Can I somehow show context-specific information in an {.error.} ?

[monster]

I'm trying to debug a compilation problem: the generic parameter of a proc 
doesn't seem to match my expectation, so I'd like to write something like this:
    
    
    let b: byte = 42'u8
    
    proc test*[T](t: T): bool =
      if sizeof(T) == 1:
        result = true # ...
      else:
        {.error: "invalid parameter size: " & $sizeof(T).}
    
    test(b)
    

But the compiler returns this:
    
    
    Error: invalid pragma: error: "invalid parameter size: " & $ sizeof(T)
    

I tried searching in the Nim codebase, but found no example. So is it 
impossible?
    
    
    find . -name "*.nim" | xargs fgrep "{.error"