TM2 Result/Response clarifications

[jaekwon]

Suggested changes:

diff --git a/tm2/pkg/bft/abci/types/types.go b/tm2/pkg/bft/abci/types/types.go
index 637d09b9..0ac05520 100644
--- a/tm2/pkg/bft/abci/types/types.go
+++ b/tm2/pkg/bft/abci/types/types.go
@@ -163,8 +163,8 @@ type ResponseBeginBlock struct {
 
 type ResponseCheckTx struct {
        ResponseBase
-       GasWanted int64 // nondeterministic
-       GasUsed   int64
+       GasWanted int64
+       GasUsed   int64 // nondeterminstic
 }
 
 type ResponseDeliverTx struct {
diff --git a/tm2/pkg/bft/types/results.go b/tm2/pkg/bft/types/results.go
index fd2c787f..c872b8b9 100644
--- a/tm2/pkg/bft/types/results.go
+++ b/tm2/pkg/bft/types/results.go
@@ -8,7 +8,10 @@ import (
 
 //-----------------------------------------------------------------------------
 
-// ABCIResult is the deterministic component of a ResponseDeliverTx.
+// ABCIResult is the deterministic component of a ResponseDeliverTx
+// which gets saved in the blockchain per block.
+// NOTE: ResponseCheckTx does not get stored separately since
+// ResponseDeliverTx includes any errors from the ante handler.
 // TODO: add tags and other fields
 // https://github.com/tendermint/classic/issues/1007
 type ABCIResult struct {
diff --git a/tm2/pkg/sdk/helpers.go b/tm2/pkg/sdk/helpers.go
index d61e8115..8f0cf761 100644
--- a/tm2/pkg/sdk/helpers.go
+++ b/tm2/pkg/sdk/helpers.go
@@ -37,6 +37,7 @@ func ABCIError(err error) abci.Error {
        return abci.ABCIErrorOrStringError(err)
 }
 
+// XXX rename to ResultFromError?
 func ABCIResultFromError(err error) (res Result) {
        res.Error = ABCIError(err)
        res.Log = fmt.Sprintf("%#v", err)
diff --git a/tm2/pkg/sdk/types.go b/tm2/pkg/sdk/types.go
index 47395362..2be8e133 100644
--- a/tm2/pkg/sdk/types.go
+++ b/tm2/pkg/sdk/types.go
@@ -20,7 +20,9 @@ type Handler interface {
        Query(ctx Context, req abci.RequestQuery) abci.ResponseQuery
 }
 
-// Result is the union of ResponseDeliverTx and ResponseCheckTx plus events.
+// Result is the result of processing a tx from the SDK.
+// It becomes either a ResponseDeliverTx or ResponseCheckTx
+// depending on the mode of execution.
 type Result struct {
        abci.ResponseBase
        GasWanted int64