+    if coinflip():
+        def method(self, x): ...
+    elif coinflip():
+        @overload
+        def method(self, x: str) -> str: ...
+        @overload
+        def method(self, x: int) -> int: ...
+        @override
+        def method(self, x: str | int) -> str | int:  # error: [invalid-explicit-override]
+            return x
+    elif coinflip():
+        @override
+        def method(self, x): ...
+```
+
+stub.pyi\`:
+
+```pyi
+from typing_extensions import override, overload
+
+def coinflip() -> bool:
+    return True
+
+class Foo:
+    if coinflip():
+        def method(self, x): ...
+    elif coinflip():
+        @overload
+        @override
+        def method(self, x: str) -> str: ...  # error: [invalid-explicit-override]
+        @overload
+        def method(self, x: int) -> int: ...
+
+    if coinflip():
+        def method2(self, x): ...
+    elif coinflip():
+        @overload
+        @override
+        def method2(self, x: str) -> str: ...
+        @overload
+        def method2(self, x: int) -> int: ...
+    else:
+       # TODO: not sure why this is being emitted on this line rather than on
+       # the first overload in the `elif` block? Ideally it would be emitted
+       # on the first reachable definition, but perhaps this is due to the way
+       # name lookups are deferred in stub files...? -- AW
+       @override
+       def method2(self, x): ...  # error: [invalid-explicit-override]
+```
+
+## Definitions in statically known branches
+
+```toml
+[environment]
+python-version = "3.10"
+```
+
+```py
+import sys
+from typing_extensions import override, overload
+
+class Parent:
+    if sys.version_info >= (3, 10):
+        def foo(self) -> None: ...
+        def foooo(self) -> None: ...
+    else:
+        def bar(self) -> None: ...
+        def baz(self) -> None: ...
+        def spam(self) -> None: ...
+
+class Child(Parent):
+    @override
+    def foo(self) -> None: ...
+
+    # The declaration on `Parent` is not reachable,
+    # so this is an error
+    @override
+    def bar(self) -> None: ...  # error: [invalid-explicit-override]
+
+    if sys.version_info >= (3, 10):
+        @override
+        def foooo(self) -> None: ...
+        @override
+        def baz(self) -> None: ...  # error: [invalid-explicit-override]
+    else:
+        # This doesn't override any reachable definitions,
+        # but the subclass definition also isn't a reachable definition
+        # from the end of the scope with the given configuration,
+        # so it's not flagged
+        @override
+        def foooo(self) -> None: ...
+        @override
+        def spam(self) -> None: ...
+```
+
 ## Overloads
 
 The typing spec states that for an overloaded method, `@override` should only be applied to the
@@ -293,6 +465,39 @@ class Spam:
     def baz(self, x: int) -> int: ...
 ```
 
+## Overloads in statically-known branches in stub files
+
+```toml
+[environment]
+python-version = "3.10"
+```
+
+```pyi
+import sys
+from typing_extensions import overload, override
+
+class Foo:
+    if sys.version_info >= (3, 10):
+        @overload
+        @override
+        def method(self, x: int) -> int: ...  # error: [invalid-explicit-override]
+    else:
+        @overload
+        def method(self, x: int) -> int: ...
+    @overload
+    def method(self, x: str) -> str: ...
+
+    if sys.version_info >= (3, 10):
+        @overload
+        def method2(self, x: int) -> int: ...
+    else:
+        @overload
+        @override
+        def method2(self, x: int) -> int: ...
+    @overload
+    def method2(self, x: str) -> str: ...
+```
+
 ## Classes inheriting from `Any`
 
 ```py

crates/ty_python_semantic/resources/mdtest/snapshots/final.md_-_Tests_for_the_`@typi…_-_A_possibly-undefined…_(fc7b496fd1986deb).snap

@@ -65,13 +65,18 @@ mdtest path: crates/ty_python_semantic/resources/mdtest/final.md
 51 |         pass
 52 | 
 53 |     if coinflip():
-54 |         def method2(self) -> None: ...  # TODO: should emit [override-of-final-method]
+54 |         def method2(self) -> None: ...  # error: [override-of-final-method]
 55 |     else:
-56 |         def method2(self) -> None: ...  # TODO: should emit [override-of-final-method]
+56 |         def method2(self) -> None: ...
 57 | 
 58 |     if coinflip():
 59 |         def method3(self) -> None: ...  # error: [override-of-final-method]
-60 |         def method4(self) -> None: ...  # error: [override-of-final-method]
+60 | 
+61 |     # TODO: we should emit Liskov violations here too:
+62 |     if coinflip():
+63 |         method4 = 42  # error: [override-of-final-method]
+64 |     else:
+65 |         method4 = 56
 ```
 
 # Diagnostics
@@ -240,6 +245,33 @@ info: rule `override-of-final-method` is enabled by default
 
 ```
 
+```
+error[override-of-final-method]: Cannot override `A.method2`
+  --> src/mdtest_snippet.py:54:13
+   |
+53 |     if coinflip():
+54 |         def method2(self) -> None: ...  # error: [override-of-final-method]
+   |             ^^^^^^^ Overrides a definition from superclass `A`
+55 |     else:
+56 |         def method2(self) -> None: ...
+   |
+info: `A.method2` is decorated with `@final`, forbidding overrides
+  --> src/mdtest_snippet.py:16:9
+   |
+14 |         def method2(self) -> None: ...
+15 |     else:
+16 |         @final
+   |         ------
+17 |         def method2(self) -> None: ...
+   |             ------- `A.method2` defined here
+18 |
+19 |     if coinflip():
+   |
+help: Remove the override of `method2`
+info: rule `override-of-final-method` is enabled by default
+
+```
+
 ```
 error[override-of-final-method]: Cannot override `A.method3`
   --> src/mdtest_snippet.py:59:13
@@ -247,7 +279,8 @@ error[override-of-final-method]: Cannot override `A.method3`
 58 |     if coinflip():
 59 |         def method3(self) -> None: ...  # error: [override-of-final-method]
    |             ^^^^^^^ Overrides a definition from superclass `A`
-60 |         def method4(self) -> None: ...  # error: [override-of-final-method]
+60 |
+61 |     # TODO: we should emit Liskov violations here too:
    |
 info: `A.method3` is decorated with `@final`, forbidding overrides
   --> src/mdtest_snippet.py:20:9
@@ -267,12 +300,14 @@ info: rule `override-of-final-method` is enabled by default
 
 ```
 error[override-of-final-method]: Cannot override `A.method4`
-  --> src/mdtest_snippet.py:60:13
+  --> src/mdtest_snippet.py:63:9
    |
-58 |     if coinflip():
+61 |     # TODO: we should emit Liskov violations here too:
-59 |         def method3(self) -> None: ...  # error: [override-of-final-method]
+62 |     if coinflip():
-60 |         def method4(self) -> None: ...  # error: [override-of-final-method]
+63 |         method4 = 42  # error: [override-of-final-method]
-   |             ^^^^^^^ Overrides a definition from superclass `A`
+   |         ^^^^^^^ Overrides a definition from superclass `A`
+64 |     else:
+65 |         method4 = 56
    |
 info: `A.method4` is decorated with `@final`, forbidding overrides
   --> src/mdtest_snippet.py:29:9

crates/ty_python_semantic/resources/mdtest/snapshots/final.md_-_Tests_for_the_`@typi…_-_Overloads_in_statica…_(29a698d9deaf7318).snap

@@ -0,0 +1,94 @@
+---
+source: crates/ty_test/src/lib.rs
+expression: snapshot
+---
+---
+mdtest name: final.md - Tests for the `@typing(_extensions).final` decorator - Overloads in statically-known branches in stub files
+mdtest path: crates/ty_python_semantic/resources/mdtest/final.md
+---
+
+# Python source files
+
+## mdtest_snippet.pyi
+
+```
+ 1 | import sys
+ 2 | from typing_extensions import overload, final
+ 3 | 
+ 4 | class Foo:
+ 5 |     if sys.version_info >= (3, 10):
+ 6 |         @overload
+ 7 |         @final
+ 8 |         def method(self, x: int) -> int: ...
+ 9 |     else:
+10 |         @overload
+11 |         def method(self, x: int) -> int: ...
+12 |     @overload
+13 |     def method(self, x: str) -> str: ...
+14 | 
+15 |     if sys.version_info >= (3, 10):
+16 |         @overload
+17 |         def method2(self, x: int) -> int: ...
+18 |     else:
+19 |         @overload
+20 |         @final
+21 |         def method2(self, x: int) -> int: ...
+22 |     @overload
+23 |     def method2(self, x: str) -> str: ...
+24 | 
+25 | class Bar(Foo):
+26 |     @overload
+27 |     def method(self, x: int) -> int: ...
+28 |     @overload
+29 |     def method(self, x: str) -> str: ...  # error: [override-of-final-method]
+30 | 
+31 |     # This is fine: the only overload that is marked `@final`
+32 |     # is in a statically-unreachable branch
+33 |     @overload
+34 |     def method2(self, x: int) -> int: ...
+35 |     @overload
+36 |     def method2(self, x: str) -> str: ...
+```
+
+# Diagnostics
+
+```
+error[override-of-final-method]: Cannot override `Foo.method`
+  --> src/mdtest_snippet.pyi:29:9
+   |
+27 |     def method(self, x: int) -> int: ...
+28 |     @overload
+29 |     def method(self, x: str) -> str: ...  # error: [override-of-final-method]
+   |         ^^^^^^ Overrides a definition from superclass `Foo`
+30 |
+31 |     # This is fine: the only overload that is marked `@final`
+   |
+info: `Foo.method` is decorated with `@final`, forbidding overrides
+  --> src/mdtest_snippet.pyi:7:9
+   |
+ 5 |     if sys.version_info >= (3, 10):
+ 6 |         @overload
+ 7 |         @final
+   |         ------
+ 8 |         def method(self, x: int) -> int: ...
+   |             ------ `Foo.method` defined here
+ 9 |     else:
+10 |         @overload
+   |
+help: Remove all overloads for `method`
+info: rule `override-of-final-method` is enabled by default
+23 |     def method2(self, x: str) -> str: ...
+24 | 
+25 | class Bar(Foo):
+   -     @overload
+   -     def method(self, x: int) -> int: ...
+   -     @overload
+   -     def method(self, x: str) -> str: ...  # error: [override-of-final-method]
+26 +     
+27 +       # error: [override-of-final-method]
+28 | 
+29 |     # This is fine: the only overload that is marked `@final`
+30 |     # is in a statically-unreachable branch
+note: This is an unsafe fix and may change runtime behavior
+
+```

crates/ty_python_semantic/resources/mdtest/snapshots/named_tuple.md_-_`NamedTuple`_-_Edge_case___multiple_…_(f30babd05c89dce9).snap

