[ty] Experiment: half-baked typing.TypeAlias support

Author: sharkdp

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

@@ -16,7 +16,8 @@ Alias: TypeAlias = int
 
 def f(*args: Unpack[Ts]) -> tuple[Unpack[Ts]]:
     reveal_type(args)  # revealed: tuple[@Todo(`Unpack[]` special form), ...]
-    reveal_type(Alias)  # revealed: @Todo(Support for `typing.TypeAlias`)
+    # TODO: this is not correct. At runtime, this is `type` (`Alias` is just `<class 'int'>`).
+    reveal_type(Alias)  # revealed: typing.TypeAliasType
 
 def g() -> TypeGuard[int]: ...
 def h() -> TypeIs[int]: ...

crates/ty_python_semantic/resources/mdtest/attributes.md

@@ -1736,9 +1736,9 @@ reveal_type(False.real)  # revealed: Literal[0]
 All attribute access on literal `bytes` types is currently delegated to `builtins.bytes`:
 
 ```py
-# revealed: bound method Literal[b"foo"].join(iterable_of_bytes: Iterable[@Todo(Support for `typing.TypeAlias`)], /) -> bytes
+# revealed: bound method Literal[b"foo"].join(iterable_of_bytes: Iterable[Buffer], /) -> bytes
 reveal_type(b"foo".join)
-# revealed: bound method Literal[b"foo"].endswith(suffix: @Todo(Support for `typing.TypeAlias`) | tuple[@Todo(Support for `typing.TypeAlias`), ...], start: SupportsIndex | None = ellipsis, end: SupportsIndex | None = ellipsis, /) -> bool
+# revealed: bound method Literal[b"foo"].endswith(suffix: Buffer | tuple[Buffer, ...], start: SupportsIndex | None = ellipsis, end: SupportsIndex | None = ellipsis, /) -> bool
 reveal_type(b"foo".endswith)
 ```
 

crates/ty_python_semantic/resources/mdtest/binary/instances.md

@@ -313,8 +313,7 @@ reveal_type(A() + "foo")  # revealed: A
 reveal_type("foo" + A())  # revealed: A
 
 reveal_type(A() + b"foo")  # revealed: A
-# TODO should be `A` since `bytes.__add__` doesn't support `A` instances
-reveal_type(b"foo" + A())  # revealed: bytes
+reveal_type(b"foo" + A())  # revealed: A
 
 reveal_type(A() + ())  # revealed: A
 reveal_type(() + A())  # revealed: A

crates/ty_python_semantic/resources/mdtest/binary/integers.md

@@ -54,10 +54,8 @@ reveal_type(2**largest_u32)  # revealed: int
 
 def variable(x: int):
     reveal_type(x**2)  # revealed: int
-    # TODO: should be `Any` (overload 5 on `__pow__`), requires correct overload matching
-    reveal_type(2**x)  # revealed: int
-    # TODO: should be `Any` (overload 5 on `__pow__`), requires correct overload matching
-    reveal_type(x**x)  # revealed: int
+    reveal_type(2**x)  # revealed: Any
+    reveal_type(x**x)  # revealed: Any
 ```
 
 If the second argument is \<0, a `float` is returned at runtime. If the first argument is \<0 but

crates/ty_python_semantic/resources/mdtest/narrow/isinstance.md

@@ -146,13 +146,11 @@ def _(flag: bool):
 def _(flag: bool):
     x = 1 if flag else "a"
 
-    # TODO: this should cause us to emit a diagnostic during
-    # type checking
+    # error: [invalid-argument-type]
     if isinstance(x, "a"):
         reveal_type(x)  # revealed: Literal[1, "a"]
 
-    # TODO: this should cause us to emit a diagnostic during
-    # type checking
+    # error: [invalid-argument-type]
     if isinstance(x, "int"):
         reveal_type(x)  # revealed: Literal[1, "a"]
 ```

crates/ty_python_semantic/resources/mdtest/narrow/issubclass.md

@@ -214,8 +214,7 @@ def flag() -> bool:
 
 t = int if flag() else str
 
-# TODO: this should cause us to emit a diagnostic during
-# type checking
+# error: [invalid-argument-type]
 if issubclass(t, "str"):
     reveal_type(t)  # revealed: <class 'int'> | <class 'str'>
 

crates/ty_python_semantic/resources/mdtest/pep695_type_aliases.md

@@ -28,7 +28,7 @@ def f() -> None:
 ```py
 type IntOrStr = int | str
 
-reveal_type(IntOrStr.__value__)  # revealed: @Todo(Support for `typing.TypeAlias`)
+reveal_type(IntOrStr.__value__)  # revealed: Any
 ```
 
