#9230: Make -fwarn-tabs the default -------------------------------+------------------------------------------- Reporter: dfeuer | Owner: Type: feature | Status: new request | Milestone: Priority: normal | Version: 7.8.2 Component: Compiler | Keywords: Resolution: | Architecture: Unknown/Multiple Operating System: | Difficulty: Easy (less than 1 hour) Unknown/Multiple | Blocked By: Type of failure: | Related Tickets: None/Unknown | Test Case: | Blocking: | -------------------------------+------------------------------------------- Comment (by tibbe): I've been bitten by files that mixed tabs and spaces before, so +1 from me. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9230#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#9230: Make -fwarn-tabs the default -------------------------------+------------------------------------------- Reporter: dfeuer | Owner: jstolarek Type: feature | Status: new request | Milestone: Priority: normal | Version: 7.8.2 Component: Compiler | Keywords: Resolution: | Architecture: Unknown/Multiple Operating System: | Difficulty: Easy (less than 1 hour) Unknown/Multiple | Blocked By: Type of failure: | Related Tickets: None/Unknown | Test Case: | Blocking: | -------------------------------+------------------------------------------- Comment (by dfeuer): I looked into what making -fwarn-tabs the default would break in the GHC tree, and the answer appears to be "very little". It looks like the only files that use tabs for layout, use -Werror, and don't specify -fno-warn- tabs are libraries/time/Test/{ShowDST.hs,TimeZone.hs,CurrentTime.hs} and a test file that's designed to break from the tab warning. So contrary to some initial fears thoughtpolice raised in IRC, it will *not* be necessary to detab the whole GHC source to make this change. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9230#comment:4 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#9230: Make -fwarn-tabs the default -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: mlen Type: feature | Status: new request | Milestone: Priority: normal | Version: 7.8.2 Component: Compiler | Keywords: Resolution: | Architecture: Unknown/Multiple Operating System: | Difficulty: Easy (less than 1 Unknown/Multiple | hour) Type of failure: | Blocked By: None/Unknown | Related Tickets: Test Case: | Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- Comment (by mlen): I implemented this feature and a test case. Implementation took only few lines of code, but in order compile the compiler I needed to add quite a lot GHC_OPTIONS pragmas with -fno-warn-tabs (few git submodules were affected by this change). I have a week off and I won't have access to my computer, but I'll continue working on the patch when I get back. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9230#comment:6 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#9230: Make -fwarn-tabs the default -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: mlen Type: feature | Status: new request | Milestone: Priority: normal | Version: 7.8.2 Component: Compiler | Keywords: Resolution: | Architecture: Unknown/Multiple Operating System: | Difficulty: Easy (less than 1 Unknown/Multiple | hour) Type of failure: | Blocked By: None/Unknown | Related Tickets: Test Case: | Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- Comment (by mlen): The main patch can be found here: https://github.com/mlen/ghc/commit/62cd7b983aee6b581f42184fcc38b3d9bf50780e, while this commit includes only additions of -fno-warn-tabs: https://github.com/mlen/ghc/commit/1c60eaffe373bf6a6324d1a243130b9dbbf843b5 I still need to take care of submodules. libraries/{haskeline,hpc,stm,time,unix,xhtml} and utils/hsc2hs need to be patched because of -Werror. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9230#comment:8 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#9230: Make -fwarn-tabs the default -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: mlen Type: feature | Status: new request | Milestone: Priority: normal | Version: 7.8.2 Component: Compiler | Keywords: Resolution: | Architecture: Unknown/Multiple Operating System: | Difficulty: Easy (less than 1 Unknown/Multiple | hour) Type of failure: | Blocked By: None/Unknown | Related Tickets: Test Case: | Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- Comment (by mlen): I added the comment(s) and rebased over master. Will continue to work on patches for submodules during the weekend. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9230#comment:10 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#9230: Make -fwarn-tabs the default -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: mlen Type: feature | Status: new request | Milestone: 7.10.1 Priority: normal | Version: 7.8.2 Component: Compiler | Keywords: Resolution: | Architecture: Unknown/Multiple Operating System: | Difficulty: Easy (less than 1 Unknown/Multiple | hour) Type of failure: | Blocked By: None/Unknown | Related Tickets: Test Case: | Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- Changes (by asr): * cc: asr (added) -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9230#comment:12 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#9230: Make -fwarn-tabs the default -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: mlen Type: feature | Status: new request | Milestone: 7.10.1 Priority: normal | Version: 7.8.2 Component: Compiler | Keywords: Resolution: | Architecture: Unknown/Multiple Operating System: | Difficulty: Easy (less than 1 Unknown/Multiple | hour) Type of failure: | Blocked By: None/Unknown | Related Tickets: Test Case: | Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- Comment (by mlen): Great to hear that. I prepared the patches to suppress tab warnings in the submodules that caused troubles. Now I got stuck while de-tabbing the testsuite, as some tests won't pass. For example there are errors about wrong std{out,err} in should_compile (and others), but I should get that working soon. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9230#comment:14 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#9230: Make -fwarn-tabs the default -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: mlen Type: feature | Status: new request | Milestone: 7.10.1 Priority: normal | Version: 7.8.2 Component: Compiler | Keywords: Resolution: | Architecture: Unknown/Multiple Operating System: | Difficulty: Easy (less than 1 Unknown/Multiple | hour) Type of failure: | Blocked By: None/Unknown | Related Tickets: Test Case: | Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- Comment (by simonpj): I'm sorry, I'm quite confused. GHC already has a `-fwarn-tabs` flag, doesn't it? There are two patches offered above, but I'm not clear what the purpose of either is. Maybe I have not ready through this ticket carefully enough. Would someone just like to write down what the issue is, what the alternatives are, their pros and cons, and which of the alternatives they recommend following. I have no opinion myself; I'd just like see this resolved. Simon -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9230#comment:16 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#9230: Make -fwarn-tabs the default -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: mlen Type: feature | Status: new request | Milestone: 7.10.1 Priority: normal | Version: 7.8.2 Component: Compiler | Keywords: Resolution: | Architecture: Unknown/Multiple Operating System: | Difficulty: Easy (less than 1 Unknown/Multiple | hour) Type of failure: | Blocked By: None/Unknown | Related Tickets: Test Case: | Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- Comment (by thoughtpolice): The above patch does all of the above correctly; it is also on Phabricator - see Phab:D255 (which also built correctly). In essence it just adds `Opt_WarnTabs` (AKA `-fwarn-tabs`) to `standardWarnings` in `DynFlags`, which is the correct move. Next, it disables `-fno-warn-tabs` when building the libraries by modifying `mk /validate-settings.mk` to include `-fno-warn-tabs`, so that everything can validate correctly. I need to do a review on the testsuite changes in the patch, but it seems fine at a quick glance (I mostly wonder about the changes to the testsuite driver). -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9230#comment:18 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#9230: Make -fwarn-tabs the default -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: mlen Type: feature | Status: new request | Milestone: 7.10.1 Priority: normal | Version: 7.8.2 Component: Compiler | Keywords: Resolution: | Architecture: Unknown/Multiple Operating System: | Difficulty: Easy (less than 1 Unknown/Multiple | hour) Type of failure: | Blocked By: None/Unknown | Related Tickets: Test Case: | Blocking: | Differential Revisions: Phab:D255 | -------------------------------------+------------------------------------- Comment (by dfeuer): Replying to [comment:18 thoughtpolice]:

