#9764: Home package modules silently override available modules from package database -------------------------------------+------------------------------------- Reporter: ezyang | Owner: ezyang Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.9 Keywords: | Operating System: Architecture: Unknown/Multiple | Unknown/Multiple Difficulty: Unknown | Type of failure: GHC Blocked By: | accepts invalid program Related Tickets: | Test Case: | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- To see this, define a module with the same name as some module in base. GHC will compile this: {{{ module Data.List where foo = 2 module A where import Data.List x = print foo }}} This behavior is intentional; the most compelling reason of behaving this way is that if you are calling `ghc` without `-hide-all-packages`, some random package you installed which just happened to provide a module name that conflicted with yours could cause your code to stop compiling if we treated the package database and home packages equally. However, this behavior seems undesirable when `-hide-all-packages` is provided; at the very least, it seems like you might want to provide a warning that you're defining a module which conflicts with a module from a package you have exposed. This behavior will be further undesirable when signatures come into the picture. Now, I will want to include a package containing a signature for `A`, and FURTHERMORE I may want to declare a signature `A.hsig` in the local package which augments this signature with some extra declarations I need. Under the current behavior, the externally imported signature is just ignored entirely, even though I wanted them to be merged together. My proposal is to switch the behavior so that we don't prefer home modules if `-hide-all-packages` is provided. What's not great about this proposal is that it adds yet another discrepancy between bare GHC use and GHC use with `-hide-all-packages`. I'm interested to know what people would like. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9764 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler