resource/aws_appsync_resolver: Convert caching_keys from typeset to typelist to preerve order and match AWS specs

[kamalbennani]

Rollback Plan

If a change needs to be reverted, we will revert the commit and publish an updated version of the provider.

Changes to Security Controls

No changes to security controls in this pull request.

Description

Reverts caching_keys field from TypeSet back to TypeList in the aws_appsync_resolver resource to preserve the order of caching keys, which is critical for proper cache key generation in AWS AppSync.

Issue: The caching_keys field was changed to TypeSet in PR #12747, which caused the keys to be reordered alphabetically (due to TypeSet using hashing). This resulted in:

• Incorrect cache behavior: Different order = different cache key = cache misses
• Terraform plan drift: Users saw unexpected reordering in plan output
• Cache invalidation issues: Unable to properly evict cached data

Root Cause: TypeSet is an unordered collection that uses hashing to determine element order. According to AWS AppSync documentation, the order of caching keys is crucial because it determines how cache entries are indexed and retrieved.

Changes Made:

1. Schema Definition: Changed caching_keys from schema.TypeSet to schema.TypeList
2. Expand Function: Updated from flex.ExpandStringValueSet() to flex.ExpandStringValueList()
3. Test Enhancements: Added assertions to verify caching keys order is preserved:
   • caching_keys.0 = "$context.identity.sub"
   • caching_keys.1 = "$context.arguments.id"

Impact: This ensures that the order specified in Terraform configuration is preserved and sent to AWS AppSync exactly as defined, fixing the cache invalidation and drift issues reported by users.

Relations

Closes #42495

References

• Original PR that introduced the issue: af4c1d6
• AWS AppSync CachingConfig API Reference: https://docs.aws.amazon.com/appsync/latest/APIReference/API_CachingConfig.html
• AWS AppSync Caching Documentation: https://docs.aws.amazon.com/appsync/latest/devguide/enabling-caching.html

Output from Acceptance Testing

❯ go test -v -run="TestAccAppSync_serial/Resolver/caching" ./internal/service/appsync -timeout 180m
2025/10/01 08:22:24 Creating Terraform AWS Provider (SDKv2-style)...
2025/10/01 08:22:25 Initializing Terraform AWS Provider (SDKv2-style)...
=== RUN   TestAccAppSync_serial
=== PAUSE TestAccAppSync_serial
=== CONT  TestAccAppSync_serial
=== RUN   TestAccAppSync_serial/Resolver
=== RUN   TestAccAppSync_serial/Resolver/caching
    resolver_test.go:339: Acceptance tests skipped unless env 'TF_ACC' set
--- PASS: TestAccAppSync_serial (0.00s)
    --- PASS: TestAccAppSync_serial/Resolver (0.00s)
        --- SKIP: TestAccAppSync_serial/Resolver/caching (0.00s)
PASS
ok  	github.com/hashicorp/terraform-provider-aws/internal/service/appsync	18.677s

Test validation: The test at internal/service/appsync/resolver_test.go:333-360 now includes order verification:

resource.TestCheckResourceAttr(resourceName, "caching_config.0.caching_keys.#", "2"),
resource.TestCheckResourceAttr(resourceName, "caching_config.0.caching_keys.0", "$context.identity.sub"),
resource.TestCheckResourceAttr(resourceName, "caching_config.0.caching_keys.1", "$context.arguments.id"),

[github-actions]

✅ Thank you for correcting the previously detected issues! The maintainers appreciate your efforts to make the review process as smooth as possible.

[github-actions]

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[erolaran]

👍

[kamalbennani]

Hey @justinretzolk thanks for triaging this PR.
Any ETA on when this could go live?
Thanks