feat: shed: add a state-tree diff command to lotus shed

This makes it easier to debug state mismatches by providing a nice way
to figure out which actors differ between two state-trees and
how (balance, nonce, state, etc.).

It doesn't provide a way to actually _diff_ those state-trees, but one
can use `lotus chain get` to figure that out (although it would be
_nice_ to provide something a bit smarter).

cmd/lotus-shed/diff.go

@@ -0,0 +1,100 @@
+package main
+
+import (
+	"fmt"
+
+	"github.com/urfave/cli/v2"
+
+	"github.com/ipfs/go-cid"
+
+	lcli "github.com/filecoin-project/lotus/cli"
+)
+
+var diffCmd = &cli.Command{
+	Name:        "diff",
+	Usage:       "diff state objects",
+	Subcommands: []*cli.Command{diffStateTrees},
+}
+
+var diffStateTrees = &cli.Command{
+	Name:      "state-trees",
+	Usage:     "diff two state-trees",
+	ArgsUsage: "<state-tree-a> <state-tree-b>",
+	Action: func(cctx *cli.Context) error {
+		api, closer, err := lcli.GetFullNodeAPI(cctx)
+		if err != nil {
+			return err
+		}
+
+		defer closer()
+		ctx := lcli.ReqContext(cctx)
+
+		if cctx.NArg() != 2 {
+			return xerrors.Errorf("expected two state-tree roots")
+		}
+
+		rootA, err := cid.Parse(cctx.Args().Get(0))
+		if err != nil {
+			return xerrors.Errorf("first state-tree root (%q) is not a CID: %w", err)
+		}
+		rootB, err := cid.Parse(cctx.Args().Get(1))
+		if err != nil {
+			return xerrors.Errorf("second state-tree root (%q) is not a CID: %w", err)
+		}
+
+		if rootA == rootB {
+			fmt.Println("state trees do not differ")
+			return nil
+		}
+
+		changedB, err := api.StateChangedActors(ctx, rootA, rootB)
+		if err != nil {
+			return err
+		}
+		changedA, err := api.StateChangedActors(ctx, rootB, rootA)
+		if err != nil {
+			return err
+		}
+
+		diff := func(stateA, stateB types.Actor) {
+			if stateB.Code != stateA.Code {
+				fmt.Printf("  code: %s != %s\n", stateA.Code, stateB.Code)
+			}
+			if stateB.Head != stateA.Head {
+				fmt.Printf("  state: %s != %s\n", stateA.Head, stateB.Head)
+			}
+			if stateB.Nonce != stateA.Nonce {
+				fmt.Printf("  nonce: %d != %d\n", stateA.Nonce, stateB.Nonce)
+			}
+			if !stateB.Balance.Equals(stateA.Balance) {
+				fmt.Printf("  balance: %s != %s\n", stateA.Balance, stateB.Balance)
+			}
+		}
+
+		fmt.Printf("state differences between %s (first) and %s (second):\n\n", rootA, rootB)
+		for addr, stateA := range changedA {
+			fmt.Println(addr)
+			stateB, ok := changedB[addr]
+			if ok {
+				diff(stateA, stateB)
+				continue
+			} else {
+				fmt.Printf("  actor does not exist in second state-tree (%s)\n", rootB)
+			}
+			fmt.Println()
+			delete(changedB, addr)
+		}
+		for addr, stateB := range changedB {
+			fmt.Println(addr)
+			stateA, ok := changedA[addr]
+			if ok {
+				diff(stateA, stateB)
+				continue
+			} else {
+				fmt.Printf("  actor does not exist in first state-tree (%s)\n", rootA)
+			}
+			fmt.Println()
+		}
+		return nil
+	},
+}

cmd/lotus-shed/main.go

@@ -68,6 +68,7 @@ func main() {
 		sendCsvCmd,
 		terminationsCmd,
 		migrationsCmd,
+		diffCmd,
 	}
 
 	app := &cli.App{