Move from platform versions to symbol availability (#48)

### Motivation

Packages such as valkey-swift and async-http-client don't use platform
versions in their Package.swift, so they can't depend on this package
unless we drop it too.

### Modifications

Switched from Package.swift platform versions to per-symbol
availability.

### Result

This does NOT actually make the code work on older versions than before,
just changes how we express availability. It's still macOS 15.0+.

### Test Plan

All tests passed locally.

Author: czechboy0

Package.swift

@@ -70,9 +70,6 @@ traits.insert(
 
 let package = Package(
     name: "swift-configuration",
-    platforms: [
-        .macOS(.v15), .iOS(.v18), .macCatalyst(.v18), .tvOS(.v18), .watchOS(.v11), .visionOS(.v2),
-    ],
     products: [
         .library(name: "Configuration", targets: ["Configuration"]),
         .library(name: "ConfigurationTesting", targets: ["ConfigurationTesting"]),
@@ -170,21 +167,21 @@ let package = Package(
 )
 
 for target in package.targets {
-    if target.type != .plugin {
-        var settings = target.swiftSettings ?? []
+    var settings = target.swiftSettings ?? []
+
+    // https://github.com/apple/swift-evolution/blob/main/proposals/0335-existential-any.md
+    // Require `any` for existential types.
+    settings.append(.enableUpcomingFeature("ExistentialAny"))
 
-        // https://github.com/apple/swift-evolution/blob/main/proposals/0335-existential-any.md
-        // Require `any` for existential types.
-        settings.append(.enableUpcomingFeature("ExistentialAny"))
+    // https://github.com/swiftlang/swift-evolution/blob/main/proposals/0444-member-import-visibility.md
+    settings.append(.enableUpcomingFeature("MemberImportVisibility"))
 
-        // https://github.com/swiftlang/swift-evolution/blob/main/proposals/0444-member-import-visibility.md
-        settings.append(.enableUpcomingFeature("MemberImportVisibility"))
+    // https://github.com/swiftlang/swift-evolution/blob/main/proposals/0409-access-level-on-imports.md
+    settings.append(.enableUpcomingFeature("InternalImportsByDefault"))
 
-        // https://github.com/swiftlang/swift-evolution/blob/main/proposals/0409-access-level-on-imports.md
-        settings.append(.enableUpcomingFeature("InternalImportsByDefault"))
+    settings.append(.enableExperimentalFeature("AvailabilityMacro=Configuration 1.0:macOS 15.0, iOS 18.0, watchOS 11.0, tvOS 18.0, visionOS 2.0"))
 
-        target.swiftSettings = settings
-    }
+    target.swiftSettings = settings
 }
 
 if addDoccPlugin {

Sources/Configuration/AccessReporter.swift

@@ -24,6 +24,7 @@ import Synchronization
 /// Access reporters track when configuration values are read, fetched, or watched,
 /// to provide visibility into configuration usage patterns. This is useful for
 /// debugging, auditing, and understanding configuration dependencies.
+@available(Configuration 1.0, *)
 public protocol AccessReporter: Sendable {
 
     /// Processes a configuration access event.
@@ -41,6 +42,7 @@ public protocol AccessReporter: Sendable {
 /// Access events are generated whenever configuration values are accessed through
 /// ``ConfigReader`` and ``ConfigSnapshotReader`` methods. They contain metadata about
 /// the access, results from individual providers, and the final outcome of the operation.
+@available(Configuration 1.0, *)
 public struct AccessEvent: Sendable {
 
     /// Metadata describing the configuration access operation.
@@ -184,6 +186,7 @@ public struct AccessEvent: Sendable {
 /// Use this reporter to send configuration access events to multiple destinations
 /// simultaneously. Each upstream reporter receives a copy of every event in the
 /// order they were provided during initialization.
+@available(Configuration 1.0, *)
 public struct BroadcastingAccessReporter: Sendable {
 
     /// The reporters that receive forwarded events.
@@ -198,6 +201,7 @@ public struct BroadcastingAccessReporter: Sendable {
     }
 }
 
+@available(Configuration 1.0, *)
 extension BroadcastingAccessReporter: AccessReporter {
     // swift-format-ignore: AllPublicDeclarationsHaveDocumentation
     public func report(_ event: AccessEvent) {

