Docs

crates/red_knot_python_semantic/resources/mdtest/annotations/any.md

@@ -11,7 +11,7 @@ x: Any = 1
 x = "foo"
 
 def f():
-    reveal_type(x)  # revealed: Any
+    reveal_type(x)  # revealed: Any | Literal["foo"]
 ```
 
 ## Aliased to a different name
@@ -25,7 +25,7 @@ x: RenamedAny = 1
 x = "foo"
 
 def f():
-    reveal_type(x)  # revealed: Any
+    reveal_type(x)  # revealed: Any | Literal["foo"]
 ```
 
 ## Shadowed class

crates/red_knot_python_semantic/resources/mdtest/annotations/unsupported_special_forms.md

@@ -18,7 +18,7 @@ def f(*args: Unpack[Ts]) -> tuple[Unpack[Ts]]:
     # TODO: should understand the annotation
     reveal_type(args)  # revealed: tuple
 
-    reveal_type(Alias)  # revealed: @Todo(Unsupported or invalid type in a type expression)
+    reveal_type(Alias)  # revealed: @Todo(Unsupported or invalid type in a type expression) | Literal[int]
 
 def g() -> TypeGuard[int]: ...
 def h() -> TypeIs[int]: ...

crates/red_knot_python_semantic/resources/mdtest/assignment/annotations.md

@@ -49,12 +49,12 @@ reveal_type(c)  # revealed: tuple[str, int]
 reveal_type(d)  # revealed: tuple[tuple[str, str], tuple[int, int]]
 
 # TODO: homogeneous tuples, PEP-646 tuples
-reveal_type(e)  # revealed: @Todo(full tuple[...] support)
-reveal_type(f)  # revealed: @Todo(full tuple[...] support)
-reveal_type(g)  # revealed: @Todo(full tuple[...] support)
+reveal_type(e)  # revealed: @Todo(full tuple[...] support) | tuple[()]
+reveal_type(f)  # revealed: @Todo(full tuple[...] support) | tuple[Literal["42"], Literal[b"42"]]
+reveal_type(g)  # revealed: @Todo(full tuple[...] support) | tuple[Literal["42"], Literal[b"42"]]
 
 # TODO: support more kinds of type expressions in annotations
-reveal_type(h)  # revealed: @Todo(full tuple[...] support)
+reveal_type(h)  # revealed: @Todo(full tuple[...] support) | tuple[list, list]
 
 reveal_type(i)  # revealed: tuple[str | int, str | int]
 reveal_type(j)  # revealed: tuple[str | int]

crates/red_knot_python_semantic/resources/mdtest/attributes.md

@@ -175,16 +175,14 @@ class C:
 
 reveal_type(C.pure_class_variable1)  # revealed: str
 
-# TODO: Should be `Unknown | Literal[1]`.
-reveal_type(C.pure_class_variable2)  # revealed: Unknown
+reveal_type(C.pure_class_variable2)  # revealed: Unknown | Literal[1]
 
 c_instance = C()
 
 # It is okay to access a pure class variable on an instance.
 reveal_type(c_instance.pure_class_variable1)  # revealed: str
 
-# TODO: Should be `Unknown | Literal[1]`.
-reveal_type(c_instance.pure_class_variable2)  # revealed: Unknown
+reveal_type(c_instance.pure_class_variable2)  # revealed: Unknown | Literal[1]
 
 # error: [invalid-attribute-access] "Cannot assign to ClassVar `pure_class_variable1` from an instance of type `C`"
 c_instance.pure_class_variable1 = "value set on instance"

crates/red_knot_python_semantic/resources/mdtest/boundness_declaredness/public.md

@@ -1,9 +1,13 @@
 # Boundness and declaredness: public uses
 
-This document demonstrates how type-inference and diagnostics works for *public* uses of a symbol,
+This document demonstrates how type-inference and diagnostics work for *public* uses of a symbol,
 that is, a use of a symbol from another scope. If a symbol has a declared type in its local scope
 (e.g. `int`), we use that as the symbol's "public type" (the type of the symbol from the perspective
-of other scopes) even if there is a more precise local inferred type for the symbol (`Literal[1]`).
+of other scopes). If there is an inferred type in addition (i.e. if we also see bindings for this
+symbol, not just declarations), we use `T_decl | T_decl & T_inf` as the public type, which
+simplifies to `T_decl` for `T_inf = Unknown` (the unbound case).
+
+[TODO: more explanation]
 
 If a symbol has no declared type, we use the union of `Unknown` with the inferred type as the public
 type. If there is no declaration, then the symbol can be reassigned to any type from another scope;
@@ -17,11 +21,11 @@ this behavior is questionable and might change in the future. See the TODOs in `
 In particular, we should raise errors in the "possibly-undeclared-and-unbound" as well as the
 "undeclared-and-possibly-unbound" cases (marked with a "?").
 
