feat: add InMemoryProvider

[mtonko-flx]

The InMemoryProvider tests assert the specification reason strings #125 introduced ("STATIC", "DISABLED", "TARGETING_MATCH", "DEFAULT"). Error codes are asserted as ErrorCode cases, so nothing here depends on that enum's representation.

Part of #105.

Intent

Appendix A asks every SDK to provide an in-memory provider: initialised with a pre-defined flag set, supporting evaluation context through callbacks, and able to update its flag set while emitting PROVIDER_CONFIGURATION_CHANGED. This SDK had none.

Motivation

• Every existing test in this repository resolves flags through a hand-written double (MockProvider, DoSomethingProvider, AlwaysBrokenProvider), so nothing exercised a real resolution path: a provider holding actual flag configuration, resolving a variant, and reporting a variant and reason.
• Provider and hook authors currently have nothing to test their own code against, and application developers have nothing to develop against locally.

Changes

Implementation

• InMemoryFlag: variants: [String: Value], a required defaultVariant, an optional contextEvaluator, flagMetadata, and disabled.
• contextEvaluator returns the key of the variant to resolve, or nil to fall back to defaultVariant.
• Reasons: STATIC with no callback, TARGETING_MATCH when the callback selects a variant, DEFAULT when it returns nil, DISABLED for a disabled flag (caller's default value, no variant, metadata retained — following Java and JS, not Go, which also attaches a GENERAL error to a non-error outcome).
• putConfiguration(_:) replaces the configuration and reports the union of all previous and all new flag keys, which is the specification's wording for a whole-configuration replacement.
• status, observe() and event emission delegate to ProviderStatusTracker, the pattern documented on FeatureProvider. initialize emits .ready; onContextSet emits .contextChanged and no .reconciling, since there is no asynchronous work and nothing is cached per context.
• Thread-safe via one NSLock around the flag dictionary. The lock is never held while emitting an event, because ProviderStatusTracker.send takes its own lock and delivers to subscribers — a subscriber calling back into the provider would otherwise deadlock through lock-order inversion.

Usage Examples

let provider = InMemoryProvider(flags: [
    "boolean-flag": InMemoryFlag(
        variants: ["on": .boolean(true), "off": .boolean(false)],
        defaultVariant: "on"),
    "context-aware": InMemoryFlag(
        variants: ["internal": .string("INTERNAL"), "external": .string("EXTERNAL")],
        defaultVariant: "external",
        contextEvaluator: { _, context in
            context?.getValue(key: "customer") == .boolean(false) ? "internal" : nil
        }),
])

await OpenFeatureAPI.shared.setProviderAndWait(provider: provider)
OpenFeatureAPI.shared.getClient().getBooleanValue(key: "boolean-flag", defaultValue: false)  // true

// Emits PROVIDER_CONFIGURATION_CHANGED for "boolean-flag".
provider.updateFlag(key: "boolean-flag", flag: InMemoryFlag(
    variants: ["on": .boolean(true), "off": .boolean(false)],
    defaultVariant: "off"))

Testing

40 new tests across four files, modelled on Java's InMemoryProviderTest:

• Each of the five flag types resolves its default variant with the right variant and STATIC; flag metadata is carried through; all five resolve end-to-end through OpenFeatureAPI and Client.
• Unknown flag key, string flag read as an integer, integer variant read as a double and vice versa, evaluation before initialize, a defaultVariant absent from variants, and a callback returning an unknown variant.
• The client turns each provider throw into details carrying the caller's fallback value, reason == "ERROR", and the mapped error code — compared as a typed case (details.errorCode == .flagNotFound), not as a raw value.
• A disabled flag returns the caller's default with DISABLED, no variant, and its metadata intact.
• Targeting: a matching context yields TARGETING_MATCH and the targeted variant; a callback returning nil yields DEFAULT and the default variant; the callback runs with a nil context; its result is still type-checked; and context set via setEvaluationContextAndWait reaches it.
• putConfiguration reports the union of old and new keys and makes removed flags resolve as FLAG_NOT_FOUND; updateFlag/removeFlag report exactly their key; removing an absent key emits nothing; .configurationChanged leaves status .ready and is observable through OpenFeatureAPI.observe().
• Concurrent evaluations interleaved with configuration replacement, and a .configurationChanged subscriber calling back into the provider without deadlocking.

