#12609: unused-top-binds wrongly warns about underscore-prefixed field names when DuplicateRecordFields enabled -------------------------------------+------------------------------------- Reporter: jml | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Given this code: {{{#!hs module Main (main) where data Foo = Foo { _foo :: String , _bar :: String } deriving (Eq, Show) main :: IO () main = do let x = Foo "apple" "bear" putStrLn $ "x = " ++ show x }}} Saved as `unused-fields.hs` Then with ghc 8.0.1: {{{ $ ghc --version The Glorious Glasgow Haskell Compilation System, version 8.0.1 }}} The following command will compile without error or warning: {{{ $ ghc -Wall -Werror -o unused-fields ./unused-fields.hs }}} But if `DuplicateRecordFields` is enabled, then: {{{ $ ghc -Wall -Werror -o unused-fields ./unused-fields.hs -XDuplicateRecordFields [1 of 1] Compiling Main ( unused-fields.hs, unused-fields.o ) [flags changed] unused-fields.hs:21:11: warning: [-Wunused-top-binds] Defined but not used: ‘_foo’ unused-fields.hs:22:11: warning: [-Wunused-top-binds] Defined but not used: ‘_bar’ <no location info>: error: Failing due to -Werror. }}} I would have no warnings, since `_foo` and `_bar` have underscore prefixes, which is a documented way of selectively disabling this warning. (c.f. https://downloads.haskell.org/~ghc/latest/docs/html/users_guide /using-warnings.html#ghc-flag--Wunused-top-binds). Details requested by https://ghc.haskell.org/trac/ghc/wiki/ReportABug: {{{ $ gcc --version Configured with: --prefix=/Applications/Xcode.app/Contents/Developer/usr --with-gxx-include-dir=/usr/include/c++/4.2.1 Apple LLVM version 8.0.0 (clang-800.0.38) Target: x86_64-apple-darwin15.6.0 Thread model: posix InstalledDir: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin }}} GOOD (without -XDuplicateRecordFields) {{{ $ ghc -dcore-lint -v -Wall -Werror -o unused-fields ./unused-fields.hs Glasgow Haskell Compiler, Version 8.0.1, stage 2 booted by GHC version 7.10.3 Using binary package database: /nix/store/vvn40k4257a2f6dlps52jnff6qa41ph3-ghc-8.0.1/lib/ghc-8.0.1/package.conf.d/package.cache loading package database /nix/store/vvn40k4257a2f6dlps52jnff6qa41ph3-ghc-8.0.1/lib/ghc-8.0.1/package.conf.d wired-in package ghc-prim mapped to ghc-prim-0.5.0.0 wired-in package integer-gmp mapped to integer-gmp-1.0.0.1 wired-in package base mapped to base-4.9.0.0 wired-in package rts mapped to rts wired-in package template-haskell mapped to template-haskell-2.11.0.0 wired-in package ghc mapped to ghc-8.0.1 wired-in package dph-seq not found. wired-in package dph-par not found. Hsc static flags: loading package database /nix/store/vvn40k4257a2f6dlps52jnff6qa41ph3-ghc-8.0.1/lib/ghc-8.0.1/package.conf.d wired-in package ghc-prim mapped to ghc-prim-0.5.0.0 wired-in package integer-gmp mapped to integer-gmp-1.0.0.1 wired-in package base mapped to base-4.9.0.0 wired-in package rts mapped to rts-1.0 wired-in package template-haskell mapped to template-haskell-2.11.0.0 wired-in package ghc mapped to ghc-8.0.1 wired-in package dph-seq not found. wired-in package dph-par not found. *** Chasing dependencies: Chasing modules from: *unused-fields.hs !!! Chasing dependencies: finished in 0.68 milliseconds, allocated 0.777 megabytes Stable obj: [Main] Stable BCO: [] Ready for upsweep [NONREC ModSummary { ms_hs_date = 2016-09-22 08:27:24 UTC ms_mod = Main, ms_textual_imps = [(Nothing, Prelude)] ms_srcimps = [] }] *** Deleting temp files: Deleting: compile: input file unused-fields.hs *** Checking old interface for Main: [1 of 1] Skipping Main ( unused-fields.hs, unused-fields.o ) Upsweep completely successful. *** Deleting temp files: Deleting: link: linkables are ... LinkableM (2016-09-22 08:45:48 UTC) Main [DotO unused-fields.o] Linking unused-fields ... Created temporary directory: /var/folders/6q/jpykk8bn6dq68ynzm6c1r7c40000gn/T/ghc62639_0 *** C Compiler: /nix/store/a5f6qqgzgmmvw0xkvlfdsjzaprmnlz2s-clang-wrapper-3.7.1/bin/cc -m64 -fno-stack-protector -DTABLES_NEXT_TO_CODE -c /var/folders/6q/jpykk8bn6dq68ynzm6c1r7c40000gn/T/ghc62639_0/ghc_1.c -o /var/folders/6q/jpykk8bn6dq68ynzm6c1r7c40000gn/T/ghc62639_0/ghc_2.o -fno- common -U__PIC__ -D__PIC__ -I/nix/store/vvn40k4257a2f6dlps52jnff6qa41ph3-ghc-8.0.1/lib/ghc-8.0.1/include *** Linker: /nix/store/a5f6qqgzgmmvw0xkvlfdsjzaprmnlz2s-clang-wrapper-3.7.1/bin/cc -m64 -fno-stack-protector -DTABLES_NEXT_TO_CODE -m64 -o unused-fields -Wl,-no_compact_unwind unused-fields.o -L/nix/store/vvn40k4257a2f6dlps52jnff6qa41ph3-ghc-8.0.1/lib/ghc-8.0.1/base-4.9.0.0 -L/nix/store/8dkzvp7d7vpprc8cblmjcyyyzyy9940i-libiconv-osx-10.9.5/lib -L/nix/store/vvn40k4257a2f6dlps52jnff6qa41ph3-ghc-8.0.1/lib/ghc-8.0.1 /integer-gmp-1.0.0.1 -L/nix/store/8b7big21k9ipi44mqlnp8njbkncwhh27-gmp-6.1.0/lib -L/nix/store/vvn40k4257a2f6dlps52jnff6qa41ph3-ghc-8.0.1/lib/ghc-8.0.1/ghc- prim-0.5.0.0 -L/nix/store/vvn40k4257a2f6dlps52jnff6qa41ph3-ghc-8.0.1/lib/ghc-8.0.1/rts /var/folders/6q/jpykk8bn6dq68ynzm6c1r7c40000gn/T/ghc62639_0/ghc_2.o -Wl,-u,_ghczmprim_GHCziTypes_Izh_static_info -Wl,-u,_ghczmprim_GHCziTypes_Czh_static_info -Wl,-u,_ghczmprim_GHCziTypes_Fzh_static_info -Wl,-u,_ghczmprim_GHCziTypes_Dzh_static_info -Wl,-u,_base_GHCziPtr_Ptr_static_info -Wl,-u,_ghczmprim_GHCziTypes_Wzh_static_info -Wl,-u,_base_GHCziInt_I8zh_static_info -Wl,-u,_base_GHCziInt_I16zh_static_info -Wl,-u,_base_GHCziInt_I32zh_static_info -Wl,-u,_base_GHCziInt_I64zh_static_info -Wl,-u,_base_GHCziWord_W8zh_static_info -Wl,-u,_base_GHCziWord_W16zh_static_info -Wl,-u,_base_GHCziWord_W32zh_static_info -Wl,-u,_base_GHCziWord_W64zh_static_info -Wl,-u,_base_GHCziStable_StablePtr_static_info -Wl,-u,_ghczmprim_GHCziTypes_Izh_con_info -Wl,-u,_ghczmprim_GHCziTypes_Czh_con_info -Wl,-u,_ghczmprim_GHCziTypes_Fzh_con_info -Wl,-u,_ghczmprim_GHCziTypes_Dzh_con_info -Wl,-u,_base_GHCziPtr_Ptr_con_info -Wl,-u,_base_GHCziPtr_FunPtr_con_info -Wl,-u,_base_GHCziStable_StablePtr_con_info -Wl,-u,_ghczmprim_GHCziTypes_False_closure -Wl,-u,_ghczmprim_GHCziTypes_True_closure -Wl,-u,_base_GHCziPack_unpackCString_closure -Wl,-u,_base_GHCziIOziException_stackOverflow_closure -Wl,-u,_base_GHCziIOziException_heapOverflow_closure -Wl,-u,_base_ControlziExceptionziBase_nonTermination_closure -Wl,-u,_base_GHCziIOziException_blockedIndefinitelyOnMVar_closure -Wl,-u,_base_GHCziIOziException_blockedIndefinitelyOnSTM_closure -Wl,-u,_base_GHCziIOziException_allocationLimitExceeded_closure -Wl,-u,_base_ControlziExceptionziBase_nestedAtomically_closure -Wl,-u,_base_GHCziEventziThread_blockedOnBadFD_closure -Wl,-u,_base_GHCziWeak_runFinalizzerBatch_closure -Wl,-u,_base_GHCziTopHandler_flushStdHandles_closure -Wl,-u,_base_GHCziTopHandler_runIO_closure -Wl,-u,_base_GHCziTopHandler_runNonIO_closure -Wl,-u,_base_GHCziConcziIO_ensureIOManagerIsRunning_closure -Wl,-u,_base_GHCziConcziIO_ioManagerCapabilitiesChanged_closure -Wl,-u,_base_GHCziConcziSync_runSparks_closure -Wl,-u,_base_GHCziConcziSignal_runHandlersPtr_closure -Wl,-search_paths_first -lHSbase-4.9.0.0 -lHSinteger-gmp-1.0.0.1 -lHSghc- prim-0.5.0.0 -lHSrts -lCffi -liconv -lgmp -lm -ldl link: done *** Deleting temp files: Deleting: /var/folders/6q/jpykk8bn6dq68ynzm6c1r7c40000gn/T/ghc62639_0/ghc_2.o /var/folders/6q/jpykk8bn6dq68ynzm6c1r7c40000gn/T/ghc62639_0/ghc_1.c *** Deleting temp dirs: Deleting: /var/folders/6q/jpykk8bn6dq68ynzm6c1r7c40000gn/T/ghc62639_0 }}} BAD {{{ $ ghc -dcore-lint -v -Wall -Werror -o unused-fields ./unused-fields.hs -XDuplicateRecordFields Glasgow Haskell Compiler, Version 8.0.1, stage 2 booted by GHC version 7.10.3 Using binary package database: /nix/store/vvn40k4257a2f6dlps52jnff6qa41ph3-ghc-8.0.1/lib/ghc-8.0.1/package.conf.d/package.cache loading package database /nix/store/vvn40k4257a2f6dlps52jnff6qa41ph3-ghc-8.0.1/lib/ghc-8.0.1/package.conf.d wired-in package ghc-prim mapped to ghc-prim-0.5.0.0 wired-in package integer-gmp mapped to integer-gmp-1.0.0.1 wired-in package base mapped to base-4.9.0.0 wired-in package rts mapped to rts wired-in package template-haskell mapped to template-haskell-2.11.0.0 wired-in package ghc mapped to ghc-8.0.1 wired-in package dph-seq not found. wired-in package dph-par not found. Hsc static flags: loading package database /nix/store/vvn40k4257a2f6dlps52jnff6qa41ph3-ghc-8.0.1/lib/ghc-8.0.1/package.conf.d wired-in package ghc-prim mapped to ghc-prim-0.5.0.0 wired-in package integer-gmp mapped to integer-gmp-1.0.0.1 wired-in package base mapped to base-4.9.0.0 wired-in package rts mapped to rts-1.0 wired-in package template-haskell mapped to template-haskell-2.11.0.0 wired-in package ghc mapped to ghc-8.0.1 wired-in package dph-seq not found. wired-in package dph-par not found. *** Chasing dependencies: Chasing modules from: *unused-fields.hs !!! Chasing dependencies: finished in 1.05 milliseconds, allocated 0.777 megabytes Stable obj: [Main] Stable BCO: [] Ready for upsweep [NONREC ModSummary { ms_hs_date = 2016-09-22 08:27:24 UTC ms_mod = Main, ms_textual_imps = [(Nothing, Prelude)] ms_srcimps = [] }] *** Deleting temp files: Deleting: compile: input file unused-fields.hs *** Checking old interface for Main: [1 of 1] Compiling Main ( unused-fields.hs, unused-fields.o ) [flags changed] *** Parser [Main]: !!! Parser [Main]: finished in 1.27 milliseconds, allocated 0.517 megabytes *** Renamer/typechecker [Main]: !!! Renamer/typechecker [Main]: finished in 128.27 milliseconds, allocated 49.950 megabytes *** Desugar [Main]: Result size of Desugar (after optimization) = {terms: 141, types: 94, coercions: 0} *** Core Linted result of Desugar (after optimization): !!! Desugar [Main]: finished in 5.14 milliseconds, allocated 1.194 megabytes unused-fields.hs:22:11: warning: [-Wunused-top-binds] Defined but not used: ‘_foo’ unused-fields.hs:23:11: warning: [-Wunused-top-binds] Defined but not used: ‘_bar’ <no location info>: error: Failing due to -Werror. Upsweep partially successful. *** Deleting temp files: Deleting: link(batch): upsweep (partially) failed OR Main.main not exported; not linking. *** Deleting temp files: Deleting: *** Deleting temp dirs: Deleting: }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12609> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler