feat: min and max operators on coins (cosmos#11200) (#360)

Closes: cosmos#10995

Adds `Min()` and `Max()` operations on `sdk.Coins` for per-denom minimum and maximum.

Replaced an example of manual low-level construction of `Coins` with higher-level operators.
Upcoming enhancements to vesting accounts make heavy use of this pattern.

---

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please add links to any relevant follow up issues.*

I have...

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

*All items are required. Please add a note if the item is not applicable and please add
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)

Co-authored-by: Jim Larson <32469398+JimLarson@users.noreply.github.com>

types/coin.go

@@ -390,6 +390,91 @@ func (coins Coins) SafeSub(coinsB Coins) (Coins, bool) {
 	return diff, diff.IsAnyNegative()
 }
 
+// Max takes two valid Coins inputs and returns a valid Coins result
+// where for every denom D, AmountOf(D) of the result is the maximum
+// of AmountOf(D) of the inputs.  Note that the result might be not
+// be equal to either input. For any valid Coins a, b, and c, the
+// following are always true:
+//     a.IsAllLTE(a.Max(b))
+//     b.IsAllLTE(a.Max(b))
+//     a.IsAllLTE(c) && b.IsAllLTE(c) == a.Max(b).IsAllLTE(c)
+//     a.Add(b...).IsEqual(a.Min(b).Add(a.Max(b)...))
+//
+// E.g.
+// {1A, 3B, 2C}.Max({4A, 2B, 2C} == {4A, 3B, 2C})
+// {2A, 3B}.Max({1B, 4C}) == {2A, 3B, 4C}
+// {1A, 2B}.Max({}) == {1A, 2B}
+func (coins Coins) Max(coinsB Coins) Coins {
+	max := make([]Coin, 0)
+	indexA, indexB := 0, 0
+	for indexA < len(coins) && indexB < len(coinsB) {
+		coinA, coinB := coins[indexA], coinsB[indexB]
+		switch strings.Compare(coinA.Denom, coinB.Denom) {
+		case -1: // denom missing from coinsB
+			max = append(max, coinA)
+			indexA++
+		case 0: // same denom in both
+			maxCoin := coinA
+			if coinB.Amount.GT(maxCoin.Amount) {
+				maxCoin = coinB
+			}
+			max = append(max, maxCoin)
+			indexA++
+			indexB++
+		case 1: // denom missing from coinsA
+			max = append(max, coinB)
+			indexB++
+		}
+	}
+	for ; indexA < len(coins); indexA++ {
+		max = append(max, coins[indexA])
+	}
+	for ; indexB < len(coinsB); indexB++ {
+		max = append(max, coinsB[indexB])
+	}
+	return NewCoins(max...)
+}
+
+// Min takes two valid Coins inputs and returns a valid Coins result
+// where for every denom D, AmountOf(D) of the result is the minimum
+// of AmountOf(D) of the inputs.  Note that the result might be not
+// be equal to either input. For any valid Coins a, b, and c, the
+// following are always true:
+//     a.Min(b).IsAllLTE(a)
+//     a.Min(b).IsAllLTE(b)
+//     c.IsAllLTE(a) && c.IsAllLTE(b) == c.IsAllLTE(a.Min(b))
+//     a.Add(b...).IsEqual(a.Min(b).Add(a.Max(b)...))
+//
+// E.g.
+// {1A, 3B, 2C}.Min({4A, 2B, 2C} == {1A, 2B, 2C})
+// {2A, 3B}.Min({1B, 4C}) == {1B}
+// {1A, 2B}.Min({3C}) == empty
+//
+// See also DecCoins.Intersect().
+func (coins Coins) Min(coinsB Coins) Coins {
+	min := make([]Coin, 0)
+	for indexA, indexB := 0, 0; indexA < len(coins) && indexB < len(coinsB); {
+		coinA, coinB := coins[indexA], coinsB[indexB]
+		switch strings.Compare(coinA.Denom, coinB.Denom) {
+		case -1: // denom missing from coinsB
+			indexA++
+		case 0: // same denom in both
+			minCoin := coinA
+			if coinB.Amount.LT(minCoin.Amount) {
+				minCoin = coinB
+			}
+			if !minCoin.IsZero() {
+				min = append(min, minCoin)
+			}
+			indexA++
+			indexB++
+		case 1: // denom missing from coins
+			indexB++
+		}
+	}
+	return NewCoins(min...)
+}
+
 // IsAllGT returns true if for every denom in coinsB,
 // the denom is present at a greater amount in coins.
 func (coins Coins) IsAllGT(coinsB Coins) bool {

types/coin_test.go

@@ -656,6 +656,33 @@ func (s *coinTestSuite) TestCoins_Validate() {
 	}
 }
 
+func (s *coinTestSuite) TestMinMax() {
+	one := sdk.OneInt()
+	two := sdk.NewInt(2)
+
+	cases := []struct {
+		name   string
+		input1 sdk.Coins
+		input2 sdk.Coins
+		min    sdk.Coins
+		max    sdk.Coins
+	}{
+		{"zero-zero", sdk.Coins{}, sdk.Coins{}, sdk.Coins{}, sdk.Coins{}},
+		{"zero-one", sdk.Coins{}, sdk.Coins{{testDenom1, one}}, sdk.Coins{}, sdk.Coins{{testDenom1, one}}},
+		{"two-zero", sdk.Coins{{testDenom2, two}}, sdk.Coins{}, sdk.Coins{}, sdk.Coins{{testDenom2, two}}},
+		{"disjoint", sdk.Coins{{testDenom1, one}}, sdk.Coins{{testDenom2, two}}, sdk.Coins{}, sdk.Coins{{testDenom1, one}, {testDenom2, two}}},
+		{"overlap", sdk.Coins{{testDenom1, one}, {testDenom2, two}}, sdk.Coins{{testDenom1, two}, {testDenom2, one}},
+			sdk.Coins{{testDenom1, one}, {testDenom2, one}}, sdk.Coins{{testDenom1, two}, {testDenom2, two}}},
+	}
+
+	for _, tc := range cases {
+		min := tc.input1.Min(tc.input2)
+		max := tc.input1.Max(tc.input2)
+		s.Require().True(min.IsEqual(tc.min), tc.name)
+		s.Require().True(max.IsEqual(tc.max), tc.name)
+	}
+}
+
 func (s *coinTestSuite) TestCoinsGT() {
 	one := sdk.OneInt()
 	two := sdk.NewInt(2)

types/dec_coin.go

@@ -319,8 +319,9 @@ func (coins DecCoins) SafeSub(coinsB DecCoins) (DecCoins, bool) {
 // Intersect will return a new set of coins which contains the minimum DecCoin
 // for common denoms found in both `coins` and `coinsB`. For denoms not common
 // to both `coins` and `coinsB` the minimum is considered to be 0, thus they
-// are not added to the final set.In other words, trim any denom amount from
+// are not added to the final set. In other words, trim any denom amount from
 // coin which exceeds that of coinB, such that (coin.Intersect(coinB)).IsLTE(coinB).
+// See also Coins.Min().
 func (coins DecCoins) Intersect(coinsB DecCoins) DecCoins {
 	res := make([]DecCoin, len(coins))
 	for i, coin := range coins {

x/auth/vesting/types/vesting_account.go

@@ -45,20 +45,10 @@ func NewBaseVestingAccount(baseAccount *authtypes.BaseAccount, originalVesting s
 //
 // CONTRACT: Delegated vesting coins and vestingCoins must be sorted.
 func (bva BaseVestingAccount) LockedCoinsFromVesting(vestingCoins sdk.Coins) sdk.Coins {
-	lockedCoins := sdk.NewCoins()
-
-	for _, vestingCoin := range vestingCoins {
-		vestingAmt := vestingCoin.Amount
-		delVestingAmt := bva.DelegatedVesting.AmountOf(vestingCoin.Denom)
-
-		max := sdk.MaxInt(vestingAmt.Sub(delVestingAmt), sdk.ZeroInt())
-		lockedCoin := sdk.NewCoin(vestingCoin.Denom, max)
-
-		if !lockedCoin.IsZero() {
-			lockedCoins = lockedCoins.Add(lockedCoin)
-		}
+	lockedCoins := vestingCoins.Sub(vestingCoins.Min(bva.DelegatedVesting))
+	if lockedCoins == nil {
+		return sdk.Coins{}
 	}
-
 	return lockedCoins
 }