refactor: generate internal Header.encodeRLP() for override (#86)

## Why this should be merged

This is a precursor to being able to override `types.Header` RLP
{en,de}coding. As there is already a `Header.EncodeRLP()` method we
either have to modify the generated code or rename the generated
method—this PR does the latter.

## How this works

The `rlpgen -internal_methods` flag changes the generated methods from
`EncodeRLP()` and `DecodeRLP()` to `encodeRLP()` and `decodeRLP()`,
respectively. A new CI job checks that generated code is up to date. We
can then implement our own `Header.EncodeRLP()` that either overrides or
falls back on the original.

It appears that `core/gen_genesis.go` was out of date but only because
of formatting.

## How this was tested

I deliberately excluded the change to `core/types/gen_header_rlp.go` to
confirm that the new workflow
[detects](https://github.com/ava-labs/libevm/actions/runs/12259667481/job/34202386378?pr=86#step:5:92)
the change and fails. The actual change can be inspected via the code
diff.

.github/workflows/go.yml

@@ -24,3 +24,20 @@ jobs:
       - name: Run non-flaky tests concurrently
         run: |
           go test -short $(go list ./... | grep -Pv "${FLAKY_REGEX}");
+          
+  go_generate:
+    env:
+      EXCLUDE_REGEX: 'ava-labs/libevm/(accounts/usbwallet/trezor)$'
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - name: Set up Go
+        uses: actions/setup-go@v5
+        with:
+          go-version: 1.21.4
+
+      - name: Run `go generate`
+        run: go list ./... | grep -Pv "${EXCLUDE_REGEX}" | xargs go generate;
+
+      - name: git diff
+        run: git diff --exit-code

core/types/block.go

@@ -59,7 +59,7 @@ func (n *BlockNonce) UnmarshalText(input []byte) error {
 }
 
 //go:generate go run github.com/fjl/gencodec -type Header -field-override headerMarshaling -out gen_header_json.go
-//go:generate go run ../../rlp/rlpgen -type Header -out gen_header_rlp.go
+//go:generate go run ../../rlp/rlpgen -type Header -internal_methods -out gen_header_rlp.go
 
 // Header represents a block header in the Ethereum blockchain.
 type Header struct {

core/types/block.libevm.go

@@ -0,0 +1,29 @@
+// Copyright 2024 the libevm authors.
+//
+// The libevm additions to go-ethereum are free software: you can redistribute
+// them and/or modify them under the terms of the GNU Lesser General Public License
+// as published by the Free Software Foundation, either version 3 of the License,
+// or (at your option) any later version.
+//
+// The libevm additions are distributed in the hope that they will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser
+// General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see
+// <http://www.gnu.org/licenses/>.
+
+package types
+
+import (
+	"io"
+
+	"github.com/ava-labs/libevm/rlp"
+)
+
+func (h *Header) EncodeRLP(w io.Writer) error {
+	return h.encodeRLP(w)
+}
+
+var _ rlp.Encoder = (*Header)(nil)

rlp/rlpgen/gen.go

@@ -35,6 +35,8 @@ type buildContext struct {
 	rawValueType *types.Named
 
 	typeToStructCache map[types.Type]*rlpstruct.Type
+
+	internalMethods bool
 }
 
 func newBuildContext(packageRLP *types.Package) *buildContext {
@@ -98,6 +100,8 @@ type genContext struct {
 	inPackage   *types.Package
 	imports     map[string]struct{}
 	tempCounter int
+
+	internalMethods bool
 }
 
 func newGenContext(inPackage *types.Package) *genContext {
@@ -736,7 +740,7 @@ func generateDecoder(ctx *genContext, typ string, op op) []byte {
 
 	result, code := op.genDecode(ctx)
 	var b bytes.Buffer
-	fmt.Fprintf(&b, "func (obj *%s) DecodeRLP(dec *rlp.Stream) error {\n", typ)
+	fmt.Fprintf(&b, "func (obj *%s) %s(dec *rlp.Stream) error {\n", typ, ctx.decoderMethod())
 	fmt.Fprint(&b, code)
 	fmt.Fprintf(&b, "  *obj = %s\n", result)
 	fmt.Fprintf(&b, "  return nil\n")
@@ -751,7 +755,7 @@ func generateEncoder(ctx *genContext, typ string, op op) []byte {
 	ctx.addImport(pathOfPackageRLP)
 
 	var b bytes.Buffer
-	fmt.Fprintf(&b, "func (obj *%s) EncodeRLP(_w io.Writer) error {\n", typ)
+	fmt.Fprintf(&b, "func (obj *%s) %s(_w io.Writer) error {\n", typ, ctx.encoderMethod())
 	fmt.Fprintf(&b, "  w := rlp.NewEncoderBuffer(_w)\n")
 	fmt.Fprint(&b, op.genWrite(ctx, "obj"))
 	fmt.Fprintf(&b, "  return w.Flush()\n")
@@ -773,6 +777,7 @@ func (bctx *buildContext) generate(typ *types.Named, encoder, decoder bool) ([]b
 		encSource []byte
 		decSource []byte
 	)
+	ctx.internalMethods = bctx.internalMethods
 	if encoder {
 		encSource = generateEncoder(ctx, typ.Obj().Name(), op)
 	}

rlp/rlpgen/gen.libevm.go

@@ -0,0 +1,31 @@
+// Copyright 2024 the libevm authors.
+//
+// The libevm additions to go-ethereum are free software: you can redistribute
+// them and/or modify them under the terms of the GNU Lesser General Public License
+// as published by the Free Software Foundation, either version 3 of the License,
+// or (at your option) any later version.
+//
+// The libevm additions are distributed in the hope that they will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser
+// General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see
+// <http://www.gnu.org/licenses/>.
+
+package main
+
+func (ctx *genContext) encoderMethod() string {
+	if ctx.internalMethods {
+		return "encodeRLP"
+	}
+	return "EncodeRLP"
+}
+
+func (ctx *genContext) decoderMethod() string {
+	if ctx.internalMethods {
+		return "decodeRLP"
+	}
+	return "DecodeRLP"
+}

rlp/rlpgen/main.go

@@ -36,6 +36,7 @@ func main() {
 		genEncoder = flag.Bool("encoder", true, "generate EncodeRLP?")
 		genDecoder = flag.Bool("decoder", false, "generate DecodeRLP?")
 		typename   = flag.String("type", "", "type to generate methods for")
+		internal   = flag.Bool("internal_methods", false, "generate internal (lower-case) method names")
 	)
 	flag.Parse()
 
@@ -44,6 +45,7 @@ func main() {
 		Type:            *typename,
 		GenerateEncoder: *genEncoder,
 		GenerateDecoder: *genDecoder,
+		InternalMethods: *internal,
 	}
 	code, err := cfg.process()
 	if err != nil {
@@ -67,6 +69,8 @@ type Config struct {
 
 	GenerateEncoder bool
 	GenerateDecoder bool
+
+	InternalMethods bool
 }
 
 // process generates the Go code.
@@ -101,6 +105,7 @@ func (cfg *Config) process() (code []byte, err error) {
 		}
 	}
 	bctx := newBuildContext(packageRLP)
+	bctx.internalMethods = cfg.InternalMethods
 
 	// Find the type and generate.
 	typ, err := lookupStructType(pkg.Scope(), cfg.Type)