Alias dereferincing between documents

[ccoVeille]

go-yaml accepts cross-document alias references, which the YAML spec forbids (anchors are scoped to a single document).

We should detect at go-yaml level if it's relevant
Originally posted by @ccoVeille in mikefarah/yq#2647 (comment)

It's confirmed by

https://yaml.org/spec/1.2.2/#91-documents

A YAML character stream may contain several documents. Each document is completely independent from the rest.

I tried with go-yaml

$ cat /tmp/alias-bug.yaml
---
&foo 42
---
*foo

$ ./go-yaml -t /tmp/alias-bug.yaml
- {token: STREAM-START}
- {token: DOCUMENT-START}
- {token: ANCHOR, value: foo}
- {token: SCALAR, value: 42}
- {token: DOCUMENT-START}
- {token: ALIAS, value: foo}
- {token: STREAM-END}

$ ./go-yaml -y /tmp/alias-bug.yaml
42
---
42

the bug is confirmed

We should report to something like this

$ ./go-yaml -y /tmp/alias-bug.yaml
42
Failed to process YAML:failed to decode YAML: go-yaml load error in composer at L4.C1: unknown anchor 'foo' referenced

Also, my IDE reported me this when I worked on the file I wanted to test 😄