[ty] Evaluate reachability of non-definitely-bound to Ambiguous

crates/ty_python_semantic/resources/mdtest/attributes.md

@@ -2288,6 +2288,26 @@ class H:
         self.x = other.x or self.x
 ```
 
+An attribute definition can be guarded by a condition involving that attribute. This is a regression
+test for <https://github.com/astral-sh/ty/issues/692>:
+
+```py
+from typing import Literal
+
+def check(x) -> Literal[False]:
+    return False
+
+class Toggle:
+    def __init__(self: "Toggle"):
+        if not self.x:
+            self.x: Literal[True] = True
+        if check(self.y):
+            self.y = True
+
+reveal_type(Toggle().x)  # revealed: Literal[True]
+reveal_type(Toggle().y)  # revealed:  Unknown | Literal[True]
+```
+
 ### Builtin types attributes
 
 This test can probably be removed eventually, but we currently include it because we do not yet

crates/ty_python_semantic/resources/mdtest/statically_known_branches.md

@@ -1564,6 +1564,25 @@ if True:
 from module import symbol
 ```
 
+## Non-definitely bound symbols in conditions
+
+When a non-definitely bound symbol is used as a (part of a) condition, we always infer an ambiguous
+truthiness. If we wouldn't do that, `x` would be considered definitely bound in the following
+example:
+
+```py
+def _(flag: bool):
+    if flag:
+        ALWAYS_TRUE_IF_BOUND = True
+
+    # error: [possibly-unresolved-reference] "Name `ALWAYS_TRUE_IF_BOUND` used when possibly not defined"
+    if True and ALWAYS_TRUE_IF_BOUND:
+        x = 1
+
+    # error: [possibly-unresolved-reference] "Name `x` used when possibly not defined"
+    x
+```
+
 ## Unreachable code
 
 A closely related feature is the ability to detect unreachable code. For example, we do not emit a

crates/ty_python_semantic/src/place.rs

@@ -135,6 +135,10 @@ impl<'db> Place<'db> {
             Place::Unbound => Place::Unbound,
         }
     }
+
+    pub(crate) fn is_definitely_bound(&self) -> bool {
+        matches!(self, Place::Type(_, Boundness::Bound))
+    }
 }
 
 impl<'db> From<LookupResult<'db>> for PlaceAndQualifiers<'db> {

crates/ty_python_semantic/src/semantic_index/reachability_constraints.rs

@@ -209,6 +209,7 @@ use crate::semantic_index::predicate::{
 };
 use crate::types::{
     IntersectionBuilder, Truthiness, Type, UnionBuilder, UnionType, infer_expression_type,
+    static_expression_truthiness,
 };
 
 /// A ternary formula that defines under what conditions a binding is visible. (A ternary formula
@@ -821,8 +822,7 @@ impl ReachabilityConstraints {
     fn analyze_single(db: &dyn Db, predicate: &Predicate) -> Truthiness {
         match predicate.node {
             PredicateNode::Expression(test_expr) => {
-                let ty = infer_expression_type(db, test_expr);
-                ty.bool(db).negate_if(!predicate.is_positive)
+                static_expression_truthiness(db, test_expr).negate_if(!predicate.is_positive)
             }
             PredicateNode::ReturnsNever(CallableAndCallExpr {
                 callable,

crates/ty_python_semantic/src/semantic_index/use_def.rs

@@ -598,7 +598,7 @@ impl<'db> UseDefMap<'db> {
             .is_always_false()
     }
 
-    pub(crate) fn is_declaration_reachable(
+    pub(crate) fn declaration_reachability(
         &self,
         db: &dyn crate::Db,
         declaration: &DeclarationWithConstraint<'db>,
@@ -610,7 +610,7 @@ impl<'db> UseDefMap<'db> {
         )
     }
 
