[GHC] #11789: Flag suggestion does not always work

[GHC]

#11789: Flag suggestion does not always work
-------------------------------------+-------------------------------------
        Reporter:  nomeata           |                Owner:
            Type:  feature request   |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Driver            |              Version:  8.0.1
      Resolution:                    |             Keywords:  newcomer
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #11429            |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------
Changes (by thomie):

 * version:  8.1 => 8.0.1
 * related:   => #11429


Comment:

 ghc-8.0.1 never suggests alternative spellings for misspelled //warning//
 flags. This should be fixed as well.

 With `-Wno-unrecognised-warning-flags` (#11429), unknown warning flags on
 the command line are now reported as warnings instead of errors, so they
 never reach the `unknownFlagsErr` function in `ghc/Main.hs`.

 The issue with `-fppr-cols=1000` vs `-dppr-cols=1000` is that the edit
 distance is too large. The flag passed to the fuzzy matcher should
 probably break at the `'='` character.

 From `fuzzyLookup` in `compiler/utils/Util.hs`:
 {{{
     -- Work out an approriate match threshold:
     -- We report a candidate if its edit distance is <= the threshold,
     -- The threshhold is set to about a quarter of the # of characters the
 user entered
     --   Length    Threshold
     --     1         0          -- Don't suggest *any* candidates
     --     2         1          -- for single-char identifiers
     --     3         1
     --     4         1
     --     5         1
     --     6         2
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11789#comment:1>
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