cmd/utils: enable snapshot generation in import-mode (#25990)

This PR fixes a regression causing snapshots not to be generated in "geth --import" mode.  It also fixes the geth export command to be truly readonly, and adds a new test for geth export.

cmd/geth/chaincmd.go

@@ -252,7 +252,7 @@ func importChain(ctx *cli.Context) error {
 	stack, _ := makeConfigNode(ctx)
 	defer stack.Close()
 
-	chain, db := utils.MakeChain(ctx, stack)
+	chain, db := utils.MakeChain(ctx, stack, false)
 	defer db.Close()
 
 	// Start periodically gathering memory profiles
@@ -327,7 +327,7 @@ func exportChain(ctx *cli.Context) error {
 	stack, _ := makeConfigNode(ctx)
 	defer stack.Close()
 
-	chain, _ := utils.MakeChain(ctx, stack)
+	chain, _ := utils.MakeChain(ctx, stack, true)
 	start := time.Now()
 
 	var err error

cmd/geth/exportcmd_test.go

@@ -0,0 +1,45 @@
+// Copyright 2022 The go-ethereum Authors
+// This file is part of go-ethereum.
+//
+// go-ethereum is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// go-ethereum is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with go-ethereum. If not, see <http://www.gnu.org/licenses/>.
+
+package main
+
+import (
+	"bytes"
+	"fmt"
+	"os"
+	"testing"
+
+	"github.com/ethereum/go-ethereum/common"
+)
+
+// TestExport does a basic test of "geth export", exporting the test-genesis.
+func TestExport(t *testing.T) {
+	outfile := fmt.Sprintf("%v/testExport.out", os.TempDir())
+	defer os.Remove(outfile)
+	geth := runGeth(t, "--datadir", initGeth(t), "export", outfile)
+	geth.WaitExit()
+	if have, want := geth.ExitStatus(), 0; have != want {
+		t.Errorf("exit error, have %d want %d", have, want)
+	}
+	have, err := os.ReadFile(outfile)
+	if err != nil {
+		t.Fatal(err)
+	}
+	want := common.FromHex("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")
+	if !bytes.Equal(have, want) {
+		t.Fatalf("wrong content exported")
+	}
+}