fix(client/v2): *big.Int unmarshal (#21853)

client/v2/CHANGELOG.md

@@ -53,6 +53,10 @@ Ref: https://keepachangelog.com/en/1.0.0/
 
 * [#17709](https://github.com/cosmos/cosmos-sdk/pull/17709) Address codecs have been removed from `autocli.AppOptions` and `flag.Builder`. Instead client/v2 uses the address codecs present in the context (introduced in [#17503](https://github.com/cosmos/cosmos-sdk/pull/17503)).
 
+### Bug Fixes
+
+* [#21853](https://github.com/cosmos/cosmos-sdk/pull/21853) Fix `*big.Int` unmarshalling in txs.
+
 ## [v2.0.0-beta.5] - 2024-09-18
 
 ### Improvements

client/v2/autocli/flag/builder.go

@@ -26,6 +26,7 @@ const (
 	ValidatorAddressStringScalarType = "cosmos.ValidatorAddressString"
 	ConsensusAddressStringScalarType = "cosmos.ConsensusAddressString"
 	PubkeyScalarType                 = "cosmos.Pubkey"
+	DecScalarType                    = "cosmos.Dec"
 )
 
 // Builder manages options for building pflag flags for protobuf messages.
@@ -67,6 +68,7 @@ func (b *Builder) init() {
 		b.scalarFlagTypes[ValidatorAddressStringScalarType] = validatorAddressStringType{}
 		b.scalarFlagTypes[ConsensusAddressStringScalarType] = consensusAddressStringType{}
 		b.scalarFlagTypes[PubkeyScalarType] = pubkeyType{}
+		b.scalarFlagTypes[DecScalarType] = decType{}
 	}
 }
 

client/v2/autocli/flag/legacy_dec.go

@@ -0,0 +1,48 @@
+package flag
+
+import (
+	"context"
+
+	"google.golang.org/protobuf/reflect/protoreflect"
+
+	"cosmossdk.io/math"
+)
+
+type decType struct{}
+
+func (a decType) NewValue(_ *context.Context, _ *Builder) Value {
+	return &decValue{}
+}
+
+func (a decType) DefaultValue() string {
+	return "0"
+}
+
+type decValue struct {
+	value string
+}
+
+func (a decValue) Get(protoreflect.Value) (protoreflect.Value, error) {
+	return protoreflect.ValueOf(a.value), nil
+}
+
+func (a decValue) String() string {
+	return a.value
+}
+
+func (a *decValue) Set(s string) error {
+	dec, err := math.LegacyNewDecFromStr(s)
+	if err != nil {
+		return err
+	}
+
+	// we need to convert from float representation to non-float representation using default precision
+	// 0.5 -> 500000000000000000
+	a.value = dec.BigInt().String()
+
+	return nil
+}
+
+func (a decValue) Type() string {
+	return "cosmos.Dec"
+}