Detailed diff shows diff on __defaults when number of elements changes

[VenelinMartinov]

What happened?

When adding/removing elements from a block type we seem to display a diff on the __defaults:

  ~ prov:index/test:Test: (update)
      [id=newid]
      [urn=urn:pulumi:test::test::prov:index/test:Test::mainRes]
    ~ listBlocks: [
        ~ [0]: {
                + __defaults: []
                  prop      : "val1"
              }
        ~ [1]: {
                + __defaults: []
                  prop      : "val2"
              }
        + [2]: {
                + prop      : "val3"
              }
      ]

Example

#2398
list block element added back

Output of pulumi about

.

Additional context

No response

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[VenelinMartinov]

This one is not an issue with the detailed diff calculation:

detailedDiff=map[string]*pulumirpc.PropertyDiff{
           "maxItemsOneBlock": &pulumirpc.PropertyDiff{
               state:         impl.MessageState{},
               sizeCache:     0,
               unknownFields: nil,
               Kind:          4,
               InputDiff:     false,
           },
           "maxItemsOneBlock.prop": &pulumirpc.PropertyDiff{
               state:         impl.MessageState{},
               sizeCache:     0,
               unknownFields: nil,
               Kind:          4,
               InputDiff:     false,
           },
       }

There is no __defaults marked here - instead this seems to be an issue with the news - the block object contains the __defaults key when it looks like there is no reason for that:

pulumi-terraform-bridge/pkg/tfbridge/schema.go

Line 131 in 6b95c60

// Each object-typed value contains metadata about the properties that were set using default values under a

Non-top level defaults don't seem to get used anywhere.

Also:

pulumi-terraform-bridge/pkg/tfbridge/schema.go

Line 1749 in 6b95c60

// TODO: We should probably remove the extraneous defaultsKey here.

suggests the __defaults are not necessary.

[VenelinMartinov]

Perhaps we can remove all empty nested defaults arrays.

[VenelinMartinov]

this is all sidestepped if we only return the bottom-most property which has a diff, instead of all the properties in the tree - this works so much better.

[t0yv0]

__defaults is a special property used by the bridge and it should never be presented in the diffs AFAIK. It's "about" some other properties. Whether they were populated from a default value or not.