This code:

  [CCode (has_target = false)]
  public delegate bool SourcePrepareFunc (Source source, out int timeout_);

  public void main() {
     SourcePrepareFunc spf = (src, timeout) => {
        timeout = 0;
        return true;
     };
  }

when built with valac 0.11.7 gives:

  bug03.vala:5.22-8.4: warning: local variable `spf' declared but never used
  /w2/v/cwrk/vala/uazu/bug03.vala.c: In function '__lambda0__source_prepare_func':
  /w2/v/cwrk/vala/uazu/bug03.vala.c:28: warning: passing argument 2 of '_lambda0_' makes integer from
  pointer without a cast
  /w2/v/cwrk/vala/uazu/bug03.vala.c:17: note: expected 'gint' but argument is of type 'gint *'
  Compilation succeeded - 1 warning(s)

Part of the C code is expecting a gint for timeout and the other part a gint*.  Both should be gint*.