Fixed a bug in the handling of for loops that resulted in incorrect type inference for the target expression.

msfterictraut · msfterictraut · commit 26cfeb97c7ab · 2022-07-01T01:30:33.000-07:00
diff --git a/packages/pyright-internal/src/analyzer/binder.ts b/packages/pyright-internal/src/analyzer/binder.ts
@@ -1016,11 +1016,18 @@ export class Binder extends ParseTreeWalker {
         this._addAntecedent(preForLabel, this._currentFlowNode!);
         this._currentFlowNode = preForLabel;
         this._addAntecedent(preElseLabel, this._currentFlowNode);
-        this._createAssignmentTargetFlowNodes(node.targetExpression, /* walkTargets */ true, /* unbound */ false);
+        const targetExpressions = this._trackCodeFlowExpressions(() => {
+            this._createAssignmentTargetFlowNodes(node.targetExpression, /* walkTargets */ true, /* unbound */ false);
+        });
 
         this._bindLoopStatement(preForLabel, postForLabel, () => {
             this.walk(node.forSuite);
             this._addAntecedent(preForLabel, this._currentFlowNode!);
+
+            // Add any target expressions since they are modified in the loop.
+            targetExpressions.forEach((value) => {
+                this._currentScopeCodeFlowExpressions?.add(value);
+            });
         });
 
         this._currentFlowNode = this._finishFlowLabel(preElseLabel);
diff --git a/packages/pyright-internal/src/tests/samples/forLoop1.py b/packages/pyright-internal/src/tests/samples/forLoop1.py
@@ -86,3 +86,10 @@ def __init__(self):
 
 for b in B():
     ...
+
+def func3():
+    x = None
+    for x in range(1):
+        pass
+
+    reveal_type(x, expected_text="int | None")
