ReadOnlyFs: MkdirAll on existing path should return nil

readonlyfs.go

@@ -88,6 +88,10 @@ func (r *ReadOnlyFs) Mkdir(n string, p os.FileMode) error {
 }
 
 func (r *ReadOnlyFs) MkdirAll(n string, p os.FileMode) error {
+	fi, err := r.source.Stat(n)
+	if err == nil && fi.IsDir() {
+		return nil
+	}
 	return syscall.EPERM
 }
 

readonlyfs_test.go

@@ -0,0 +1,24 @@
+package afero
+
+import (
+	"testing"
+)
+
+func TestMkdirAllReadonly(t *testing.T) {
+	base := &MemMapFs{}
+	ro := &ReadOnlyFs{source: base}
+
+	base.MkdirAll("/home/test", 0o777)
+	if err := ro.MkdirAll("/home/test", 0o777); err != nil {
+		t.Errorf("Failed to MkdirAll on existing path in ReadOnlyFs: %s", err)
+	}
+
+	if err := ro.MkdirAll("/home/test/newdir", 0o777); err == nil {
+		t.Error("Creating new dir with MkdirAll on ReadOnlyFs should fail but returned nil")
+	}
+
+	base.Create("/home/test/file")
+	if err := ro.MkdirAll("/home/test/file", 0o777); err == nil {
+		t.Error("Creating new dir with MkdirAll on ReadOnlyFs where a file already exists should fail but returned nil")
+	}
+}