doc: adding migration doc for v7.1 localhost client

docs/.vuepress/config.js

@@ -545,6 +545,11 @@ module.exports = {
               directory: false,
               path: "/migrations/v6-to-v7.html",
             },
+            {
+              title: "IBC-Go v7 to v7.1",
+              directory: false,
+              path: "/migrations/v7-to-v7_1.html",
+            },
           ],
         },
         {

docs/migrations/v7-to-v7_1.md

@@ -1,19 +1,47 @@
 # Migrating from v7 to v7.1
 
-This guide provides instructions for migrating to a new version of ibc-go.
+This guide provides instructions for migrating to version `v7.1.0` of ibc-go.
 
 There are four sections based on the four potential user groups of this document:
 
-- [Chains](#chains)
-- [IBC Apps](#ibc-apps)
-- [Relayers](#relayers)
-- [IBC Light Clients](#ibc-light-clients)
+- [Migrating from v7 to v7.1](#migrating-from-v7-to-v71)
+  - [Chains](#chains)
+  - [IBC Apps](#ibc-apps)
+  - [Relayers](#relayers)
+  - [IBC Light Clients](#ibc-light-clients)
 
 **Note:** ibc-go supports golang semantic versioning and therefore all imports must be updated on major version releases.
 
 ## Chains
 
-- No relevant changes were made in this release.
+In the previous release of ibc-go, the localhost `v1` light client module was deprecated and removed. The ibc-go `v7.1.0` release introduces `v2` of the 09-localhost light client module.
+
+<!-- TODO: Update the links to use release version instead of feat branch -->
+An [automatic migration handler](https://github.com/cosmos/ibc-go/blob/09-localhost/modules/core/module.go#L133-L145) is configured in the core IBC module to set the localhost `ClientState` and sentintel `ConnectionEnd` in state.
+
+In order to use the 09-localhost client chains must update the `AllowedClients` parameter in the 02-client submodule of core IBC. This can be configured directly in the application upgrade handler or alternatively updated via the legacy governance parameter change proposal.
+We __strongly__ recommend chains to perform this action.
+
+See the upgrade handler code sample provided below or [follow this link](https://github.com/cosmos/ibc-go/blob/09-localhost/testing/simapp/upgrades/upgrades.go#L85) for the upgrade handler used by the ibc-go simapp.
+
+```go
+func CreateV7LocalhostUpgradeHandler(
+  mm *module.Manager,
+  configurator module.Configurator,
+  clientKeeper clientkeeper.Keeper,
+) upgradetypes.UpgradeHandler {
+  return func(ctx sdk.Context, _ upgradetypes.Plan, vm module.VersionMap) (module.VersionMap, error) {
+    // explicitly update the IBC 02-client params, adding the localhost client type
+    params := clientKeeper.GetParams(ctx)
+    params.AllowedClients = append(params.AllowedClients, exported.Localhost)
+    clientKeeper.SetParams(ctx, params)
+
+    return mm.RunMigrations(ctx, configurator, vm)
+  }
+}
+```
+
+[For more information please refer to the 09-localhost light client module documentation](../ibc/light-clients/localhost/overview.md).
 
 ## IBC Apps
 

testing/simapp/upgrades/upgrades.go

@@ -88,7 +88,7 @@ func CreateV7LocalhostUpgradeHandler(
 	clientKeeper clientkeeper.Keeper,
 ) upgradetypes.UpgradeHandler {
 	return func(ctx sdk.Context, _ upgradetypes.Plan, vm module.VersionMap) (module.VersionMap, error) {
-		// explicitly update the IBC 02-client params with the new default allowed clients
+		// explicitly update the IBC 02-client params, adding the localhost client type
 		params := clientKeeper.GetParams(ctx)
 		params.AllowedClients = append(params.AllowedClients, exported.Localhost)
 		clientKeeper.SetParams(ctx, params)