Merge pull request #1074 from lightninglabs/backward-compat-itest

custom channels: add itest to demonstrate that backward compatibility with v0.14.1-alpha is restored

.github/workflows/main.yml

@@ -279,11 +279,11 @@ jobs:
       matrix:
         include:
           - name: bbolt
-            args: itest icase=terminal dbbackend=bbolt
+            args: itest-no-backward-compat icase=terminal dbbackend=bbolt
           - name: sqlite
-            args: itest icase=terminal dbbackend=sqlite
+            args: itest-no-backward-compat icase=terminal dbbackend=sqlite
           - name: postgres
-            args: itest icase=terminal dbbackend=postgres
+            args: itest-no-backward-compat icase=terminal dbbackend=postgres
           - name: custom-channels
             args: itest-only icase=custom_channels
             

.gitignore

@@ -9,11 +9,12 @@ litcli-debug
 .DS_Store
 
 itest/btcd-itest
-itest/litd-itest
+itest/litd-itest*
 itest/lnd-itest
 itest/itest.test
 itest/.logs
 itest/*.log
+itest/backward-compat
 
 vendor
 *.idea

Makefile

@@ -24,6 +24,12 @@ PUBLIC_URL :=
 # versions are checked against this version.
 GO_VERSION = 1.23.6
 
+# LITD_COMPAT_VERSIONS is a space-separated list of litd versions that are
+# installed before running the integration tests which include backward
+# compatibility tests. The list of versions must be in sync with any version
+# used in the backwardCompat map in itest/litd_test_list_on_test.go.
+LITD_COMPAT_VERSIONS = v0.14.1-alpha
+
 LOOP_COMMIT := $(shell cat go.mod | \
 		grep $(LOOP_PKG) | \
 		head -n1 | \
@@ -233,7 +239,11 @@ build-itest:
 	CGO_ENABLED=0 $(GOBUILD) -tags="$(ITEST_TAGS)" -o itest/btcd-itest -ldflags "$(ITEST_LDFLAGS)" $(BTCD_PKG)
 	CGO_ENABLED=0 $(GOBUILD) -tags="$(ITEST_TAGS)" -o itest/lnd-itest -ldflags "$(ITEST_LDFLAGS)" $(LND_PKG)/cmd/lnd
 
-itest-only: build-itest
+install-backward-compat-versions:
+	@$(call print, "Installing old versions of litd for backward compatibility tests.")
+	scripts/install-backward-compat-versions.sh '$(LITD_COMPAT_VERSIONS)'
+
+run-itest-only:
 	@$(call print, "Building itest binary.")
 	CGO_ENABLED=0 $(GOBUILD) -tags="$(ITEST_TAGS)" -o itest/litd-itest -ldflags "$(ITEST_LDFLAGS)" $(PKG)/cmd/litd
 	CGO_ENABLED=0 $(GOTEST) -v ./itest -tags="$(DEV_TAGS) $(ITEST_TAGS)" -c -o itest/itest.test
@@ -242,8 +252,12 @@ itest-only: build-itest
 	rm -rf itest/*.log itest/.logs*; date
 	scripts/itest_part.sh $(ITEST_FLAGS)
 
+itest-only: build-itest install-backward-compat-versions run-itest-only
+
 itest: app-build build-itest itest-only
 
+itest-no-backward-compat: app-build build-itest build-itest run-itest-only
+
 # =============
 # FLAKE HUNTING
 # =============

go.mod

@@ -29,7 +29,7 @@ require (
 	github.com/lightninglabs/pool v0.6.5-beta.0.20250305125211-4e860ec4e77f
 	github.com/lightninglabs/pool/auctioneerrpc v1.1.3-0.20250305125211-4e860ec4e77f
 	github.com/lightninglabs/pool/poolrpc v1.0.1-0.20250305125211-4e860ec4e77f
-	github.com/lightninglabs/taproot-assets v0.6.0-rc1.0.20250515090148-95af3680134e
+	github.com/lightninglabs/taproot-assets v0.6.0-rc1.0.20250515215758-1660f9ccd5d4
 	github.com/lightninglabs/taproot-assets/taprpc v1.0.3
 	github.com/lightningnetwork/lnd v0.19.0-beta.rc3
 	github.com/lightningnetwork/lnd/cert v1.2.2

