Update YamlParser and YamlPrinter to support Mapping and Sequence anchors. (issue #1161)

[pway99]

No description provided.

[github-actions]

Test Results

   495 files   -    456     495 suites   - 456   44m 18s ⏱️ - 36m 29s
3 311 tests  -    262  3 202 ✔️  -    248  109 💤  - 14  0 ❌ ±0 
3 676 runs   - 4 190  3 565 ✔️  - 4 136  111 💤  - 54  0 ❌ ±0 

Results for commit 0021a9e. ± Comparison against base commit b37eb51.

[nmck257]

Confirming scope:

• This case (and scalarKeyAnchor up at line 224) are still disabled. And I believe YAML allows anchors on mapping keys, too. Are those included in this PR?
• I see the mappingAnchor case below is no longer disabled, and it features the merge-key syntax <<. So, this PR covers Add support for merge in yaml grammar #2133, too?

[pway99]

This case (and scalarKeyAnchor up at line 224) are still disabled. relatedly, And I believe YAML allows anchors on mapping keys, too. Are those included in this PR?

Thanks for noticing, yes I would agree the YAML does allow anchors on mapping keys also.
https://yaml.org/spec/1.2.2/#3222-anchors-and-aliases

It's interesting though while the spec seems to allow defining an anchor for a key I have not been able to find a YAML validator that successfully validates the example.

Sequence entry validation error:

foo:
  - start: start
  - &anchor buz: buz ## Bad indentation for a sequence entry validation error
  - *anchor: baz
  - end: end

An example that passes validation:

bar:
  &abc yo: friend
baz:
  *abc: friendly

I will give this a bit more investigation and see if I can't make it work for keys also

I see the mappingAnchor case below is no longer disabled, and it features the merge-key syntax <<. So, this PR covers #2133, too?

Good question I will have a look and get back to you on that also.

[pway99]

@nmck257 I am going to merge these changes and leave the issue open then work on the keys having anchors and aliases in another PR

[traceyyoshima]

YamlLinter: link