Make updates to external package state idempotent.

Without this, concurrent updates to the EPS could introduce
overlapping instances (even though they came from the same module).

diff --git a/compiler/iface/LoadIface.lhs b/compiler/iface/LoadIface.lhs
index 3a4cfe5..cedc447 100644 (file)
--- a/compiler/iface/LoadIface.lhs
+++ b/compiler/iface/LoadIface.lhs
@@ -257,6 +257,7 @@ loadInterface doc_str mod from
                }
 
        ; updateEps_  $ \ eps -> 
+           if elemModuleEnv mod (eps_PIT eps) then eps else
            eps { 
              eps_PIT          = extendModuleEnv (eps_PIT eps) mod final_iface,
              eps_PTE          = addDeclsToPTE   (eps_PTE eps) new_eps_decls,