[GHC] #5624: Delay Errors Until Runtime

[GHC]

#5624: Delay Errors Until Runtime
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    Reporter:  atnnn             |       Owner:  atnnn           
        Type:  feature request   |      Status:  new             
    Priority:  high              |   Milestone:  7.6.1           
   Component:  Compiler          |     Version:  7.3             
    Keywords:                    |          Os:  Unknown/Multiple
Architecture:  Unknown/Multiple  |     Failure:  None/Unknown    
  Difficulty:                    |    Testcase:                  
   Blockedby:                    |    Blocking:                  
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Comment(by simonpj@…):

 commit 5508ada4b1d90ee54d92f69bbff7f66b3e8eceef
 {{{
 Author: Simon Peyton Jones <simonpj at microsoft.com>
 Date:   Thu Jan 12 15:10:54 2012 +0000

     Implememt -fdefer-type-errors (Trac #5624)

     This patch implements the idea of deferring (most) type errors to
     runtime, instead emitting only a warning at compile time.  The
     basic idea is very simple:

      * The on-the-fly unifier in TcUnify never fails; instead if it
        gets stuck it emits a constraint.

      * The constraint solver tries to solve the constraints (and is
        entirely unchanged, hooray).

      * The remaining, unsolved constraints (if any) are passed to
        TcErrors.reportUnsolved.  With -fdefer-type-errors, instead of
        emitting an error message, TcErrors emits a warning, AND emits
        a binding for the constraint witness, binding it
        to (error "the error message"), via the new form of evidence
        TcEvidence.EvDelayedError.  So, when the program is run,
        when (and only when) that witness is needed, the program will
        crash with the exact same error message that would have been
        given at compile time.

     Simple really.  But, needless to say, the exercise forced me
     into some major refactoring.

      * TcErrors is almost entirely rewritten

      * EvVarX and WantedEvVar have gone away entirely

      * ErrUtils is changed a bit:
          * New Severity field in ErrMsg
          * Renamed the type Message to MsgDoc (this change
            touches a lot of files trivially)

      * One minor change is that in the constraint solver we try
        NOT to combine insoluble constraints, like Int~Bool, else
        all such type errors get combined together and result in
        only one error message!

      * I moved some definitions from TcSMonad to TcRnTypes,
        where they seem to belong more

  compiler/coreSyn/CoreLint.lhs      |   76 ++--
  compiler/deSugar/DsBinds.lhs       |    7 +-
  compiler/deSugar/DsMonad.lhs       |    5 +-
  compiler/ghci/Linker.lhs           |    4 +-
  compiler/hsSyn/Convert.lhs         |   20 +-
  compiler/iface/LoadIface.lhs       |   10 +-
  compiler/iface/MkIface.lhs         |    2 +-
  compiler/iface/TcIface.lhs         |    2 +-
  compiler/main/CmdLineParser.hs     |    3 +-
  compiler/main/DynFlags.hs          |   16 +-
  compiler/main/ErrUtils.lhs         |  157 ++++----
  compiler/main/ErrUtils.lhs-boot    |    4 +-
  compiler/main/HeaderInfo.hs        |    2 +-
  compiler/main/HscMain.hs           |    8 +-
  compiler/main/HscTypes.lhs         |    4 +-
  compiler/main/Packages.lhs         |    8 +-
  compiler/parser/Lexer.x            |    6 +-
  compiler/rename/RnEnv.lhs          |    4 +-
  compiler/rename/RnNames.lhs        |    6 +-
  compiler/simplCore/CoreMonad.lhs   |    2 +-
  compiler/stgSyn/StgLint.lhs        |   40 +-
  compiler/typecheck/Inst.lhs        |   60 +--
  compiler/typecheck/TcBinds.lhs     |    4 +-
  compiler/typecheck/TcCanonical.lhs |  106 +++--
  compiler/typecheck/TcDeriv.lhs     |   10 +-
  compiler/typecheck/TcErrors.lhs    |  876
 +++++++++++++++++++++---------------
  compiler/typecheck/TcEvidence.lhs  |   19 +-
  compiler/typecheck/TcExpr.lhs      |    2 +-
  compiler/typecheck/TcForeign.lhs   |    4 +-
  compiler/typecheck/TcHsSyn.lhs     |    3 +
  compiler/typecheck/TcInteract.lhs  |   77 ++--
  compiler/typecheck/TcMType.lhs     |   13 +-
  compiler/typecheck/TcMatches.lhs   |   18 +
  compiler/typecheck/TcRnDriver.lhs  |    2 +-
  compiler/typecheck/TcRnMonad.lhs   |  149 ++++---
  compiler/typecheck/TcRnTypes.lhs   |  202 +++++----
  compiler/typecheck/TcSMonad.lhs    |   84 +----
  compiler/typecheck/TcSimplify.lhs  |  140 ++++--
  compiler/typecheck/TcSplice.lhs    |    8 +-
  compiler/typecheck/TcType.lhs      |   75 +++-
  compiler/typecheck/TcUnify.lhs     |  162 +++-----
  compiler/types/InstEnv.lhs         |    2 +-
  compiler/types/Unify.lhs           |    6 +-
  docs/users_guide/flags.xml         |   32 +-
  docs/users_guide/using.xml         |   26 ++
  45 files changed, 1340 insertions(+), 1126 deletions(-)
 }}}

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/5624#comment:7>
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