Full suite green on macOS (swift test, 168 tests) and the iOS simulator.

Breaking Changes

None, only additive changes.

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📥 Commits

Reviewing files that changed from the base of the PR and between df62f0b and 0f811f5.

📒 Files selected for processing (2)

• Sources/OpenFeature/Provider/InMemoryProvider/InMemoryProvider.swift
• Tests/OpenFeatureTests/InMemoryProviderErrorTests.swift

📝 Walkthrough

Walkthrough

The change adds InMemoryFlag and InMemoryProvider to support in-memory flag evaluation, targeting, lifecycle events, runtime configuration changes, metadata, and typed resolution. It also adds documentation and comprehensive provider tests.

Changes

InMemoryProvider

Layer / File(s)	Summary
Provider contract and public surface Sources/OpenFeature/Provider/InMemoryProvider/InMemoryFlag.swift, Sources/OpenFeature/Provider/InMemoryProvider/InMemoryProvider.swift, README.md	InMemoryFlag defines variants, default selection, targeting, metadata, and disabled state. InMemoryProvider exposes the provider API and metadata. The README documents registration, evaluation reasons, and configuration methods.
Lifecycle, configuration, and evaluation Sources/OpenFeature/Provider/InMemoryProvider/InMemoryProvider.swift	The provider implements initialization, context changes, configuration replacement, flag updates and removals, event emission, typed evaluation, targeting, disabled handling, variant lookup, and type coercion.
Provider behavior validation Tests/OpenFeatureTests/Helpers/InMemoryTestFlags.swift, Tests/OpenFeatureTests/InMemoryProvider*.swift	Tests cover typed resolution, metadata, disabled flags, provider and client errors, targeting, lifecycle events, configuration changes, concurrency, and event callbacks.

Estimated code review effort: 4 (Complex) | ~45 minutes

Merge Risk: 🟡 Moderate · up to df62f

Object flag evaluations can incorrectly succeed with primitive values, causing callers to receive an invalid flag type rather than their fallback and an error. Add structure validation before merging.

Sequence Diagram(s)

sequenceDiagram
  participant OpenFeatureAPI
  participant InMemoryProvider
  participant ContextEvaluator
  participant EventSubscribers
  OpenFeatureAPI->>InMemoryProvider: setProviderAndWait
  InMemoryProvider-->>OpenFeatureAPI: ready status
  OpenFeatureAPI->>InMemoryProvider: typed flag evaluation
  InMemoryProvider->>ContextEvaluator: resolve variant key
  ContextEvaluator-->>InMemoryProvider: variant key or nil
  InMemoryProvider-->>OpenFeatureAPI: ProviderEvaluation
  InMemoryProvider->>EventSubscribers: configurationChanged event

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🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 21.54% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 65 functions across 7 files. (1 skipped: …	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely identifies the main change: adding the InMemoryProvider.
Description check	✅ Passed	The description directly explains the InMemoryProvider implementation, API behavior, events, testing, and additive scope.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

Full details: Docstring Coverage

Explanation

Docstring coverage is 21.54% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 65 functions across 7 files. (1 skipped: 1 unsupported.)

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Actionable comments posted: 1

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Inline comments:
In `@Sources/OpenFeature/Provider/InMemoryProvider/InMemoryProvider.swift`:
- Line 119: Update getObjectEvaluation to accept only Value.structure results
from resolve; reject boolean, string, number, and other non-structure variants
by throwing the existing typeMismatchError.

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⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Team

Run ID: 71471bf4-09cc-4e00-ae67-9a44c2f18e50

📥 Commits

Reviewing files that changed from the base of the PR and between ab62ca3 and df62f0b.

📒 Files selected for processing (8)

• README.md
• Sources/OpenFeature/Provider/InMemoryProvider/InMemoryFlag.swift
• Sources/OpenFeature/Provider/InMemoryProvider/InMemoryProvider.swift
• Tests/OpenFeatureTests/Helpers/InMemoryTestFlags.swift
• Tests/OpenFeatureTests/InMemoryProviderErrorTests.swift
• Tests/OpenFeatureTests/InMemoryProviderEventTests.swift
• Tests/OpenFeatureTests/InMemoryProviderTargetingTests.swift
• Tests/OpenFeatureTests/InMemoryProviderTests.swift

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