@@ -0,0 +1,74 @@
+---
+source: crates/ty_test/src/lib.rs
+expression: snapshot
+---
+---
+mdtest name: named_tuple.md - `NamedTuple` - Edge case: multiple reachable definitions with distinct issues
+mdtest path: crates/ty_python_semantic/resources/mdtest/named_tuple.md
+---
+
+# Python source files
+
+## mdtest_snippet.py
+
+```
+ 1 | from typing import NamedTuple
+ 2 | 
+ 3 | def coinflip() -> bool:
+ 4 |     return True
+ 5 | 
+ 6 | class Foo(NamedTuple):
+ 7 |     if coinflip():
+ 8 |         _asdict: bool  # error: [invalid-named-tuple] "NamedTuple field `_asdict` cannot start with an underscore"
+ 9 |     else:
+10 |         # TODO: there should only be one diagnostic here...
+11 |         #
+12 |         # error: [invalid-named-tuple] "Cannot overwrite NamedTuple attribute `_asdict`"
+13 |         # error: [invalid-named-tuple] "Cannot overwrite NamedTuple attribute `_asdict`"
+14 |         _asdict = True
+```
+
+# Diagnostics
+
+```
+error[invalid-named-tuple]: NamedTuple field name cannot start with an underscore
+  --> src/mdtest_snippet.py:8:9
+   |
+ 6 | class Foo(NamedTuple):
+ 7 |     if coinflip():
+ 8 |         _asdict: bool  # error: [invalid-named-tuple] "NamedTuple field `_asdict` cannot start with an underscore"
+   |         ^^^^^^^^^^^^^ Class definition will raise `TypeError` at runtime due to this field
+ 9 |     else:
+10 |         # TODO: there should only be one diagnostic here...
+   |
+info: rule `invalid-named-tuple` is enabled by default
+
+```
+
+```
+error[invalid-named-tuple]: Cannot overwrite NamedTuple attribute `_asdict`
+  --> src/mdtest_snippet.py:14:9
+   |
+12 |         # error: [invalid-named-tuple] "Cannot overwrite NamedTuple attribute `_asdict`"
+13 |         # error: [invalid-named-tuple] "Cannot overwrite NamedTuple attribute `_asdict`"
+14 |         _asdict = True
+   |         ^^^^^^^
+   |
+info: This will cause the class creation to fail at runtime
+info: rule `invalid-named-tuple` is enabled by default
+
+```
+
+```
+error[invalid-named-tuple]: Cannot overwrite NamedTuple attribute `_asdict`
+  --> src/mdtest_snippet.py:14:9
+   |
+12 |         # error: [invalid-named-tuple] "Cannot overwrite NamedTuple attribute `_asdict`"
+13 |         # error: [invalid-named-tuple] "Cannot overwrite NamedTuple attribute `_asdict`"
+14 |         _asdict = True
+   |         ^^^^^^^
+   |
+info: This will cause the class creation to fail at runtime
+info: rule `invalid-named-tuple` is enabled by default
+
+```

crates/ty_python_semantic/src/place.rs

@@ -459,7 +459,7 @@ fn core_module_scope(db: &dyn Db, core_module: KnownModule) -> Option<ScopeId<'_
 pub(super) fn place_from_bindings<'db>(
     db: &'db dyn Db,
     bindings_with_constraints: BindingWithConstraintsIterator<'_, 'db>,
-) -> Place<'db> {
+) -> PlaceWithDefinition<'db> {
     place_from_bindings_impl(db, bindings_with_constraints, RequiresExplicitReExport::No)
 }
 
@@ -487,20 +487,21 @@ type DeclaredTypeAndConflictingTypes<'db> = (
 pub(crate) struct PlaceFromDeclarationsResult<'db> {
     place_and_quals: PlaceAndQualifiers<'db>,
     conflicting_types: Option<Box<indexmap::set::Slice<Type<'db>>>>,
-    /// Contains `Some(declaration)` if the declared type originates from exactly one declaration.
+    /// Contains the first reachable declaration for this place, if any.
     /// This field is used for backreferences in diagnostics.
-    pub(crate) single_declaration: Option<Definition<'db>>,
+    pub(crate) first_declaration: Option<Definition<'db>>,
 }
 
 impl<'db> PlaceFromDeclarationsResult<'db> {
     fn conflict(
         place_and_quals: PlaceAndQualifiers<'db>,
         conflicting_types: Box<indexmap::set::Slice<Type<'db>>>,
+        first_declaration: Option<Definition<'db>>,
     ) -> Self {
         PlaceFromDeclarationsResult {
             place_and_quals,
             conflicting_types: Some(conflicting_types),
-            single_declaration: None,
+            first_declaration,
         }
     }
 
