swift-concurrency-expert

Reviews and repairs Swift concurrency problems in codebases on version 6.2 or newer, applying actor isolation and data-race safety with the smallest safe edit rather than a rewrite. That restraint suits code already in production that only needs to satisfy compiler diagnostics. It expects the actual compiler output and the offending symbol up front, so a vague report of occasional runtime strangeness gives it little to work with. The guidance prefers immutable value types and warns against unchecked conformance to the sendable protocol unless thread safety can be proven. Reference notes ship alongside the main file, and attribution credits an outside contributor.

Use case: Clearing data-race compiler errors in an existing app

This skill reviews and repairs concurrency issues in modern swift code by applying isolation and sendability rules with minimal behavioural change. The workflow is deliberately conservative: capture the diagnostics, work out the current isolation context, then make the smallest fix that satisfies the compiler. ## What it does - Triages by capturing the exact compiler diagnostics and the offending symbol. - Identifies the current isolation context and whether a default isolation mode is enabled. - Annotates ui bound types with main actor isolation. - Moves expensive work to a concurrent async function or guards mutable state with an actor. - Handles sendable errors by preferring immutable value types, and treats an unchecked annotation as a last resort. ## When it is the wrong choice It targets a recent language version, so a codebase pinned to an older toolchain will not accept the patterns it recommends. It also assumes the diagnostics are available and specific; a vague error message leads to a guess rather than a fix. The conservative bias toward the smallest edit is a strength until a deeper design problem is the real cause, at which point patching the symptom produces a type that satisfies the compiler while staying awkward to use. Some fixes, such as marking a conformance as isolated, also change the surface other code sees, so downstream call sites may need attention. ```json { "ui_bound_types": "annotate with main actor isolation", "global_state": "protect or move into an actor", "background_work": "move to a concurrent async function", "sendable_errors": "prefer immutable value types" } ``` ## Working notes - Reference material covers the current language version and the ui framework specifics. - Default isolation mode affects which fixes are available. - The preferred outcome is a fix that preserves existing behaviour.