Sources/Configuration/AccessReporters/AccessLogger.swift

@@ -53,6 +53,7 @@ import Synchronization
 /// - `value`: The resolved configuration value (redacted for secrets)
 /// - `counter`: An incrementing counter for tracking access frequency
 /// - Provider-specific information for each provider in the hierarchy
+@available(Configuration 1.0, *)
 public final class AccessLogger: Sendable {
 
     /// The logger used to emit configuration access events.
@@ -94,6 +95,7 @@ public final class AccessLogger: Sendable {
     }
 }
 
+@available(Configuration 1.0, *)
 extension AccessLogger: AccessReporter {
     // swift-format-ignore: AllPublicDeclarationsHaveDocumentation
     public func report(_ event: AccessEvent) {
@@ -109,6 +111,7 @@ extension AccessLogger: AccessReporter {
     }
 }
 
+@available(Configuration 1.0, *)
 extension AccessEvent.Metadata {
     /// Add log metadata.
     /// - Parameter metadata: The metadata to which to add values.
@@ -119,6 +122,7 @@ extension AccessEvent.Metadata {
     }
 }
 
+@available(Configuration 1.0, *)
 extension AccessEvent.ProviderResult {
     /// Add log metadata.
     /// - Parameters:
@@ -136,6 +140,7 @@ extension AccessEvent.ProviderResult {
     }
 }
 
+@available(Configuration 1.0, *)
 extension AccessEvent {
     /// Add log metadata.
     /// - Parameter metadata: The metadata to which to add values.
@@ -151,6 +156,7 @@ extension AccessEvent {
     }
 }
 
+@available(Configuration 1.0, *)
 extension Result<ConfigValue?, any Error> {
     /// Add log metadata.
     /// - Parameter metadata: The metadata to which to add values.

Sources/Configuration/AccessReporters/FileAccessLogger.swift

@@ -64,6 +64,7 @@ import Synchronization
 /// - Resolved value (redacted for secrets)
 /// - Provider that supplied the value or error information
 /// - Access metadata (operation type, value type, source location, timestamp)
+@available(Configuration 1.0, *)
 public final class FileAccessLogger: Sendable {
 
     /// The file descriptor used for writing access events to the log file.
@@ -199,6 +200,7 @@ public final class FileAccessLogger: Sendable {
     }
 }
 
+@available(Configuration 1.0, *)
 extension FileAccessLogger: AccessReporter {
     // swift-format-ignore: AllPublicDeclarationsHaveDocumentation
     public func report(_ event: AccessEvent) {
@@ -213,6 +215,7 @@ extension FileAccessLogger: AccessReporter {
     }
 }
 
+@available(Configuration 1.0, *)
 extension FileAccessLogger {
     /// Renders a string summary for the event.
     /// - Parameter event: The event to render.
@@ -222,6 +225,7 @@ extension FileAccessLogger {
     }
 }
 
+@available(Configuration 1.0, *)
 extension AccessEvent {
     /// Returns a human-readable single line string summarizing the access event.
     /// - Parameter dateFormatStyle: The format style used for rendering dates.
@@ -280,6 +284,7 @@ extension AccessEvent {
     }
 }
 
+@available(Configuration 1.0, *)
 extension ConfigContent {
     /// Returns a string representation of the config value, formatting complex types appropriately.
     ///

Sources/Configuration/ConfigProvider.swift

@@ -45,6 +45,7 @@
 ///
 /// **Dynamic providers**: Implement `watch` methods to emit real-time updates from
 /// polling, file system monitoring, or other change detection mechanisms.
+@available(Configuration 1.0, *)
 public protocol ConfigProvider: Sendable {
 
     /// The human-readable name of the configuration provider.
@@ -137,6 +138,7 @@ public protocol ConfigProvider: Sendable {
 /// Snapshots enable consistent reads of multiple related configuration keys by
 /// capturing the provider's state at a specific moment. This prevents the underlying
 /// data from changing between individual key lookups.
+@available(Configuration 1.0, *)
 public protocol ConfigSnapshotProtocol: Sendable {
 
