fix(clickpipes): change excluded columns type from list to set to avoid ordering issue

[tpanetti]

Why

excluded_columns was modeled as a List rather than a Set. The backend returns excluded columns in an unguaranteed order, so a refresh could rewrite state in a different order than the config. The ModifyPlan "table mappings are immutable" guard compared them with order-sensitive List.Equal, so every subsequent plan then hard-failed with Cannot modify excluded_columns ... — even though the set of excluded columns was unchanged.

What

• Converts excluded_columns from List to Set (Postgres, MySQL, BigQuery) so comparisons are order-insensitive. sorting_keys is intentionally left a List (ClickHouse sort-key order is semantically meaningful).
• Updates API↔state sync to write excluded_columns as a types.Set, and brings the BigQuery branch to parity with Postgres/MySQL by preserving an empty set from prior state (avoids null↔empty churn on refresh).
• Adds a ModifyPlan regression test: a reordered excluded_columns must not be flagged as a modification, while a real target_table change still is.

State migration

No StateUpgrader is needed (the earlier description's "state migration path" wording was inaccurate). A List→Set change is wire-compatible in terraform-plugin-framework: both serialize as JSON arrays and are disambiguated only by the schema type. When the stored state's schema version matches the current one, the framework's UpgradeResourceState passthrough re-decodes the existing array against the new Set type, so existing resources migrate automatically with a clean, no-op plan. No schema Version bump or upgrader is required.

Implements #558

[Copilot]

Pull request overview

This PR addresses ClickPipe plan/refresh instability caused by backend-returned excluded_columns ordering by modeling excluded_columns as an unordered Set, aligning provider semantics with the API behavior (Issue #558).

Changes:

• Convert excluded_columns in ClickPipe table-mapping models and schema from List to Set to make comparisons order-insensitive.
• Update state sync logic to write excluded_columns as a types.Set (instead of types.List) when reading from the API.
• Add a regression test ensuring ModifyPlan does not reject reordered excluded_columns.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
pkg/resource/models/clickpipe_resource.go	Switches table-mapping ExcludedColumns model fields and object types from List to Set.
pkg/resource/clickpipe.go	Updates resource schema and API↔state sync to use Set for excluded_columns.
pkg/resource/clickpipe_test.go	Updates existing test fixture state to represent excluded_columns as SetNull.
pkg/resource/clickpipe_bug_fixes_test.go	Adds/updates regression coverage for Issue #558 and updates fixtures for Set-typed excluded_columns.
docs/resources/clickpipe.md	Updates documentation to reflect excluded_columns as a Set of String.

Comments suppressed due to low confidence (1)

pkg/resource/clickpipe.go:1049

• excluded_columns changed from List to Set in the schema, but this PR description mentions a state migration path and ClickPipeResource does not implement UpgradeState(...) (no state upgrader is present in this file). If Terraform/plugin-framework cannot automatically coerce the prior List state to the new Set type, existing states may fail to decode after upgrade. Either add an explicit state upgrader (List->Set) for excluded_columns in the ClickPipe resource or update the PR description to reflect the actual migration behavior.

										"excluded_columns": schema.SetAttribute{
											Description: "Columns to exclude from replication.",
											Optional:    true,
											ElementType: types.StringType,
										},

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