feat: add genesis validator subcommand (#1259)

## Description

This PR adds support for the `genesis validator` sub-commands, as
outlined in #1228.

Closes #1228 

Example `genesis validator add` command you can use to test out the
functionality:
```bash
genesis validator add --name milos -pub-key gpub1pgfj7ard9eg82cjtv4u4xetrwqer2dntxyfzxz3pqvknvnspy43c9zp0ts7wgvupldfzkws8kmvvz2eelfmzzupfymwpwzhh9m3 -address g1wpewvuxtyvqqwysndt4f8425tpdg3lf0mhu6fm
```
<details><summary>Contributors' checklist...</summary>

- [x] Added new tests, or not needed, or not feasible
- [x] Provided an example (e.g. screenshot) to aid review or the PR is
self-explanatory
- [x] Updated the official documentation or not needed
- [x] No breaking changes were made, or a `BREAKING CHANGE: xxx` message
was included in the description
- [x] Added references to related issues and PRs
- [x] Provided any useful hints for running manual tests
- [ ] Added new benchmarks to [generated
graphs](https://gnoland.github.io/benchmarks), if any. More info
[here](https://github.com/gnolang/gno/blob/master/.benchmarks/README.md).
</details>

gno.land/cmd/genesis/main.go

@@ -31,6 +31,7 @@ func newRootCmd(io *commands.IO) *commands.Command {
 
 	cmd.AddSubCommands(
 		newGenerateCmd(io),
+		newValidatorCmd(io),
 		newVerifyCmd(io),
 	)
 

gno.land/cmd/genesis/validator.go

@@ -0,0 +1,50 @@
+package main
+
+import (
+	"flag"
+
+	"github.com/gnolang/gno/tm2/pkg/commands"
+)
+
+type validatorCfg struct {
+	genesisPath string
+	address     string
+}
+
+// newValidatorCmd creates the genesis validator subcommand
+func newValidatorCmd(io *commands.IO) *commands.Command {
+	cfg := &validatorCfg{}
+
+	cmd := commands.NewCommand(
+		commands.Metadata{
+			Name:       "validator",
+			ShortUsage: "validator <subcommand> [flags]",
+			LongHelp:   "Manipulates the genesis.json validator set",
+		},
+		cfg,
+		commands.HelpExec,
+	)
+
+	cmd.AddSubCommands(
+		newValidatorAddCmd(cfg, io),
+		newValidatorRemoveCmd(cfg, io),
+	)
+
+	return cmd
+}
+
+func (c *validatorCfg) RegisterFlags(fs *flag.FlagSet) {
+	fs.StringVar(
+		&c.genesisPath,
+		"genesis-path",
+		"./genesis.json",
+		"the path to the genesis.json",
+	)
+
+	fs.StringVar(
+		&c.address,
+		"address",
+		"",
+		"the output path for the genesis.json",
+	)
+}

gno.land/cmd/genesis/validator_add.go

@@ -0,0 +1,137 @@
+package main
+
+import (
+	"context"
+	"errors"
+	"flag"
+	"fmt"
+
+	"github.com/gnolang/gno/tm2/pkg/bft/types"
+	"github.com/gnolang/gno/tm2/pkg/commands"
+	"github.com/gnolang/gno/tm2/pkg/crypto"
+	_ "github.com/gnolang/gno/tm2/pkg/crypto/keys"
+)
+
+var (
+	errInvalidPower      = errors.New("invalid validator power")
+	errInvalidName       = errors.New("invalid validator name")
+	errPublicKeyMismatch = errors.New("provided public key and address do not match")
+	errAddressPresent    = errors.New("validator with same address already present in genesis.json")
+)
+
+type validatorAddCfg struct {
+	rootCfg *validatorCfg
+
+	pubKey string
+	name   string
+	power  int64
+}
+
+// newValidatorAddCmd creates the genesis validator add subcommand
+func newValidatorAddCmd(validatorCfg *validatorCfg, io *commands.IO) *commands.Command {
+	cfg := &validatorAddCfg{
+		rootCfg: validatorCfg,
+	}
+
+	return commands.NewCommand(
+		commands.Metadata{
+			Name:       "add",
+			ShortUsage: "validator add [flags]",
+			LongHelp:   "Adds a new validator to the genesis.json",
+		},
+		cfg,
+		func(_ context.Context, _ []string) error {
+			return execValidatorAdd(cfg, io)
+		},
+	)
+}
+
+func (c *validatorAddCfg) RegisterFlags(fs *flag.FlagSet) {
+	fs.StringVar(
+		&c.pubKey,
+		"pub-key",
+		"",
+		"the bech32 string representation of the validator's public key",
+	)
+
+	fs.StringVar(
+		&c.name,
+		"name",
+		"",
+		"the name of the validator (must be unique)",
+	)
+
+	fs.Int64Var(
+		&c.power,
+		"power",
+		1,
+		"the voting power of the validator (must be > 0)",
+	)
+}
+
+func execValidatorAdd(cfg *validatorAddCfg, io *commands.IO) error {
+	// Load the genesis
+	genesis, loadErr := types.GenesisDocFromFile(cfg.rootCfg.genesisPath)
+	if loadErr != nil {
+		return fmt.Errorf("unable to load genesis, %w", loadErr)
+	}
+
+	// Check the validator address
+	address, err := crypto.AddressFromString(cfg.rootCfg.address)
+	if err != nil {
+		return fmt.Errorf("invalid validator address, %w", err)
+	}
+
+	// Check the voting power
+	if cfg.power < 1 {
+		return errInvalidPower
+	}
+
+	// Check the name
+	if cfg.name == "" {
+		return errors.New("invalid validator name")
+	}
+
+	// Check the public key
+	pubKey, err := crypto.PubKeyFromBech32(cfg.pubKey)
+	if err != nil {
+		return fmt.Errorf("invalid validator public key, %w", err)
+	}
+
+	// Check the public key matches the address
+	if pubKey.Address() != address {
+		return errors.New("provided public key and address do not match")
+	}
+
+	validator := types.GenesisValidator{
+		Address: address,
+		PubKey:  pubKey,
+		Power:   cfg.power,
+		Name:    cfg.name,
+	}
+
+	// Check if the validator exists
+	for _, genesisValidator := range genesis.Validators {
+		// There is no need to check if the public keys match
+		// since the address is derived from it, and the derivation
+		// is checked already
+		if validator.Address == genesisValidator.Address {
+			return errAddressPresent
+		}
+	}
+
+	// Add the validator
+	genesis.Validators = append(genesis.Validators, validator)
+
+	// Save the updated genesis
+	if err := genesis.SaveAs(cfg.rootCfg.genesisPath); err != nil {
+		return fmt.Errorf("unable to save genesis.json, %w", err)
+	}
+
+	io.Printfln(
+		"Validator with address %s added to genesis file",
+		cfg.rootCfg.address,
+	)
+
+	return nil
+}