YAML inheritance broken when using yaml.MapSlice

[mattes]

See comments in code below:

package main

import (
    "fmt"
    "gopkg.in/yaml.v2"
)

var body = `
foo: &foo
  some: "var"

bar:
  <<: *foo
`

type Foobar struct {
    Foo interface{}
    Bar interface{}
}

func main() {
    // works as expected
    f := &Foobar{}
    if err := yaml.Unmarshal([]byte(body), &f); err != nil {
        fmt.Println(err)
    }
    fmt.Printf("%+v\n", f) // &{Foo:map[some:var] Bar:map[some:var]}

    // fails parsing yaml inheritance
    f1 := &yaml.MapSlice{}
    if err := yaml.Unmarshal([]byte(body), &f1); err != nil {
        fmt.Println(err)
    }
    fmt.Printf("%+v\n", f1) // &[{Key:foo Value:[{Key:some Value:var}]} {Key:bar Value:[]}]
    // expected: &[{Key:foo Value:[{Key:some Value:var}]} {Key:bar Value:[{Key:some Value:var}]}]
}

[amolokoedov]

Not yet fixed. Is there a patch for this?

[vinzenz]

@mattes @amolokoedov Would be cool if you could check that your use cases are covered with the PR I have sent

[rogpeppe]

@vinzenz I cannot find a description of the << operator in any of the YAML 1.x specifications.

Should this actually be a supported feature?

[vinzenz]

@rogpeppe http://yaml.org/type/merge.html

[rogpeppe]

@vinzenz How many other "working drafts" are actually part of the YAML spec without being mentioned there? How is one supposed to know what YAML actually is without a full specification?

[vinzenz]

@rogpeppe Well I don't know, YAML is a beast ;-) I just added the support for MapSlice - Merge support was there already before

[hjdr4]

I need to use both merge and override and keep order.
Using vinzenz@764aa8c I'm able to use merge with MapSlice but overriding a merged key does not work, keys are just duplicated.

[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.