txn LastLog (#3525)

* txn LastLog

* Insulate test from the type of field

10 files changed, 70 insertions, 11 deletions

diff --git a/data/transactions/logic/README.md b/data/transactions/logic/README.md
index 104a0d661..79cf215f9 100644
--- a/data/transactions/logic/README.md
+++ b/data/transactions/logic/README.md
@@ -454,6 +454,7 @@ Some of these have immediate data in the byte or bytes after the opcode.
 | 59 | NumLogs | uint64 | v5  | Number of Logs (only with `itxn` in v5). Application mode only |
 | 60 | CreatedAssetID | uint64 | v5  | Asset ID allocated by the creation of an ASA (only with `itxn` in v5). Application mode only |
 | 61 | CreatedApplicationID | uint64 | v5  | ApplicationID allocated by the creation of an application (only with `itxn` in v5). Application mode only |
+| 62 | LastLog | []byte | v6  | The last message emitted. Empty bytes if none were emitted. Application mode only |
 
 
 Additional details in the [opcodes document](TEAL_opcodes.md#txn) on the `txn` op.
diff --git a/data/transactions/logic/TEAL_opcodes.md b/data/transactions/logic/TEAL_opcodes.md
index 94ecee800..b68d7e3f7 100644
--- a/data/transactions/logic/TEAL_opcodes.md
+++ b/data/transactions/logic/TEAL_opcodes.md
@@ -436,6 +436,7 @@ The notation J,K indicates that two uint64 values J and K are interpreted as a u
 | 59 | NumLogs | uint64 | v5  | Number of Logs (only with `itxn` in v5). Application mode only |
 | 60 | CreatedAssetID | uint64 | v5  | Asset ID allocated by the creation of an ASA (only with `itxn` in v5). Application mode only |
 | 61 | CreatedApplicationID | uint64 | v5  | ApplicationID allocated by the creation of an application (only with `itxn` in v5). Application mode only |
+| 62 | LastLog | []byte | v6  | The last message emitted. Empty bytes if none were emitted. Application mode only |
 
 
 TypeEnum mapping:
diff --git a/data/transactions/logic/assembler_test.go b/data/transactions/logic/assembler_test.go
index 0758e5b2e..f310d7f21 100644
--- a/data/transactions/logic/assembler_test.go
+++ b/data/transactions/logic/assembler_test.go
@@ -1396,6 +1396,7 @@ itxna Logs 1
 itxn NumLogs
 itxn CreatedAssetID
 itxn CreatedApplicationID
+itxn LastLog
 `, AssemblerMaxVersion)
 	for _, globalField := range GlobalFieldNames {
 		if !strings.Contains(text, globalField) {
diff --git a/data/transactions/logic/doc.go b/data/transactions/logic/doc.go
index c7ac55212..185d212e2 100644
--- a/data/transactions/logic/doc.go
+++ b/data/transactions/logic/doc.go
@@ -471,6 +471,7 @@ var txnFieldDocs = map[string]string{
 
