confix: clean up and document transformations (#8301)

Right now the confix tool works up to v0.35. This change is preparation for
extending the tool to handle additional changes in v0.36.

Mostly this is adding documentation. The one functional change is to fix the
name of the moved "fast-sync" parameter, which was renamed "enable".

- Document the origin of each transformation step.
- Update fast-sync target name.

scripts/confix/confix.go

@@ -80,24 +80,28 @@ func main() {
 
 var plan = transform.Plan{
 	{
+		// Since https://github.com/tendermint/tendermint/pull/5777.
 		Desc: "Rename everything from snake_case to kebab-case",
 		T:    transform.SnakeToKebab(),
 	},
 	{
+		// Since https://github.com/tendermint/tendermint/pull/6896.
 		Desc:    "Rename [fastsync] to [blocksync]",
 		T:       transform.Rename(parser.Key{"fastsync"}, parser.Key{"blocksync"}),
 		ErrorOK: true,
 	},
 	{
-		Desc: "Move top-level fast_sync key under [blocksync]",
+		// Since https://github.com/tendermint/tendermint/pull/7159.
+		Desc: "Move top-level fast_sync key to blocksync.enable",
 		T: transform.MoveKey(
 			parser.Key{"fast-sync"},
 			parser.Key{"blocksync"},
-			parser.Key{"fast-sync"},
+			parser.Key{"enable"},
 		),
 		ErrorOK: true,
 	},
 	{
+		// Since https://github.com/tendermint/tendermint/pull/6462.
 		Desc: "Move priv-validator settings under [priv-validator]",
 		T: transform.Func(func(_ context.Context, doc *tomledit.Document) error {
 			const pvPrefix = "priv-validator-"
@@ -144,6 +148,8 @@ var plan = transform.Plan{
 		}),
 	},
 	{
+		// v1 removed: https://github.com/tendermint/tendermint/pull/5728
+		// v2 deprecated: https://github.com/tendermint/tendermint/pull/6730
 		Desc: `Set blocksync.version to "v0"`,
 		T: transform.Func(func(_ context.Context, doc *tomledit.Document) error {
 			v := doc.First("blocksync", "version")
@@ -166,7 +172,7 @@ func ApplyFixes(ctx context.Context, doc *tomledit.Document) error {
 	tmVersion := GuessConfigVersion(doc)
 	if tmVersion == vUnknown {
 		return errors.New("cannot tell what Tendermint version created this config")
-	} else if tmVersion < v34 {
+	} else if tmVersion < v34 || tmVersion > v36 {
 		// TODO(creachadair): Add in rewrites for older versions.  This will
 		// require some digging to discover what the changes were.  The upgrade
 		// instructions do not give specifics.