@@ -798,6 +799,7 @@ pub(crate) fn place_by_id<'db>(
     if let Some(qualifiers) = declared.is_bare_final() {
         let bindings = all_considered_bindings();
         return place_from_bindings_impl(db, bindings, requires_explicit_reexport)
+            .place
             .with_qualifiers(qualifiers);
     }
 
@@ -809,7 +811,7 @@ pub(crate) fn place_by_id<'db>(
             qualifiers,
         } if qualifiers.contains(TypeQualifiers::CLASS_VAR) => {
             let bindings = all_considered_bindings();
-            match place_from_bindings_impl(db, bindings, requires_explicit_reexport) {
+            match place_from_bindings_impl(db, bindings, requires_explicit_reexport).place {
                 Place::Defined(inferred, origin, boundness) => Place::Defined(
                     UnionType::from_elements(db, [Type::unknown(), inferred]),
                     origin,
@@ -835,7 +837,7 @@ pub(crate) fn place_by_id<'db>(
             let boundness_analysis = bindings.boundness_analysis;
             let inferred = place_from_bindings_impl(db, bindings, requires_explicit_reexport);
 
-            let place = match inferred {
+            let place = match inferred.place {
                 // Place is possibly undeclared and definitely unbound
                 Place::Undefined => {
                     // TODO: We probably don't want to report `AlwaysDefined` here. This requires a bit of
@@ -864,7 +866,8 @@ pub(crate) fn place_by_id<'db>(
         } => {
             let bindings = all_considered_bindings();
             let boundness_analysis = bindings.boundness_analysis;
-            let mut inferred = place_from_bindings_impl(db, bindings, requires_explicit_reexport);
+            let mut inferred =
+                place_from_bindings_impl(db, bindings, requires_explicit_reexport).place;
 
             if boundness_analysis == BoundnessAnalysis::AssumeBound {
                 if let Place::Defined(ty, origin, Definedness::PossiblyUndefined) = inferred {
@@ -1010,7 +1013,7 @@ fn place_from_bindings_impl<'db>(
     db: &'db dyn Db,
     bindings_with_constraints: BindingWithConstraintsIterator<'_, 'db>,
     requires_explicit_reexport: RequiresExplicitReExport,
-) -> Place<'db> {
+) -> PlaceWithDefinition<'db> {
     let predicates = bindings_with_constraints.predicates;
     let reachability_constraints = bindings_with_constraints.reachability_constraints;
     let boundness_analysis = bindings_with_constraints.boundness_analysis;
@@ -1039,6 +1042,8 @@ fn place_from_bindings_impl<'db>(
         })
     };
 
+    let mut first_definition = None;
+
     let mut types = bindings_with_constraints.filter_map(
         |BindingWithConstraints {
              binding,
@@ -1119,12 +1124,13 @@ fn place_from_bindings_impl<'db>(
                 return None;
             }
 
+            first_definition.get_or_insert(binding);
             let binding_ty = binding_type(db, binding);
             Some(narrowing_constraint.narrow(db, binding_ty, binding.place(db)))
         },
     );
 
-    if let Some(first) = types.next() {
+    let place = if let Some(first) = types.next() {
         let ty = if let Some(second) = types.next() {
             let mut builder = PublicTypeBuilder::new(db);
             builder.add(first);
@@ -1161,9 +1167,19 @@ fn place_from_bindings_impl<'db>(
         }
     } else {
         Place::Undefined
+    };
+
+    PlaceWithDefinition {
+        place,
+        first_definition,
     }
 }
 
+pub(super) struct PlaceWithDefinition<'db> {
+    pub(super) place: Place<'db>,
+    pub(super) first_definition: Option<Definition<'db>>,
+}
+
 /// Accumulates types from multiple bindings or declarations, and eventually builds a
 /// union type from them.
 ///
@@ -1294,7 +1310,6 @@ fn place_from_declarations_impl<'db>(
     let boundness_analysis = declarations.boundness_analysis;
     let mut declarations = declarations.peekable();
     let mut first_declaration = None;
-    let mut exactly_one_declaration = false;
 
     let is_non_exported = |declaration: Definition<'db>| {
         requires_explicit_reexport.is_yes() && !is_reexported(db, declaration)
@@ -1325,12 +1340,7 @@ fn place_from_declarations_impl<'db>(
                 return None;
             }
 
-            if first_declaration.is_none() {
+            first_declaration.get_or_insert(declaration);
-                first_declaration = Some(declaration);
-                exactly_one_declaration = true;
-            } else {
-                exactly_one_declaration = false;
-            }
 
             let static_reachability =
                 reachability_constraints.evaluate(db, predicates, reachability_constraint);
@@ -1387,19 +1397,19 @@ fn place_from_declarations_impl<'db>(
                 .with_qualifiers(declared.qualifiers());
 
         if let Some(conflicting) = conflicting {
-            PlaceFromDeclarationsResult::conflict(place_and_quals, conflicting)
+            PlaceFromDeclarationsResult::conflict(place_and_quals, conflicting, first_declaration)
         } else {
             PlaceFromDeclarationsResult {
                 place_and_quals,
                 conflicting_types: None,
-                single_declaration: first_declaration.filter(|_| exactly_one_declaration),
+                first_declaration,
             }
         }
     } else {
         PlaceFromDeclarationsResult {
             place_and_quals: Place::Undefined.into(),
             conflicting_types: None,
-            single_declaration: None,
+            first_declaration: None,
         }
     }
 }

crates/ty_python_semantic/src/semantic_model.rs

@@ -82,7 +82,7 @@ impl<'db> SemanticModel<'db> {
                     memberdef.member.name,
                     MemberDefinition {
                         ty: memberdef.member.ty,
-                        definition: memberdef.definition,
+                        first_reachable_definition: memberdef.first_reachable_definition,
                     },
                 );
             }
@@ -328,11 +328,11 @@ impl<'db> SemanticModel<'db> {
     }
 }
 
-/// The type and definition (if available) of a symbol.
+/// The type and definition of a symbol.
 #[derive(Clone, Debug)]
 pub struct MemberDefinition<'db> {
     pub ty: Type<'db>,
-    pub definition: Option<Definition<'db>>,
+    pub first_reachable_definition: Definition<'db>,
 }
 
 /// A classification of symbol names.

crates/ty_python_semantic/src/types/class.rs

@@ -1375,9 +1375,9 @@ pub(crate) struct Field<'db> {
     pub(crate) declared_ty: Type<'db>,
     /// Kind-specific metadata for this field
     pub(crate) kind: FieldKind<'db>,
-    /// The original declaration of this field, if there is exactly one.
+    /// The first declaration of this field.
     /// This field is used for backreferences in diagnostics.
-    pub(crate) single_declaration: Option<Definition<'db>>,
+    pub(crate) first_declaration: Option<Definition<'db>>,
 }
 
 impl Field<'_> {
@@ -3039,7 +3039,7 @@ impl<'db> ClassLiteral<'db> {
             let symbol = table.symbol(symbol_id);
 
             let result = place_from_declarations(db, declarations.clone());
-            let single_declaration = result.single_declaration;
+            let first_declaration = result.first_declaration;
             let attr = result.ignore_conflicting_declarations();
             if attr.is_class_var() {
                 continue;
@@ -3047,7 +3047,9 @@ impl<'db> ClassLiteral<'db> {
 
             if let Some(attr_ty) = attr.place.ignore_possibly_undefined() {
                 let bindings = use_def.end_of_scope_symbol_bindings(symbol_id);
-                let mut default_ty = place_from_bindings(db, bindings).ignore_possibly_undefined();
+                let mut default_ty = place_from_bindings(db, bindings)
+                    .place
+                    .ignore_possibly_undefined();
 
                 default_ty =
                     default_ty.map(|ty| ty.apply_optional_specialization(db, specialization));
@@ -3105,7 +3107,7 @@ impl<'db> ClassLiteral<'db> {
                 let mut field = Field {
                     declared_ty: attr_ty.apply_optional_specialization(db, specialization),
                     kind,
-                    single_declaration,
+                    first_declaration,
                 };
 
                 // Check if this is a KW_ONLY sentinel and mark subsequent fields as keyword-only
@@ -3588,7 +3590,7 @@ impl<'db> ClassLiteral<'db> {
                     // The attribute is declared in the class body.
 
                     let bindings = use_def.end_of_scope_symbol_bindings(symbol_id);
-                    let inferred = place_from_bindings(db, bindings);
+                    let inferred = place_from_bindings(db, bindings).place;
                     let has_binding = !inferred.is_undefined();
 
                     if has_binding {
@@ -3831,7 +3833,9 @@ impl<'db> VarianceInferable<'db> for ClassLiteral<'db> {
                     (symbol_id, place_and_qual)
                 })
                 .chain(use_def_map.all_end_of_scope_symbol_bindings().map(
-                    |(symbol_id, bindings)| (symbol_id, place_from_bindings(db, bindings).into()),
+                    |(symbol_id, bindings)| {
+                        (symbol_id, place_from_bindings(db, bindings).place.into())
+                    },
                 ))
                 .filter_map(|(symbol_id, place_and_qual)| {
                     if let Some(name) = table.place(symbol_id).as_symbol().map(Symbol::name) {

crates/ty_python_semantic/src/types/enums.rs

@@ -77,7 +77,7 @@ pub(crate) fn enum_metadata<'db>(
 
     let ignored_names: Option<Vec<&str>> = if let Some(ignore) = table.symbol_id("_ignore_") {
         let ignore_bindings = use_def_map.all_reachable_symbol_bindings(ignore);
-        let ignore_place = place_from_bindings(db, ignore_bindings);
+        let ignore_place = place_from_bindings(db, ignore_bindings).place;
 
         match ignore_place {
             Place::Defined(Type::StringLiteral(ignored_names), _, _) => {
@@ -111,7 +111,7 @@ pub(crate) fn enum_metadata<'db>(
                 return None;
             }
 
-            let inferred = place_from_bindings(db, bindings);
+            let inferred = place_from_bindings(db, bindings).place;
 
             let value_ty = match inferred {
                 Place::Undefined => {

crates/ty_python_semantic/src/types/function.rs

@@ -373,7 +373,7 @@ impl<'db> OverloadLiteral<'db> {
             .scoped_use_id(db, scope);
 
         let Place::Defined(Type::FunctionLiteral(previous_type), _, Definedness::AlwaysDefined) =
-            place_from_bindings(db, use_def.bindings_at_use(use_id))
+            place_from_bindings(db, use_def.bindings_at_use(use_id)).place
         else {
             return None;
         };

crates/ty_python_semantic/src/types/infer/builder.rs

@@ -634,7 +634,7 @@ impl<'db, 'ast> TypeInferenceBuilder<'db, 'ast> {
                             &self.context,
                             class,
                             &field_name,
-                            field.single_declaration,
+                            field.first_declaration,
                         );
                     }
 
@@ -645,13 +645,13 @@ impl<'db, 'ast> TypeInferenceBuilder<'db, 'ast> {
                         }
                     ) {
                         field_with_default_encountered =
-                            Some((field_name, field.single_declaration));
+                            Some((field_name, field.first_declaration));
                     } else if let Some(field_with_default) = field_with_default_encountered.as_ref()
                     {
                         report_namedtuple_field_without_default_after_field_with_default(
                             &self.context,
                             class,
-                            (&field_name, field.single_declaration),
+                            (&field_name, field.first_declaration),
                             field_with_default,
                         );
                     }
@@ -1034,6 +1034,7 @@ impl<'db, 'ast> TypeInferenceBuilder<'db, 'ast> {
                     self.db(),
                     use_def.end_of_scope_symbol_bindings(place.as_symbol().unwrap()),
                 )
+                .place
             {
                 if function.file(self.db()) != self.file() {
                     // If the function is not in this file, we don't need to check it.
@@ -1727,6 +1728,7 @@ impl<'db, 'ast> TypeInferenceBuilder<'db, 'ast> {
         let prior_bindings = use_def.bindings_at_definition(declaration);
         // unbound_ty is Never because for this check we don't care about unbound
         let inferred_ty = place_from_bindings(self.db(), prior_bindings)
+            .place
             .with_qualifiers(TypeQualifiers::empty())
             .or_fall_back_to(self.db(), || {
                 // Fallback to bindings declared on `types.ModuleType` if it's a global symbol
@@ -8673,7 +8675,7 @@ impl<'db, 'ast> TypeInferenceBuilder<'db, 'ast> {
         // If we're inferring types of deferred expressions, look them up from end-of-scope.
         if self.is_deferred() {
             let place = if let Some(place_id) = place_table.place_id(expr) {
-                place_from_bindings(db, use_def.all_reachable_bindings(place_id))
+                place_from_bindings(db, use_def.all_reachable_bindings(place_id)).place
             } else {
                 assert!(
                     self.deferred_state.in_string_annotation(),
@@ -8691,7 +8693,7 @@ impl<'db, 'ast> TypeInferenceBuilder<'db, 'ast> {
             }
 
             let use_id = expr_ref.scoped_use_id(db, scope);
-            let place = place_from_bindings(db, use_def.bindings_at_use(use_id));
+            let place = place_from_bindings(db, use_def.bindings_at_use(use_id)).place;
 
             (place, Some(use_id))
         }
@@ -8832,7 +8834,7 @@ impl<'db, 'ast> TypeInferenceBuilder<'db, 'ast> {
                             }
                         }
                         EnclosingSnapshotResult::FoundBindings(bindings) => {
-                            let place = place_from_bindings(db, bindings).map_type(|ty| {
+                            let place = place_from_bindings(db, bindings).place.map_type(|ty| {
                                 self.narrow_place_with_applicable_constraints(
                                     place_expr,
                                     ty,
@@ -8952,13 +8954,14 @@ impl<'db, 'ast> TypeInferenceBuilder<'db, 'ast> {
                                 return Place::Undefined.into();
                             }
                             EnclosingSnapshotResult::FoundBindings(bindings) => {
-                                let place = place_from_bindings(db, bindings).map_type(|ty| {
+                                let place =
-                                    self.narrow_place_with_applicable_constraints(
+                                    place_from_bindings(db, bindings).place.map_type(|ty| {
-                                        place_expr,
+                                        self.narrow_place_with_applicable_constraints(
-                                        ty,
+                                            place_expr,
-                                        &constraint_keys,
+                                            ty,
-                                    )
+                                            &constraint_keys,
-                                });
+                                        )
+                                    });
                                 constraint_keys.push((
                                     FileScopeId::global(),
                                     ConstraintKey::NestedScope(file_scope_id),

crates/ty_python_semantic/src/types/list_members.rs

@@ -12,7 +12,9 @@ use rustc_hash::FxHashSet;
 
