Enforce the use of a blank identifier for interface compliance (ava-l…

…abs#1493)

scripts/lint.sh

@@ -21,7 +21,7 @@ fi
 # by default, "./scripts/lint.sh" runs all lint tests
 # to run only "license_header" test
 # TESTS='license_header' ./scripts/lint.sh
-TESTS=${TESTS:-"golangci_lint license_header require_error_is_no_funcs_as_params single_import"}
+TESTS=${TESTS:-"golangci_lint license_header require_error_is_no_funcs_as_params single_import interface_compliance_nil"}
 
 function test_golangci_lint {
   go install -v github.com/golangci/golangci-lint/cmd/[email protected]
@@ -57,6 +57,17 @@ function test_require_error_is_no_funcs_as_params {
   fi
 }
 
+# Ref: https://go.dev/doc/effective_go#blank_implements
+function test_interface_compliance_nil {
+  if grep -R -o -P '_ .+? = &.+?\{\}' .; then
+    echo ""
+    echo "Interface compliance checks need to be of the form:"
+    echo "  var _ json.Marshaler = (*RawMessage)(nil)"
+    echo ""
+    return 1
+  fi
+}
+
 function run {
   local test="${1}"
   shift 1

vms/avm/txs/mempool/mempool.go

@@ -33,7 +33,7 @@ const (
 )
 
 var (
-	_ Mempool = &mempool{}
+	_ Mempool = (*mempool)(nil)
 
 	errDuplicateTx          = errors.New("duplicate tx")
 	errTxTooLarge           = errors.New("tx too large")

vms/rpcchainvm/gruntime/runtime_server.go

@@ -13,7 +13,7 @@ import (
 	pb "github.com/ava-labs/avalanchego/proto/pb/vm/runtime"
 )
 
-var _ pb.RuntimeServer = &Server{}
+var _ pb.RuntimeServer = (*Server)(nil)
 
 // Server is a VM runtime initializer controlled by RPC.
 type Server struct {

x/merkledb/batch.go

@@ -5,7 +5,7 @@ package merkledb
 
 import "github.com/ava-labs/avalanchego/database"
 
-var _ database.Batch = &batch{}
+var _ database.Batch = (*batch)(nil)
 
 // batch is a write-only database that commits changes to its host database
 // when Write is called.

x/merkledb/db.go

@@ -38,8 +38,8 @@ const (
 )
 
 var (
-	_ TrieView          = &Database{}
-	_ database.Database = &Database{}
+	_ TrieView          = (*Database)(nil)
+	_ database.Database = (*Database)(nil)
 
 	Codec, Version = newCodec()
 

x/merkledb/iterator.go

@@ -5,7 +5,7 @@ package merkledb
 
 import "github.com/ava-labs/avalanchego/database"
 
-var _ database.Iterator = &iterator{}
+var _ database.Iterator = (*iterator)(nil)
 
 type iterator struct {
 	db       *Database

x/merkledb/metrics.go

@@ -12,8 +12,8 @@ import (
 )
 
 var (
-	_ merkleMetrics = &mockMetrics{}
-	_ merkleMetrics = &metrics{}
+	_ merkleMetrics = (*mockMetrics)(nil)
+	_ merkleMetrics = (*metrics)(nil)
 )
 
 type merkleMetrics interface {

x/merkledb/trieview.go

@@ -26,6 +26,8 @@ import (
 const defaultPreallocationSize = 100
 
 var (
+	_ TrieView = (*trieView)(nil)
+
 	ErrCommitted          = errors.New("view has been committed")
 	ErrInvalid            = errors.New("the trie this view was based on has changed, rendering this view invalid")
 	ErrOddLengthWithValue = errors.New(
@@ -36,8 +38,6 @@ var (
 	ErrViewIsNotAChild  = errors.New("passed in view is required to be a child of the current view")
 	ErrNoValidRoot      = errors.New("a valid root was not provided to the trieView constructor")
 
-	_ TrieView = &trieView{}
-
 	numCPU = runtime.NumCPU()
 )
 

x/sync/client.go

@@ -29,7 +29,7 @@ const (
 )
 
 var (
-	_ Client = &client{}
+	_ Client = (*client)(nil)
 
 	errInvalidRangeProof = errors.New("failed to verify range proof")
 	errTooManyKeys       = errors.New("response contains more than requested keys")

x/sync/metrics.go

@@ -12,8 +12,8 @@ import (
 )
 
 var (
-	_ SyncMetrics = &mockMetrics{}
-	_ SyncMetrics = &metrics{}
+	_ SyncMetrics = (*mockMetrics)(nil)
+	_ SyncMetrics = (*metrics)(nil)
 )
 
 type SyncMetrics interface {

x/sync/network_client.go

@@ -25,7 +25,7 @@ import (
 const minRequestHandlingDuration = 100 * time.Millisecond
 
 var (
-	_ NetworkClient = &networkClient{}
+	_ NetworkClient = (*networkClient)(nil)
 
 	ErrAcquiringSemaphore = errors.New("error acquiring semaphore")
 	ErrRequestFailed      = errors.New("request failed")

x/sync/response_handler.go

@@ -7,7 +7,7 @@ package sync
 // Look into making a struct to handle requests/responses that uses a sync pool
 // to avoid allocations.
 
-var _ ResponseHandler = &responseHandler{}
+var _ ResponseHandler = (*responseHandler)(nil)
 
 // Handles responses/failure notifications for a sent request.
 // Exactly one of OnResponse or OnFailure is eventually called.

x/sync/sync_test.go

@@ -26,7 +26,7 @@ import (
 	syncpb "github.com/ava-labs/avalanchego/proto/pb/sync"
 )
 
-var _ Client = &mockClient{}
+var _ Client = (*mockClient)(nil)
 
 func newNoopTracer() trace.Tracer {
 	tracer, _ := trace.New(trace.Config{Enabled: false})

x/sync/syncworkheap.go

@@ -10,7 +10,7 @@ import (
 	"github.com/google/btree"
 )
 
-var _ heap.Interface = &syncWorkHeap{}
+var _ heap.Interface = (*syncWorkHeap)(nil)
 
 type heapItem struct {
 	workItem  *syncWorkItem