MapSlice does not support anchors/merges

[Mange]

Hi! I seem to have found a bug in MapSlice:

import (
    "gopkg.in/yaml.v2"
    "reflect"
    "testing"
)

func TestMapMerging(t *testing.T) {
    data := `---
world: &world
  greeting: Hello
earth:
  << : *world`

    config := map[string]interface{}{}
    err := yaml.Unmarshal([]byte(data), &config)
    if err != nil {
        t.Errorf("Failed to parse\n%v\n\ninto a %T: %v", data, config, err)
    }

    earth := config["earth"]
    expected := map[interface{}]interface{}{
        "greeting": "Hello",
    }

    if !reflect.DeepEqual(earth, expected) {
        t.Errorf("Merging does not work. Expected %v (%T), got %v (%T)", expected, expected, earth, earth)
    }
}

func TestMapSliceMerging(t *testing.T) {
    data := `---
world: &world
  greeting: Hello
earth:
  << : *world`

    config := make(yaml.MapSlice, 0)
    err := yaml.Unmarshal([]byte(data), &config)
    if err != nil {
        t.Errorf("Failed to parse\n%v\n\ninto a %T: %v", data, config, err)
    }

    earth := config[1].Value
    expected := yaml.MapSlice{{Key: "greeting", Value: "Hello"}}

    if !reflect.DeepEqual(earth, expected) {
        t.Errorf("Merging does not work. Expected %v (%T), got %v (%T)", expected, expected, earth, earth)
    }
}

Output:

--- FAIL: TestMapSliceMerging (0.00s)
    foo_test.go:264: Merging does not work. Expected [{greeting Hello}] (yaml.MapSlice), got [] (yaml.MapSlice)

Note how the test with the normal map[string]interface{} works properly. I'm still a beginner in Go, so I'm not sure where to start to fix this one. I have a really hard time understanding the decoding code, but a small pointer in the right direction might help me find some way of fixing this.

[bradrydzewski]

@niemeyer if we send a patch for this what is the process for getting it merged? Is the v2 branch frozen or are you accepting changes? If not, is there a timeline for v3?

cc @donny-dont

[vinzenz]

@bradrydzewski could you please try with #220
This issue might be related to #91

[vinzenz]

@bradrydzewski @Mange Its fixed by #220 I took the liberty to add the above test cases to the tests

[Mange]

Thank you!

[bradrydzewski]

@vinzenz yep, that did the trick. I'm vendoring your patch at the moment, but hopefully the pull request can get merged in the near future. Thanks!

[niemeyer]

Sorry for the lack of feedback here. I can't just merge the PR fixing this as there are a number of unrelated changes in it. That said, MapSlice is about to die. yaml.v3 is on the way and a more comprehensive way to decode content partially and preserve style will be introduced.

I'll keep this issue open and close it when it's ready.

[lox]

Thanks for the update @niemeyer. Given lots of us are likely to be on v2 for some time, would you still be amenable to accepting a patch for this specific issue in v2?

[fredbi]

Thank you @niemeyer. I am also watching this one.

[niemeyer]

No problem, @fredbi.

@lox Sure, as long as it's indeed fixing the issue alone and the patch is clean and tested, happy to apply.

[niemeyer]

I'd like to put a tombstone on this issue. MapSlice will die in v3, and be replaced by a much more flexible intermediate representation. I want to focus on that instead, and anyone that really wants such MapSlices and merges, which is not quite common, can move forward and migrate into it.

v3 is on the way and coming soon.

[gsemet]

Damned, still no support of anchor in yo-yaml? Still is it a pretty standard way of using yaml ...

when is v3 expected?

[lox]

We maintain a fork that we use for Buildkite at https://github.com/buildkite/yaml that includes the patches for anchors with MapSlice @gsemet

[ghost]

for anyone tired of waiting - these tools give correct output:

• https://github.com/0k/shyaml
• https://github.com/dbohdan/remarshal
• https://github.com/martinlindhe/validyaml