-| **Public type**  | declared     | possibly-undeclared        | undeclared              |
-| ---------------- | ------------ | -------------------------- | ----------------------- |
-| bound            | `T_declared` | `T_declared \| T_inferred` | `Unknown \| T_inferred` |
-| possibly-unbound | `T_declared` | `T_declared \| T_inferred` | `Unknown \| T_inferred` |
-| unbound          | `T_declared` | `T_declared`               | `Unknown`               |
+| **Public type**  | declared                   | possibly-undeclared | undeclared         |
+| ---------------- | -------------------------- | ------------------- | ------------------ |
+| bound            | `T_decl \| T_decl & T_inf` | `T_decl \| T_inf`   | `Unknown \| T_inf` |
+| possibly-unbound | `T_decl \| T_decl & T_inf` | `T_decl \| T_inf`   | `Unknown \| T_inf` |
+| unbound          | `T_decl`                   | `T_decl`            | `Unknown`          |
 
 | **Diagnostic**   | declared | possibly-undeclared       | undeclared          |
 | ---------------- | -------- | ------------------------- | ------------------- |
@@ -37,17 +41,27 @@ If a symbol has a declared type (`int`), we use that even if there is a more pre
 (`Literal[1]`), or a conflicting inferred type (`Literal[2]`):
 
 ```py path=mod.py
-x: int = 1
+from typing import Any
+
+def any() -> Any: ...
+
+a: int = 1
 
 # error: [invalid-assignment]
-y: str = 2
+b: str = 2
+
+c: Any = 3
+
+d: int = any()
 ```
 
 ```py
-from mod import x, y
+from mod import a, b, c, d
 
-reveal_type(x)  # revealed: int
-reveal_type(y)  # revealed: str
+reveal_type(a)  # revealed: int
+reveal_type(b)  # revealed: str
+reveal_type(c)  # revealed: Any | Literal[3]
+reveal_type(d)  # revealed: int
 ```
 
 ### Declared and possibly unbound
@@ -56,21 +70,31 @@ If a symbol is declared and *possibly* unbound, we trust that other module and u
 without raising an error.
 
 ```py path=mod.py
+from typing import Any
+
+def any() -> Any: ...
 def flag() -> bool: ...
 
-x: int
-y: str
+a: int
+b: str
+c: Any
+d: int
+
 if flag:
-    x = 1
+    a = 1
     # error: [invalid-assignment]
-    y = 2
+    b = 2
+    c = 3
+    d = any()
 ```
 
 ```py
-from mod import x, y
+from mod import a, b, c, d
 
-reveal_type(x)  # revealed: int
-reveal_type(y)  # revealed: str
+reveal_type(a)  # revealed: int
+reveal_type(b)  # revealed: str
+reveal_type(c)  # revealed: Any | Literal[3]
+reveal_type(d)  # revealed: int
 ```
 
 ### Declared and unbound
@@ -79,13 +103,17 @@ Similarly, if a symbol is declared but unbound, we do not raise an error. We tru
 is available somehow and simply use the declared type.
 
 ```py path=mod.py
-x: int
+from typing import Any
+
+a: int
+b: Any
 ```
 
 ```py
-from mod import x
+from mod import a, b
 
-reveal_type(x)  # revealed: int
+reveal_type(a)  # revealed: int
+reveal_type(b)  # revealed: Any
 ```
 
 ## Possibly undeclared
@@ -100,56 +128,56 @@ from typing import Any
 
 def flag() -> bool: ...
 
-x = 1
-y = 2
-z = 3
+a = 1
+b = 2
+c = 3
 if flag():
-    x: int
-    y: Any
+    a: int
+    b: Any
     # error: [invalid-declaration]
-    z: str
+    c: str
 ```
 
 ```py
-from mod import x, y, z
+from mod import a, b, c
 
-reveal_type(x)  # revealed: int
-reveal_type(y)  # revealed: Literal[2] | Any
-reveal_type(z)  # revealed: Literal[3] | Unknown
+reveal_type(a)  # revealed: int
+reveal_type(b)  # revealed: Literal[2] | Any
+reveal_type(c)  # revealed: Literal[3] | Unknown
 
-# External modifications of `x` that violate the declared type are not allowed:
+# External modifications of `a` that violate the declared type are not allowed:
 # error: [invalid-assignment]
-x = None
+a = None
 ```
 
 ### Possibly undeclared and possibly unbound
 
 If a symbol is possibly undeclared and possibly unbound, we also use the union of the declared and
 inferred types. This case is interesting because the "possibly declared" definition might not be the
-same as the "possibly bound" definition (symbol `y`). Note that we raise a `possibly-unbound-import`
-error for both `x` and `y`:
+same as the "possibly bound" definition (symbol `b`). Note that we raise a `possibly-unbound-import`
+error for both `a` and `b`:
 
