std.parseYaml: merge key (<<) conversion produces bogus "true" key and drops fields

[He-Pin]

Description

std.parseYaml mishandles YAML merge keys (<<: *anchor): merged fields are replaced by a bogus "true" key, and the corruption can extend to the anchor sources themselves.

Reproduction 1

std.parseYaml("base: &b {x: 1}\nchild:\n  <<: *b\n  y: 2")

Actual (go-jsonnet v0.22.0):

{
   "base": {
      "x": 1
   },
   "child": {
      "true": 2,
      "x": 1
   }
}

Expected (YAML merge-key semantics):

{
   "base": {
      "x": 1
   },
   "child": {
      "x": 1,
      "y": 2
   }
}

Reproduction 2 (multi-anchor merge)

std.parseYaml("a: &a {x: 1}\nb: &b {y: 2}\nc:\n  <<: [*a, *b]")

Actual:

{
   "a": {
      "x": 1
   },
   "b": {
      "true": 2
   },
   "c": {
      "true": 2,
      "x": 1
   }
}

Expected:

{
   "a": {
      "x": 1
   },
   "b": {
      "y": 2
   },
   "c": {
      "x": 1,
      "y": 2
   }
}

Note b is corrupted as well (y replaced by "true"), even though it is only referenced as an anchor.

Notes

• It looks as if the merge-key sentinel (<<, represented as a boolean by the YAML library) leaks into converted mappings as the string "true", displacing a real key.
• Both sjsonnet and jrsonnet produce the Expected output for both reproductions.
• Found while differential-testing sjsonnet against go-jsonnet.