"Failed to desugar pulse extension text" with identifier errors

[gebner]

This is with the new #lang-pulse block from #168. If a Pulse definition has an identifier not found error, then we get an extra "Failed to desugar pulse extension text" error. Additionally, this error is shown not on the problematic identifier or its enclosing definition, but on a previous definition. There also seems to be an issue with incremental processing in the IDE; if you fix the error, check the file, and then introduce the error again, then there is no "Failed to desugar pulse extension text" message.

module BlockBug
#lang-pulse
open Pulse.Lib.Pervasives

// - Failed to desugar pulse extension text
let is_sublist (a b : Seq.seq nat) : prop = true

fn check_is_sublist (m: SiveT.t)
  requires emp
  ensures emp
{
  ()
}