Fix handling of whitelisted directories in dockerignore

This code snippet closely follows the reference implementation from
github.com/docker/docker/pkg/archive/archive.go

Signed-off-by: Cornelius Weig <22861411+corneliusweig@users.noreply.github.com>

pkg/skaffold/docker/dependencies.go

@@ -146,9 +146,28 @@ func WalkWorkspace(workspace string, excludes, deps []string) (map[string]bool,
 					}
 
 					if info.IsDir() {
-						if ignored {
+						if !ignored {
+							return nil
+						}
+						// exclusion handling closely follows vendor/github.com/docker/docker/pkg/archive/archive.go
+						// No exceptions (!...) in patterns so just skip dir
+						if !pExclude.Exclusions() {
 							return filepath.SkipDir
 						}
+
+						dirSlash := relPath + string(filepath.Separator)
+
+						for _, pat := range pExclude.Patterns() {
+							if !pat.Exclusion() {
+								continue
+							}
+							if strings.HasPrefix(pat.String()+string(filepath.Separator), dirSlash) {
+								// found a match - so can't skip this dir
+								return nil
+							}
+						}
+
+						return filepath.SkipDir
 					} else if !ignored {
 						files[relPath] = true
 					}

pkg/skaffold/docker/dependencies_test.go

@@ -357,7 +357,7 @@ func TestGetDependencies(t *testing.T) {
 			description: "dockerignore with context in parent directory",
 			dockerfile:  copyDirectory,
 			workspace:   "docker/..",
-			ignore:      "bar\ndocker/*\n*.go",
+			ignore:      "bar\ndocker\n*.go",
 			expected:    []string{".dot", "Dockerfile", "file", "test.conf"},
 		},
 		{
@@ -484,6 +484,20 @@ func TestGetDependencies(t *testing.T) {
 			buildArgs:   map[string]*string{"FOO": util.StringPtr("{{")},
 			shouldErr:   true,
 		},
+		{
+			description: "ignore with whitelisting",
+			dockerfile:  copyAll,
+			workspace:   ".",
+			ignore:      "**\n!docker/**",
+			expected:    []string{"Dockerfile", "docker/bar", "docker/nginx.conf"},
+		},
+		{
+			description: "ignore with whitelisting files",
+			dockerfile:  copyAll,
+			workspace:   ".",
+			ignore:      "**\n!server.go",
+			expected:    []string{"Dockerfile", "server.go"},
+		},
 	}
 
 	for _, test := range tests {