Allow dynamically calculated inherit-product path

Bug: 193566316
Test: internal
Change-Id: Iaa7b68cf459f9a694ae9d37a32c9372cf8a8335a
diff --git a/mk2rbc/find_mockfs.go b/mk2rbc/find_mockfs.go
new file mode 100644
index 0000000..73eff07
--- /dev/null
+++ b/mk2rbc/find_mockfs.go
@@ -0,0 +1,121 @@
+package mk2rbc
+
+import (
+	"io/fs"
+	"os"
+	"path/filepath"
+	"time"
+)
+
+// Mock FS. Maps a directory name to an array of entries.
+// An entry implements fs.DirEntry, fs.FIleInfo and fs.File interface
+type FindMockFS struct {
+	dirs map[string][]myFileInfo
+}
+
+func (m FindMockFS) locate(name string) (myFileInfo, bool) {
+	if name == "." {
+		return myFileInfo{".", true}, true
+	}
+	dir := filepath.Dir(name)
+	base := filepath.Base(name)
+	if entries, ok := m.dirs[dir]; ok {
+		for _, e := range entries {
+			if e.name == base {
+				return e, true
+			}
+		}
+	}
+	return myFileInfo{}, false
+}
+
+func (m FindMockFS) create(name string, isDir bool) {
+	dir := filepath.Dir(name)
+	m.dirs[dir] = append(m.dirs[dir], myFileInfo{filepath.Base(name), isDir})
+}
+
+func (m FindMockFS) Stat(name string) (fs.FileInfo, error) {
+	if fi, ok := m.locate(name); ok {
+		return fi, nil
+	}
+	return nil, os.ErrNotExist
+}
+
+type myFileInfo struct {
+	name  string
+	isDir bool
+}
+
+func (m myFileInfo) Info() (fs.FileInfo, error) {
+	panic("implement me")
+}
+
+func (m myFileInfo) Size() int64 {
+	panic("implement me")
+}
+
+func (m myFileInfo) Mode() fs.FileMode {
+	panic("implement me")
+}
+
+func (m myFileInfo) ModTime() time.Time {
+	panic("implement me")
+}
+
+func (m myFileInfo) Sys() interface{} {
+	return nil
+}
+
+func (m myFileInfo) Stat() (fs.FileInfo, error) {
+	return m, nil
+}
+
+func (m myFileInfo) Read(bytes []byte) (int, error) {
+	panic("implement me")
+}
+
+func (m myFileInfo) Close() error {
+	panic("implement me")
+}
+
+func (m myFileInfo) Name() string {
+	return m.name
+}
+
+func (m myFileInfo) IsDir() bool {
+	return m.isDir
+}
+
+func (m myFileInfo) Type() fs.FileMode {
+	return m.Mode()
+}
+
+func (m FindMockFS) Open(name string) (fs.File, error) {
+	panic("implement me")
+}
+
+func (m FindMockFS) ReadDir(name string) ([]fs.DirEntry, error) {
+	if d, ok := m.dirs[name]; ok {
+		var res []fs.DirEntry
+		for _, e := range d {
+			res = append(res, e)
+		}
+		return res, nil
+	}
+	return nil, os.ErrNotExist
+}
+
+func NewFindMockFS(files []string) FindMockFS {
+	myfs := FindMockFS{make(map[string][]myFileInfo)}
+	for _, f := range files {
+		isDir := false
+		for f != "." {
+			if _, ok := myfs.locate(f); !ok {
+				myfs.create(f, isDir)
+			}
+			isDir = true
+			f = filepath.Dir(f)
+		}
+	}
+	return myfs
+}