In essence it just adds `Opt_WarnTabs` (AKA `-fwarn-tabs`) to `standardWarnings` in `DynFlags`, which is the correct move. Next, it disables `-fno-warn-tabs` when building the libraries by modifying `mk /validate-settings.mk` to include `-fno-warn-tabs`, so that everything can validate correctly.

This may very well be the best thing for right now, but here's another idea that would take more work but might pay off in the long run, especially if other warnings are added to the defaults in the future. Instead of ''actually'' running ghc with `-Werror`, make the validation script watch for warnings. That is, replace an `Error` monad with a `Writer` monad. Given appropriate options, validation could ''collect'' warnings instead of halting immediately. This would allow us to automatically create lists of files for which specific warnings should be tolerated. Obviously, these lists would need to be maintained in order to prevent regressions, but this is easy: Phabricator (or whatever) would collect a "warning diff" from each build that passes validation, which could be used to update the lists. Ideally, we'd also find a way to trim down the warning list generated by a differential to just those files it changed, so as to get notice that something else might need to be fixed. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9230#comment:20 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#9230: Make -fwarn-tabs the default -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: mlen Type: feature | Status: patch request | Milestone: 7.10.1 Priority: normal | Version: 7.8.2 Component: Compiler | Keywords: Resolution: | Architecture: Unknown/Multiple Operating System: | Difficulty: Easy (less than 1 Unknown/Multiple | hour) Type of failure: | Blocked By: None/Unknown | Related Tickets: Test Case: | Blocking: | Differential Revisions: Phab:D255 | -------------------------------------+------------------------------------- Changes (by mlen): * status: new => patch -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9230#comment:22 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#9230: Make -fwarn-tabs the default -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: mlen Type: feature | Status: patch request | Milestone: 7.10.1 Priority: normal | Version: 7.8.2 Component: Compiler | Keywords: Resolution: | Architecture: Unknown/Multiple Operating System: | Difficulty: Easy (less than 1 Unknown/Multiple | hour) Type of failure: | Blocked By: None/Unknown | Related Tickets: Test Case: | Blocking: | Differential Revisions: Phab:D255 | -------------------------------------+------------------------------------- Changes (by oerjan): * cc: oerjan (added) Comment: This is an excellent change, but if it is to be newbie-friendly (which I ideally and egoistically define as "telling the user enough ''not'' to make yet another confused post on Stackoverflow"), maybe it could use a more explanatory error message than "Warning: Tab character"? Something like Tab characters aren't displayed portably. They can cause code to look correctly indented when it isn't, or vice versa, wildly varying dependent on the setup of the editor/browser/web site etc. used to view it. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9230#comment:24 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#9230: Make -fwarn-tabs the default -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: mlen Type: feature | Status: infoneeded request | Milestone: 7.10.1 Priority: normal | Version: 7.8.2 Component: Compiler | Keywords: Resolution: | Architecture: Unknown/Multiple Operating System: | Difficulty: Easy (less than 1 Unknown/Multiple | hour) Type of failure: | Blocked By: None/Unknown | Related Tickets: Test Case: | Blocking: | Differential Revisions: Phab:D255 | -------------------------------------+------------------------------------- Changes (by thomie): * status: patch => infoneeded -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9230#comment:26 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#9230: Make -fwarn-tabs the default -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: mlen Type: feature | Status: patch request | Milestone: 7.10.1 Priority: normal | Version: 7.8.2 Component: Compiler | Keywords: Resolution: | Architecture: Unknown/Multiple Operating System: | Difficulty: Easy (less than 1 Unknown/Multiple | hour) Type of failure: | Blocked By: None/Unknown | Related Tickets: Test Case: | Blocking: | Differential Revisions: Phab:D255, | Phab:D399 | -------------------------------------+------------------------------------- Comment (by Austin Seipp ): In [changeset:"c6d4ae6f437fb041ea70f3d2b4f7f0d03ff797bf/ghc"]: {{{ #!CommitTicketReference repository="ghc" revision="c6d4ae6f437fb041ea70f3d2b4f7f0d03ff797bf" Fix test driver python3 compatibility issues Summary: Fixes python3 compatibility issues by replacing filter with a list comperhension and a potential issue with python2 when override_flags would be an empty list. Reviewers: austin, thomie Reviewed By: austin, thomie Subscribers: thomie, carter, simonmar, mlen Differential Revision: https://phabricator.haskell.org/D399 GHC Trac Issues: #9230 }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9230#comment:28 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#9230: Make -fwarn-tabs the default -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: mlen Type: feature | Status: closed request | Milestone: 7.10.1 Priority: normal | Version: 7.8.2 Component: Compiler | Keywords: Resolution: fixed | Architecture: Unknown/Multiple Operating System: | Difficulty: Easy (less than 1 Unknown/Multiple | hour) Type of failure: | Blocked By: None/Unknown | Related Tickets: Test Case: | Blocking: | Differential Revisions: Phab:D255, | Phab:D399 | -------------------------------------+------------------------------------- Comment (by Polarina): Tabs are generally not the cause for incorrect indentation. It is mixing them with spaces that do. An alternative approach would be to warn if a tab character is preceded by a space. That would keep the tabs people happy, even those that use tabs for indentation and spaces for alignment; while catching most cases of tab/space mix-ups. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9230#comment:30 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

Tabs are generally not the cause for incorrect indentation. It is mixing

#9230: Make -fwarn-tabs the default -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: mlen Type: feature | Status: closed request | Milestone: 7.10.1 Priority: normal | Version: 7.8.2 Component: Compiler | Keywords: Resolution: fixed | Architecture: Unknown/Multiple Operating System: | Difficulty: Easy (less than 1 Unknown/Multiple | hour) Type of failure: | Blocked By: None/Unknown | Related Tickets: Test Case: | Blocking: | Differential Revisions: Phab:D255, | Phab:D399 | -------------------------------------+------------------------------------- Comment (by dfeuer): Replying to [comment:30 Polarina]: them with spaces that do.

An alternative approach would be to warn if a tab character is preceded

by a space. That would keep the tabs people happy, even those that use tabs for indentation and spaces for alignment; while catching most cases of tab/space mix-ups. I don't think that will do the trick, but this ticket's comments aren't the right venue for the discussion. If you have an idea for improving `-fwarn-tabs`, you should open a new ticket. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9230#comment:32 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#9230: Make -fwarn-tabs the default -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: mlen Type: feature request | Status: closed Priority: normal | Milestone: 7.10.1 Component: Compiler | Version: 7.8.2 Resolution: fixed | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: None/Unknown | Unknown/Multiple Blocked By: | Test Case: Related Tickets: | Blocking: | Differential Revisions: Phab:D255, | Phab:D399 -------------------------------------+------------------------------------- Comment (by oerjan): Replying to [comment:33 beroal]:

What about people who use tab characters for indentation regularly? My code looks correct for any tab character width chosen.

People who are sure they know what they're doing can use the `-fno-warn- tabs` flag. The reason for making this the default is that tabs trip up a ''lot'' of people who are new to Haskell. It also makes their pleas for help ''extremely'' confusing and time-wasting on a site like Stack Overflow, which autoconverts tabs to spaces - with a ''different'' width rule than Haskell uses. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9230#comment:34 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler