manifest: rename PrefixReplacement methods

The `ReplaceArg / ReplaceResult` methods are not too descriptive, I
always have to look at the code to remember which does what. Renaming
to `Apply` and `Invert`.

sstable/reader_common.go

@@ -79,14 +79,14 @@ type PrefixReplacement struct {
 	SyntheticPrefix []byte
 }
 
-// ReplaceArg replaces the new prefix in the argument with the original prefix.
-func (p *PrefixReplacement) ReplaceArg(src []byte) []byte {
-	return p.replace(src, p.SyntheticPrefix, p.ContentPrefix)
+// Apply replaces the content prefix in the key with the synthetic prefix.
+func (p *PrefixReplacement) Apply(key []byte) []byte {
+	return p.replace(key, p.ContentPrefix, p.SyntheticPrefix)
 }
 
-// ReplaceResult replaces the original prefix in the result with the new prefix.
-func (p *PrefixReplacement) ReplaceResult(key []byte) []byte {
-	return p.replace(key, p.ContentPrefix, p.SyntheticPrefix)
+// Invert replaces the synthetic prefix in the key with the content prefix.
+func (p *PrefixReplacement) Invert(src []byte) []byte {
+	return p.replace(src, p.SyntheticPrefix, p.ContentPrefix)
 }
 
 func (p *PrefixReplacement) replace(key, from, to []byte) []byte {

sstable/reader_virtual.go

@@ -160,8 +160,8 @@ func (v *VirtualReader) NewRawRangeDelIter(
 	upper := &v.vState.upper
 
 	if v.vState.prefixChange != nil {
-		lower = &InternalKey{UserKey: v.vState.prefixChange.ReplaceArg(lower.UserKey), Trailer: lower.Trailer}
-		upper = &InternalKey{UserKey: v.vState.prefixChange.ReplaceArg(upper.UserKey), Trailer: upper.Trailer}
+		lower = &InternalKey{UserKey: v.vState.prefixChange.Invert(lower.UserKey), Trailer: lower.Trailer}
+		upper = &InternalKey{UserKey: v.vState.prefixChange.Invert(upper.UserKey), Trailer: upper.Trailer}
 
 		iter = keyspan.Truncate(
 			v.reader.Compare, iter, lower.UserKey, upper.UserKey,
@@ -229,8 +229,8 @@ func (v *VirtualReader) NewRawRangeKeyIter(
 	}
 
 	if v.vState.prefixChange != nil {
-		lower = &InternalKey{UserKey: v.vState.prefixChange.ReplaceArg(lower.UserKey), Trailer: lower.Trailer}
-		upper = &InternalKey{UserKey: v.vState.prefixChange.ReplaceArg(upper.UserKey), Trailer: upper.Trailer}
+		lower = &InternalKey{UserKey: v.vState.prefixChange.Invert(lower.UserKey), Trailer: lower.Trailer}
+		upper = &InternalKey{UserKey: v.vState.prefixChange.Invert(upper.UserKey), Trailer: upper.Trailer}
 		iter = keyspan.Truncate(
 			v.reader.Compare, iter, lower.UserKey, upper.UserKey,
 			lower, upper, !v.vState.upper.IsExclusiveSentinel(), /* panicOnUpperTruncate */
@@ -287,8 +287,8 @@ func (v *virtualState) constrainBounds(
 		}
 	}
 	if v.prefixChange != nil {
-		first = v.prefixChange.ReplaceArg(first)
-		last = v.prefixChange.ReplaceArg(last)
+		first = v.prefixChange.Invert(first)
+		last = v.prefixChange.Invert(last)
 	}
 	// TODO(bananabrick): What if someone passes in bounds completely outside of
 	// virtual sstable bounds?