[GHC] #10993: Bad error message reported when -XBinaryLiterals is not enabled

[GHC]

#10993: Bad error message reported when -XBinaryLiterals is not enabled
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           Reporter:  osa1           |             Owner:
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  7.11
  (Parser)                           |
           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:
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 When `-XBinaryLiterals` is not enabled, expressions like `0b10101` is
 causing
 this horrible error message: `Not in scope: ‘b10101’`.

 The reason, as far as I understand, is that lexer is not lexing `0b0101`
 as a
 single token when `-XBinaryLiterals` is not enabled. Then the parser is
 parsing
 this as an application of `0` to `b0101`. (this can be observed with
 `-ddump-parsed`)

 My suggestion:

 Lexer should always generate a single token for `0b0101`. We don't do
 `ifExtension binaryLiteralsEnabled` checks in the lexer anymore. We
 somehow
 mark generated token as "requires extension: BinaryLiterals"(I don't know
 if we
 have the infrastructure for this right now). Then, when the parser sees an
 integer that requires `-XBinaryLiterals`, checks the flag and reports the
 error
 etc.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10993>
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