#10982: Warn about unused pattern variables in type families -------------------------------------+------------------------------------- Reporter: jstolarek | Owner: msosn Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.11 Resolution: | Keywords: newcomer Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by msosn): * owner: => msosn -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10982#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

The code below is accepted when the extension is disabled, because the identifiers starting with _ are parsed as ordinary type variables. From what I read on the ghc mailing list, the type families should also be accepted with the NamedWildCards on. If so, shouldn't the wildcards be

I also wonder if the warnings in type families should be enabled with

#10982: Warn about unused pattern variables in type families -------------------------------------+------------------------------------- Reporter: jstolarek | Owner: msosn Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.11 Resolution: | Keywords: newcomer Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by jstolarek): Replying to [comment:2 msosn]: treated as type variables in the other cases as well? I think you're right. I mean if this code is valid when `NamedWildCards` are turned off, then it certainly should be valid when we enable `NamedWildCards`. After all named wild cards can't possibly appear in any of these declarations, so whenever a name that looks like a wildcard appears we can safely assume that it must be a type variable. Note however, that we only want to generate warnings for unused pattern variables in type families. the -fwarn-unused-matches option or should I make a new flag? I say we use the existing flag. If anyone complains that they want a separate flag for unused type-level patterns then we can add it. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10982#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#10982: Warn about unused pattern variables in type families -------------------------------------+------------------------------------- Reporter: jstolarek | Owner: msosn Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.11 Resolution: | Keywords: newcomer Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D1576 Wiki Page: | -------------------------------------+------------------------------------- Comment (by Jan Stolarek ): In [changeset:"be92c288839e0bfcf0b15e3bb4136d60f8ef2575/ghc" be92c288/ghc]: {{{ #!CommitTicketReference repository="ghc" revision="be92c288839e0bfcf0b15e3bb4136d60f8ef2575" Update hoopl submodule Hoopl changes required to implement #10982 }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10982#comment:5 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#10982: Warn about unused pattern variables in type families -------------------------------------+------------------------------------- Reporter: jstolarek | Owner: msosn Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.11 Resolution: | Keywords: newcomer Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: #11098 | Differential Rev(s): Phab:D1576 Wiki Page: | -------------------------------------+------------------------------------- Changes (by jstolarek): * related: => #11098 Comment: This looks like a manifestation of #11098. I tried fixing it by "making renamer do its job" but got stuck because I didn't know how to tell whether a type variable was introduced using a forall or not - see [ticket:11098#comment:3]. But this was before wildcard refactor patch (Phab:D1428). Now, looking at Note [HsType binders] in HsTypes, I think it is easy to tell whether a type variable was quantified explicitly or not. Michał, does this allow you to make progress? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10982#comment:7 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#10982: Warn about unused pattern variables in type families -------------------------------------+------------------------------------- Reporter: jstolarek | Owner: msosn Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.11 Resolution: | Keywords: newcomer Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: | UnusedTyVarWarnings, | UnusedTyVarWarningsNamedWCs Blocked By: | Blocking: Related Tickets: #11098 | Differential Rev(s): Phab:D1576 Wiki Page: | -------------------------------------+------------------------------------- Comment (by Ben Gamari ): In [changeset:"eb7796f13e701cce4e7d1d86f36c966aa17f1e9c/ghc" eb7796f/ghc]: {{{ #!CommitTicketReference repository="ghc" revision="eb7796f13e701cce4e7d1d86f36c966aa17f1e9c" Warn about unused type variables in type families The warnings are enabled with the flag -fwarn-unused-matches, the same one that enables warnings on the term level. Identifiers starting with an underscore are now always parsed as type variables. When the NamedWildCards extension is enabled, the renamer replaces those variables with named wildcards. An additional NameSet nwcs is added to LocalRdrEnv. It's used to keep names of the type variables that should be replaced with wildcards. While renaming HsForAllTy, when a name is explicitly bound it is removed from the nwcs NameSet. As a result, the renamer doesn't replace them in the quantifier body. (Trac #11098) Fixes #10982, #11098 Reviewers: alanz, bgamari, hvr, austin, jstolarek Reviewed By: jstolarek Subscribers: goldfire, mpickering, RyanGlScott, thomie Differential Revision: https://phabricator.haskell.org/D1576 GHC Trac Issues: #10982 }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10982#comment:9 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#10982: Warn about unused pattern variables in type families -------------------------------------+------------------------------------- Reporter: jstolarek | Owner: msosn Type: feature request | Status: closed Priority: normal | Milestone: Component: Compiler | Version: 7.11 Resolution: fixed | Keywords: newcomer Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: | UnusedTyVarWarnings, | UnusedTyVarWarningsNamedWCs Blocked By: | Blocking: Related Tickets: #11098 | Differential Rev(s): Phab:D1576 Wiki Page: | -------------------------------------+------------------------------------- Comment (by Simon Peyton Jones ): In [changeset:"575a98e4d245c1e60526ed6d6711d96cea08e9d2/ghc" 575a98e4/ghc]: {{{ #!CommitTicketReference repository="ghc" revision="575a98e4d245c1e60526ed6d6711d96cea08e9d2" Refactor named wildcards (again) Michal's work on #10982, #11098, refactored the handling of named wildcards by making them more like ordinary type variables. This patch takes the same idea to its logical conclusion, resulting in a much tidier, tighter implementation. Read Note [The wildcard story for types] in HsTypes. Changes: * Named wildcards are ordinary type variables, throughout * HsType no longer has a data constructor for named wildcards (was NamedWildCard in HsWildCardInfo). Named wildcards are simply HsTyVars * Similarly named wildcards disappear from Template Haskell * I refactored RnTypes to avoid polluting LocalRdrEnv with something as narrow as named wildcards. Instead the named wildcard set is carried in RnTyKiEnv. There is a submodule update for Haddock. }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10982#comment:11 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler