Merge pull request #148 from cyphar/compare-improvements

compare: allow nil newDh and oldDh

.travis.yml

@@ -1,9 +1,9 @@
 language: go
 go:
   - 1.x
+  - 1.10.x
+  - 1.9.x
   - 1.8.x
-  - 1.7.x
-  - 1.6.3
 
 sudo: false
 

compare.go

@@ -325,6 +325,10 @@ func compareEntry(oldEntry, newEntry Entry) ([]KeyDelta, error) {
 // missing entries and the like). A missing or extra key is treated as a
 // Modified type.
 //
+// If oldDh or newDh are empty, we assume they are a hierarchy that is
+// completely empty. This is purely for helping callers create synthetic
+// InodeDeltas.
+//
 // NB: The order of the parameters matters (old, new) because Extra and
 //     Missing are considered as different discrepancy types.
 func Compare(oldDh, newDh *DirectoryHierarchy, keys []Keyword) ([]InodeDelta, error) {
@@ -338,7 +342,8 @@ func Compare(oldDh, newDh *DirectoryHierarchy, keys []Keyword) ([]InodeDelta, er
 	// map to make sure we don't start comparing unrelated entries.
 	diffs := map[string]*stateT{}
 
-	// First, iterate over the old hierarchy.
+	// First, iterate over the old hierarchy. If nil, pretend it's empty.
+	if oldDh != nil {
 		for _, e := range oldDh.Entries {
 			if e.Type == RelativeType || e.Type == FullType {
 				path, err := e.Path()
@@ -357,8 +362,10 @@ func Compare(oldDh, newDh *DirectoryHierarchy, keys []Keyword) ([]InodeDelta, er
 				diffs[path].Old = copy
 			}
 		}
+	}
 
-	// Then, iterate over the new hierarchy.
+	// Then, iterate over the new hierarchy. If nil, pretend it's empty.
+	if newDh != nil {
 		for _, e := range newDh.Entries {
 			if e.Type == RelativeType || e.Type == FullType {
 				path, err := e.Path()
@@ -377,6 +384,7 @@ func Compare(oldDh, newDh *DirectoryHierarchy, keys []Keyword) ([]InodeDelta, er
 				diffs[path].New = copy
 			}
 		}
+	}
 
 	// Now we compute the diff.
 	var results []InodeDelta