add x/mint QueryServer for backwards compatibility (#1420)

x/kavamint/keeper/grpc_query.go

@@ -3,7 +3,12 @@ package keeper
 import (
 	"context"
 
+	"google.golang.org/grpc/codes"
+	"google.golang.org/grpc/status"
+
 	sdk "github.com/cosmos/cosmos-sdk/types"
+	minttypes "github.com/cosmos/cosmos-sdk/x/mint/types"
+
 	"github.com/kava-labs/kava/x/kavamint/types"
 )
 
@@ -24,3 +29,57 @@ func (k Keeper) Inflation(c context.Context, _ *types.QueryInflationRequest) (*t
 
 	return &types.QueryInflationResponse{Inflation: inflation}, nil
 }
+
+// MintQueryServer implements cosmos sdk's x/mint querier.
+// x/mint was removed from kava, but the standard inflation endpoint is still registered
+// for easier third party integration and backwards compatibility.
+type MintQueryServer struct {
+	keeper Keeper
+}
+
+// NewMintQueryServer returns a service that implements x/mint's QueryServer
+func NewMintQueryServer(kavamintKeeper Keeper) MintQueryServer {
+	return MintQueryServer{kavamintKeeper}
+}
+
+var _ minttypes.QueryServer = MintQueryServer{}
+
+// Params is not implemented. There is no mint module.
+func (MintQueryServer) Params(
+	_ context.Context, _ *minttypes.QueryParamsRequest,
+) (*minttypes.QueryParamsResponse, error) {
+	return nil, status.Error(codes.Unimplemented, "x/mint has been replaced by x/kavamint")
+}
+
+// Inflation returns an adjusted inflation rate.
+// The `/cosmos/mint/v1beta1/inflation` endpoint is used by third parties to calculate staking APY.
+// The usual staking APY calculation takes the inflation and determines the portion of it devoted
+// to staking rewards after adjusting for the bonded ratio and x/distribution community_tax.
+// staking_apy = (inflation - community_tax) * total_supply / total_bonded
+// Staking APY is not set directly via the x/kavamint staking_rewards_apy param.
+// This endpoint returns the inflation that makes the above calculation equal to the param:
+// inflation = staking_apy * total_bonded / total_supply
+// NOTE: assumes x/distribution community_tax = 0
+func (mq MintQueryServer) Inflation(
+	c context.Context, _ *minttypes.QueryInflationRequest,
+) (*minttypes.QueryInflationResponse, error) {
+	ctx := sdk.UnwrapSDKContext(c)
+
+	stakingApy := mq.keeper.GetParams(ctx).StakingRewardsApy
+	totalBonded := mq.keeper.TotalBondedTokens(ctx)
+	totalSupply := mq.keeper.TotalSupply(ctx)
+
+	// inflation = staking_apy * total_bonded / total_supply
+	inflation := stakingApy.MulInt(totalBonded).QuoInt(totalSupply)
+
+	return &minttypes.QueryInflationResponse{
+		Inflation: inflation,
+	}, nil
+}
+
+// AnnualProvisions is not implemented.
+func (MintQueryServer) AnnualProvisions(
+	_ context.Context, _ *minttypes.QueryAnnualProvisionsRequest,
+) (*minttypes.QueryAnnualProvisionsResponse, error) {
+	return nil, status.Error(codes.Unimplemented, "x/mint has been replaced by x/kavamint")
+}

x/kavamint/keeper/grpc_query_test.go

@@ -5,11 +5,15 @@ import (
 	"testing"
 
 	"github.com/stretchr/testify/suite"
+	"google.golang.org/grpc/codes"
+	"google.golang.org/grpc/status"
 
 	"github.com/cosmos/cosmos-sdk/baseapp"
 	sdk "github.com/cosmos/cosmos-sdk/types"
+	minttypes "github.com/cosmos/cosmos-sdk/x/mint/types"
 	"github.com/cosmos/cosmos-sdk/x/staking"
 
+	"github.com/kava-labs/kava/x/kavamint/keeper"
 	"github.com/kava-labs/kava/x/kavamint/testutil"
 	"github.com/kava-labs/kava/x/kavamint/types"
 )
@@ -18,6 +22,7 @@ type grpcQueryTestSuite struct {
 	testutil.KavamintTestSuite
 
 	queryClient     types.QueryClient
+	mintQueryClient minttypes.QueryClient
 }
 
 func (suite *grpcQueryTestSuite) SetupTest() {
@@ -26,6 +31,10 @@ func (suite *grpcQueryTestSuite) SetupTest() {
 	queryHelper := baseapp.NewQueryServerTestHelper(suite.Ctx, suite.App.InterfaceRegistry())
 	types.RegisterQueryServer(queryHelper, suite.Keeper)
 	suite.queryClient = types.NewQueryClient(queryHelper)
+
+	mintQueryServer := keeper.NewMintQueryServer(suite.Keeper)
+	minttypes.RegisterQueryServer(queryHelper, mintQueryServer)
+	suite.mintQueryClient = minttypes.NewQueryClient(queryHelper)
 }
 
 func TestGRPCQueryTestSuite(t *testing.T) {
@@ -116,6 +125,35 @@ func (suite *grpcQueryTestSuite) TestGRPCInflationQuery() {
 			suite.Require().NoError(err)
 			suite.Require().Equal(inflation.Inflation, kavamintKeeper.CumulativeInflation(ctx))
 			suite.Require().Equal(inflation.Inflation, tc.expectedInflation)
+
+			// ensure overridden x/mint query for inflation returns the adjusted inflation
+			// the adjusted inflation is the inflation that returns the correct staking apy for the
+			// standard staking apy calculation used by third parties:
+			// staking_apy = (inflation - community_tax) * total_supply / total_bonded
+			// => inflation = staking_apy * total_bonded / total_supply
+			expectedAdjustedInflation := tc.stakingApy.Mul(tc.bondedRatio)
+			mintQ, err := suite.mintQueryClient.Inflation(
+				context.Background(),
+				&minttypes.QueryInflationRequest{},
+			)
+			suite.NoError(err)
+			suite.Equal(expectedAdjustedInflation, mintQ.Inflation)
 		})
 	}
 }
+
+func (suite *grpcQueryTestSuite) TestUnimplementedMintQueries() {
+	suite.SetupTest()
+
+	suite.Run("Params is unimplemented", func() {
+		_, err := suite.mintQueryClient.Params(context.Background(), nil)
+		suite.Error(err)
+		suite.Equal(codes.Unimplemented, status.Code(err))
+	})
+
+	suite.Run("AnnualProvisions is unimplemented", func() {
+		_, err := suite.mintQueryClient.AnnualProvisions(context.Background(), nil)
+		suite.Error(err)
+		suite.Equal(codes.Unimplemented, status.Code(err))
+	})
+}

x/kavamint/module.go

@@ -15,6 +15,8 @@ import (
 	cdctypes "github.com/cosmos/cosmos-sdk/codec/types"
 	sdk "github.com/cosmos/cosmos-sdk/types"
 	"github.com/cosmos/cosmos-sdk/types/module"
+	minttypes "github.com/cosmos/cosmos-sdk/x/mint/types"
+
 	"github.com/kava-labs/kava/x/kavamint/client/cli"
 	"github.com/kava-labs/kava/x/kavamint/keeper"
 	"github.com/kava-labs/kava/x/kavamint/types"
@@ -66,6 +68,8 @@ func (AppModuleBasic) RegisterRESTRoutes(clientCtx client.Context, rtr *mux.Rout
 func (AppModuleBasic) RegisterGRPCGatewayRoutes(clientCtx client.Context, mux *runtime.ServeMux) {
 	types.RegisterQueryHandlerClient(context.Background(), mux, types.NewQueryClient(clientCtx))
 
+	// add x/mint query handler for better 3rd party compatibility
+	minttypes.RegisterQueryHandlerClient(context.Background(), mux, minttypes.NewQueryClient(clientCtx))
 }
 
 // GetTxCmd returns no root tx command for the kavamint module.
@@ -118,6 +122,11 @@ func (am AppModule) LegacyQuerierHandler(legacyQuerierCdc *codec.LegacyAmino) sd
 // module-specific gRPC queries.
 func (am AppModule) RegisterServices(cfg module.Configurator) {
 	types.RegisterQueryServer(cfg.QueryServer(), am.keeper)
+
+	// register x/mint query server.
+	// x/mint was replaced by this module but we still want 3rd parties to be able to
+	// request the original sdk endpoints.
+	minttypes.RegisterQueryServer(cfg.QueryServer(), keeper.NewMintQueryServer(am.keeper))
 }
 
 // InitGenesis performs genesis initialization for the kavamint module. It returns