Refactor the List and ListDir interface

Gives more accurate error propagation, control of depth of recursion
and short circuit recursion where possible.

Most of the the heavy lifting is done in the "fs" package, making file
system implementations a bit simpler.

This commit contains some code originally by Klaus Post.

Fixes #316

fs/filter_test.go

@@ -6,6 +6,8 @@ import (
 	"strings"
 	"testing"
 	"time"
+
+	"github.com/stretchr/testify/assert"
 )
 
 func TestAgeSuffix(t *testing.T) {
@@ -192,6 +194,20 @@ func testInclude(t *testing.T, f *Filter, tests []includeTest) {
 	}
 }
 
+type includeDirTest struct {
+	in   string
+	want bool
+}
+
+func testDirInclude(t *testing.T, f *Filter, tests []includeDirTest) {
+	for _, test := range tests {
+		got := f.IncludeDirectory(test.in)
+		if test.want != got {
+			t.Errorf("%q: want %v got %v", test.in, test.want, got)
+		}
+	}
+}
+
 func TestNewFilterIncludeFiles(t *testing.T) {
 	f, err := NewFilter()
 	if err != nil {
@@ -205,6 +221,11 @@ func TestNewFilterIncludeFiles(t *testing.T) {
 	if err != nil {
 		t.Error(err)
 	}
+	assert.Equal(t, filesMap{
+		"file1.jpg": {},
+		"file2.jpg": {},
+	}, f.files)
+	assert.Equal(t, filesMap{}, f.dirs)
 	testInclude(t, f, []includeTest{
 		{"file1.jpg", 0, 0, true},
 		{"file2.jpg", 1, 0, true},
@@ -216,6 +237,42 @@ func TestNewFilterIncludeFiles(t *testing.T) {
 	}
 }
 
+func TestNewFilterIncludeFilesDirs(t *testing.T) {
+	f, err := NewFilter()
+	if err != nil {
+		t.Fatal(err)
+	}
+	for _, path := range []string{
+		"path/to/dir/file1.png",
+		"/path/to/dir/file2.png",
+		"/path/to/file3.png",
+		"/path/to/dir2/file4.png",
+	} {
+		err = f.AddFile(path)
+		if err != nil {
+			t.Error(err)
+		}
+	}
+	assert.Equal(t, filesMap{
+		"path":         {},
+		"path/to":      {},
+		"path/to/dir":  {},
+		"path/to/dir2": {},
+	}, f.dirs)
+	testDirInclude(t, f, []includeDirTest{
+		{"path", true},
+		{"path/to", true},
+		{"path/to/", true},
+		{"/path/to", true},
+		{"/path/to/", true},
+		{"path/to/dir", true},
+		{"path/to/dir2", true},
+		{"path/too", false},
+		{"path/three", false},
+		{"four", false},
+	})
+}
+
 func TestNewFilterMinSize(t *testing.T) {
 	f, err := NewFilter()
 	if err != nil {
@@ -340,6 +397,16 @@ func TestNewFilterMatches(t *testing.T) {
 		{"sausage3/potato", 101, 0, true},
 		{"unicorn", 99, 0, false},
 	})
+	testDirInclude(t, f, []includeDirTest{
+		{"sausage1", false},
+		{"sausage2", false},
+		{"sausage2/sub", false},
+		{"sausage2/sub/dir", false},
+		{"sausage3", true},
+		{"sausage3/sub", true},
+		{"sausage3/sub/dir", true},
+		{"sausage4", false},
+	})
 	if f.InActive() {
 		t.Errorf("want !InActive")
 	}