Template instance type synonym polish (#3054)

* Release note

* Desugaring is hard to type

* Upgrade hlint version to new ghc lib

* Use template instance type synonym in some tests

* Rm space

WORKSPACE

@@ -572,7 +572,7 @@ hazel_repositories(
             # Read [Working on ghc-lib] for ghc-lib update instructions at
             # https://github.com/digital-asset/daml/blob/master/ghc-lib/working-on-ghc-lib.md.
             hazel_ghclibs(GHC_LIB_VERSION, "02c71094a0bb06d6f6c4bbd444f9a26804c8eca423cc77fd3824ccd498ddaefe", "4aa88ed404dcf8a67f712ad37d8ad9f4ed51fe6180c15978a97034acf7dee834") +
-            hazel_github_external("digital-asset", "hlint", "f407a620cf38821320fb000e6ccd52f6bb081fc6", "5b5429a332910ebec481fe0f99ffce3159b10aef9188ba661512f8267fcde9a8") +
+            hazel_github_external("digital-asset", "hlint", "193b3eb89d186ae901ff6d95a70653258ed5eed9", "4f99badd7058b10f89207622bc719bd22b65ad401bf21cf8b33a7d79bbc000f6") +
             hazel_github_external("awakesecurity", "proto3-wire", "4f355bbac895d577d8a28f567ab4380f042ccc24", "031e05d523a887fbc546096618bc11dceabae224462a6cdd6aab11c1658e17a3") +
             hazel_github_external(
                 "awakesecurity",

compiler/damlc/daml-lf-conversion/src/DA/Daml/LFConversion.hs

@@ -496,7 +496,7 @@ convertTypeDef env (ATyCon t)
   , getOccFS t `elementOfUniqSet` internalTypes
   = pure []
 convertTypeDef env (ATyCon t)
-    -- NOTE(MH): We detect type synonyms produced by the desugring
+    -- NOTE(MH): We detect type synonyms produced by the desugaring
     -- of `template instance` declarations and inline the record definition
     -- of the generic template.
     | Just ([], TypeCon tpl args) <- synTyConDefn_maybe t

compiler/damlc/tests/daml-test-files/AnyTemplate.daml

@@ -40,9 +40,9 @@ main = scenario do
   fromAnyTemplate @T2 (toAnyTemplate t1) === None
   fromAnyTemplate @T2 (toAnyTemplate t2) === Some t2
   fromAnyTemplate @T1 (toAnyTemplate t2) === None
-  fromAnyTemplate @(GenericT T1) (toAnyTemplate gT1) === Some gT1
-  fromAnyTemplate @(GenericT T2) (toAnyTemplate gT1) === None
+  fromAnyTemplate @GT1 (toAnyTemplate gT1) === Some gT1
+  fromAnyTemplate @GT2 (toAnyTemplate gT1) === None
   fromAnyTemplate @T1 (toAnyTemplate gT1) === None
-  fromAnyTemplate @(GenericT T2) (toAnyTemplate gT2) === Some gT2
-  fromAnyTemplate @(GenericT T1) (toAnyTemplate gT2) === None
+  fromAnyTemplate @GT2 (toAnyTemplate gT2) === Some gT2
+  fromAnyTemplate @GT1 (toAnyTemplate gT2) === None
   fromAnyTemplate @T2 (toAnyTemplate gT2) === None

compiler/damlc/tests/daml-test-files/ComposedKey.daml

@@ -56,6 +56,6 @@ test = scenario do
     let fact = Fact with owner = alice; name = "Answer"; value = 23
     let prop = Proposal with asset = fact; proposers = [bob]; receivers = [alice]
     propId <- submit bob do create prop
-    (propId', prop') <- submit bob do fetchByKey @(Proposal Fact (Party, Text)) ([bob], (alice, "Answer"))
+    (propId', prop') <- submit bob do fetchByKey @ProposalFact ([bob], (alice, "Answer"))
     propId' === propId
     prop' === prop

compiler/damlc/tests/daml-test-files/ProposalDesugared.daml

@@ -176,7 +176,7 @@ instance IouInstance where
 
 
 -- The instantiation of the generic `Proposal a` template for `a = Iou`
--- in its deugared form.
+-- in its desugared form.
 type ProposalIou = Proposal Iou -- ^ TEMPLATE_INSTANCE
 
 instance ProposalInstance Iou where

compiler/damlc/tests/daml-test-files/ProposalIou.daml

@@ -36,11 +36,11 @@ test = scenario do
   propId <- submit bank do
     create prop
   (propId', prop') <- submit bank do
-    fetchByKey @(Proposal Iou) ([bank], "present")
+    fetchByKey @ProposalIou ([bank], "present")
   propId' === propId
   prop' === prop
   mbPropId <- submit bank do
-    lookupByKey @(Proposal Iou) ([bank], "present")
+    lookupByKey @ProposalIou ([bank], "present")
   mbPropId === Some propId
   iouId <- submit alice do
     exercise propId Accept

unreleased.rst

@@ -24,7 +24,11 @@ HEAD — ongoing
 - [DAML Tool - Visual]
   Adding `daml damlc visual-web` command. visual-command generates webpage with `d3 <https://d3js.org>`_ network.
 + [DAML Ledger Integration Kit] The transaction service is now fully tested.
-- [DAML Compiler] Fix a problem where constraints of the form `Template (Foo t)` caused the compiler to suggest enabling the `UndecidableInstances` language extension.
+- [DAML Compiler] Fix a problem where constraints of the form ``Template (Foo t)`` caused the compiler to suggest enabling the ``UndecidableInstances`` language extension.
 - [Security] Document how to verify the signature on release tarballs.
 + [DAML Ledger Integration Kit] The TTL for commands is now read from the configuration service.
 + [DAML Ledger Integration Kit] The contract key tests now live under a single test suite and are multi-node aware.
+- [DAML Compiler] **BREAKING CHANGE** Desugar template instances to ``type`` synonyms instead of ``newtype``s.
+  This type definition is easier to use in the surface DAML and consistent with the types translated to DAML LF.
+  The only change to user DAML is that uses of the ``TI`` ``newtype`` generated from
+  ``template instance TI = T A1 .. AN`` should be simplified to use the type synonym ``type TI = T A1 .. AN``.