pickfirst: Remove old pickfirst (#8672)

Fixes: #8561
Addresses: #6472

The new pickfirst has been the default since [gRPC Go
v1.71.0](https://github.com/grpc/grpc-go/releases/tag/v1.71.0) and all
reported bugs have been fixed. This PR removes the old pickfirst policy
completely.

The exported symbols in the `pickfirstleaf` package are retained with a
deprecation notice for removal after one release.

RELEASE NOTES: 
* pickfirst: Remove the old `pick_first` LB policy. The new `pick_first`
has been the default since v 1.71.0.

Author: arjan-bal

.github/workflows/coverage.yml

@@ -19,9 +19,6 @@ jobs:
       - name: Run coverage
         run: go test -coverprofile=coverage.out -coverpkg=./... ./...
 
-      - name: Run coverage with old pickfirst
-        run: GRPC_EXPERIMENTAL_ENABLE_NEW_PICK_FIRST=false go test -coverprofile=coverage_old_pickfirst.out -coverpkg=./... ./...
-
       - name: Upload coverage to Codecov
         uses: codecov/codecov-action@v4
         with:

.github/workflows/testing.yml

@@ -69,11 +69,6 @@ jobs:
           - type: tests
             goversion: '1.24'
 
-          - type: tests
-            goversion: '1.25'
-            testflags: -race
-            grpcenv: 'GRPC_EXPERIMENTAL_ENABLE_NEW_PICK_FIRST=false'
-
     steps:
       # Setup the environment.
       - name: Setup GOARCH

balancer/endpointsharding/endpointsharding_ext_test.go

@@ -31,7 +31,7 @@ import (
 	"google.golang.org/grpc/backoff"
 	"google.golang.org/grpc/balancer"
 	"google.golang.org/grpc/balancer/endpointsharding"
-	"google.golang.org/grpc/balancer/pickfirst/pickfirstleaf"
+	"google.golang.org/grpc/balancer/pickfirst"
 	"google.golang.org/grpc/codes"
 	"google.golang.org/grpc/connectivity"
 	"google.golang.org/grpc/credentials/insecure"
@@ -84,7 +84,7 @@ func (fakePetioleBuilder) Build(cc balancer.ClientConn, opts balancer.BuildOptio
 		ClientConn: cc,
 		bOpts:      opts,
 	}
-	fp.Balancer = endpointsharding.NewBalancer(fp, opts, balancer.Get(pickfirstleaf.Name).Build, endpointsharding.Options{})
+	fp.Balancer = endpointsharding.NewBalancer(fp, opts, balancer.Get(pickfirst.Name).Build, endpointsharding.Options{})
 	return fp
 }
 
@@ -222,7 +222,7 @@ func (s) TestEndpointShardingReconnectDisabled(t *testing.T) {
 	bf := stub.BalancerFuncs{
 		Init: func(bd *stub.BalancerData) {
 			epOpts := endpointsharding.Options{DisableAutoReconnect: true}
-			bd.ChildBalancer = endpointsharding.NewBalancer(bd.ClientConn, bd.BuildOptions, balancer.Get(pickfirstleaf.Name).Build, epOpts)
+			bd.ChildBalancer = endpointsharding.NewBalancer(bd.ClientConn, bd.BuildOptions, balancer.Get(pickfirst.Name).Build, epOpts)
 		},
 		UpdateClientConnState: func(bd *stub.BalancerData, ccs balancer.ClientConnState) error {
 			return bd.ChildBalancer.UpdateClientConnState(ccs)
@@ -303,7 +303,7 @@ func (s) TestEndpointShardingExitIdle(t *testing.T) {
 	bf := stub.BalancerFuncs{
 		Init: func(bd *stub.BalancerData) {
 			epOpts := endpointsharding.Options{DisableAutoReconnect: true}
-			bd.ChildBalancer = endpointsharding.NewBalancer(bd.ClientConn, bd.BuildOptions, balancer.Get(pickfirstleaf.Name).Build, epOpts)
+			bd.ChildBalancer = endpointsharding.NewBalancer(bd.ClientConn, bd.BuildOptions, balancer.Get(pickfirst.Name).Build, epOpts)
 		},
 		UpdateClientConnState: func(bd *stub.BalancerData, ccs balancer.ClientConnState) error {
 			return bd.ChildBalancer.UpdateClientConnState(ccs)

balancer/lazy/lazy_ext_test.go

@@ -29,7 +29,7 @@ import (
 	"google.golang.org/grpc"
 	"google.golang.org/grpc/balancer"
 	"google.golang.org/grpc/balancer/lazy"
-	"google.golang.org/grpc/balancer/pickfirst/pickfirstleaf"
+	"google.golang.org/grpc/balancer/pickfirst"
 	"google.golang.org/grpc/connectivity"
 	"google.golang.org/grpc/credentials/insecure"
 	"google.golang.org/grpc/internal/balancer/stub"
@@ -79,7 +79,7 @@ func (s) TestExitIdle(t *testing.T) {
 
 	bf := stub.BalancerFuncs{
 		Init: func(bd *stub.BalancerData) {
-			bd.ChildBalancer = lazy.NewBalancer(bd.ClientConn, bd.BuildOptions, balancer.Get(pickfirstleaf.Name).Build)
+			bd.ChildBalancer = lazy.NewBalancer(bd.ClientConn, bd.BuildOptions, balancer.Get(pickfirst.Name).Build)
 		},
 		ExitIdle: func(bd *stub.BalancerData) {
 			bd.ChildBalancer.ExitIdle()
@@ -144,7 +144,7 @@ func (s) TestPicker(t *testing.T) {
 
 	bf := stub.BalancerFuncs{
 		Init: func(bd *stub.BalancerData) {
-			bd.ChildBalancer = lazy.NewBalancer(bd.ClientConn, bd.BuildOptions, balancer.Get(pickfirstleaf.Name).Build)
+			bd.ChildBalancer = lazy.NewBalancer(bd.ClientConn, bd.BuildOptions, balancer.Get(pickfirst.Name).Build)
 		},
 		ExitIdle: func(*stub.BalancerData) {
 			t.Log("Ignoring call to ExitIdle, calling the picker should make the lazy balancer exit IDLE state.")
@@ -201,7 +201,7 @@ func (s) TestGoodUpdateThenResolverError(t *testing.T) {
 
 	childBF := stub.BalancerFuncs{
 		Init: func(bd *stub.BalancerData) {
-			bd.ChildBalancer = balancer.Get(pickfirstleaf.Name).Build(bd.ClientConn, bd.BuildOptions)
+			bd.ChildBalancer = balancer.Get(pickfirst.Name).Build(bd.ClientConn, bd.BuildOptions)
 		},
 		UpdateClientConnState: func(bd *stub.BalancerData, ccs balancer.ClientConnState) error {
 			if resolverErrorReceived.HasFired() {
@@ -306,7 +306,7 @@ func (s) TestResolverErrorThenGoodUpdate(t *testing.T) {
 
 	childBF := stub.BalancerFuncs{
 		Init: func(bd *stub.BalancerData) {
-			bd.ChildBalancer = balancer.Get(pickfirstleaf.Name).Build(bd.ClientConn, bd.BuildOptions)
+			bd.ChildBalancer = balancer.Get(pickfirst.Name).Build(bd.ClientConn, bd.BuildOptions)
 		},
 		UpdateClientConnState: func(bd *stub.BalancerData, ccs balancer.ClientConnState) error {
 			return bd.ChildBalancer.UpdateClientConnState(ccs)
@@ -407,7 +407,7 @@ func (s) TestExitIdlePassthrough(t *testing.T) {
 
 	bf := stub.BalancerFuncs{
 		Init: func(bd *stub.BalancerData) {
-			bd.ChildBalancer = lazy.NewBalancer(bd.ClientConn, bd.BuildOptions, balancer.Get(pickfirstleaf.Name).Build)
+			bd.ChildBalancer = lazy.NewBalancer(bd.ClientConn, bd.BuildOptions, balancer.Get(pickfirst.Name).Build)
 		},
 		ExitIdle: func(bd *stub.BalancerData) {
 			bd.ChildBalancer.ExitIdle()

balancer/leastrequest/leastrequest.go

@@ -28,7 +28,7 @@ import (
 
 	"google.golang.org/grpc/balancer"
 	"google.golang.org/grpc/balancer/endpointsharding"
-	"google.golang.org/grpc/balancer/pickfirst/pickfirstleaf"
+	"google.golang.org/grpc/balancer/pickfirst"
 	"google.golang.org/grpc/connectivity"
 	"google.golang.org/grpc/grpclog"
 	internalgrpclog "google.golang.org/grpc/internal/grpclog"
@@ -90,7 +90,7 @@ func (bb) Build(cc balancer.ClientConn, bOpts balancer.BuildOptions) balancer.Ba
 		ClientConn:        cc,
 		endpointRPCCounts: resolver.NewEndpointMap[*atomic.Int32](),
 	}
-	b.child = endpointsharding.NewBalancer(b, bOpts, balancer.Get(pickfirstleaf.Name).Build, endpointsharding.Options{})
+	b.child = endpointsharding.NewBalancer(b, bOpts, balancer.Get(pickfirst.Name).Build, endpointsharding.Options{})
 	b.logger = internalgrpclog.NewPrefixLogger(logger, fmt.Sprintf("[%p] ", b))
 	b.logger.Infof("Created")
 	return b
@@ -141,7 +141,7 @@ func (lrb *leastRequestBalancer) UpdateClientConnState(ccs balancer.ClientConnSt
 	return lrb.child.UpdateClientConnState(balancer.ClientConnState{
 		// Enable the health listener in pickfirst children for client side health
 		// checks and outlier detection, if configured.
-		ResolverState: pickfirstleaf.EnableHealthListener(ccs.ResolverState),
+		ResolverState: pickfirst.EnableHealthListener(ccs.ResolverState),
 	})
 }
 

balancer/pickfirst/pickfirstleaf/metrics_test.go renamed to balancer/pickfirst/metrics_test.go

@@ -16,15 +16,15 @@
  *
  */
 
-package pickfirstleaf_test
+package pickfirst_test
 
 import (
 	"context"
 	"fmt"
 	"testing"
 
 	"google.golang.org/grpc"
-	"google.golang.org/grpc/balancer/pickfirst/pickfirstleaf"
+	"google.golang.org/grpc/balancer/pickfirst"
 	"google.golang.org/grpc/connectivity"
 	"google.golang.org/grpc/credentials/insecure"
 	"google.golang.org/grpc/internal"
@@ -54,7 +54,7 @@ func init() {
       		}
     	}
   	]
-	}`, pickfirstleaf.Name)
+	}`, pickfirst.Name)
 }
 
 // TestPickFirstMetrics tests pick first metrics. It configures a pick first