decode key expressions in scala correctly. fixes #177 (#214)

* decode key expressions in scala correctly. fixes #177

replaced a `foldRight` with a `foldLeft`, projections were decoded
backwards.

* remove ContractKeysSimple -- superseded by ContractKeys

daml-foundations/daml-ghc/tests/ContractKeys.daml

@@ -1,9 +1,7 @@
 -- Check that the compiler bits of contract keys work.
--- @TODO (#177): Fix the engine such that this test passes. Remove `ContractKeysSimple.daml` when it does.
 -- @IGNORE-LF 1.0
 -- @IGNORE-LF 1.1
 -- @IGNORE-LF 1.2
--- @ERROR CRASH: RecProj on non-record
 daml 1.2
 module ContractKeys where
 

daml-foundations/daml-ghc/tests/ContractKeysSimple.daml

@@ -1,51 +0,0 @@
--- Check that the compiler bits of contract keys work.
--- @TODO (#177): Remove this test when #177 has been fixed.
--- @IGNORE-LF 1.0
--- @IGNORE-LF 1.1
--- @IGNORE-LF 1.2
-daml 1.2
-module ContractKeysSimple where
-
-template AccountInvitation with
-    account : Account
-  where
-    signatory account.bank
-
-    controller account.accountHolder can
-      Accept : ContractId Account
-        do create account
-
-template Account with
-    bank : Party
-    accountHolder : Party
-    accountCode : Text
-    accountNumber : Int
-  where
-    signatory [bank, accountHolder]
-
-instance Key Account (Party, Text, Int) where
-    key acc = (acc.bank, acc.accountCode, acc.accountNumber)
-    keyMaintainers Proxy (bank, _, _) = [bank]
-
-test = scenario do
-    bank <- getParty "Bank"
-    alice <- getParty "Alice"
-    let account = Account with
-            bank
-            accountHolder = alice
-            accountCode = "CH"
-            accountNumber = 123
-    let accountKey = (bank, "CH", 123)
-    invitationCid <- submit bank do
-        create AccountInvitation with account
-    accountCid <- submit alice do
-        exercise invitationCid Accept
-
-    accountCid' <- submit bank do
-        lookupByKey accountKey
-    assert $ accountCid' == Some accountCid
-
-    (accountCid', account') <- submit bank do
-        fetchByKey accountKey
-    assert $ accountCid' == accountCid
-    assert $ account' == account

daml-lf/lfpackage/src/main/scala/com/digitalasset/daml/lf/lfpackage/DecodeV1.scala

@@ -164,8 +164,8 @@ private[lf] class DecodeV1(minor: LanguageMinorVersion) extends Decode.OfPackage
 
         case PLF.KeyExpr.SumCase.PROJECTIONS =>
           val lfProjs = expr.getProjections.getProjectionsList.asScala
-          (lfProjs :\ (EVar(tplVar): Expr)) {
-            case (lfProj, acc) =>
+          lfProjs.foldLeft(EVar(tplVar): Expr) {
+            case (acc, lfProj) =>
               ERecProj(decodeTypeConApp(lfProj.getTycon), lfProj.getField, acc)
           }