[GHC] #9573: Add warning for invalid digits in integer literals

[GHC]

#9573: Add warning for invalid digits in integer literals
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              Reporter:  vlopez      |            Owner:  vlopez
                  Type:  bug         |           Status:  new
              Priority:  normal      |        Milestone:  7.10.1
             Component:  Compiler    |          Version:  7.9
  (Parser)                           |         Keywords:  parsing, integer,
            Resolution:              |  octal, binary, hexadecimal,
      Operating System:              |     Architecture:  Unknown/Multiple
  Unknown/Multiple                   |       Difficulty:  Difficult (2-5
       Type of failure:              |  days)
  None/Unknown                       |       Blocked By:
             Test Case:              |  Related Tickets:
              Blocking:              |
Differential Revisions:              |
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Comment (by vlopez):

 I fully agree with making it an error, and simplifying lexing of numeric
 literals

 However, there's at least one test case which would fail.¹ As for the
 Haskell report, there's no explicit rule about number literals being
 separated by whitespace.

 I'd suggest giving a deprecated warning for 7.10. Then, for 7.12, the
 lexer can be switched to the new behaviour, and the language report
 updated accordingly.

 1.
 [http://git.haskell.org/ghc.git/blob/c0fa383d9109800a4e46a81b418f1794030ba1bd:/testsuite/tests/parser/should_run/BinaryLiterals0.hs]

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9573#comment:4>
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