 use crate::{
     Db, NameKind,
-    place::{Place, imported_symbol, place_from_bindings, place_from_declarations},
+    place::{
+        Place, PlaceWithDefinition, imported_symbol, place_from_bindings, place_from_declarations,
+    },
     semantic_index::{
         attribute_scopes, definition::Definition, global_scope, place_table, scope::ScopeId,
         semantic_index, use_def_map,
@@ -35,48 +37,40 @@ pub(crate) fn all_members_of_scope<'db>(
         .all_end_of_scope_symbol_declarations()
         .filter_map(move |(symbol_id, declarations)| {
             let place_result = place_from_declarations(db, declarations);
-            let definition = place_result.single_declaration;
+            let first_reachable_definition = place_result.first_declaration?;
-            place_result
+            let ty = place_result
                 .ignore_conflicting_declarations()
                 .place
-                .ignore_possibly_undefined()
+                .ignore_possibly_undefined()?;
-                .map(|ty| {
+            let symbol = table.symbol(symbol_id);
-                    let symbol = table.symbol(symbol_id);
+            let member = Member {
-                    let member = Member {
+                name: symbol.name().clone(),
-                        name: symbol.name().clone(),
+                ty,
-                        ty,
+            };
-                    };
+            Some(MemberWithDefinition {
-                    MemberWithDefinition { member, definition }
+                member,
-                })
+                first_reachable_definition,
+            })
         })
         .chain(use_def_map.all_end_of_scope_symbol_bindings().filter_map(
             move |(symbol_id, bindings)| {
-                // It's not clear to AG how to using a bindings
+                let PlaceWithDefinition {
-                // iterator here to get the correct definition for
+                    place,
-                // this binding. Below, we look through all bindings
+                    first_definition,
-                // with a definition and only take one if there is
+                } = place_from_bindings(db, bindings);
-                // exactly one. I don't think this can be wrong, but
+
-                // it's probably omitting definitions in some cases.
+                let first_reachable_definition = first_definition?;
-                let mut definition = None;
+                let ty = place.ignore_possibly_undefined()?;
-                for binding in bindings.clone() {
+
-                    if let Some(def) = binding.binding.definition() {
+                let symbol = table.symbol(symbol_id);
-                        if definition.is_some() {
+                let member = Member {
-                            definition = None;
+                    name: symbol.name().clone(),
-                            break;
+                    ty,
-                        }
+                };
-                        definition = Some(def);
+                Some(MemberWithDefinition {
-                    }
+                    member,
-                }
+                    first_reachable_definition,
-                place_from_bindings(db, bindings)
+                })
-                    .ignore_possibly_undefined()
-                    .map(|ty| {
-                        let symbol = table.symbol(symbol_id);
-                        let member = Member {
-                            name: symbol.name().clone(),
-                            ty,
-                        };
-                        MemberWithDefinition { member, definition }
-                    })
             },
         ))
 }
@@ -457,11 +451,11 @@ impl<'db> AllMembers<'db> {
     }
 }
 
-/// A member of a type or scope, with an optional definition.
+/// A member of a type or scope, with the first reachable definition of that member.
 #[derive(Clone, Debug, Eq, PartialEq, Hash)]
 pub struct MemberWithDefinition<'db> {
     pub member: Member<'db>,
-    pub definition: Option<Definition<'db>>,
+    pub first_reachable_definition: Definition<'db>,
 }
 
 /// A member of a type or scope.

crates/ty_python_semantic/src/types/member.rs

@@ -75,7 +75,7 @@ pub(super) fn class_member<'db>(db: &'db dyn Db, scope: ScopeId<'db>, name: &str
                 // Otherwise, we need to check if the symbol has bindings
                 let use_def = use_def_map(db, scope);
                 let bindings = use_def.end_of_scope_symbol_bindings(symbol_id);
-                let inferred = place_from_bindings(db, bindings);
+                let inferred = place_from_bindings(db, bindings).place;
 
                 // TODO: we should not need to calculate inferred type second time. This is a temporary
                 // solution until the notion of Boundness and Declaredness is split. See #16036, #16264

crates/ty_python_semantic/src/types/overrides.rs

@@ -12,8 +12,8 @@ use crate::{
     lint::LintId,
     place::Place,
     semantic_index::{
-        definition::DefinitionKind, place_table, scope::ScopeId, symbol::ScopedSymbolId,
+        definition::DefinitionKind, place::ScopedPlaceId, place_table, scope::ScopeId,
-        use_def_map,
+        symbol::ScopedSymbolId, use_def_map,
     },
     types::{
         ClassBase, ClassLiteral, ClassType, KnownClass, Type,
@@ -53,10 +53,11 @@ pub(super) fn check_class<'db>(context: &InferContext<'db, '_>, class: ClassLite
     }
 
     let class_specialized = class.identity_specialization(db);
-    let own_class_members: FxHashSet<_> = all_members_of_scope(db, class.body_scope(db)).collect();
+    let scope = class.body_scope(db);
+    let own_class_members: FxHashSet<_> = all_members_of_scope(db, scope).collect();
 
     for member in own_class_members {
-        check_class_declaration(context, configuration, class_specialized, &member);
+        check_class_declaration(context, configuration, class_specialized, scope, &member);
     }
 }
 
