Account Vec<defined type> fields are decoded with from_json() instead of from_decoded()

[kristinaNikolaevaa]

The Python generator produces incorrect account decoding code for fields with this IDL shape with arrayTypeNode
where

count.kind == "prefixedCountNode" (Vec<T>)
item.kind == "definedTypeLinkNode"

This affects:

- Vec<defined struct>
- Vec<defined enum>

The most visible failure happens when a Vec contains an enum field.
Generated account decode() uses from_json(...) for vector items, but Borsh account parsing returns decoded objects, not JSON objects. It should use from_decoded(...).
Minimal IDL to reproduse

`{
   ...
    "accounts": [
      {
        "kind": "accountNode",
        "name": "bag",
        "data": {
          "kind": "structTypeNode",
          "fields": [
            {
              "kind": "structFieldTypeNode",
              "name": "items",
              "type": {
                "kind": "arrayTypeNode",
                "item": {
                  "kind": "definedTypeLinkNode",
                  "name": "item"
                },
                "count": {
                  "kind": "prefixedCountNode",
                  "prefix": {
                    "kind": "numberTypeNode",
                    "format": "u32",
                    "endian": "le"
                  }
                }
              }
            }
          ]
        }
      }
    ],
    "definedTypes": [
      {
        "kind": "definedTypeNode",
        "name": "kind",
        "type": {
          "kind": "enumTypeNode",
          "variants": [
            { "kind": "enumEmptyVariantTypeNode", "name": "A" },
            { "kind": "enumEmptyVariantTypeNode", "name": "B" }
          ]
        }
      },
      {
        "kind": "definedTypeNode",
        "name": "item",
        "type": {
          "kind": "structTypeNode",
          "fields": [
            {
              "kind": "structFieldTypeNode",
              "name": "kind",
              "type": {
                "kind": "definedTypeLinkNode",
                "name": "kind"
              }
  }`

Actual Generated code looks like:
items=list(map(lambda item: types.item.Item.from_json(item), dec.items))
Expected It should be:
items=list(map(lambda item: types.item.Item.from_decoded(item), dec.items))

Nested enums expect JSON like:
{"kind": "Buy"}
But account decoding receives decoded Borsh objects like:
{"Buy": Container()}
That leads to runtime errors such as:
KeyError: 'kind'

Diff file how to fix it is attached

fix.diff.txt

[daog1]

Thanks for the clear report and for attaching the diff. That made it easy to confirm the root cause.

Fixed in commit 69025c5.

Root cause:
In visitArrayType, the prefixedCountNode (Vec<T>) branch was using the JSON conversion path for account decoding when T was a linked defined type. In practice, account decoding receives decoded Borsh objects, not JSON objects, so fromDecode must use inner.fromDecode, not inner.fromJSON.

This was especially visible for:

• Vec<defined struct>
• Vec<defined enum>
• nested cases such as Vec<defined struct> where the struct contains a linked enum field

Fix:
The Vec<T> branch now builds fromDecodeStr explicitly and returns it from fromDecode, instead of reusing fromJSONStr.

For encodable items, the generated decode path now maps with inner.fromDecode.
For non-encodable items, the branch now also sets explicit passthrough decode behavior where appropriate.

While reviewing the surrounding array logic, I also found the same missing non-encodable decode handling in the remainderCountNode branch and fixed that as well, so the array handling is now consistent across:

• fixed-size arrays
• prefixed arrays (Vec<T>)
• remainder arrays

Test coverage:
Added regression coverage for:

• Vec<defined struct>:
  • decode() uses from_decoded()
  • from_json() still uses from_json()
• Vec<defined enum>:
  • decode() uses from_decoded()
  • from_json() still uses from_json()
• remainder primitive arrays:
  • decode passes through directly
• remainder public key arrays:
  • decode passes through directly
  • JSON conversion still maps through SolPubkey.from_string(...)

Test file:
test/accountsPage.test.ts

Verified with vitest:

• 13 test files
• 30 tests
• all passing

Thanks again for the detailed report and the proposed patch. PRs for similar fixes are very welcome in the future.