 	"Logs":                 "Log messages emitted by an application call (only with `itxn` in v5)",
 	"NumLogs":              "Number of Logs (only with `itxn` in v5)",
+	"LastLog":              "The last message emitted. Empty bytes if none were emitted",
 	"CreatedAssetID":       "Asset ID allocated by the creation of an ASA (only with `itxn` in v5)",
 	"CreatedApplicationID": "ApplicationID allocated by the creation of an application (only with `itxn` in v5)",
 }
diff --git a/data/transactions/logic/eval.go b/data/transactions/logic/eval.go
index 4cacc6396..c4dabbcf2 100644
--- a/data/transactions/logic/eval.go
+++ b/data/transactions/logic/eval.go
@@ -2231,6 +2231,12 @@ func (cx *EvalContext) txnFieldToStack(stxn *transactions.SignedTxnWithAD, fs *t
 		sv.Bytes = nilToEmpty([]byte(stxn.EvalDelta.Logs[arrayFieldIdx]))
 	case NumLogs:
 		sv.Uint = uint64(len(stxn.EvalDelta.Logs))
+	case LastLog:
+		if logs := len(stxn.EvalDelta.Logs); logs > 0 {
+			sv.Bytes = nilToEmpty([]byte(stxn.EvalDelta.Logs[logs-1]))
+		} else {
+			sv.Bytes = nilToEmpty(nil)
+		}
 	case CreatedAssetID:
 		sv.Uint = uint64(stxn.ApplyData.ConfigAsset)
 	case CreatedApplicationID:
diff --git a/data/transactions/logic/evalStateful_test.go b/data/transactions/logic/evalStateful_test.go
index cafc496fd..729d5a606 100644
--- a/data/transactions/logic/evalStateful_test.go
+++ b/data/transactions/logic/evalStateful_test.go
@@ -336,7 +336,19 @@ func testApps(t *testing.T, programs []string, txgroup []transactions.SignedTxn,
 			codes[i] = testProg(t, program, version).Program
 		}
 	}
+	if txgroup == nil {
+		for _, program := range programs {
+			sample := makeSampleTxn()
+			if program != "" {
+				sample.Txn.Type = protocol.ApplicationCallTx
+			}
+			txgroup = append(txgroup, sample)
+		}
+	}
 	ep := NewEvalParams(transactions.WrapSignedTxnsWithAD(txgroup), makeTestProtoV(version), &transactions.SpecialAddresses{})
+	if ledger == nil {
+		ledger = MakeLedger(nil)
+	}
 	ep.Ledger = ledger
 	testAppsBytes(t, codes, ep, expected...)
 }
@@ -2386,6 +2398,32 @@ func TestReturnTypes(t *testing.T) {
 	}
 }
 
+func TestTxnEffects(t *testing.T) {
+	partitiontest.PartitionTest(t)
+	t.Parallel()
+	ep, _, _ := makeSampleEnv()
+	// We don't allow the effects fields to see the current or future transactions
+	testApp(t, "byte 0x32; log; txn NumLogs; int 1; ==", ep)
+	testApp(t, "byte 0x32; log; txn Logs 0; byte 0x32; ==", ep)
+	testApp(t, "byte 0x32; log; txn LastLog; byte 0x32; ==", ep)
+	testApp(t, "byte 0x32; log; gtxn 0 NumLogs; int 1; ==", ep)
+	testApp(t, "byte 0x32; log; gtxn 0 Logs 0; byte 0x32; ==", ep)
+	testApp(t, "byte 0x32; log; gtxn 0 LastLog; byte 0x32; ==", ep)
+
+	// Look at the logs of tx 0
+	testApps(t, []string{"", "byte 0x32; log; gtxn 0 LastLog; byte 0x; =="}, nil, AssemblerMaxVersion, nil)
+	testApps(t, []string{"byte 0x33; log; int 1", "gtxn 0 LastLog; byte 0x33; =="}, nil, AssemblerMaxVersion, nil)
+	testApps(t, []string{"byte 0x33; dup; log; log; int 1", "gtxn 0 NumLogs; int 2; =="}, nil, AssemblerMaxVersion, nil)
+	testApps(t, []string{"byte 0x37; log; int 1", "gtxn 0 Logs 0; byte 0x37; =="}, nil, AssemblerMaxVersion, nil)
+	testApps(t, []string{"byte 0x37; log; int 1", "int 0; gtxnas 0 Logs; byte 0x37; =="}, nil, AssemblerMaxVersion, nil)
+
+	// Look past the logs of tx 0
+	testApps(t, []string{"byte 0x37; log; int 1", "gtxna 0 Logs 1; byte 0x37; =="}, nil, AssemblerMaxVersion, nil,
+		Expect{1, "invalid Logs index 1"})
+	testApps(t, []string{"byte 0x37; log; int 1", "int 6; gtxnas 0 Logs; byte 0x37; =="}, nil, AssemblerMaxVersion, nil,
+		Expect{1, "invalid Logs index 6"})
+}
+
 func TestRound(t *testing.T) {
 	partitiontest.PartitionTest(t)
 	t.Parallel()
diff --git a/data/transactions/logic/eval_test.go b/data/transactions/logic/eval_test.go
index c7f703b9f..841f180af 100644
--- a/data/transactions/logic/eval_test.go
+++ b/data/transactions/logic/eval_test.go
@@ -1390,6 +1390,11 @@ byte "prefilled"
 ==
 assert
 
