Warning on Unused Record Primary Constructor Parameter

I was recently playing with positional records and overriding the property declarations, e.g.:

public record Person(string FirstName, string LastName) {
    public string FirstName { get; set; }
    public string LastName { get; set; }
}

I was surprised to find that the constructor that is emitted in this case does not actually wire up the primary constructor parameters with the explicitly declared properties. I understand that this is because the implicit property declarations which are being overridden include an initializer which wires up the property.

In my opinion this would be an easy detail to miss and there is currently no indication that it’s happening. I think it would be useful if the compiler would warn (or otherwise indicate) when the primary constructor parameter is unused.

[jnm2]

However, I would also see a ton of value in a general refactoring from a primary constructor to a regular constructor. I can see wanting to do this even when there are no current code issues.

(When records get validators, explicitly declared constructors might be less good.)

[jnm2]

@Youssef1313 In that case I think the necessary change would be:

 public record A
 {
     public string P1 { get; set; }
 }
 
 
-record C(string P1) : A
+record C : A
 {
+    public C(string P1)
+    {
+        this.P1 = P1;
+    }
 }

This is still in the territory of “The fix for this would be drastic enough that I wouldn’t really expect there to be a fix offered for this case” for me personally, as a Roslyn user.