 ## Invalid assignment

crates/ty_python_semantic/resources/mdtest/protocols.md

@@ -243,7 +243,8 @@ def f(
 Nonetheless, `Protocol` can still be used as the second argument to `issubclass()` at runtime:
 
 ```py
-# Could also be `Literal[True]`, but `bool` is fine:
+# TODO: Should be `Literal[True]`, but `bool` is also fine
+# error: [invalid-argument-type]
 reveal_type(issubclass(MyProtocol, Protocol))  # revealed: bool
 ```
 

crates/ty_python_semantic/resources/mdtest/sys_version_info.md

@@ -122,7 +122,7 @@ properties on instance types:
 
 ```py
 reveal_type(sys.version_info.micro)  # revealed: int
-reveal_type(sys.version_info.releaselevel)  # revealed: @Todo(Support for `typing.TypeAlias`)
+reveal_type(sys.version_info.releaselevel)  # revealed: Literal["alpha", "beta", "candidate", "final"]
 reveal_type(sys.version_info.serial)  # revealed: int
 ```
 

crates/ty_python_semantic/resources/primer/bad.txt

@@ -1,19 +1,26 @@
 Tanjun  # hangs
+alerta  # too many iterations
 antidote  # hangs / slow
 artigraph  # cycle panics (value_type_)
 core  # cycle panics (value_type_)
 cpython  # access to field whilst being initialized, too many cycle iterations
 discord.py  # some kind of hang, only when multi-threaded?
 freqtrade  # hangs
 hydpy  # too many iterations
+hydra-zen  # too many iterations
 ibis  # too many iterations
+isort  # too many iterations
 jax  # too many iterations
+meson  # too many iterations
+mypy  # too many iterations
 packaging  # too many iterations
 pandas  # slow
 pandas-stubs  # hangs/slow, or else https://github.com/salsa-rs/salsa/issues/831
 pandera  # stack overflow
 pip  # vendors packaging, see above
 prefect # slow
+psycopg2  # too many iterations
+pydantic  # too many iterations
 pylint  # cycle panics (self-recursive type alias)
 pyodide  # too many cycle iterations
 pywin32  # bad use-def map (binding with definitely-visible unbound)
@@ -23,4 +30,5 @@ setuptools  # vendors packaging, see above
 spack  # success, but mypy-primer hangs processing the output
 spark  # too many iterations
 steam.py  # hangs
+strawberry  # too many iterations
 xarray  # too many iterations

crates/ty_python_semantic/resources/primer/good.txt

@@ -8,7 +8,6 @@ aiohttp-devtools
 aioredis
 aiortc
 alectryon
-alerta
 altair
 anyio
 apprise
@@ -41,10 +40,8 @@ flake8-pyi
 git-revise
 graphql-core
 httpx-caching
-hydra-zen
 ignite
 imagehash
-isort
 itsdangerous
 janus
 jinja
@@ -53,13 +50,11 @@ kopf
 kornia
 manticore
 materialize
-meson
 mitmproxy
 mkdocs
 mkosi
 mongo-python-driver
 more-itertools
-mypy
 mypy-protobuf
 mypy_primer
 nionutils
@@ -74,11 +69,9 @@ pegen
 poetry
 porcupine
 ppb-vector
-psycopg
 pwndbg
 pybind11
 pycryptodome
-pydantic
 pyinstrument
 pyjwt
 pylox
@@ -101,7 +94,6 @@ sphinx
 starlette
 static-frame
 stone
-strawberry
 streamlit
 sympy
 tornado

crates/ty_python_semantic/src/types.rs

@@ -4922,7 +4922,9 @@ impl<'db> Type<'db> {
                         TypeVarKind::Legacy,
                     )))
                 }
-                KnownInstanceType::TypeAlias => Ok(todo_type!("Support for `typing.TypeAlias`")),
+                KnownInstanceType::TypeAlias => {
+                    Ok(Type::KnownInstance(KnownInstanceType::TypeAlias))
+                }
                 KnownInstanceType::TypedDict => Ok(todo_type!("Support for `typing.TypedDict`")),
 
                 KnownInstanceType::Protocol(_) => Err(InvalidTypeExpressionError {

crates/ty_python_semantic/src/types/infer.rs

@@ -3575,7 +3575,29 @@ impl<'db> TypeInferenceBuilder<'db> {
         debug_assert!(target.is_name_expr());
 
         if let Some(value) = value {
+            if declared_ty.inner_type() == Type::KnownInstance(KnownInstanceType::TypeAlias) {
+                let value_ty = self.infer_type_expression(value);
+
+                let type_alias_ty = Type::KnownInstance(KnownInstanceType::TypeAliasType(
+                    TypeAliasType::Bare(BareTypeAliasType::new(
+                        self.db(),
+                        ast::name::Name::new("dummy"),
+                        Some(definition),
+                        value_ty,
+                    )),
+                ));
+
+                self.add_declaration_with_binding(
+                    target.into(),
+                    definition,
+                    &DeclaredAndInferredType::AreTheSame(type_alias_ty),
+                );
+                self.store_expression_type(target, type_alias_ty);
+                return;
+            }
+
             let inferred_ty = self.infer_expression(value);
+
             let inferred_ty = if target
                 .as_name_expr()
                 .is_some_and(|name| &name.id == "TYPE_CHECKING")