Apply suggestions from code review

x/bank/exported/exported.go

@@ -21,5 +21,6 @@ type (
 	// NOTE: This is used solely for migration of x/params managed parameters.
 	Subspace interface {
 		GetParamSet(ctx sdk.Context, ps ParamSet)
+		Get(ctx sdk.Context, key []byte, ptr interface{})
 	}
 )

x/bank/keeper/migrations.go

@@ -32,10 +32,8 @@ func (m Migrator) Migrate2to3(ctx sdk.Context) error {
 
 // Migrate3to4 migrates x/bank storage from version 3 to 4.
 func (m Migrator) Migrate3to4(ctx sdk.Context) error {
-	var oldParams types.Params
-	m.legacySubspace.GetParamSet(ctx, &oldParams)
-	m.keeper.SetAllSendEnabled(ctx, oldParams.GetSendEnabled())
-	currParams := types.NewParams(oldParams.DefaultSendEnabled)
-	m.keeper.SetParams(ctx, currParams)
-	return v4.MigrateStore(ctx, m.keeper.storeKey, currParams, m.keeper.cdc)
+	var sendEnabled []*types.SendEnabled
+	m.legacySubspace.Get(ctx, types.KeySendEnabled, &sendEnabled)
+	m.keeper.SetAllSendEnabled(ctx, sendEnabled)
+	return v4.MigrateStore(ctx, m.keeper.storeKey, m.legacySubspace, m.keeper.cdc)
 }

x/bank/migrations/v4/store.go

@@ -4,6 +4,7 @@ import (
 	"github.com/cosmos/cosmos-sdk/codec"
 	storetypes "github.com/cosmos/cosmos-sdk/store/types"
 	sdk "github.com/cosmos/cosmos-sdk/types"
+	"github.com/cosmos/cosmos-sdk/x/bank/exported"
 	"github.com/cosmos/cosmos-sdk/x/bank/types"
 )
 
@@ -15,16 +16,16 @@ var ParamsKey = []byte{0x05}
 // version 4. Specifically, it takes the parameters that are currently stored
 // and managed by the x/params module and stores them directly into the x/bank
 // module state.
-func MigrateStore(ctx sdk.Context, storeKey storetypes.StoreKey, currParams types.Params, cdc codec.BinaryCodec) error {
+func MigrateStore(ctx sdk.Context, storeKey storetypes.StoreKey, legacySubspace exported.Subspace, cdc codec.BinaryCodec) error {
 	store := ctx.KVStore(storeKey)
-	if err := currParams.Validate(); err != nil {
-		return err
-	}
+	var currParams types.Params
+	legacySubspace.GetParamSet(ctx, &currParams)
 
 	bz, err := cdc.Marshal(&currParams)
 	if err != nil {
 		return err
 	}
+
 	store.Set(ParamsKey, bz)
 
 	return nil

x/bank/migrations/v4/store_test.go

@@ -7,11 +7,26 @@ import (
 	sdk "github.com/cosmos/cosmos-sdk/types"
 	moduletestutil "github.com/cosmos/cosmos-sdk/types/module/testutil"
 	"github.com/cosmos/cosmos-sdk/x/bank"
+	"github.com/cosmos/cosmos-sdk/x/bank/exported"
 	v4 "github.com/cosmos/cosmos-sdk/x/bank/migrations/v4"
 	"github.com/cosmos/cosmos-sdk/x/bank/types"
 	"github.com/stretchr/testify/require"
 )
 
+type mockSubspace struct {
+	ps types.Params
+}
+
+func newMockSubspace(ps types.Params) mockSubspace {
+	return mockSubspace{ps: ps}
+}
+
+func (ms mockSubspace) GetParamSet(ctx sdk.Context, ps exported.ParamSet) {
+	*ps.(*types.Params) = ms.ps
+}
+
+func (ms mockSubspace) Get(ctx sdk.Context, key []byte, ptr interface{}) {}
+
 func TestMigrate(t *testing.T) {
 	encCfg := moduletestutil.MakeTestEncodingConfig(bank.AppModuleBasic{})
 	cdc := encCfg.Codec
@@ -21,10 +36,11 @@ func TestMigrate(t *testing.T) {
 	ctx := testutil.DefaultContext(storeKey, tKey)
 	store := ctx.KVStore(storeKey)
 
-	require.NoError(t, v4.MigrateStore(ctx, storeKey, types.DefaultParams(), cdc))
+	legacySubspace := newMockSubspace(types.DefaultParams())
+	require.NoError(t, v4.MigrateStore(ctx, storeKey, legacySubspace, cdc))
 
 	var res types.Params
 	bz := store.Get(v4.ParamsKey)
 	require.NoError(t, cdc.Unmarshal(bz, &res))
-	require.Equal(t, types.DefaultParams(), res)
+	require.Equal(t, legacySubspace.ps, res)
 }