#12056: Too aggressive `-w` option -------------------------------------+------------------------------------- Reporter: asr | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Resolution: | Keywords: newcomer Operating System: Unknown/Multiple | Architecture: Type of failure: Incorrect | Unknown/Multiple warning at compile-time | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by thomie): * keywords: => newcomer Comment: It looks like this only happens when `-w` is combined with `-Wunrecognised-warning-flags`. GHC seems to do the right thing when using `-w` and some other warning flag (make sure to use `-fforce-recomp` during testing). For a newcomer. The code to change is in `compiler/main/DynFlags.hs`. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12056#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#12056: Too aggressive `-w` option -------------------------------------+------------------------------------- Reporter: asr | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Resolution: | Keywords: newcomer Operating System: Unknown/Multiple | Architecture: Type of failure: Incorrect | Unknown/Multiple warning at compile-time | Test Case: Blocked By: | Blocking: Related Tickets: #11429, #11789 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by wozgonon): Seems to occur for any option prefixed with -W. Note the warnings for -W<...> are: 1) displayed first, out of order 2) displayed with a prefix "\non the commandline:" {{{ ghc -wfoo -wbar -sfoo -sbar -Sfoo -Wfoo -Wbar -Wa -Wb -Wc on the commandline: warning: unrecognised warning flag: -Wfoo on the commandline: warning: unrecognised warning flag: -Wbar on the commandline: warning: unrecognised warning flag: -Wa on the commandline: warning: unrecognised warning flag: -Wb on the commandline: warning: unrecognised warning flag: -Wc ghc.exe: unrecognised flag: -wfoo unrecognised flag: -wbar unrecognised flag: -sfoo unrecognised flag: -sbar unrecognised flag: -Sfoo }}} When -w is added (even as a suffix) warnings for -W<...> options disappear {{{ ghc -wfoo -wbar -sfoo -sbar -Sfoo -Wfoo -Wbar -Wa -Wb -Wc -w ghc.exe: unrecognised flag: -wfoo unrecognised flag: -wbar unrecognised flag: -sfoo unrecognised flag: -sbar unrecognised flag: -Sfoo }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12056#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#12056: Too aggressive `-w` option -------------------------------------+------------------------------------- Reporter: asr | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Resolution: | Keywords: newcomer Operating System: Unknown/Multiple | Architecture: Type of failure: Incorrect | Unknown/Multiple warning at compile-time | Test Case: Blocked By: | Blocking: Related Tickets: #11429, #11789 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by thomie):

It looks like this only happens when -w is combined with `-Wunrecognised-warning-flags`.

To be clear, what I meant by that is that `-w` is too aggressive only when placed before `-Wunrecognised-warning-flags`. When `-w` is combined with other (existing) `-W` flags, GHC does the right thing (take the order in which the flags are passed into account). Here is an example, with `Test.hs` containing: {{{ module Test where import System.FilePath }}} * TEST `-w` BEFORE. `-w` disables all warning flags, but since we supply `-Wunused-imports` afterwards, we *do* get a warning: {{{ $ ghc -w -Wunused-imports -fforce-recomp Test.hs [1 of 1] Compiling Test ( Test.hs, Test.o ) Test.hs:2:1: warning: [-Wunused-imports] The import of ‘System.FilePath’ is redundant except perhaps to import instances from ‘System.FilePath’ To import instances alone, use: import System.FilePath() }}} * TEST `-w` AFTER We give `-Wunused-imports` first. But since we give `-w` afterwards, which reverts the previous flag, we do *not* get a warning: {{{ $ ghc -Wunused-imports -w -fforce-recomp Test.hs }}} Both are expected behavior. == Question What should happen in the following example: {{{ ghc -Wfoo1 -w -Wfoo2 -Wunrecognised-warning-flags -Wfoo3 Main.hs }}} == Option 1 * warn about `-Wfoo` (since `-Wunrecognised-warning-flags` is on by default) * not warn about `-Wfoo2` (since it comes after `-w`) * warn about `-Wfoo3` (since it comes after `-Wunrecognised-warning- flags`) == Option 2 * warn about all `-Wfoo*`, since `-Wunrecognised-warning-flags` came after `-w`, so `-Wunrecognised-warning-flags` is enabled wozgonon: thanks for working on this! I think all these flags are Dynamic though, so I'm not sure that `Note` is relevant. The text "on the commandline" is coming from `ghc/Main.hs` most likely. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12056#comment:5 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#12056: Too aggressive `-w` option -------------------------------------+------------------------------------- Reporter: asr | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Resolution: | Keywords: newcomer Operating System: Unknown/Multiple | Architecture: Type of failure: Incorrect | Unknown/Multiple warning at compile-time | Test Case: Blocked By: | Blocking: Related Tickets: #11429, #11789 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by sgillespie): I hacked on this a bit over the weekend. The first thing I found was this: {{{ $ ghc Main.hs -Wfoo -w -Wunrecognised-warning-flags -Wbar }}} Does not print warnings, as was noted in the ticket originally. Now if I add {{{-Wdeprecated-flags}}}, I now see all unrecognised warnings: {{{ $ ghc Main.hs -Wfoo -w -Wunrecognised-warning-flags -Wdeprecated-flags -Wbar on the commandline: warning: unrecognised warning flag: -Wfoo on the commandline: warning: unrecognised warning flag: -Wbar }}} This is most likely due to the logic to show flag warnings {{{ handleFlagWarnings :: DynFlags -> [Located String] -> IO () handleFlagWarnings dflags warns = when (wopt Opt_WarnDeprecatedFlags dflags) $ do -- It would be nicer if warns :: [Located MsgDoc], but that -- has circular import problems. let bag = listToBag [ mkPlainWarnMsg dflags loc (text warn) | L loc warn <- warns ] printOrThrowWarnings dflags bag }}} So it would seem that Option 2 above is already implemented, albeit with some restrictions. The most straightforward way to fix this would be to add `Opt_UnrecognisedWarningFlags` to `handleFlagWarnings` -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12056#comment:7 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#12056: Too aggressive `-w` option -------------------------------------+------------------------------------- Reporter: asr | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Resolution: | Keywords: newcomer Operating System: Unknown/Multiple | Architecture: Type of failure: Incorrect | Unknown/Multiple warning at compile-time | Test Case: Blocked By: | Blocking: Related Tickets: #11429, #11789 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by sgillespie): * differential: Phab:D3581 => -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12056#comment:9 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#12056: Too aggressive `-w` option -------------------------------------+------------------------------------- Reporter: asr | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Resolution: | Keywords: newcomer Operating System: Unknown/Multiple | Architecture: Type of failure: Incorrect | Unknown/Multiple warning at compile-time | Test Case: Blocked By: | Blocking: Related Tickets: #11429, #11789 | Differential Rev(s): Phab:D3581 Wiki Page: | -------------------------------------+------------------------------------- Comment (by sgillespie): I added a Phab differential. The changeset does indeed solve the original symptom, but it is probably not polished enough to be accepted. Nevertheless, I would really like to get some feedback, as I had to make changes in several places. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12056#comment:11 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#12056: Too aggressive `-w` option -------------------------------------+------------------------------------- Reporter: asr | Owner: (none) Type: bug | Status: patch Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Resolution: | Keywords: newcomer Operating System: Unknown/Multiple | Architecture: Type of failure: Incorrect | Unknown/Multiple warning at compile-time | Test Case: Blocked By: | Blocking: Related Tickets: #11429, #11789 | Differential Rev(s): Phab:D3581 Wiki Page: | -------------------------------------+------------------------------------- Comment (by Ben Gamari ): In [changeset:"af9612bf862daaa99384eefa3059054053ecbee8/ghc" af9612b/ghc]: {{{ #!CommitTicketReference repository="ghc" revision="af9612bf862daaa99384eefa3059054053ecbee8" Make -w less aggressive (Trac #12056) Previously -w combined with -Wunrecognised-warning-flags would not report unrecognized flags. Reviewers: austin, bgamari, dfeuer Reviewed By: bgamari Subscribers: dfeuer, rwbarton, thomie GHC Trac Issues: #12056 Differential Revision: https://phabricator.haskell.org/D3581 }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12056#comment:13 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler