[GHC] #12034: Template Haskell + hs-boot = Not in scope during type checking, but it passed the renamer
#12034: Template Haskell + hs-boot = Not in scope during type checking, but it passed the renamer -------------------------------------+------------------------------------- Reporter: ezyang | Owner: Type: bug | Status: new Priority: low | Milestone: Component: Compiler | Version: 8.0.1-rc2 (Type checker) | Keywords: backpack | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- I don't think this is a very harmful bug but it definitely is a bug. Consider: {{{ -- A.hs-boot module A where data T -- B.hs module B (module A) where import {-# SOURCE #-} A -- A.hs {-# LANGUAGE TemplateHaskell #-} module A where import qualified B import Language.Haskell.TH f :: B.T -> B.T f x = x $( return [] ) data T = T B.T }}} The point of the splice is to convince GHC to typecheck `f :: B.T -> B.T` before it typechecks the type declaration. But this is not going to work, because `tcLookupGlobal` is going to bail if (1) T is not in the `tcg_type_env` and (2) T comes from this module. It would be a simple matter to improve the error message but from a user's perspective, there is no good reason for this to not typecheck. On the implementation side, I am sympathetic to not letting this typecheck: if it does typecheck, then some `TyCon`s will incorrectly refer to the definition from the hs-boot file, rather than our local definition. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12034 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#12034: Template Haskell + hs-boot = Not in scope during type checking, but it passed the renamer -------------------------------------+------------------------------------- Reporter: ezyang | Owner: Type: bug | Status: new Priority: low | Milestone: Component: Template Haskell | Version: 8.0.1-rc2 Resolution: | Keywords: backpack 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 goldfire): * component: Compiler (Type checker) => Template Haskell -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12034#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#12034: Template Haskell + hs-boot = Not in scope during type checking, but it passed the renamer -------------------------------------+------------------------------------- Reporter: ezyang | Owner: Type: bug | Status: new Priority: low | Milestone: Component: Template Haskell | Version: 8.0.1-rc2 Resolution: | Keywords: backpack hs- | boot 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 ezyang): * keywords: backpack => backpack hs-boot -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12034#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#12034: Template Haskell + hs-boot = Not in scope during type checking, but it passed the renamer -------------------------------------+------------------------------------- Reporter: ezyang | Owner: Type: bug | Status: new Priority: low | Milestone: Component: Template Haskell | Version: 8.0.1-rc2 Resolution: | Keywords: backpack hs- | boot 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 ezyang): Here is a restriction for hs-boot files and TH which might solve this problem: all TYPEs in the hs-boot file (values can wait) must be defined in the section of the file PRIOR to the first Template Haskell splice. This ensures we have a consistent environment for knot-tying, and also is an obvious place to check for missing types #12063 or type synonym loops #12042. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12034#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#12034: Template Haskell + hs-boot = Not in scope during type checking, but it passed the renamer -------------------------------------+------------------------------------- Reporter: ezyang | Owner: Type: bug | Status: new Priority: low | Milestone: Component: Template Haskell | Version: 8.0.1-rc2 Resolution: | Keywords: backpack hs- | boot 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 simonpj): Or alternatively re-typecheck the interface produced from the bit before the splice, just as we would do if the bit before the splice was in another module. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12034#comment:4 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#12034: Template Haskell + hs-boot = Not in scope during type checking, but it passed the renamer -------------------------------------+------------------------------------- Reporter: ezyang | Owner: Type: bug | Status: new Priority: low | Milestone: Component: Template Haskell | Version: 8.0.1-rc2 Resolution: | Keywords: backpack hs- | boot 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 ezyang): How do would you suggest we actually do the retypechecking? For example, in GhcMake we can retypecheck because we're responsible for managing the HPT; but the retypecheck would have to work within the typechecker code. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12034#comment:5 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
Here is a restriction for hs-boot files and TH which might solve this
#12034: Template Haskell + hs-boot = Not in scope during type checking, but it passed the renamer -------------------------------------+------------------------------------- Reporter: ezyang | Owner: (none) Type: bug | Status: new Priority: low | Milestone: Component: Template Haskell | Version: 8.0.1-rc2 Resolution: | Keywords: backpack hs- | boot 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 Ericson2314): I have a situation with a {{{makeClassy}} classy lens class cycle that I cannot break (modulo manually expanding the TH). I'd like something like an ''intra''-module hs-boot file to fix this. I gather from this issue that I shouldn't waste time breaking up my module, as .hs-boot as it currently stands won't save me. Replying to [comment:3 ezyang]: problem.... Ezyang's proposal would also not help because the splice defines the Has* class. I believe the staging restriction as it currently stands ought just to apply to code executed as part of a TH splice. Quoted variable resolution should be fine: if and only the user uses one of the APIs to learn more about a defintion, they should only hit a Nothing/exception because a staging restriction. intra-module hs-boot would then be a way to assert that some further-down splice defines some names, enough for names, including quoted names, to resolve. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12034#comment:6 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
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