feat(codebuild): improve merging of BuildSpecs

[hoegertn]

First steps for #15169

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[gitpod-io]

[hoegertn]

@rix0rrr for visibility

[rix0rrr]

I'd prefer doing a fully recursive function here that type-analyzes, of the form:

function mergeDeep(lhs, rhs) {

  if (Array.isArray(lhs) && Array.isArray(rhs)) {
    return [...lhs, ...rhs];
  }
  if (Array.isArray(lhs) || Array.isArray(rhs)) { return rhs; }

  if (isObject(lhs) && isObject(rhs)) {
    const ret: any = {...lhs};
    for (const k of Object.keys(rhs)) {
      ret[k] = k in lhs ? mergeDeep(lhs[k], rhs[k]) : rhs[k];
    }
    return ret;
  }

  return rhs;
}

This will take care to create new objects instead of mutating when necessary, and otherwise structurally reuse when not.

If you MUST, I would accept a single parse(stringify(x)) on both structures at the start, to make sure nobody is holding "illegal" references to the starting structures that would be structure-shared in the final result. But we don't need to parse(stringify(x)) at every level of the recursion.

[rix0rrr]

Sweet, thanks!

[mergify]

Thank you for contributing! Your pull request will be updated from master and then merged automatically (do not update manually, and be sure to allow changes to be pushed to your fork).

[aws-cdk-automation]

AWS CodeBuild CI Report

• CodeBuild project: AutoBuildProject89A8053A-LhjRyN9kxr8o
• Commit ID: 0a05edc
• Result: SUCCEEDED
• Build Logs (available for 30 days)

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[mergify]

Thank you for contributing! Your pull request will be updated from master and then merged automatically (do not update manually, and be sure to allow changes to be pushed to your fork).