valkyrjaio / valkyrja-php / 30415744196

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[Dispatch] Fold the exhaustive match's last arm into default (#943)

# Description

`DispatchFactory::fromReflection()` used a `match (true)` whose five
`instanceof`
arms already covered every member of the parameter's union type. PHP
still
compiles an implicit `UnhandledMatchError` throw into an exhaustive
`match` with
no `default`, so two branches (and one path) in this method are
unreachable by
any input — no test can close them.

This is one of the two known unreachable-branch categories recorded in
the
architecture repo's `php/TODO.md`, and the prescribed remedy is to fold
the last
arm into `default`. `ReflectionFunction` is the only type left once the
four
preceding arms have been ruled out, so `default` is exactly equivalent
in
behavior — the `is_callable()` guard and its
`DispatchInvalidReflectionFunctionException` are untouched.

Verified per-shard (never merged — Xdebug builds a different branch map
for a
function depending on whether it ran, so merged shard data invents
branches):

```
composer phpunit-path-coverage-shard Dispatch
```

**`src/Valkyrja/Dispatch/Factory/DispatchFactory.php`: branches 14/16 →
14/14,
paths 6/7 → 6/6.**

## Types of changes

- [x] Improvement _(non-breaking change which improves code)_
- [ ] Bug fix _(non-breaking change which fixes an issue)_
- [ ] New feature _(non-breaking change which adds functionality)_
- [ ] Deprecation _(breaking change which removes functionality)_
- [ ] Breaking change _(fix or feature that would cause existing
functionality to change)_
- [ ] Documentation improvement

## Changes

- **`src/Valkyrja/Dispatch/Factory/DispatchFactory.php`** — replaced the
final
`$reflection instanceof ReflectionFunction` arm of `fromReflection()`'s
`match (true)` with `default`, removing the unreachable
`UnhandledMatchError`
  branch, and noted in a comment why the arm is spelled that way.

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