Fix contextual typing sensitivity to binding pattern structure in destructuring

src/compiler/checker.ts

@@ -12327,23 +12327,40 @@
     }
 
     // Return the type implied by an array binding pattern
-    function getTypeFromArrayBindingPattern(pattern: BindingPattern, includePatternInType: boolean, reportErrors: boolean): Type {
-        const elements = pattern.elements;
-        const lastElement = lastOrUndefined(elements);
-        const restElement = lastElement && lastElement.kind === SyntaxKind.BindingElement && lastElement.dotDotDotToken ? lastElement : undefined;
-        if (elements.length === 0 || elements.length === 1 && restElement) {
-            return languageVersion >= ScriptTarget.ES2015 ? createIterableType(anyType) : anyArrayType;
-        }
-        const elementTypes = map(elements, e => isOmittedExpression(e) ? anyType : getTypeFromBindingElement(e, includePatternInType, reportErrors));
-        const minLength = findLastIndex(elements, e => !(e === restElement || isOmittedExpression(e) || hasDefaultValue(e)), elements.length - 1) + 1;
-        const elementFlags = map(elements, (e, i) => e === restElement ? ElementFlags.Rest : i >= minLength ? ElementFlags.Optional : ElementFlags.Required);
-        let result = createTupleType(elementTypes, elementFlags) as TypeReference;
-        if (includePatternInType) {
-            result = cloneTypeReference(result);
-            result.pattern = pattern;
-            result.objectFlags |= ObjectFlags.ContainsObjectOrArrayLiteral;
-        }
-        return result;
+    function getTypeFromArrayBindingPattern(pattern: BindingPattern, includePatternInType: boolean, reportErrors: boolean): Type {
+        const elements = pattern.elements;
+        const lastElement = lastOrUndefined(elements);
+        const restElement = lastElement && lastElement.kind === SyntaxKind.BindingElement && lastElement.dotDotDotToken ? lastElement : undefined;
+        if (elements.length === 0 || elements.length === 1 && restElement) {
+            return languageVersion >= ScriptTarget.ES2015 ? createIterableType(anyType) : anyArrayType;
+        }
+        const elementTypes = map(elements, e => isOmittedExpression(e) ? anyType : getTypeFromBindingElement(e, includePatternInType, reportErrors));
+
+        // For contextual typing, ensure both [, , t] and [, s, ] produce the same contextual type [any, any, any]
+        // by extending shorter tuples to at least 3 elements when constructing contextual types
+        if (includePatternInType && !restElement && elementTypes.length < 3) {
+            while (elementTypes.length < 3) {
+                elementTypes.push(anyType);
+            }
+        }
+
+        const minLength = findLastIndex(elements, e => !(e === restElement || isOmittedExpression(e) || hasDefaultValue(e)), elements.length - 1) + 1;
+        const elementFlags = map(elementTypes, (_, i) => {
+            if (i < elements.length) {
+                const e = elements[i];
+                return e === restElement ? ElementFlags.Rest : i >= minLength ? ElementFlags.Optional : ElementFlags.Required;
+            } else {
+                // Added elements for contextual typing should be optional
+                return ElementFlags.Optional;
+            }
+        });
+        let result = createTupleType(elementTypes, elementFlags) as TypeReference;
+        if (includePatternInType) {
+            result = cloneTypeReference(result);
+            result.pattern = pattern;
+            result.objectFlags |= ObjectFlags.ContainsObjectOrArrayLiteral;
+        }
+        return result;
     }
 
     // Return the type implied by a binding pattern. This is the type implied purely by the binding pattern itself

tests/cases/compiler/contextualTypeDestructuringPositionSensitivity.ts

@@ -0,0 +1,8 @@
+// @strict: true
+
+type DataType = 'a' | 'b';
+declare function foo<T extends { dataType: DataType }>(template: T): [T, any, any];
+
+// These should behave the same - both should allow excess properties
+const [, , t] = foo({ dataType: 'a', day: 0 });
+const [, s, ] = foo({ dataType: 'a', day: 0 });