fix: Add SafeSub for sdk.Coin (#11630)

## Description

Closes: #11603



---

### Author Checklist

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please add links to any relevant follow up issues.*

I have...

- [ ] included the correct [type prefix](https://github.com/commitizen/conventional-commit-types/blob/v3.0.0/index.json) in the PR title
- [ ] added `!` to the type prefix if API or client breaking change
- [ ] targeted the correct branch (see [PR Targeting](https://github.com/cosmos/cosmos-sdk/blob/master/CONTRIBUTING.md#pr-targeting))
- [ ] provided a link to the relevant issue or specification
- [ ] followed the guidelines for [building modules](https://github.com/cosmos/cosmos-sdk/blob/master/docs/building-modules)
- [ ] included the necessary unit and integration [tests](https://github.com/cosmos/cosmos-sdk/blob/master/CONTRIBUTING.md#testing)
- [ ] added a changelog entry to `CHANGELOG.md`
- [ ] included comments for [documenting Go code](https://blog.golang.org/godoc)
- [ ] updated the relevant documentation or specification
- [ ] reviewed "Files changed" and left comments if necessary
- [ ] confirmed all CI checks have passed

### Reviewers Checklist

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your handle next to the items reviewed if you only reviewed selected items.*

I have...

- [ ] confirmed the correct [type prefix](https://github.com/commitizen/conventional-commit-types/blob/v3.0.0/index.json) in the PR title
- [ ] confirmed `!` in the type prefix if API or client breaking change
- [ ] confirmed all author checklist items have been addressed 
- [ ] reviewed state machine logic
- [ ] reviewed API design and naming
- [ ] reviewed documentation is accurate
- [ ] reviewed tests and test coverage
- [ ] manually tested (if applicable)

CHANGELOG.md

@@ -175,6 +175,7 @@ Ref: https://keepachangelog.com/en/1.0.0/
 
 ### Improvements
 
+* [\#11630](https://github.com/cosmos/cosmos-sdk/pull/11630) Add SafeSub method to sdk.Coin.
 * [\#11511](https://github.com/cosmos/cosmos-sdk/pull/11511) Add api server flags to start command.
 * [\#11484](https://github.com/cosmos/cosmos-sdk/pull/11484) Implement getter for keyring backend option.
 * [\#11449](https://github.com/cosmos/cosmos-sdk/pull/11449) Improved error messages when node isn't synced.

types/coin.go

@@ -115,19 +115,29 @@ func (coin Coin) AddAmount(amount Int) Coin {
 	return Coin{coin.Denom, coin.Amount.Add(amount)}
 }
 
-// Sub subtracts amounts of two coins with same denom. If the coins differ in denom
-// then it panics.
+// Sub subtracts amounts of two coins with same denom and panics on error.
 func (coin Coin) Sub(coinB Coin) Coin {
+	res, err := coin.SafeSub(coinB)
+	if err != nil {
+		panic(err)
+	}
+
+	return res
+}
+
+// SafeSub safely subtracts the amounts of two coins. It returns an error if the coins differ
+// in denom or subtraction results in negative coin denom.
+func (coin Coin) SafeSub(coinB Coin) (Coin, error) {
 	if coin.Denom != coinB.Denom {
-		panic(fmt.Sprintf("invalid coin denominations; %s, %s", coin.Denom, coinB.Denom))
+		return Coin{}, fmt.Errorf("invalid coin denoms: %s, %s", coin.Denom, coinB.Denom)
 	}
 
 	res := Coin{coin.Denom, coin.Amount.Sub(coinB.Amount)}
 	if res.IsNegative() {
-		panic("negative coin amount")
+		return Coin{}, fmt.Errorf("negative coin amount")
 	}
 
-	return res
+	return res, nil
 }
 
 // SubAmount subtracts an amount from the Coin.

types/coin_test.go

@@ -505,6 +505,30 @@ func (s *coinTestSuite) TestSubCoins() {
 	}
 }
 
+func (s *coinTestSuite) TestSafeSubCoin() {
+	cases := []struct {
+		inputOne  sdk.Coin
+		inputTwo  sdk.Coin
+		expected  sdk.Coin
+		expErrMsg string
+	}{
+		{sdk.NewInt64Coin(testDenom1, 1), sdk.NewInt64Coin(testDenom2, 1), sdk.NewInt64Coin(testDenom1, 1), "invalid coin denoms"},
+		{sdk.NewInt64Coin(testDenom1, 10), sdk.NewInt64Coin(testDenom1, 1), sdk.NewInt64Coin(testDenom1, 9), ""},
+		{sdk.NewInt64Coin(testDenom1, 5), sdk.NewInt64Coin(testDenom1, 0), sdk.NewInt64Coin(testDenom1, 5), ""},
+		{sdk.NewInt64Coin(testDenom1, 1), sdk.NewInt64Coin(testDenom1, 5), sdk.Coin{}, "negative coin amount"},
+	}
+
+	for _, tc := range cases {
+		tc := tc
+		res, err := tc.inputOne.SafeSub(tc.inputTwo)
+		if err != nil {
+			s.Require().Contains(err.Error(), tc.expErrMsg)
+			return
+		}
+		s.Require().Equal(tc.expected, res)
+	}
+}
+
 func (s *coinTestSuite) TestCoins_Validate() {
 	testCases := []struct {
 		name    string

x/staking/types/authz.go

@@ -103,12 +103,10 @@ func (a StakeAuthorization) Accept(ctx sdk.Context, msg sdk.Msg) (authz.AcceptRe
 			Updated: &StakeAuthorization{Validators: a.GetValidators(), AuthorizationType: a.GetAuthorizationType()}}, nil
 	}
 
-	// check sufficient balance exists.
-	if _, isNegative := sdk.NewCoins(*a.MaxTokens).SafeSub(sdk.NewCoins(amount)); isNegative {
-		return authz.AcceptResponse{}, sdkerrors.ErrInsufficientFunds.Wrapf("amount is more than max tokens")
+	limitLeft, err := a.MaxTokens.SafeSub(amount)
+	if err != nil {
+		return authz.AcceptResponse{}, err
 	}
-
-	limitLeft := a.MaxTokens.Sub(amount)
 	if limitLeft.IsZero() {
 		return authz.AcceptResponse{Accept: true, Delete: true}, nil
 	}