feat(functions)!: make FunctionException a sealed class

[YadneshTeli]

Description

Makes FunctionException a sealed class in packages/functions_client/lib/src/types.dart so consumers can perform compile-time checked exhaustive switch expressions over all Edge Function failure modes:

• FunctionsFetchException: Network/transport error before reaching the Edge Function.
• FunctionsApiException (formerly FunctionsHttpException, renamed in refactor!: spell out abbreviations in the public API #1712): Edge Function returned a non-2xx status code.
• FunctionsRelayException: Error returned by the Supabase relay (x-relay-error).

Example:

try {
  await supabase.functions.invoke('hello');
} on FunctionException catch (error) {
  final message = switch (error) {
    FunctionsFetchException() => 'Network failure',
    FunctionsRelayException() => 'Relay error',
    FunctionsApiException()   => 'Function returned ${error.statusCode}',
  };
}

Breaking Changes

sealed implies abstract, which means:

• External packages can no longer directly instantiate a bare FunctionException (e.g. in tests/mocks) or subclass/implement it.
• Consumers should instantiate/match on one of the concrete subtypes instead (FunctionsFetchException, FunctionsApiException, FunctionsRelayException).

Documented in MIGRATION.md.

Verification

• melos analyze: 0 issues across all 20 packages
• melos format: 0 files changed
• Unit tests: functions_client (51 tests) and supabase tests all pass

Closes #1550

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro Plus

Run ID: c6941d3e-0160-44b4-aa87-dc4e5d0c75c3

📥 Commits

Reviewing files that changed from the base of the PR and between a0be827 and 59e013b.

📒 Files selected for processing (3)

• MIGRATION.md
• packages/functions_client/lib/src/types.dart
• packages/functions_client/test/functions_dart_test.dart

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📝 Walkthrough

Walkthrough

FunctionException is now a sealed class with three documented failure subtypes. Migration guidance explains the breaking changes and exhaustive pattern matching. Tests verify matching for fetch, relay, and API exceptions.

Changes

FunctionException sealing

Layer / File(s)	Summary
Sealed exception contract and migration guidance packages/functions_client/lib/src/types.dart, packages/functions_client/test/functions_dart_test.dart, MIGRATION.md	FunctionException is sealed. Documentation identifies FunctionsFetchException, FunctionsRelayException, and FunctionsApiException. Migration guidance describes exhaustive matching and restrictions on external construction or extension. Tests cover all three subtypes.

Estimated code review effort: 2 (Simple) | ~10 minutes

Merge Risk: ⚪ Minimal · up to 59e01

This PR makes FunctionException sealed and documents the resulting breaking change while preserving the listed concrete failure types; no actionable merge-blocking risk remains after normal checks and review.

Possibly related PRs

• supabase/supabase-flutter#1644: Introduced related FunctionException subtype changes that this sealing update builds on.

Suggested labels: v3

Suggested reviewers: spydon

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Linked Issues check	⚠️ Warning	The PR makes FunctionException sealed, but it documents and tests FunctionsApiException instead of the linked issue's required FunctionsHttpException subtype.	Align the implementation, documentation, and tests with issue #1550, or update the linked issue if FunctionsApiException is the intended replacement for FunctionsHttpException.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Out of Scope Changes check	✅ Passed	The migration documentation and exhaustive pattern-matching test directly support the sealed-class change and remain within the linked issue scope.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the primary breaking change: making FunctionException a sealed class.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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