@@ -64,6 +65,7 @@ fn check_class_declaration<'db>(
     context: &InferContext<'db, '_>,
     configuration: OverrideRulesConfig,
     class: ClassType<'db>,
+    class_scope: ScopeId<'db>,
     member: &MemberWithDefinition<'db>,
 ) {
     /// Salsa-tracked query to check whether any of the definitions of a symbol
@@ -103,11 +105,10 @@ fn check_class_declaration<'db>(
 
     let db = context.db();
 
-    let MemberWithDefinition { member, definition } = member;
+    let MemberWithDefinition {
-
+        member,
-    let Some(definition) = definition else {
+        first_reachable_definition,
-        return;
+    } = member;
-    };
 
     let Place::Defined(type_on_subclass_instance, _, _) =
         Type::instance(db, class).member(db, &member.name).place
@@ -126,12 +127,14 @@ fn check_class_declaration<'db>(
     if class_kind == Some(CodeGeneratorKind::NamedTuple)
         && configuration.check_prohibited_named_tuple_attrs()
         && PROHIBITED_NAMEDTUPLE_ATTRS.contains(&member.name.as_str())
-        // accessing `.kind()` here is fine as `definition`
+        && let Some(symbol_id) = place_table(db, class_scope).symbol_id(&member.name)
-        // will always be a definition in the file currently being checked
+        && let Some(bad_definition) = use_def_map(db, class_scope)
-        && !matches!(definition.kind(db), DefinitionKind::AnnotatedAssignment(_))
+            .all_reachable_bindings(ScopedPlaceId::Symbol(symbol_id))
+            .filter_map(|binding| binding.binding.definition())
+            .find(|def| !matches!(def.kind(db), DefinitionKind::AnnotatedAssignment(_)))
         && let Some(builder) = context.report_lint(
             &INVALID_NAMED_TUPLE,
-            definition.focus_range(db, context.module()),
+            bad_definition.focus_range(db, context.module()),
         )
     {
         let mut diagnostic = builder.into_diagnostic(format_args!(
@@ -187,8 +190,6 @@ fn check_class_declaration<'db>(
                     .unwrap_or_default();
         }
 
-        subclass_overrides_superclass_declaration = true;
-
         let Place::Defined(superclass_type, _, _) = Type::instance(db, superclass)
             .member(db, &member.name)
             .place
@@ -197,6 +198,8 @@ fn check_class_declaration<'db>(
             break;
         };
 
+        subclass_overrides_superclass_declaration = true;
+
         if configuration.check_final_method_overridden() {
             overridden_final_method = overridden_final_method.or_else(|| {
                 let superclass_symbol_id = superclass_symbol_id?;
@@ -272,7 +275,7 @@ fn check_class_declaration<'db>(
             context,
             &member.name,
             class,
-            *definition,
+            *first_reachable_definition,
             subclass_function,
             superclass,
             superclass_type,
@@ -308,7 +311,7 @@ fn check_class_declaration<'db>(
         && !has_dynamic_superclass
         // accessing `.kind()` here is fine as `definition`
         // will always be a definition in the file currently being checked
-        && definition.kind(db).is_function_def()
+        && first_reachable_definition.kind(db).is_function_def()
     {
         check_explicit_overrides(context, member, class);
     }
@@ -317,7 +320,7 @@ fn check_class_declaration<'db>(
         report_overridden_final_method(
             context,
             &member.name,
-            *definition,
+            *first_reachable_definition,
             member.ty,
             superclass,
             class,
@@ -396,16 +399,16 @@ fn check_explicit_overrides<'db>(
     let Some(functions) = underlying_functions else {
         return;
     };
-    if !functions
+    let Some(decorated_function) = functions
         .iter()
-        .any(|function| function.has_known_decorator(db, FunctionDecorators::OVERRIDE))
+        .find(|function| function.has_known_decorator(db, FunctionDecorators::OVERRIDE))
-    {
+    else {
         return;
-    }
+    };
     let function_literal = if context.in_stub() {
-        functions[0].first_overload_or_implementation(db)
+        decorated_function.first_overload_or_implementation(db)
     } else {
-        functions[0].literal(db).last_definition(db)
+        decorated_function.literal(db).last_definition(db)
     };
 
     let Some(builder) = context.report_lint(

crates/ty_python_semantic/src/types/protocol_class.rs

@@ -896,7 +896,10 @@ fn cached_protocol_interface<'db>(
         // type narrowing that uses `isinstance()` or `issubclass()` with
         // runtime-checkable protocols.
         for (symbol_id, bindings) in use_def_map.all_end_of_scope_symbol_bindings() {
-            let Some(ty) = place_from_bindings(db, bindings).ignore_possibly_undefined() else {
+            let Some(ty) = place_from_bindings(db, bindings)
+                .place
+                .ignore_possibly_undefined()
+            else {
                 continue;
             };
             direct_members.insert(

crates/ty_python_semantic/src/types/typed_dict.rs

@@ -365,7 +365,7 @@ pub(super) fn validate_typed_dict_key_assignment<'db, 'ast>(
         };
 
     let add_item_definition_subdiagnostic = |diagnostic: &mut Diagnostic, message| {
-        if let Some(declaration) = item.single_declaration {
+        if let Some(declaration) = item.first_declaration {
             let file = declaration.file(db);
             let module = parsed_module(db, file).load(db);