 ```py path=mod.py
 def flag() -> bool: ...
 
 if flag():
-    x: Any = 1
-    y = 2
+    a: Any = 1
+    b = 2
 else:
-    y: str
+    b: str
 ```
 
 ```py
 # error: [possibly-unbound-import]
 # error: [possibly-unbound-import]
-from mod import x, y
+from mod import a, b
 
-reveal_type(x)  # revealed: Literal[1] | Any
-reveal_type(y)  # revealed: Literal[2] | str
+reveal_type(a)  # revealed: Literal[1] | Any
+reveal_type(b)  # revealed: Literal[2] | str
 
-# External modifications of `y` that violate the declared type are not allowed:
+# External modifications of `b` that violate the declared type are not allowed:
 # error: [invalid-assignment]
-y = None
+b = None
 ```
 
 ### Possibly undeclared and unbound
@@ -161,19 +189,19 @@ seems inconsistent when compared to the case just above.
 def flag() -> bool: ...
 
 if flag():
-    x: int
+    a: int
 ```
 
 ```py
 # TODO: this should raise an error. Once we fix this, update the section description and the table
 # on top of this document.
-from mod import x
+from mod import a
 
-reveal_type(x)  # revealed: int
+reveal_type(a)  # revealed: int
 
-# External modifications to `x` that violate the declared type are not allowed:
+# External modifications to `a` that violate the declared type are not allowed:
 # error: [invalid-assignment]
-x = None
+a = None
 ```
 
 ## Undeclared
@@ -181,16 +209,16 @@ x = None
 ### Undeclared but bound
 
 ```py path=mod.py
-x = 1
+a = 1
 ```
 
 ```py
-from mod import x
+from mod import a
 
-reveal_type(x)  # revealed: Unknown | Literal[1]
+reveal_type(a)  # revealed: Unknown | Literal[1]
 
-# All external modifications of `x` are allowed:
-x = None
+# All external modifications of `a` are allowed:
+a = None
 ```
 
 ### Undeclared and possibly unbound
@@ -202,18 +230,18 @@ inconsistent when compared to the "possibly-undeclared-and-possibly-unbound" cas
 def flag() -> bool: ...
 
 if flag:
-    x = 1
+    a = 1
 ```
 
 ```py
 # TODO: this should raise an error. Once we fix this, update the section description and the table
 # on top of this document.
-from mod import x
+from mod import a
 
-reveal_type(x)  # revealed: Unknown | Literal[1]
+reveal_type(a)  # revealed: Unknown | Literal[1]
 
-# All external modifications of `x` are allowed:
-x = None
+# All external modifications of `a` are allowed:
+a = None
 ```
 
 ### Undeclared and unbound
@@ -222,15 +250,15 @@ If a symbol is undeclared *and* unbound, we infer `Unknown` and raise an error.
 
