[GHC] #5273: error and undefined should print a location

[GHC]

#5273: error and undefined should print a location
-------------------------------------+-------------------------------------
        Reporter:  augustss          |                   Owner:
            Type:  feature request   |                  Status:  patch
        Priority:  low               |               Milestone:  7.12.1
       Component:  Compiler          |                 Version:  7.1
      Resolution:                    |                Keywords:
Operating System:  Unknown/Multiple  |            Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |               Test Case:
      Blocked By:                    |                Blocking:
 Related Tickets:  9049              |  Differential Revisions:  Phab:D861
-------------------------------------+-------------------------------------

Comment (by Ben Gamari <ben@…>):

 In [changeset:"6740d70d95cb81cea3859ff847afc61ec439db4f/ghc"
 6740d70d/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="6740d70d95cb81cea3859ff847afc61ec439db4f"
 Use IP based CallStack in error and undefined

 This patch modifies `error`, `undefined`, and `assertError` to use
 implicit call-stacks to provide better error messages to users.

 There are a few knock-on effects:

 - `GHC.Classes.IP` is now wired-in so it can be used in the wired-in
   types for `error` and `undefined`.

 - `TysPrim.tyVarList` has been replaced with a new function
   `TysPrim.mkTemplateTyVars`. `tyVarList` made it easy to introduce
   subtle bugs when you need tyvars of different kinds. The naive

   ```
   tv1 = head $ tyVarList kind1
   tv2 = head $ tyVarList kind2
   ```

   would result in `tv1` and `tv2` sharing a `Unique`, thus substitutions
   would be applied incorrectly, treating `tv1` and `tv2` as the same
   tyvar. `mkTemplateTyVars` avoids this pitfall by taking a list of kinds
   and producing a single tyvar of each kind.

 - The types `GHC.SrcLoc.SrcLoc` and `GHC.Stack.CallStack` now live in
   ghc-prim.

 - The type `GHC.Exception.ErrorCall` has a new constructor
   `ErrorCallWithLocation` that takes two `String`s instead of one, the
   2nd one being arbitrary metadata about the error (but usually the
   call-stack). A bi-directional pattern synonym `ErrorCall` continues to
   provide the old API.

 Updates Cabal, array, and haddock submodules.

 Reviewers: nh2, goldfire, simonpj, hvr, rwbarton, austin, bgamari

 Reviewed By: simonpj

 Subscribers: rwbarton, rodlogic, goldfire, maoe, simonmar, carter,
 liyang, bgamari, thomie

 Differential Revision: https://phabricator.haskell.org/D861

 GHC Trac Issues: #5273
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/5273#comment:10>
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