Fix NotSupportedException when parsing nested object initialization

[Copilot]

Parsing expressions with nested new initializers like new (new (3 as Id) as CurrentDepartment) throws a NotSupportedException when the result type is a known class (e.g. Customer).

Root cause: The parser propagates _resultType into nested new expressions that have no explicit type. So new (3 as Id) becomes new Customer() {Id=3}. When the outer expression then tries to bind this to CurrentDepartment (type Department), ExpressionPromoter.Promote returns null and Expression.Convert throws since Customer and Department are incompatible.

Fix: In CreateNewExpression's member-bindings path, when Promote returns null and the source expression is a MemberInitExpression, attempt to rebuild it for the target member type via a new TryRebuildMemberInitExpression helper. The helper:

• Requires a default constructor on the target type
• Remaps each binding by member name from source type to target type
• Recurses for deeply nested MemberInitExpression values
• Returns null (falls back to Expression.Convert) if any member is absent on the target

Example — previously threw, now works:

var lambda = DynamicExpressionParser.ParseLambda(
    ParsingConfig.DefaultEFCore21,
    typeof(Customer), typeof(Customer),
    "new (new (3 as Id) as CurrentDepartment)");

// Produces: Customer { CurrentDepartment = Department { Id = 3 } }

---

📱 Kick off Copilot coding agent tasks wherever you are with GitHub Mobile, available on iOS and Android.

[StefH]

rewrite this method to:

private static bool TryRebuildMemberInitExpression(MemberInitExpression memberInitExpression, Type targetType, [NotNullWhen(true)] out Expression? expression)

[Copilot]

Done in 417258d. Rewrote the method signature to private static bool TryRebuildMemberInitExpression(MemberInitExpression memberInitExpression, Type targetType, [NotNullWhen(true)] out Expression? expression) and updated the call site accordingly.

[StefH]

Add a unit test which goes 1 level deeper so that the code

if (bindingExpression is MemberInitExpression nestedMemberInit && bindingExpression.Type != targetMemberType)
{
    if (!TryRebuildMemberInitExpression(nestedMemberInit, targetMemberType, out var rebuiltNested))
    {
        return false;
    }
    bindingExpression = rebuiltNested;
}
else if (bindingExpression.Type != targetMemberType)
{
    bindingExpression = Expression.Convert(bindingExpression, targetMemberType);
}

is also tested

[Copilot]

Added in ddb00b9. The new test DynamicExpressionParser_ParseLambda_NestedObjectInitialization_ThreeLevelsDeep uses expression new (new (new (3 as Id) as Sub) as Sub) with models that have a shared Sub property name at each level (CustomerForNestedNewTest.Sub → DepartmentForNestedNewTest, DepartmentForNestedNewTest.Sub → SubDepartmentForNestedNewTest). This causes the outer rebuild to encounter an inner MemberInitExpression binding, triggering the recursive call path.