Typescript actually calls this function to "fix" parent nodes.

https://github.com/microsoft/TypeScript/blob/9ba45fcaace07510ef259d4cda2bc5ec523cf6d1/src/compiler/parser.ts#L887-L917

normally parent references are set during binding. However, for clients that only need a syntax tree, and no semantic features, then the binding process is an unnecessary overhead. This functions allows us to set all the parents, without all the expense of binding.

i'm tempted to remove calls to parent node from converter as we are already traversing nodes,
that should allow me to remove this code and remove it from other places

currently in all other parsing modes we are setting up setParentNodes property as true to get this fixed just for this,

Update:
few missing comments about parent nodes are added

Codecov Report

Merging #1516 into master will increase coverage by <.01%.
The diff coverage is 100%.

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+ Coverage   95.42%   95.42%   +<.01%     
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  Lines        6400     6401       +1     
  Branches     1832     1832              
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+ Hits         6107     6108       +1     
  Misses        108      108              
  Partials      185      185