From d202d1e9ae7a0b77ba054ac98e9305a0e473a5cf Mon Sep 17 00:00:00 2001
From: A5rocks <git@helvetica.moe>
Date: Sun, 26 Dec 2021 13:18:34 +0900
Subject: [PATCH] Tests for literals

---
 mypy/typeanal.py                              | 34 +++++--------
 .../unit/check-parameter-specification.test   | 51 +++++++++++++++++++
 2 files changed, 64 insertions(+), 21 deletions(-)

diff --git a/mypy/typeanal.py b/mypy/typeanal.py
index 2953e6a83822..23498e6957a3 100644
--- a/mypy/typeanal.py
+++ b/mypy/typeanal.py
@@ -423,18 +423,15 @@ def analyze_type_with_type_info(
         if len(args) > 0 and info.fullname == 'builtins.tuple':
             fallback = Instance(info, [AnyType(TypeOfAny.special_form)], ctx.line)
             return TupleType(self.anal_array(args), fallback, ctx.line)
-        # Only allow ParamSpec literals if there's a ParamSpec arg type:
-        # This might not be necessary.
-        allow_param_spec_literal = any(isinstance(tvar, ParamSpecType) for tvar in info.defn.type_vars)
 
         # Analyze arguments and (usually) construct Instance type. The
         # number of type arguments and their values are
         # checked only later, since we do not always know the
         # valid count at this point. Thus we may construct an
         # Instance with an invalid number of type arguments.
-        instance = Instance(info, self.anal_array(args, allow_param_spec=True,
-                                                  allow_param_spec_literal=allow_param_spec_literal),
+        instance = Instance(info, self.anal_array(args, allow_param_spec=True),
                             ctx.line, ctx.column)
+
         # Check type argument count.
         if len(instance.args) != len(info.type_vars) and not self.defining_alias:
             fix_instance(instance, self.fail, self.note,
@@ -566,9 +563,15 @@ def visit_deleted_type(self, t: DeletedType) -> Type:
         return t
 
     def visit_type_list(self, t: TypeList) -> Type:
-        self.fail('Bracketed expression "[...]" is not valid as a type', t)
-        self.note('Did you mean "List[...]"?', t)
-        return AnyType(TypeOfAny.from_error)
+        # paramspec literal (Z[[int, str, Whatever]])
+        # TODO: invalid usage restrictions
+        params = self.analyze_callable_args(t)
+        if params:
+            ts, kinds, names = params
+            # bind these types
+            return Parameters(self.anal_array(ts), kinds, names)
+        else:
+            return AnyType(TypeOfAny.from_error)
 
     def visit_callable_argument(self, t: CallableArgument) -> Type:
         self.fail('Invalid type', t)
@@ -1040,21 +1043,10 @@ def is_defined_type_var(self, tvar: str, context: Context) -> bool:
     def anal_array(self,
                    a: Iterable[Type],
                    nested: bool = True, *,
-                   allow_param_spec: bool = False,
-                   allow_param_spec_literal: bool = False) -> List[Type]:
+                   allow_param_spec: bool = False) -> List[Type]:
         res: List[Type] = []
         for t in a:
-            if allow_param_spec_literal and isinstance(t, TypeList):
-                # paramspec literal (Z[[int, str, Whatever]])
-                params = self.analyze_callable_args(t)
-                if params:
-                    ts, kinds, names = params
-                    # bind these types
-                    res.append(Parameters(self.anal_array(ts), kinds, names))
-                else:
-                    res.append(AnyType(TypeOfAny.from_error))
-            else:
-                res.append(self.anal_type(t, nested, allow_param_spec=allow_param_spec))
+            res.append(self.anal_type(t, nested, allow_param_spec=allow_param_spec))
         return res
 
     def anal_type(self, t: Type, nested: bool = True, *, allow_param_spec: bool = False) -> Type:
diff --git a/test-data/unit/check-parameter-specification.test b/test-data/unit/check-parameter-specification.test
index f6123915aada..fb6dd4e7728f 100644
--- a/test-data/unit/check-parameter-specification.test
+++ b/test-data/unit/check-parameter-specification.test
@@ -406,3 +406,54 @@ with f() as x:
     pass
 [builtins fixtures/dict.pyi]
 [typing fixtures/typing-full.pyi]
+
+[case testParamSpecLiterals]
+from typing_extensions import ParamSpec, TypeAlias
+from typing import Generic, TypeVar
+
+P = ParamSpec("P")
+T = TypeVar("T")
+
+class Z(Generic[P]): ...
+
+# literals can be applied
+n: Z[[int]]
+
+# type aliases too
+nt1 = Z[[int]]
+nt2: TypeAlias = Z[[int]]
+
+unt1: nt1
+unt2: nt2
+
+# literals actually keep types
+reveal_type(n)  # N: Revealed type is "__main__.Z[[builtins.int]]"
+reveal_type(unt1)  # N: Revealed type is "__main__.Z[[builtins.int]]"
+reveal_type(unt2)  # N: Revealed type is "__main__.Z[[builtins.int]]"
+
+# passing into a function keeps the type
+def fT(a: T) -> T: ...
+def fP(a: Z[P]) -> Z[P]: ...
+
+reveal_type(fT(n))  # N: Revealed type is "__main__.Z*[[builtins.int]]"
+reveal_type(fP(n))  # N: Revealed type is "__main__.Z[[builtins.int]]"
+
+# literals can be in function args and return type
+def k(a: Z[[int]]) -> Z[[str]]: ...
+
+# functions work
+reveal_type(k(n))  # N: Revealed type is "__main__.Z[[builtins.str]]"
+
+# literals can be matched in arguments
+def kb(a: Z[[bytes]]) -> Z[[str]]: ...
+
+# TODO: return type is a bit weird, return Any
+reveal_type(kb(n))  # N: Revealed type is "__main__.Z[[builtins.str]]" \
+                    # E: Argument 1 to "kb" has incompatible type "Z[[int]]"; expected "Z[[bytes]]"
+
+
+# TODO(PEP612): fancy "aesthetic" syntax defined in PEP
+# n2: Z[bytes]
+# 
+# reveal_type(kb(n2))  # N: Revealed type is "__main__.Z[[builtins.str]]"
+[builtins fixtures/tuple.pyi]