Loading values from a migrated emulator state fails

[SupunS]

Issue to be solved

Loading already stored values from a migrated emulator state fails for certain values. e.g: Dictionary values.

This could be either:

• A problem in the way the updated payloads are written back to the emulator state, or
• A problem with the migration

Needs to investigate further.

Suggested Solution

No response

[turbolent]

Is there any kind of error that is reported?

[SupunS]

The two errors that I ran into so far was:

• Loading a dictionary (say {String:Int}) loads some random dictionary value.

  error: failed to force-cast value: expected type `{String: Int}`, got `{UInt64: Never?}`
    --> d15604fc4f6a3ebafa9de405add09237341bcb45505cd167798de1d65f3fbaa4:16:16
     |
  16 |     var dict1 = acct.storage.load<{String: Int}>(from: /storage/dictionary_with_string_keys)
     |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  

  The value is indeed something else (e.g: {2: nil})

• Imports cannot be found after migrating the contract

[SupunS]

It seems the registers are somehow messed up

[turbolent]

It's weird that this happens, given that the we have a test case in flow-go that works

[turbolent]

Maybe this is caused by the gap that #3141 fills?

[SupunS]

Maybe this is caused by the gap that #3141 fills?

It shouldn't be: the said dictionary value doesn't change it's static type (its a {String: Int} value), so #3141 wouldn't really impact this one.

[SupunS]

Values in the storage seems to be correct: onflow/flow-emulator#584 (PR is failing CI due to unrelated changes, but the updated test TestCadence1Migration assertions pass)

[SupunS]

Maybe the way the register keys are created/encoded got changed in the emulator latest version, or something like that? 🤔

[SupunS]

So it turns out to be the snapshot was taken before shutting down the emulator, which may have left the store with some unwritten data.

[turbolent]

What are the steps for creating a valid snapshot? We'll have to document this and provide it to developers