test: add regression tests for IMMUTABLE plpgsql functions with user-defined return types (#329)

[tianzhou]

Summary

• Adds regression tests for issue Bug: unresolvable plan drift for IMMUTABLE plpgsql functions returning a user-defined type #329: perpetual plan drift for IMMUTABLE plpgsql functions returning user-defined types (e.g., custom enums)
• The bug was reported against pgschema v1.6.2 but does not reproduce on the current codebase (v1.7.2)
• The underlying issue was likely fixed by earlier normalization improvements, specifically:
  • 29c1b67 - strip same-schema qualifiers in normalizeSchemaNames (issue Plan wants to change a column that hasn't changed. #283)
  • 0daf757 - strip schema qualifiers from function/procedure bodies (issue Force qualified names in dump #252)
• These tests serve as regression guards to prevent the issue from recurring

Test cases added

• issue_329_immutable_udt_return — IMMUTABLE plpgsql function returning a custom enum type (idempotency check: plan should detect no changes)
• issue_329_immutable_udt_generated_col — same function used in a GENERATED ALWAYS AS STORED column (verifies both function comparison and generated expression handling)

Fixes #329

Test plan

• PGSCHEMA_TEST_FILTER="create_function/issue_329" go test -v ./internal/diff -run TestDiffFromFiles — passes
• PGSCHEMA_TEST_FILTER="create_function/issue_329" go test -v ./cmd -run TestPlanAndApply — passes (including idempotency check)
• PGSCHEMA_TEST_FILTER="create_function/" go test -v ./cmd -run TestPlanAndApply — all 10 function tests pass
• Full CI suite validates no regressions

🤖 Generated with Claude Code

[greptile-apps]

Greptile Summary

Adds two regression test cases for issue #329 to prevent perpetual plan drift with IMMUTABLE plpgsql functions returning user-defined types.

Test Coverage:

• issue_329_immutable_udt_return - Verifies idempotency for IMMUTABLE function returning custom enum type
• issue_329_immutable_udt_generated_col - Extends test to include GENERATED ALWAYS AS STORED column using the UDT-returning function

Both test cases follow the standard diff test pattern: old.sql and new.sql are identical, and all expected outputs (diff.sql, plan.sql, plan.txt, plan.json) correctly indicate no changes detected. The tests serve as regression guards for normalization fixes in commits 29c1b67 and 0daf757.

Confidence Score: 5/5

• This PR is safe to merge with no risk
• Test-only PR with well-structured regression tests following established project patterns. All test files are correctly formatted with proper idempotency checks (old.sql = new.sql, empty diffs, "No changes detected" outputs). Tests passed in CI per PR description.
• No files require special attention

Important Files Changed

Filename	Overview
testdata/diff/create_function/issue_329_immutable_udt_return/old.sql	Defines baseline schema with custom enum type and IMMUTABLE function returning that type
testdata/diff/create_function/issue_329_immutable_udt_return/new.sql	Identical to old.sql - tests idempotency (no false drift detection)
testdata/diff/create_function/issue_329_immutable_udt_return/plan.txt	Correctly shows "No changes detected." message
testdata/diff/create_function/issue_329_immutable_udt_generated_col/old.sql	Extends first test with table having GENERATED column using the UDT-returning function
testdata/diff/create_function/issue_329_immutable_udt_generated_col/new.sql	Identical to old.sql - tests idempotency with generated column expressions
testdata/diff/create_function/issue_329_immutable_udt_generated_col/plan.txt	Correctly shows "No changes detected." message

_{Last reviewed commit: 4bc9f01}

[Copilot]

Pull request overview

Adds regression coverage for issue #329 to ensure pgschema plan remains idempotent for IMMUTABLE plpgsql functions that return user-defined types, including when referenced by generated columns.

Changes:

• Adds a no-op plan regression fixture for an IMMUTABLE plpgsql function returning a custom enum.
• Adds a no-op plan regression fixture for the same function referenced by a GENERATED ALWAYS AS STORED column.
• Includes expected plan outputs across human (plan.txt), SQL (plan.sql), and JSON (plan.json) formats for CLI/integration tests.

Reviewed changes

Copilot reviewed 8 out of 12 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
testdata/diff/create_function/issue_329_immutable_udt_return/old.sql	Baseline schema defining enum + IMMUTABLE function returning UDT.
testdata/diff/create_function/issue_329_immutable_udt_return/new.sql	Target schema identical to old to assert no drift.
testdata/diff/create_function/issue_329_immutable_udt_return/plan.txt	Expected human output: no changes detected.
testdata/diff/create_function/issue_329_immutable_udt_return/plan.json	Expected JSON output for a no-op plan.
testdata/diff/create_function/issue_329_immutable_udt_return/plan.sql	Expected SQL output for a no-op plan (empty).
testdata/diff/create_function/issue_329_immutable_udt_return/diff.sql	Expected internal diff output for a no-op migration (empty).
testdata/diff/create_function/issue_329_immutable_udt_generated_col/old.sql	Baseline schema adds generated column referencing the function.
testdata/diff/create_function/issue_329_immutable_udt_generated_col/new.sql	Target schema identical to old to assert no drift and no planning error.
testdata/diff/create_function/issue_329_immutable_udt_generated_col/plan.txt	Expected human output: no changes detected.
testdata/diff/create_function/issue_329_immutable_udt_generated_col/plan.json	Expected JSON output for a no-op plan.
testdata/diff/create_function/issue_329_immutable_udt_generated_col/plan.sql	Expected SQL output for a no-op plan (empty).
testdata/diff/create_function/issue_329_immutable_udt_generated_col/diff.sql	Expected internal diff output for a no-op migration (empty).

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