Don't include the root tree in MaxPathDepth

It is more natural to define the length of a relative path
`foo/bar/baz.txt` as 3 rather than 4, so tweak the code to do so.

Author: mhagger

README.md

@@ -132,7 +132,7 @@ Processing references: 539
 |                              |           |                                |
 | Biggest checkouts            |           |                                |
 | * Number of directories  [6] |  4.38 k   | **                             |
-| * Maximum path depth     [7] |    14     | *                              |
+| * Maximum path depth     [7] |    13     | *                              |
 | * Maximum path length    [8] |   134 B   | *                              |
 | * Number of files        [9] |  62.3 k   | *                              |
 | * Total size of files    [9] |   747 MiB |                                |

git_sizer_test.go

@@ -190,7 +190,7 @@ func TestBomb(t *testing.T) {
 
 	assert.Equal(counts.Count32(1), h.ReferenceCount, "reference count")
 
-	assert.Equal(counts.Count32(11), h.MaxPathDepth, "max path depth")
+	assert.Equal(counts.Count32(10), h.MaxPathDepth, "max path depth")
 	assert.Equal("refs/heads/master^{tree}", h.MaxPathDepthTree.Path(), "max path depth tree")
 	assert.Equal(counts.Count32(29), h.MaxPathLength, "max path length")
 	assert.Equal("refs/heads/master^{tree}", h.MaxPathLengthTree.Path(), "max path length tree")
@@ -272,10 +272,11 @@ func TestFromSubdir(t *testing.T) {
 
 	repo2, err := git.NewRepository(filepath.Join(path, "subdir"))
 	require.NoError(t, err, "creating Repository object in subdirectory")
-	_, err = sizes.ScanRepositoryUsingGraph(
+	h, err := sizes.ScanRepositoryUsingGraph(
 		repo2, git.AllReferencesFilter, sizes.NameStyleNone, false,
 	)
 	require.NoError(t, err, "scanning repository")
+	assert.Equal(t, counts.Count32(2), h.MaxPathDepth, "max path depth")
 }
 
 func TestSubmodule(t *testing.T) {

sizes/graph.go

@@ -609,9 +609,6 @@ func (r *treeRecord) initialize(g *Graph, oid git.OID, tree *git.Tree) error {
 
 func (r *treeRecord) maybeFinalize(g *Graph) {
 	if r.pending == 0 {
-		// Add one for this tree itself:
-		r.size.MaxPathDepth.Increment(1)
-
 		g.finalizeTreeSize(r.oid, r.size, r.objectSize, r.entryCount)
 		for _, listener := range r.listeners {
 			listener(r.size)

sizes/sizes.go

@@ -17,7 +17,7 @@ type BlobSize struct {
 
 type TreeSize struct {
 	// The maximum depth of trees and blobs starting at this object
-	// (including this object).
+	// (not including this object).
 	MaxPathDepth counts.Count32 `json:"max_path_depth"`
 
 	// The maximum length of any path relative to this object, in
@@ -41,7 +41,7 @@ type TreeSize struct {
 }
 
 func (s *TreeSize) addDescendent(filename string, s2 TreeSize) {
-	s.MaxPathDepth.AdjustMaxIfNecessary(s2.MaxPathDepth)
+	s.MaxPathDepth.AdjustMaxIfNecessary(s2.MaxPathDepth.Plus(1))
 	if s2.MaxPathLength > 0 {
 		s.MaxPathLength.AdjustMaxIfNecessary(
 			(counts.NewCount32(uint64(len(filename))) + 1).Plus(s2.MaxPathLength),
@@ -164,7 +164,7 @@ type HistorySize struct {
 	// attribute is maximized separately).
 
 	// The maximum depth of trees and blobs starting at this object
-	// (including this object).
+	// (not including this object).
 	MaxPathDepth counts.Count32 `json:"max_path_depth"`
 
 	// The tree with the maximum path depth.