Implemented support for bidirectional type inference when an assignment has a LHS consisting of an index expression.

server/src/analyzer/typeAnalyzer.ts

@@ -1892,6 +1892,21 @@ export class TypeAnalyzer extends ParseTreeWalker {
             if (classMemberInfo) {
                 symbol = classMemberInfo.symbol;
             }
+        } else if (expression.nodeType === ParseNodeType.Index) {
+            const baseType = this._getTypeOfExpression(expression.baseExpression, EvaluatorFlags.None, true);
+            if (baseType.category === TypeCategory.Object) {
+                const setItemMember = TypeUtils.lookUpClassMember(baseType.classType, '__setitem__');
+                if (setItemMember) {
+                    if (setItemMember.symbolType.category === TypeCategory.Function) {
+                        const boundFunction = TypeUtils.bindFunctionToClassOrObject(baseType, setItemMember.symbolType);
+                        if (boundFunction.category === TypeCategory.Function) {
+                            if (boundFunction.details.parameters.length === 2) {
+                                return FunctionType.getEffectiveParameterType(boundFunction, 1);
+                            }
+                        }
+                    }
+                }
+            }
         }
 
         if (symbol) {

server/src/tests/samples/assignment4.py

@@ -0,0 +1,18 @@
+# This sample tests various assignment scenarios where
+# there is an expected type, so bidirectional type
+# inference is used.
+
+# pyright: strict
+
+from typing import Dict, Callable, Sequence, Tuple
+AAA = float
+BBB = int
+CCC = str
+DDD = str
+AAATuple = Tuple[AAA, BBB, Callable[[Sequence[int], AAA], Sequence[float]]]
+
+def foo():
+    var1: Dict[str, Tuple[AAA, BBB, CCC, DDD]] = {}
+    var2: Dict[str, AAATuple] = {}
+    for k, (var3, var4, _, _) in var1.items():
+        var2[k] = (var3, var4, lambda var5, var6: [v * var6 for v in var5])

server/src/tests/typeAnalyzer.test.ts

@@ -565,6 +565,12 @@ test('Assignment3', () => {
     validateResults(analysisResults, 4);
 });
 
+test('Assignment4', () => {
+    const analysisResults = TestUtils.typeAnalyzeSampleFiles(['assignment4.py']);
+
+    validateResults(analysisResults, 0);
+});
+
 test('AugmentedAssignment1', () => {
     const analysisResults = TestUtils.typeAnalyzeSampleFiles(['augmentedAssignment1.py']);