Linear types (#15981)

This is the first step towards implementation of the linear types proposal
(https://github.com/ghc-proposals/ghc-proposals/pull/111).

It features

* A language extension -XLinearTypes
* Syntax for linear functions in the surface language
* Linearity checking in Core Lint, enabled with -dlinear-core-lint
* Core-to-core passes are mostly compatible with linearity
* Fields in a data type can be linear or unrestricted; linear fields
  have multiplicity-polymorphic constructors.
  If -XLinearTypes is disabled, the GADT syntax defaults to linear fields

The following items are not yet supported:

* a # m -> b syntax (only prefix FUN is supported for now)
* Full multiplicity inference (multiplicities are really only checked)
* Decent linearity error messages
* Linear let, where, and case expressions in the surface language
  (each of these currently introduce the unrestricted variant)
* Multiplicity-parametric fields
* Syntax for annotating lambda-bound or let-bound with a multiplicity
* Syntax for non-linear/multiple-field-multiplicity records
* Linear projections for records with a single linear field
* Linear pattern synonyms
* Multiplicity coercions (test LinearPolyType)

A high-level description can be found at
https://ghc.haskell.org/trac/ghc/wiki/LinearTypes/Implementation
Following the link above you will find a description of the changes made to Core.
This commit has been authored by

* Richard Eisenberg
* Krzysztof Gogolewski
* Matthew Pickering
* Arnaud Spiwack

With contributions from:

* Mark Barbone
* Alexander Vershilov

Updates haddock submodule.

1 files changed, 6 insertions, 4 deletions

diff --git a/compiler/GHC/CoreToByteCode.hs b/compiler/GHC/CoreToByteCode.hs
index 96f1f96e63..5c6b034360 100644
--- a/compiler/GHC/CoreToByteCode.hs
+++ b/compiler/GHC/CoreToByteCode.hs
@@ -1,6 +1,7 @@
 {-# LANGUAGE CPP, MagicHash, RecordWildCards, BangPatterns #-}
 {-# LANGUAGE DeriveFunctor #-}
 {-# LANGUAGE GeneralizedNewtypeDeriving #-}
+{-# LANGUAGE PatternSynonyms #-}
 {-# OPTIONS_GHC -fprof-auto-top #-}
 {-# OPTIONS_GHC -Wno-incomplete-uni-patterns #-}
 --
@@ -28,7 +29,7 @@ import GHC.Platform
 import GHC.Types.Name
 import GHC.Types.Id.Make
 import GHC.Types.Id
-import GHC.Types.Var ( updateVarType )
+import GHC.Types.Var ( updateVarTypeButNotMult )
 import GHC.Types.ForeignCall
 import GHC.Driver.Types
 import GHC.Core.Utils
@@ -37,6 +38,7 @@ import GHC.Core.Ppr
 import GHC.Types.Literal
 import GHC.Builtin.PrimOps
 import GHC.Core.FVs
+import GHC.Core.Multiplicity ( pattern Many )
 import GHC.Core.Type
 import GHC.Types.RepType
 import GHC.Core.DataCon
@@ -625,7 +627,7 @@ schemeE d s p exp@(AnnTick (Breakpoint _id _fvs) _rhs)
           -- Here (k n) :: a :: Type r, so we don't know if it's lifted
           -- or not; but that should be fine provided we add that void arg.
 
-          id <- newId (mkVisFunTy realWorldStatePrimTy ty)
+          id <- newId (mkVisFunTyMany realWorldStatePrimTy ty)
           st <- newId realWorldStatePrimTy
           let letExp = AnnLet (AnnNonRec id (fvs, AnnLam st (emptyDVarSet, exp)))
                               (emptyDVarSet, (AnnApp (emptyDVarSet, AnnVar id)
@@ -708,7 +710,7 @@ protectNNLJoinPointBind x rhs@(fvs, _)
 protectNNLJoinPointId :: Id -> Id
 protectNNLJoinPointId x
   = ASSERT( isNNLJoinPoint x )
-    updateVarType (voidPrimTy `mkVisFunTy`) x
+    updateVarTypeButNotMult (voidPrimTy `mkVisFunTyMany`) x
 
 {-
    Ticked Expressions
@@ -2060,7 +2062,7 @@ getTopStrings = BcM $ \st -> return (st, topStrings st)
 newId :: Type -> BcM Id
 newId ty = do
     uniq <- newUnique
-    return $ mkSysLocal tickFS uniq ty
+    return $ mkSysLocal tickFS uniq Many ty
 
 tickFS :: FastString
 tickFS = fsLit "ticked"