Default overwrites existing value

[JeanMertz]

The transformer name default to me implies that the key is set to the value only if no value is already set. Instead, as far as I can tell, right now it simply means "always set this value, no matter what".

I'm writing my own transformer to override this behaviour, but I figured I'd report this issue, in case you agree with me that the current behaviour is unexpected, based on the name.

[JeanMertz]

FYI, here's the transformer I wrote, in case this is helpful to someone (this depends on #72):

func transformSetIfMissing(spec *transform.Config, data []byte) ([]byte, error) {
	for k, v := range *spec.Spec {
		var err error

		// If no error is returned, it means the path was found, and we return the
		// existing value.
		if _, err = transform.GetJSONRaw(data, k, true); err == nil {
			return data, nil
		}

		// If any error other than `NonExistentPath` is returned, something went
		// wrong and we return the error.
		if err != nil && err != transform.NonExistentPath {
			return nil, err
		}

		b, err := json.Marshal(v)
		if err != nil {
			return nil, transform.ParseError(fmt.Sprintf("Warn: Unable to coerce element to json string: %v", v))
		}

		data, err = transform.SetJSONRaw(data, b, k)
		if err != nil {
			return nil, err
		}
	}

	return data, nil
}

and the tests:

func TestTransformSetIfMissing(t *testing.T) {
	t.Parallel()

	tests := map[string]struct {
		spec map[string]interface{}
		in   string
		out  string
	}{
		"set default": {
			map[string]interface{}{"hello": "world"},
			`{ "hi": "universe" }`,
			`{ "hi": "universe", "hello": "world" }`,
		},

		"ignore if exists": {
			map[string]interface{}{"hi": "world"},
			`{ "hi": "universe" }`,
			`{ "hi": "universe" }`,
		},

		"set nested default": {
			map[string]interface{}{"hi.world": false},
			`{ "hi": { "universe": true } }`,
			`{ "hi": { "universe": true, "world": false } }`,
		},

		"complex structure": {
			map[string]interface{}{"hi": map[string]interface{}{"my": "world"}},
			`{ "hello": "universe" }`,
			`{ "hello": "universe", "hi": { "my": "world" } }`,
		},
	}

	for name, tt := range tests {
		t.Run(name, func(t *testing.T) {
			cfg := &transform.Config{Spec: &tt.spec}

			b, err := transformSetIfMissing(cfg, []byte(tt.in))
			require.NoError(t, err)

			assert.JSONEq(t, tt.out, string(b))
		})
	}
}

[ryanleary]

Thanks for the report!

[thomas-tharp]

Closing as this is the documented behavior of the default transformer