don't add redundant types to unions to prevent unnecessary unknown/any errors

packages/pyright-internal/src/analyzer/binder.ts

@@ -1394,8 +1394,11 @@ export class Binder extends ParseTreeWalker {
                 this._sysImportAliases
             );
 
-            this._bindConditional(node.d.testExpr, thenLabel, elseLabel);
-
+            this._bindConditional(node.d.testExpr, thenLabel, elseLabel, [
+                ParseNodeType.AssignmentExpression,
+                ParseNodeType.Index,
+                ParseNodeType.MemberAccess,
+            ]);
             // Handle the if clause.
             if (constExprValue === false) {
                 this._currentFlowNode =
@@ -1424,7 +1427,10 @@ export class Binder extends ParseTreeWalker {
             if (node.d.elseSuite) {
                 this.walk(node.d.elseSuite);
             } else {
+                const savedExpressions = new Set(this._currentScopeCodeFlowExpressions);
                 this._bindNeverCondition(node.d.testExpr, postIfLabel, /* isPositiveTest */ false);
+                this._currentScopeCodeFlowExpressions!.clear();
+                savedExpressions.forEach((it) => this._currentScopeCodeFlowExpressions!.add(it));
             }
             this._addAntecedent(postIfLabel, this._currentFlowNode);
             this._currentFlowNode = this._finishFlowLabel(postIfLabel);
@@ -3014,19 +3020,24 @@ export class Binder extends ParseTreeWalker {
         }
     }
 
-    private _bindConditional(node: ExpressionNode, trueTarget: FlowLabel, falseTarget: FlowLabel) {
+    private _bindConditional(
+        node: ExpressionNode,
+        trueTarget: FlowLabel,
+        falseTarget: FlowLabel,
+        nodeTypeFilter?: ParseNodeType[]
+    ) {
         this._setTrueFalseTargets(trueTarget, falseTarget, () => {
             this.walk(node);
         });
 
         if (!this._isLogicalExpression(node)) {
             this._addAntecedent(
                 trueTarget,
-                this._createFlowConditional(FlowFlags.TrueCondition, this._currentFlowNode!, node)
+                this._createFlowConditional(FlowFlags.TrueCondition, this._currentFlowNode!, node, nodeTypeFilter)
             );
             this._addAntecedent(
                 falseTarget,
-                this._createFlowConditional(FlowFlags.FalseCondition, this._currentFlowNode!, node)
+                this._createFlowConditional(FlowFlags.FalseCondition, this._currentFlowNode!, node, nodeTypeFilter)
             );
         }
     }
@@ -3051,7 +3062,12 @@ export class Binder extends ParseTreeWalker {
         this._currentFalseTarget = savedFalseTarget;
     }
 
-    private _createFlowConditional(flags: FlowFlags, antecedent: FlowNode, expression: ExpressionNode): FlowNode {
+    private _createFlowConditional(
+        flags: FlowFlags,
+        antecedent: FlowNode,
+        expression: ExpressionNode,
+        nodeTypeFilter?: ParseNodeType[]
+    ): FlowNode {
         if (antecedent.flags & FlowFlags.Unreachable) {
             return antecedent;
         }
@@ -3080,7 +3096,9 @@ export class Binder extends ParseTreeWalker {
 
         expressionList.forEach((expr) => {
             const referenceKey = createKeyForReference(expr);
-            this._currentScopeCodeFlowExpressions!.add(referenceKey);
+            if (!nodeTypeFilter || nodeTypeFilter.includes(expr.nodeType)) {
+                this._currentScopeCodeFlowExpressions!.add(referenceKey);
+            }
         });
 
         // Select the first name expression.

packages/pyright-internal/src/tests/samples/typeNarrowingIsinstance15.py

@@ -37,5 +37,5 @@ def func2(arg: T2) -> T2:
     if isinstance(arg, str):
         reveal_type(arg, expected_text="str*")
 
-    reveal_type(arg, expected_text="str* | object*")
+    reveal_type(arg, expected_text="T2@func2")
     return arg

packages/pyright-internal/src/tests/samples/typeNarrowingIsinstance16.py

@@ -9,11 +9,11 @@ def bar(cls, other: type):
             reveal_type(other, expected_text="type[Self@ClassA]")
 
         if issubclass(other, (int, cls)):
-            reveal_type(other, expected_text="type[Self@ClassA] | type[int]")
+            reveal_type(other, expected_text="type[int] | type[Self@ClassA]")
 
     def baz(self, other: object):
         if isinstance(other, type(self)):
             reveal_type(other, expected_text="Self@ClassA")
 
         if isinstance(other, (int, type(self))):
-            reveal_type(other, expected_text="Self@ClassA | int")
+            reveal_type(other, expected_text="int | Self@ClassA")

packages/pyright-internal/src/tests/samples/typeNarrowingIsinstance5.py

@@ -34,7 +34,7 @@ def func1(
     if isinstance(obj, Callable):
         reveal_type(obj, expected_text="((int, str) -> int) | B | TCall1@func1")
     else:
-        reveal_type(obj, expected_text="Sequence[Unknown] | C | list[int] | D | A")
+        reveal_type(obj, expected_text="list[int] | A | C | D")
 
 
 class CB1:

packages/pyright-internal/src/tests/samples/typeNarrowingTypeEquals1.py

@@ -90,7 +90,7 @@ def func7(val: Any):
     else:
         reveal_type(val, expected_text="Any")
 
-    reveal_type(val, expected_text="int | Any")
+    reveal_type(val, expected_text="Any")
 
 
 class CParent: ...

packages/pyright-internal/src/tests/samples/typeNarrowingTypeIs1.py

@@ -90,7 +90,7 @@ def func7(val: Any):
     else:
         reveal_type(val, expected_text="Any")
 
-    reveal_type(val, expected_text="int | Any")
+    reveal_type(val, expected_text="Any")
 
 
 class CParent: ...