Modified the isinstance type narrowing logic to retain a TypeVar wh…

…en narrowing in the positive case and the value is not a constrained TypeVar. This addresses #6434. (#6439)
microsoft · Nov 14, 2023 · f0aad20 · f0aad20
1 parent 6edcade
commit f0aad20
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Showing 5 changed files with 12 additions and 7 deletions.
diff --git a/packages/pyright-internal/src/analyzer/typeGuards.ts b/packages/pyright-internal/src/analyzer/typeGuards.ts
@@ -1394,7 +1394,12 @@ function narrowTypeForIsInstance(
                     if (filterIsSuperclass) {
                         // If the variable type is a subclass of the isinstance filter,
                         // we haven't learned anything new about the variable type.
-                        filteredTypes.push(addConditionToType(concreteVarType, conditions));
+
+                        // If the varType is a constrained TypeVar, narrow to the specific
+                        // constraint. Otherwise retain the varType.
+                        const unnarrowedType =
+                            isTypeVar(varType) && varType.details.constraints.length > 0 ? concreteVarType : varType;
+                        filteredTypes.push(addConditionToType(unnarrowedType, conditions));
                     } else if (filterIsSubclass) {
                         if (
                             evaluator.assignType(

diff --git a/packages/pyright-internal/src/tests/samples/isinstance4.py b/packages/pyright-internal/src/tests/samples/isinstance4.py
@@ -52,7 +52,7 @@ def get_type_of_object(object: Union[Callable[..., Any], CustomClass]):
 
 def func1(cls: Type[_T1], val: _T1):
     if issubclass(cls, CustomClass):
-        reveal_type(cls, expected_text="type[CustomClass]*")
+        reveal_type(cls, expected_text="type[_T1@func1]")
     else:
         reveal_type(cls, expected_text="Never")
 

diff --git a/packages/pyright-internal/src/tests/samples/typeNarrowingIsinstance14.py b/packages/pyright-internal/src/tests/samples/typeNarrowingIsinstance14.py
@@ -18,7 +18,7 @@ def func1(cls: type[T], obj: Any) -> T:
 
 def func2(klass: type[T], obj: T | int) -> T:
     assert isinstance(obj, klass)
-    reveal_type(obj, expected_text="object*")
+    reveal_type(obj, expected_text="T@func2")
     return obj
 
 

diff --git a/packages/pyright-internal/src/tests/samples/typeNarrowingIsinstance16.py b/packages/pyright-internal/src/tests/samples/typeNarrowingIsinstance16.py
@@ -16,4 +16,4 @@ def baz(self, other: object):
             reveal_type(other, expected_text="Self@ClassA")
 
         if isinstance(other, (int, type(self))):
-            reveal_type(other, expected_text="ClassA | int | Self@ClassA")
+            reveal_type(other, expected_text="Self@ClassA | int")
diff --git a/packages/pyright-internal/src/tests/samples/typeNarrowingIsinstance2.py b/packages/pyright-internal/src/tests/samples/typeNarrowingIsinstance2.py
@@ -24,7 +24,7 @@ class ClassC:
     @classmethod
     def test(cls: type[TC], id: int | TC):
         if isinstance(id, cls):
-            reveal_type(id, expected_text="object*")
+            reveal_type(id, expected_text="TC@test")
         else:
             reveal_type(id, expected_text="int")
 
@@ -36,7 +36,7 @@ class ClassD:
     @classmethod
     def test(cls: type[TD], id: int | TD):
         if isinstance(id, cls):
-            reveal_type(id, expected_text="ClassD*")
+            reveal_type(id, expected_text="TD@test")
         else:
             reveal_type(id, expected_text="int")
 
@@ -45,6 +45,6 @@ class ClassE:
     @classmethod
     def test(cls: type[Self], id: int | Self):
         if isinstance(id, cls):
-            reveal_type(id, expected_text="ClassE")
+            reveal_type(id, expected_text="Self@ClassE")
         else:
             reveal_type(id, expected_text="int")