Add navigation support for OmegaConfig Syntax

[noklam]

Rough idea:

• YAML return every config with a __line__ attribute
  • OmegaConf consume this __line__ metadata, then update the following constructors:
    • ContainerMetadata
    • OmegaConf.create
    • OmegaConf._create_impl
    • DictConfig.__init__

[noklam]

The pre-requisite for building this is to store the YAML line no/cursor position of the catalog entry at load-time.

For reference, ruamel.yaml provides the cursor information:

In [11]: from ruamel.yaml import YAML

In [12]: yaml = YAML()

In [13]: data = yaml.load("""
    ...:      # testing line and column based on SO
    ...:      # http://stackoverflow.com/questions/13319067/
    ...:      - key1: item 1
    ...:        key2: item 2
    ...:      - key3: another item 1
    ...:        key4: another item 2
    ...:         """)

In [14]: data
Out[14]: [{'key1': 'item 1', 'key2': 'item 2'}, {'key3': 'another item 1', 'key4': 'another item 2'}]

In [15]: type(data)
Out[15]: ruamel.yaml.comments.CommentedSeq

In [16]: data[0].lc
Out[16]: LineCol(3, 7)

In [17]: type(data[0])
Out[17]: ruamel.yaml.comments.CommentedMap

It was mentioned that some YAML loader preserve metadata about line and col from kedro-org/kedro#2821 (comment). After some investigation, it is less strictforward than expected. The example is a list, so you can do data[0].lc where data[0] is a CommentedSeq object. You can do similar things if the value is a dictionary. It doesn't work if it's a simple str or int. For example

# abc.yml
a: 1
b: 2

yaml = YAML()
with open("abc.yml") as f:
    data = yaml.load(f)

>>> data["a"]
1

In this case, data["a"] returns an int directly and all the metadata are lost.