core: support editing CfnResource and Stack dependencies

[jusdino]

Describe the feature

Currently, a user has the ability to use CfnResource.addDependsOn() to neatly add explicit dependencies between resources within or across stack boundaries. The catch is that, Node.tryRemoveChild() can then render a CFT completely invalid, since it can remove the referenced resource from a template entirely but a lingering DependsOn value remains set to a logical id that no longer exists. Node.tryRemoveChild() is, of course, in the 'escape hatch' api space, so I wouldn't expect it to gracefully search out any existing dependency references and remove them for me. However, since there is no visibility into already-set dependencies or any ability to gracefully remove individual dependencies, once a depended-on resource is removed, it becomes impossible for a user to salvage the template through the public API, short of something extreme like blindly adding DependsOn overrides to every resource they think might have a reference to the removed resource, possibly causing a lot more damage in the process. Adding some new methods that give a user the visibility and edit-ability to dependencies would be very powerful in a situation like this.

Use Case

Let's say a user has some code:

let foo = CfnResource(this, 'Foo', ...);
let bar = CfnResource(this, 'Bar', ...);
// We need bar deployed first
foo.addDependsOn(bar);

But then they use some construct/aspect/whatever that needs to recreate Bar for some reason:

const stack = Stack.of(this);
stack.node.tryRemoveChild('Bar');
const barReplacement = CfnResource(stack, 'BarReplacement', <some alternate properties or something>);

At this point, the construct that replaced Bar has no way of knowing that it has just irrevocably invalidated the template, because it has no way of seeing that Foo has a DependsOn reference to Bar, and the only possible way to rectify the template is to add foo.addOverride('DependsOn', ...), possibly squashing some other dependencies in the process.

Proposed Solution

Add some new methods to CfnResource that makes it possible to look into the dependency relationships and edit them if they really need to:

foo = stack.tryFindChild('Foo');
if (foo.obtainDependsOn().contains(bar)) {
  foo.removeDependsOn(bar);
fi
foo.addDependsOn(barReplacement);

These new CfnResource.obtainDependsOn() and CfnResource.removeDependsOn() would have to gracefully traverse the resource and assembly dependencies to mirror the behavior of CfnResource.addDependsOn(), for an intuitive user experience.

Other Information

No response

Acknowledgements

• I may be able to implement this feature request
• This feature might incur a breaking change

CDK version used

any

Environment details (OS name and version, etc.)

any

[comcalvi]

Closed by #23383

[github-actions]

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