 ```py path=mod.py
 if False:
-    x: int = 1
+    a: int = 1
 ```
 
 ```py
 # error: [unresolved-import]
-from mod import x
+from mod import a
 
-reveal_type(x)  # revealed: Unknown
+reveal_type(a)  # revealed: Unknown
 
 # Modifications allowed in this case:
-x = None
+a = None
 ```

crates/red_knot_python_semantic/resources/mdtest/type_qualifiers/classvar.md

@@ -21,8 +21,7 @@ class C:
 reveal_type(C.a)  # revealed: int
 reveal_type(C.b)  # revealed: int
 reveal_type(C.c)  # revealed: int
-# TODO: should be Unknown | Literal[1]
-reveal_type(C.d)  # revealed: Unknown
+reveal_type(C.d)  # revealed: Unknown | Literal[1]
 reveal_type(C.e)  # revealed: int
 
 c = C()

crates/red_knot_python_semantic/src/types.rs

@@ -103,6 +103,54 @@ fn widen_type_for_undeclared_public_symbol<'db>(
     }
 }
 
+/// Computes a possibly more precise public type for a (possibly) declared symbol where
+/// we also have an inferred type from visible bindings.
+///
+/// Below, we build the type `declared_ty | declared_ty & inferred_ty`. This represents
+/// the fact that we want to return a type that is no larger than and no smaller than
+/// `declared_ty`. If `declared_ty` is a fully static type, this means that we will
+/// simply return `declared_ty`. But if `declared_ty` is an arbitrary gradual type, this
+/// can make the public type more specific by including information about `inferred_ty`.
+///
+/// We have a special handling for the following cases, both for performance reasons
+/// and to construct the easiest possible representation of a type:
+///
+/// ```txt
+///         inferred_ty = Any/Unknown
+///        
+///             => declared_ty | declared_ty & Any = declared_ty
+///        
+///         declared_ty = Any/Unknown
+///        
+///             => Any | Any & inferred_ty = Any | inferred_ty
+/// ```
+fn widen_type_for_declared_public_symbol<'db>(
+    db: &'db dyn Db,
+    declared_ty: Type<'db>,
+    inferred: &Symbol<'db>,
+) -> Type<'db> {
+    match inferred.ignore_possibly_unbound() {
+        Some(inferred_ty) => {
+            if inferred_ty.is_dynamic() {
+                declared_ty
+            } else if declared_ty.is_dynamic() {
+                UnionType::from_elements(db, [declared_ty, inferred_ty])
+            } else if declared_ty.is_fully_static(db) {
+                declared_ty
+            } else {
+                IntersectionBuilder::new(db)
+                    .add_positive(UnionType::from_elements(
+                        db,
+                        [declared_ty, inferred_ty].iter().copied(),
+                    ))
+                    .add_positive(declared_ty)
+                    .build()
+            }
+        }
+        None => declared_ty,
+    }
+}
+
 /// Infer the public type of a symbol (its type as seen from outside its scope).
 fn symbol<'db>(db: &'db dyn Db, scope: ScopeId<'db>, name: &str) -> Symbol<'db> {
     #[salsa::tracked]
@@ -122,14 +170,17 @@ fn symbol<'db>(db: &'db dyn Db, scope: ScopeId<'db>, name: &str) -> Symbol<'db>
         let is_final = declared.as_ref().is_ok_and(SymbolAndQualifiers::is_final);
         let declared = declared.map(|SymbolAndQualifiers(symbol, _)| symbol);
 
+        let bindings = use_def.public_bindings(symbol_id);
+        let inferred = symbol_from_bindings(db, bindings);
+
         match declared {
-            // Symbol is declared, trust the declared type
-            Ok(symbol @ Symbol::Type(_, Boundness::Bound)) => symbol,
+            // Symbol is declared
+            Ok(Symbol::Type(declared_ty, Boundness::Bound)) => Symbol::Type(
+                widen_type_for_declared_public_symbol(db, declared_ty, &inferred),
+                Boundness::Bound,
+            ),
             // Symbol is possibly declared
             Ok(Symbol::Type(declared_ty, Boundness::PossiblyUnbound)) => {
-                let bindings = use_def.public_bindings(symbol_id);
-                let inferred = symbol_from_bindings(db, bindings);
-
                 match inferred {
                     // Symbol is possibly undeclared and definitely unbound
                     Symbol::Unbound => {
@@ -646,6 +697,10 @@ impl<'db> Type<'db> {
         matches!(self, Type::Dynamic(DynamicType::Todo(_)))
     }
 
+    pub const fn is_dynamic(&self) -> bool {
+        matches!(self, Type::Dynamic(_))
+    }
+
     pub const fn class_literal(class: Class<'db>) -> Self {
         Self::ClassLiteral(ClassLiteralType { class })
     }
@@ -4125,8 +4180,12 @@ impl<'db> Class<'db> {
             let use_def = use_def_map(db, body_scope);
 
             let declarations = use_def.public_declarations(symbol_id);
+            let declared = symbol_from_declarations(db, declarations);
 
-            match symbol_from_declarations(db, declarations) {
+            let bindings = use_def.public_bindings(symbol_id);
+            let inferred = symbol_from_bindings(db, bindings);
+
+            match declared {
                 Ok(SymbolAndQualifiers(Symbol::Type(declared_ty, _), qualifiers)) => {
                     if let Some(function) = declared_ty.into_function_literal() {
                         // TODO: Eventually, we are going to process all decorators correctly. This is
@@ -4138,13 +4197,16 @@ impl<'db> Class<'db> {
                             todo_type!("bound method").into()
                         }
                     } else {
-                        SymbolAndQualifiers(Symbol::Type(declared_ty, Boundness::Bound), qualifiers)
+                        SymbolAndQualifiers(
+                            Symbol::Type(
+                                widen_type_for_declared_public_symbol(db, declared_ty, &inferred),
+                                Boundness::Bound,
+                            ),
+                            qualifiers,
+                        )
                     }
                 }
                 Ok(symbol @ SymbolAndQualifiers(Symbol::Unbound, qualifiers)) => {
-                    let bindings = use_def.public_bindings(symbol_id);
-                    let inferred = symbol_from_bindings(db, bindings);
-
                     SymbolAndQualifiers(
                         widen_type_for_undeclared_public_symbol(db, inferred, symbol.is_final()),
                         qualifiers,