Catch failure to open Worker and write out port

src/Malt.jl

@@ -103,19 +103,33 @@ mutable struct Worker <: AbstractWorker
  function Worker(; env=String[], exeflags=[])
  # Spawn process
  cmd = _get_worker_cmd(; env, exeflags)
- proc = open(Cmd(
- cmd; 
- detach=true,
- windows_hide=true,
- ), "w+")
+ err = Pipe()
+ proc = open(
+ pipeline(
+ Cmd(
+ cmd; 
+ detach=true,
+ windows_hide=true,
+ ),
+ stderr = err
+ ),
+ "w+"
+ )
 
  # Keep internal list
  __iNtErNaL_get_running_procs()
  push!(__iNtErNaL_running_procs, proc)
 
  # Block until reading the port number of the process (from its stdout)
  port_str = readline(proc)
- port = parse(UInt16, port_str)
+ port = tryparse(UInt16, port_str)
+ if port === nothing
+ Base.kill(proc, Base.SIGTERM)
+ close(err.in)
+ err_t = Threads.@spawn read(err, String)
+ err_output = fetch(err_t)
+ error("""Failed to start worker process correctly. Expected to read port from stdout, got "$port_str" instead. Stderr output was:\n$err_output""")
+ end
 
  # Connect
  socket = Sockets.connect(port)

test/exceptions.jl

@@ -147,3 +147,8 @@ struct LocalStruct end
  m.stop(w)
  @test !m.isrunning(w)
 end
+
+@testset "Failure to spin up Worker" begin
+ e = @catcherror Malt.Worker(; exeflags = ["-t invalid"])
+ @test occursin("ERROR: julia: -t", e.msg)
+end