+txn LastLog
+byte "prefilled"
+==
+assert
+
 int 1
 `
 
diff --git a/data/transactions/logic/fields.go b/data/transactions/logic/fields.go
index a1c944ffb..7dbbc91f5 100644
--- a/data/transactions/logic/fields.go
+++ b/data/transactions/logic/fields.go
@@ -159,6 +159,9 @@ const (
 	// CreatedApplicationID Transaction.ApplyData.EvalDelta.ApplicationID
 	CreatedApplicationID
 
+	// LastLog Logs[len(Logs)-1]
+	LastLog
+
 	invalidTxnField // fence for some setup that loops from Sender..invalidTxnField
 )
 
@@ -275,10 +278,12 @@ var txnFieldSpecs = []txnFieldSpec{
 	{ExtraProgramPages, StackUint64, false, 4, 6, false},
 	{Nonparticipation, StackUint64, false, 5, 6, false},
 
-	{Logs, StackBytes, true, 5, 5, true},
-	{NumLogs, StackUint64, false, 5, 5, true},
-	{CreatedAssetID, StackUint64, false, 5, 5, true},
-	{CreatedApplicationID, StackUint64, false, 5, 5, true},
+	// "Effects" Last two things are always going to: 0, true
+	{Logs, StackBytes, true, 5, 0, true},
+	{NumLogs, StackUint64, false, 5, 0, true},
+	{CreatedAssetID, StackUint64, false, 5, 0, true},
+	{CreatedApplicationID, StackUint64, false, 5, 0, true},
+	{LastLog, StackBytes, false, 6, 0, true},
 }
 
 // TxnaFieldNames are arguments to the 'txna' opcode
diff --git a/data/transactions/logic/fields_string.go b/data/transactions/logic/fields_string.go
index 34515d78d..91e77a115 100644
--- a/data/transactions/logic/fields_string.go
+++ b/data/transactions/logic/fields_string.go
@@ -70,12 +70,13 @@ func _() {
 	_ = x[NumLogs-59]
 	_ = x[CreatedAssetID-60]
 	_ = x[CreatedApplicationID-61]
-	_ = x[invalidTxnField-62]
+	_ = x[LastLog-62]
+	_ = x[invalidTxnField-63]
 }
 