go.sum

@@ -506,8 +506,8 @@ github.com/lightninglabs/pool/poolrpc v1.0.1-0.20250305125211-4e860ec4e77f h1:5p
 github.com/lightninglabs/pool/poolrpc v1.0.1-0.20250305125211-4e860ec4e77f/go.mod h1:lGs2hSVZ+GFpdv3btaIl9icG5/gz7BBRfvmD2iqqNl0=
 github.com/lightninglabs/protobuf-go-hex-display v1.34.2-hex-display h1:w7FM5LH9Z6CpKxl13mS48idsu6F+cEZf0lkyiV+Dq9g=
 github.com/lightninglabs/protobuf-go-hex-display v1.34.2-hex-display/go.mod h1:qYOHts0dSfpeUzUFpOMr/WGzszTmLH+DiWniOlNbLDw=
-github.com/lightninglabs/taproot-assets v0.6.0-rc1.0.20250515090148-95af3680134e h1:l6UObl0hucKdrfdla/FC+UWON9v2VfrN3BTtHnUySo4=
-github.com/lightninglabs/taproot-assets v0.6.0-rc1.0.20250515090148-95af3680134e/go.mod h1:OdeFcj2bnJf6aaYjBB5c8KdNI3aDaEMQpsSu2EqvMlw=
+github.com/lightninglabs/taproot-assets v0.6.0-rc1.0.20250515215758-1660f9ccd5d4 h1:GOqIfTRyMRQBioFXBqL757nWXMeaHrK9Hh9HVKK8Pg0=
+github.com/lightninglabs/taproot-assets v0.6.0-rc1.0.20250515215758-1660f9ccd5d4/go.mod h1:OdeFcj2bnJf6aaYjBB5c8KdNI3aDaEMQpsSu2EqvMlw=
 github.com/lightninglabs/taproot-assets/taprpc v1.0.3 h1:Vt9vKNwAFGfJ/I29C1gSEwD0pcNeI53pFRCPf/WBgHI=
 github.com/lightninglabs/taproot-assets/taprpc v1.0.3/go.mod h1:Ccq0t2GsXzOtC8qF0U1ux/yTF5HcBbVrhCb0tb/jObM=
 github.com/lightningnetwork/lightning-onion v1.2.1-0.20240712235311-98bd56499dfb h1:yfM05S8DXKhuCBp5qSMZdtSwvJ+GFzl94KbXMNB1JDY=

itest/assets_test.go

@@ -207,20 +207,20 @@ func createTestAssetNetwork(t *harnessTest, net *NetworkHarness, charlieTap,
 	erinAssetBalance := assetSendAmount - erinFundingAmount
 
 	// Assert that we see the funding outputs in the wallet.
-	itest.AssertBalances(
+	assertBalance(
 		t.t, charlieTap, charlieFundingAmount,
 		itest.WithAssetID(assetID),
 		itest.WithScriptKeyType(asset.ScriptKeyScriptPathChannel),
 		itest.WithNumUtxos(1),
 		itest.WithScriptKey(fundingScriptKeyBytes),
 	)
-	itest.AssertBalances(
+	assertBalance(
 		t.t, daveTap, daveFundingAmount, itest.WithAssetID(assetID),
 		itest.WithScriptKeyType(asset.ScriptKeyScriptPathChannel),
 		itest.WithNumUtxos(1),
 		itest.WithScriptKey(fundingScriptKeyBytes),
 	)
-	itest.AssertBalances(
+	assertBalance(
 		t.t, erinTap, erinFundingAmount, itest.WithAssetID(assetID),
 		itest.WithScriptKeyType(asset.ScriptKeyScriptPathChannel),
 		itest.WithNumUtxos(1),
@@ -229,14 +229,13 @@ func createTestAssetNetwork(t *harnessTest, net *NetworkHarness, charlieTap,
 
 	// After opening the channels, the asset balance of the funding nodes
 	// should have been decreased with the funding amount.
-	itest.AssertBalances(
-		t.t, charlieTap, charlieAssetBalance,
-		itest.WithAssetID(assetID),
+	assertBalance(
+		t.t, charlieTap, charlieAssetBalance, itest.WithAssetID(assetID),
 	)
-	itest.AssertBalances(
+	assertBalance(
 		t.t, daveTap, daveAssetBalance, itest.WithAssetID(assetID),
 	)
-	itest.AssertBalances(
+	assertBalance(
 		t.t, erinTap, erinAssetBalance, itest.WithAssetID(assetID),
 	)
 
@@ -527,6 +526,18 @@ func createTestAssetNetworkGroupKey(ctx context.Context, t *harnessTest,
 	return chanPointCD, chanPointEF
 }
 
+// assertBalance is a thin wrapper around itest.AssertBalances that skips the
+// balance check for old versions during the backward compatibility test.
+func assertBalance(t *testing.T, client *tapClient, balance uint64,
+	opts ...itest.BalanceOption) {
+
+	if client.node.Cfg.SkipBalanceChecks {
+		return
+	}
+
+	itest.AssertBalances(t, client, balance, opts...)
+}
+
 // sendAssetsAndAssert sends the given amount of assets to the recipient and
 // asserts that the transfer was successful. It also checks that the asset
 // balance of the sender and recipient is as expected.
@@ -718,6 +729,12 @@ func assertPendingChannels(t *testing.T, node *HarnessNode,
 	require.NoError(t, err)
 	require.Len(t, pendingChannelsResp.PendingOpenChannels, numChannels)
 
+	// For older versions (during the backward compatibility test), if the
+	// channel custom data is in the old format, we can't do further checks.
+	if node.Cfg.OldChannelFormat {
+		return
+	}
+
 	pendingChan := pendingChannelsResp.PendingOpenChannels[0]
 	var pendingJSON rfqmsg.JsonAssetChannel
 	err = json.Unmarshal(
@@ -768,6 +785,12 @@ func haveFundingAsset(assetChannel *rfqmsg.JsonAssetChannel,
 func assertAssetChan(t *testing.T, src, dst *HarnessNode, fundingAmount uint64,
 	channelAssets []*taprpc.Asset) {
 
+	if src.Cfg.OldChannelFormat {
+		t.Logf("Skipping asset channel check for %s->%s, old format",
+			src.Cfg.Name, dst.Cfg.Name)
+		return
+	}
+
 	err := wait.NoError(func() error {
 		a, err := getChannelCustomData(src, dst)
 		if err != nil {
@@ -1822,8 +1845,12 @@ func closeAssetChannelAndAssert(t *harnessTest, net *NetworkHarness,
 	)
 	require.NoError(t.t, err)
 
-	assertWaitingCloseChannelAssetData(t.t, local, chanPoint)
-	assertWaitingCloseChannelAssetData(t.t, remote, chanPoint)
+	if !local.Cfg.OldChannelFormat {
+		assertWaitingCloseChannelAssetData(t.t, local, chanPoint)
+	}
+	if !remote.Cfg.OldChannelFormat {
+		assertWaitingCloseChannelAssetData(t.t, remote, chanPoint)
+	}
 
 	mineBlocks(t, net, 1, 1)
 
@@ -1846,8 +1873,12 @@ func closeAssetChannelAndAssert(t *harnessTest, net *NetworkHarness,
 		universeTap,
 	)
 
-	assertClosedChannelAssetData(t.t, local, chanPoint)
-	assertClosedChannelAssetData(t.t, remote, chanPoint)
+	if !local.Cfg.OldChannelFormat {
+		assertClosedChannelAssetData(t.t, local, chanPoint)
+	}
+	if !remote.Cfg.OldChannelFormat {
+		assertClosedChannelAssetData(t.t, remote, chanPoint)
+	}
 }
 
 // assertDefaultCoOpCloseBalance returns a default implementation of the co-op

itest/litd_custom_channels_test.go

@@ -639,20 +639,20 @@ func testCustomChannels(ctx context.Context, net *NetworkHarness,
 	erinAssetBalance += 3
 	fabiaAssetBalance -= 3
 	yaraAssetBalance -= 1
-	itest.AssertBalances(
+	assertBalance(
 		t.t, charlieTap, charlieAssetBalance,
 		itest.WithAssetID(assetID),
 	)
-	itest.AssertBalances(
+	assertBalance(
 		t.t, daveTap, daveAssetBalance, itest.WithAssetID(assetID),
 	)
-	itest.AssertBalances(
+	assertBalance(
 		t.t, erinTap, erinAssetBalance, itest.WithAssetID(assetID),
 	)
-	itest.AssertBalances(
+	assertBalance(
 		t.t, fabiaTap, fabiaAssetBalance, itest.WithAssetID(assetID),
 	)
-	itest.AssertBalances(
+	assertBalance(
 		t.t, yaraTap, yaraAssetBalance, itest.WithAssetID(assetID),
 	)
 
@@ -698,7 +698,7 @@ func testCustomChannels(ctx context.Context, net *NetworkHarness,
 	)
 
 	// Charlie should still have four asset pieces, two with the same size.
-	itest.AssertBalances(
+	assertBalance(
 		t.t, charlieTap, charlieAssetBalance,
 		itest.WithAssetID(assetID), itest.WithNumUtxos(2),
 		itest.WithScriptKeyType(asset.ScriptKeyBip86),
@@ -706,7 +706,7 @@ func testCustomChannels(ctx context.Context, net *NetworkHarness,
 
 	// Dave should have two outputs, one from the initial channel with Yara
 	// and one from the remaining amount of the channel with Charlie.
-	itest.AssertBalances(
+	assertBalance(
 		t.t, daveTap, daveAssetBalance, itest.WithAssetID(assetID),
 		itest.WithNumUtxos(2),
 		itest.WithScriptKeyType(asset.ScriptKeyBip86),
@@ -714,12 +714,12 @@ func testCustomChannels(ctx context.Context, net *NetworkHarness,
 
 	// Fabia and Yara should all have a single output each, just what was
 	// left over from the initial channel.
-	itest.AssertBalances(
+	assertBalance(
 		t.t, fabiaTap, fabiaAssetBalance, itest.WithAssetID(assetID),
 		itest.WithNumUtxos(1),
 		itest.WithScriptKeyType(asset.ScriptKeyBip86),
 	)
-	itest.AssertBalances(
+	assertBalance(
 		t.t, yaraTap, yaraAssetBalance, itest.WithAssetID(assetID),
 		itest.WithNumUtxos(1),
 		itest.WithScriptKeyType(asset.ScriptKeyBip86),
@@ -728,24 +728,24 @@ func testCustomChannels(ctx context.Context, net *NetworkHarness,
 	// Erin didn't use all of his assets when opening the channel, so he
 	// should have two outputs, the change from the channel opening and the
 	// remaining amount after closing the channel.
-	itest.AssertBalances(
+	assertBalance(
 		t.t, erinTap, erinAssetBalance, itest.WithAssetID(assetID),
 		itest.WithNumUtxos(2),
 		itest.WithScriptKeyType(asset.ScriptKeyBip86),
 	)
 
 	// The asset balances should still remain unchanged.
-	itest.AssertBalances(
+	assertBalance(
 		t.t, charlieTap, charlieAssetBalance,
 		itest.WithAssetID(assetID),
 	)
-	itest.AssertBalances(
+	assertBalance(
 		t.t, daveTap, daveAssetBalance, itest.WithAssetID(assetID),
 	)
-	itest.AssertBalances(
+	assertBalance(
 		t.t, erinTap, erinAssetBalance, itest.WithAssetID(assetID),
 	)
-	itest.AssertBalances(
+	assertBalance(
 		t.t, fabiaTap, fabiaAssetBalance, itest.WithAssetID(assetID),
 	)
 }

itest/litd_node.go

@@ -68,6 +68,26 @@ var (
 		"litdbbackend", terminal.DatabaseBackendBbolt, "Set the "+
 			"database backend to use when starting a LiT daemon.",
 	)
+
+	// backwardCompatFlagOverride is a map of LiT versions to a map of
+	// config file flags that need to be overwritten or added for the target
+	// version to work. If a flag in the map is empty, it means it will be
+	// removed from the config file of that version.
+	backwardCompatFlagOverride = map[string]map[string]string{
+		"v0.14.1-alpha": {
+			"databasebackend":            "",
+			"lnd.logging.no-commit-hash": "",
+		},
+	}
+
+	// backwardCompatConfigOverride is a map of LiT versions to a map of
+	// config file overriding functions.
+	backwardCompatConfigOverride = map[string]func(*LitNodeConfig){
+		"v0.14.1-alpha": func(cfg *LitNodeConfig) {
+			cfg.OldChannelFormat = true
+			cfg.SkipBalanceChecks = true
+		},
+	}
 )
 
 // Option is a function for updating a node's configuration.
@@ -103,6 +123,14 @@ type LitNodeConfig struct {
 	LitPort     int
 	LitRESTPort int
 
+	// OldChannelFormat is a flag for turning off certain checks for old
+	// versions of litd during the backward compatibility test.
+	OldChannelFormat bool
+
+	// SkipBalanceChecks is a flag for turning off certain checks for old
+	// versions of litd during the backward compatibility test.
+	SkipBalanceChecks bool
+
 	// backupDBDir is the path where a database backup is stored, if any.
 	backupDBDir string
 }
@@ -616,17 +644,60 @@ func renameFile(fromFileName, toFileName string) {
 	}
 }
 
+// overrideFlagsAndBinary is a helper function that checks if the passed node
+// name needs a version downgrade and if so, it will return the new binary
+// name and the new arguments.
+func (hn *HarnessNode) overrideFlagsAndBinary(backwardCompat map[string]string,
+	binary string, args []LitArgOption) (string, []LitArgOption) {
+
+	if backwardCompat == nil {
+		return binary, args
+	}
+
+	downgradeVersion, ok := backwardCompat[hn.Cfg.Name]
+	if !ok {
+		return binary, args
+	}
+
+	newBinary := fmt.Sprintf("%s-%s", binary, downgradeVersion)
+
+	flagOverride, ok := backwardCompatFlagOverride[downgradeVersion]
+	if !ok {
+		return newBinary, args
+	}
+
+	for k, v := range flagOverride {
+		if v == "" {
+			args = append(args, WithoutLitArg(k))
+		} else {
+			args = append(args, WithLitArg(k, v))
+		}
+	}
+
+	cfgOverride, ok := backwardCompatConfigOverride[downgradeVersion]
+	if ok && cfgOverride != nil {
+		cfgOverride(hn.Cfg)
+	}
+
+	return newBinary, args
+}
+
 // Start launches a new process running lnd. Additionally, the PID of the
 // launched process is saved in order to possibly kill the process forcibly
 // later.
 //
 // This may not clean up properly if an error is returned, so the caller should
 // call shutdown() regardless of the return value.
-func (hn *HarnessNode) Start(litdBinary string, litdError chan<- error,
+func (hn *HarnessNode) Start(litdBinary string,
+	backwardCompat map[string]string, litdError chan<- error,
 	waitForStart bool, litArgOpts ...LitArgOption) error {
 
 	hn.quit = make(chan struct{})
 
+	litdBinary, litArgOpts = hn.overrideFlagsAndBinary(
+		backwardCompat, litdBinary, litArgOpts,
+	)
+
 	args := hn.Cfg.GenArgs(litArgOpts...)
 	hn.cmd = exec.Command(litdBinary, args...)
 

itest/litd_test.go

@@ -71,6 +71,7 @@ func TestLightningTerminal(t *testing.T) {
 			lndSubTest := lndHarness.Subtest(t1)
 			litdHarness, err := NewNetworkHarness(
 				lndSubTest, chainBackend, binary, feeService,
+				testCase.backwardCompat,
 			)
 			require.NoError(t1, err)
 

itest/litd_test_list_on_test.go

@@ -29,6 +29,15 @@ var allTestCases = []*testCase{
 		test:       testCustomChannels,
 		noAliceBob: true,
 	},
+	{
+		name:       "custom channels backward compatibility",
+		test:       testCustomChannels,
+		noAliceBob: true,
+		backwardCompat: map[string]string{
+			"Dave":  "v0.14.1-alpha",
+			"Fabia": "v0.14.1-alpha",
+		},
+	},
 	{
 		name:       "custom channels large",
 		test:       testCustomChannelsLarge,

itest/network_harness.go

@@ -69,6 +69,11 @@ type NetworkHarness struct {
 	Alice *HarnessNode
 	Bob   *HarnessNode
 
+	// backwardCompat is a map of node names to the version of litd that
+	// should be used for them. If the map is empty, then the latest/current
+	// version will be used for all nodes.
+	backwardCompat map[string]string
+
 	// Channel for transmitting stderr output from failed lightning node
 	// to main process.
 	lndErrorChan chan error
@@ -78,19 +83,20 @@ type NetworkHarness struct {
 
 // NewNetworkHarness creates a new network test harness.
 func NewNetworkHarness(lndHarness *lntest.HarnessTest, b node.BackendConfig,
-	litdBinary string, feeService lntest.WebFeeService) (*NetworkHarness,
-	error) {
+	litdBinary string, feeService lntest.WebFeeService,
+	backwardCompat map[string]string) (*NetworkHarness, error) {
 
 	n := NetworkHarness{
-		activeNodes:  make(map[int]*HarnessNode),
-		nodesByPub:   make(map[string]*HarnessNode),
-		lndErrorChan: make(chan error),
-		netParams:    lndHarness.Miner().ActiveNet,
-		Miner:        lndHarness.Miner(),
-		LNDHarness:   lndHarness,
-		BackendCfg:   b,
-		litdBinary:   litdBinary,
-		feeService:   feeService,
+		activeNodes:    make(map[int]*HarnessNode),
+		nodesByPub:     make(map[string]*HarnessNode),
+		lndErrorChan:   make(chan error),
+		netParams:      lndHarness.Miner().ActiveNet,
+		Miner:          lndHarness.Miner(),
+		LNDHarness:     lndHarness,
+		BackendCfg:     b,
+		litdBinary:     litdBinary,
+		feeService:     feeService,
+		backwardCompat: backwardCompat,
 	}
 	return &n, nil
 }
@@ -373,7 +379,7 @@ func (n *NetworkHarness) newNode(t *testing.T, name string, extraArgs,
 	n.activeNodes[node.NodeID] = node
 	n.mtx.Unlock()
 
-	err = node.Start(n.litdBinary, n.lndErrorChan, wait)
+	err = node.Start(n.litdBinary, n.backwardCompat, n.lndErrorChan, wait)
 	if err != nil {
 		return nil, err
 	}
@@ -767,7 +773,10 @@ func (n *NetworkHarness) RestartNodeNoUnlock(node *HarnessNode,
 		}
 	}
 
-	return node.Start(n.litdBinary, n.lndErrorChan, wait, litArgOpts...)
+	return node.Start(
+		n.litdBinary, n.backwardCompat, n.lndErrorChan, wait,
+		litArgOpts...,
+	)
 }
 
 // SuspendNode stops the given node and returns a callback that can be used to
@@ -778,7 +787,9 @@ func (n *NetworkHarness) SuspendNode(node *HarnessNode) (func() error, error) {
 	}
 
 	restart := func() error {
-		return node.Start(n.litdBinary, n.lndErrorChan, true)
+		return node.Start(
+			n.litdBinary, n.backwardCompat, n.lndErrorChan, true,
+		)
 	}
 
 	return restart, nil

itest/test_harness.go

@@ -129,6 +129,12 @@ type testCase struct {
 	test func(ctx context.Context, net *NetworkHarness,
 		t *harnessTest)
 	noAliceBob bool
+
+	// backwardCompat is a map of node names to the version they are going
+	// to be downgraded to during the specific test. Make sure to update the
+	// LITD_COMPAT_VERSIONS variable in the Makefile to include all versions
+	// used for any backward compatibility tests.
+	backwardCompat map[string]string
 }
 
 // waitForNTxsInMempool polls until finding the desired number of transactions

scripts/install-backward-compat-versions.sh

@@ -0,0 +1,80 @@
+#!/bin/bash
+
+# Build and install older versions of `litd` for backward compatibility
+# integration tests.
+#
+# Usage:
+#   ./scripts/install-backward-compat-versions.sh "<version1> <version2> ..."
+#
+# Example:
+#   ./scripts/install-backward-compat-versions.sh "v0.12.0-beta v0.14.1-alpha"
+#
+# Parameters:
+#   $1        Space-separated list of `litd` versions to install (required).
+#
+# Environment Variables:
+#   REPO_URL  URL of the litd repository (defaults to:
+#             https://github.com/lightninglabs/lightning-terminal.git)
+#
+# Notes:
+#   - Each version will be installed under a version-specific path.
+
+set -ex
+
+VERSIONS="$1"
+REPO_URL="${REPO_URL:-https://github.com/lightninglabs/lightning-terminal.git}"
+
+# Make sure at least one version is set.
+if [[ -z "${VERSIONS}" ]]; then
+  echo "Usage: $0 '<version1> <version2> ...'"
+  echo "Please provide at least one version to install."
+  exit 1
+fi
+
+# Directory of the script file, independent of where it's called from.
+DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+
+ITEST_DIR="${DIR}/../itest"
+TARGET_DIR="${ITEST_DIR}/backward-compat"
+
+mkdir -p "${TARGET_DIR}" && cd "${TARGET_DIR}"
+
+# First, make sure we've cloned each version of litd.
+for VERSION in ${VERSIONS}; do
+  VERSION_DIR="${TARGET_DIR}/litd-${VERSION}"
+
+  # Check if the version is already installed.
+  if [[ -f "${VERSION_DIR}/Makefile" ]]; then
+    echo "Version ${VERSION} is already installed."
+    continue
+  fi
+
+  # Clone the specified version of litd.
+  echo "Installing litd ${VERSION} to ${VERSION_DIR}..."
+  git clone ${REPO_URL} --depth 1 -b "$VERSION" "${VERSION_DIR}"
+done
+
+# Build the itest binary for each version.
+for VERSION in ${VERSIONS}; do
+  VERSION_DIR="${TARGET_DIR}/litd-${VERSION}"
+  SRC="${VERSION_DIR}/itest/litd-itest"
+  DST="${ITEST_DIR}/litd-itest-${VERSION}"
+
+  if [[ -f "${DST}" ]]; then
+    echo "Binary ${DST} is already available, skipping build."
+    continue
+  fi
+
+  echo "Building litd ${VERSION}..."
+  cd "${VERSION_DIR}"
+  
+  # The Makefile was changed a bit, but the "itest-only" target that skips the
+  # frontend build has existed for a while. We use it to build the itest binary
+  # (but don't actually run the tests).
+  make itest-only icase=nothing
+  
+  # Copy the resulting binary to the main itest directory.
+  echo "Copying ${SRC} to ${DST}"
+  cp "${SRC}" "${DST}"
+done
+