Fix: Allow appending to struct at the end of storage layout #1136

[ginzahatemi]

Issue

When appending fields to a struct that is at the end of a contract's storage layout, the upgrades validation incorrectly reports an incompatible layout error. This happens despite the fact that this operation is safe, as it only extends into previously unused storage space.

Fix

This PR modifies the storage layout validation logic to properly handle struct field appending when:

1. The struct is at the end of the storage layout
2. Only new fields are added (no modification to existing fields)
3. The fields are appended at the end of the struct

The changes include:

• Added detection for when fields are only being appended to a struct
• Enhanced the operation filter in layoutLevenshtein to handle struct member changes
• Added appropriate documentation explaining the safety of this operation

Works With

• Regular storage variables
• Namespaced storage (ERC-7201)

Fixes #1136

[ericglau]

Thanks for the PR.
Can you please add some tests? These should include when validations should pass, and when validations should report errors (for example, when appending at the end of a struct, but the struct is not at the end of storage).

[ginzahatemi]

Hi @ericglau ,

I have implemented the changes based on your suggestions. Could you please review them at your convenience? If everything looks good, would you mind proceeding with the merge?

Thank you!

[ericglau]

I've adjusted the test cases for the second scenario to properly demonstrate insertion before the end of storage layout.

However, the first test case is still failing with the following operations even though it should have been filtered out by the new code in compare.ts:

 [
    {
      "kind": "typechange",
      "change": {
        "kind": "struct members",
        "ops": [
          {
            "kind": "append",
            "totalCost": 0,
            "predecessor": {
              "kind": "nop",
              "totalCost": 0,
              "predecessor": {
                "kind": "nop",
                "totalCost": 0,
                "predecessor": {
                  "kind": "nop",
                  "totalCost": 0
                }
              }
            },
            "updated": {
              "label": "z",
              "type": {
                "id": "t_uint256",
                "head": "t_uint256",
                "item": {
                  "label": "uint256",
                  "numberOfBytes": "32"
                }
              },
              "offset": 0,
              "slot": "2"
            }
          }
        ],
...

The logic for the comparison may need to be investigated or this may need further debugging.

[ericglau]

This is missing test cases for namespaced structs as described in #1136

[ginzahatemi]

I've added test cases for namespaced structs as requested in the latest commit. Let me know if there are any more suggestions

[ginzahatemi]

Hey @ericglau I have made the suggested changes and pushed some commit, could you review them, if they are Ok or not?