-const _TxnField_name = "SenderFeeFirstValidFirstValidTimeLastValidNoteLeaseReceiverAmountCloseRemainderToVotePKSelectionPKVoteFirstVoteLastVoteKeyDilutionTypeTypeEnumXferAssetAssetAmountAssetSenderAssetReceiverAssetCloseToGroupIndexTxIDApplicationIDOnCompletionApplicationArgsNumAppArgsAccountsNumAccountsApprovalProgramClearStateProgramRekeyToConfigAssetConfigAssetTotalConfigAssetDecimalsConfigAssetDefaultFrozenConfigAssetUnitNameConfigAssetNameConfigAssetURLConfigAssetMetadataHashConfigAssetManagerConfigAssetReserveConfigAssetFreezeConfigAssetClawbackFreezeAssetFreezeAssetAccountFreezeAssetFrozenAssetsNumAssetsApplicationsNumApplicationsGlobalNumUintGlobalNumByteSliceLocalNumUintLocalNumByteSliceExtraProgramPagesNonparticipationLogsNumLogsCreatedAssetIDCreatedApplicationIDinvalidTxnField"
+const _TxnField_name = "SenderFeeFirstValidFirstValidTimeLastValidNoteLeaseReceiverAmountCloseRemainderToVotePKSelectionPKVoteFirstVoteLastVoteKeyDilutionTypeTypeEnumXferAssetAssetAmountAssetSenderAssetReceiverAssetCloseToGroupIndexTxIDApplicationIDOnCompletionApplicationArgsNumAppArgsAccountsNumAccountsApprovalProgramClearStateProgramRekeyToConfigAssetConfigAssetTotalConfigAssetDecimalsConfigAssetDefaultFrozenConfigAssetUnitNameConfigAssetNameConfigAssetURLConfigAssetMetadataHashConfigAssetManagerConfigAssetReserveConfigAssetFreezeConfigAssetClawbackFreezeAssetFreezeAssetAccountFreezeAssetFrozenAssetsNumAssetsApplicationsNumApplicationsGlobalNumUintGlobalNumByteSliceLocalNumUintLocalNumByteSliceExtraProgramPagesNonparticipationLogsNumLogsCreatedAssetIDCreatedApplicationIDLastLoginvalidTxnField"
 
-var _TxnField_index = [...]uint16{0, 6, 9, 19, 33, 42, 46, 51, 59, 65, 81, 87, 98, 107, 115, 130, 134, 142, 151, 162, 173, 186, 198, 208, 212, 225, 237, 252, 262, 270, 281, 296, 313, 320, 331, 347, 366, 390, 409, 424, 438, 461, 479, 497, 514, 533, 544, 562, 579, 585, 594, 606, 621, 634, 652, 664, 681, 698, 714, 718, 725, 739, 759, 774}
+var _TxnField_index = [...]uint16{0, 6, 9, 19, 33, 42, 46, 51, 59, 65, 81, 87, 98, 107, 115, 130, 134, 142, 151, 162, 173, 186, 198, 208, 212, 225, 237, 252, 262, 270, 281, 296, 313, 320, 331, 347, 366, 390, 409, 424, 438, 461, 479, 497, 514, 533, 544, 562, 579, 585, 594, 606, 621, 634, 652, 664, 681, 698, 714, 718, 725, 739, 759, 766, 781}
 
 func (i TxnField) String() string {
 	if i < 0 || i >= TxnField(len(_TxnField_index)-1) {
diff --git a/data/transactions/logic/fields_test.go b/data/transactions/logic/fields_test.go
index d40ddc263..78cac3569 100644
--- a/data/transactions/logic/fields_test.go
+++ b/data/transactions/logic/fields_test.go
@@ -180,9 +180,9 @@ func TestTxnEffectsAvailable(t *testing.T) {
 		if !fs.effects {
 			continue
 		}
-		source := fmt.Sprintf("txn %s", fs.field.String())
+		source := fmt.Sprintf("txn %s; pop; int 1", fs.field)
 		if fs.array {
-			source = fmt.Sprintf("txna %s 0", fs.field.String())
+			source = fmt.Sprintf("txn %s 0; pop; int 1", fs.field)
 		}
 		for v := fs.version; v <= AssemblerMaxVersion; v++ {
 			ops := testProg(t, source, v)
@@ -193,12 +193,12 @@ func TestTxnEffectsAvailable(t *testing.T) {
 			ep.Ledger = MakeLedger(nil)
 			_, err = EvalApp(ops.Program, 0, 0, ep)
 			if v < txnEffectsVersion {
-				require.Error(t, err)
+				require.Error(t, err, source)
 			} else {
 				if fs.array {
 					continue // Array (Logs) will be 0 length, so will fail anyway
 				}
-				require.NoError(t, err)
+				require.NoError(t, err, source)
 			}
 		}
 	}