-    pub(crate) fn is_binding_reachable(
+    pub(crate) fn binding_reachability(
         &self,
         db: &dyn crate::Db,
         binding: &BindingWithConstraints<'_, 'db>,

crates/ty_python_semantic/src/types.rs

@@ -24,7 +24,7 @@ pub use self::diagnostic::TypeCheckDiagnostics;
 pub(crate) use self::diagnostic::register_lints;
 pub(crate) use self::infer::{
     infer_deferred_types, infer_definition_types, infer_expression_type, infer_expression_types,
-    infer_scope_types,
+    infer_scope_types, static_expression_truthiness,
 };
 pub(crate) use self::signatures::{CallableSignature, Signature};
 pub(crate) use self::subclass_of::{SubclassOfInner, SubclassOfType};
@@ -6910,6 +6910,10 @@ bitflags! {
         const NOT_REQUIRED = 1 << 4;
         /// `typing_extensions.ReadOnly`
         const READ_ONLY = 1 << 5;
+        /// An implicit instance attribute which is possibly unbound according
+        /// to local control flow within the method it is defined in. This flag
+        /// overrules the `Boundness` information on `PlaceAndQualifiers`.
+        const POSSIBLY_UNBOUND_IMPLICIT_ATTRIBUTE = 1 << 6;
     }
 }
 
@@ -8630,6 +8634,8 @@ pub enum Truthiness {
     Ambiguous,
 }
 
+impl get_size2::GetSize for Truthiness {}
+
 impl Truthiness {
     pub(crate) const fn is_ambiguous(self) -> bool {
         matches!(self, Truthiness::Ambiguous)

crates/ty_python_semantic/src/types/class.rs

@@ -2736,17 +2736,20 @@ impl<'db> ClassLiteral<'db> {
                 //     self.name: <annotation>
                 //     self.name: <annotation> = …
 
-                if use_def_map(db, method_scope)
-                    .is_declaration_reachable(db, &attribute_declaration)
-                    .is_always_false()
-                {
+                let reachability = use_def_map(db, method_scope)
+                    .declaration_reachability(db, &attribute_declaration);
+
+                if reachability.is_always_false() {
                     continue;
                 }
 
                 let annotation = declaration_type(db, declaration);
-                let annotation =
+                let mut annotation =
                     Place::bound(annotation.inner).with_qualifiers(annotation.qualifiers);
 
+                if reachability.is_ambiguous() {
+                    annotation.qualifiers |= TypeQualifiers::POSSIBLY_UNBOUND_IMPLICIT_ATTRIBUTE;
+                }
                 if let Some(all_qualifiers) = annotation.is_bare_final() {
                     if let Some(value) = assignment.value(&module) {
                         // If we see an annotated assignment with a bare `Final` as in
@@ -2789,7 +2792,7 @@ impl<'db> ClassLiteral<'db> {
                         .all_reachable_symbol_bindings(method_place)
                         .find_map(|bind| {
                             (bind.binding.is_defined_and(|def| def == method))
-                                .then(|| class_map.is_binding_reachable(db, &bind))
+                                .then(|| class_map.binding_reachability(db, &bind))
                         })
                         .unwrap_or(Truthiness::AlwaysFalse)
                 } else {
@@ -2818,11 +2821,15 @@ impl<'db> ClassLiteral<'db> {
                     continue;
                 };
                 match method_map
-                    .is_binding_reachable(db, &attribute_assignment)
+                    .binding_reachability(db, &attribute_assignment)
                     .and(is_method_reachable)
                 {
-                    Truthiness::AlwaysTrue | Truthiness::Ambiguous => {
+                    Truthiness::AlwaysTrue => {
+                        is_attribute_bound = true;
+                    }
+                    Truthiness::Ambiguous => {
                         is_attribute_bound = true;
+                        qualifiers |= TypeQualifiers::POSSIBLY_UNBOUND_IMPLICIT_ATTRIBUTE;
                     }
                     Truthiness::AlwaysFalse => {
                         continue;
@@ -2834,7 +2841,7 @@ impl<'db> ClassLiteral<'db> {
                 // TODO: this is incomplete logic since the attributes bound after termination are considered reachable.
                 let unbound_reachability = unbound_binding
                     .as_ref()
-                    .map(|binding| method_map.is_binding_reachable(db, binding))
+                    .map(|binding| method_map.binding_reachability(db, binding))
                     .unwrap_or(Truthiness::AlwaysFalse);
 
                 if unbound_reachability