     /// The human-readable name of the configuration provider that created this snapshot.
@@ -159,6 +161,7 @@ public protocol ConfigSnapshotProtocol: Sendable {
 }
 
 /// The result of looking up a configuration value in a provider.
+@available(Configuration 1.0, *)
 public struct LookupResult: Sendable, Equatable, Hashable {
 
     /// The provider-specific encoding of the configuration key.
@@ -181,6 +184,7 @@ public struct LookupResult: Sendable, Equatable, Hashable {
 }
 
 /// The supported configuration value types.
+@available(Configuration 1.0, *)
 @frozen public enum ConfigType: String, Sendable, Equatable, Hashable {
 
     /// A string value.
@@ -215,6 +219,7 @@ public struct LookupResult: Sendable, Equatable, Hashable {
 }
 
 /// The raw content of a configuration value.
+@available(Configuration 1.0, *)
 @frozen public enum ConfigContent: Sendable, Equatable, Hashable {
 
     /// A string value.
@@ -433,6 +438,7 @@ public struct LookupResult: Sendable, Equatable, Hashable {
 /// Configuration values include the actual content and a flag indicating whether
 /// the value contains sensitive information. Secret values are protected from
 /// accidental disclosure in logs and debug output.
+@available(Configuration 1.0, *)
 public struct ConfigValue: Sendable, Equatable, Hashable {
 
     /// The configuration content.
@@ -451,6 +457,7 @@ public struct ConfigValue: Sendable, Equatable, Hashable {
     }
 }
 
+@available(Configuration 1.0, *)
 extension ConfigValue: CustomStringConvertible {
     // swift-format-ignore: AllPublicDeclarationsHaveDocumentation
     public var description: String {
@@ -462,55 +469,63 @@ extension ConfigValue: CustomStringConvertible {
     }
 }
 
+@available(Configuration 1.0, *)
 extension ConfigValue: ExpressibleByStringLiteral {
     // swift-format-ignore: AllPublicDeclarationsHaveDocumentation
     public init(stringLiteral value: String) {
         self = .init(.string(value), isSecret: false)
     }
 }
 
+@available(Configuration 1.0, *)
 extension ConfigContent: ExpressibleByStringLiteral {
     // swift-format-ignore: AllPublicDeclarationsHaveDocumentation
     public init(stringLiteral value: String) {
         self = .string(value)
     }
 }
 
+@available(Configuration 1.0, *)
 extension ConfigValue: ExpressibleByIntegerLiteral {
     // swift-format-ignore: AllPublicDeclarationsHaveDocumentation
     public init(integerLiteral value: Int) {
         self = .init(.int(value), isSecret: false)
     }
 }
 
+@available(Configuration 1.0, *)
 extension ConfigContent: ExpressibleByIntegerLiteral {
     // swift-format-ignore: AllPublicDeclarationsHaveDocumentation
     public init(integerLiteral value: Int) {
         self = .int(value)
     }
 }
 
+@available(Configuration 1.0, *)
 extension ConfigValue: ExpressibleByFloatLiteral {
     // swift-format-ignore: AllPublicDeclarationsHaveDocumentation
     public init(floatLiteral value: Double) {
         self = .init(.double(value), isSecret: false)
     }
 }
 
+@available(Configuration 1.0, *)
 extension ConfigContent: ExpressibleByFloatLiteral {
     // swift-format-ignore: AllPublicDeclarationsHaveDocumentation
     public init(floatLiteral value: Double) {
         self = .double(value)
     }
 }
 
+@available(Configuration 1.0, *)
 extension ConfigValue: ExpressibleByBooleanLiteral {
     // swift-format-ignore: AllPublicDeclarationsHaveDocumentation
     public init(booleanLiteral value: Bool) {
         self = .init(.bool(value), isSecret: false)
     }
 }
 
+@available(Configuration 1.0, *)
 extension ConfigContent: ExpressibleByBooleanLiteral {
     // swift-format-ignore: AllPublicDeclarationsHaveDocumentation
     public init(booleanLiteral value: Bool) {

Sources/Configuration/ConfigProviderHelpers.swift

@@ -12,6 +12,7 @@
 //
 //===----------------------------------------------------------------------===//
 
+@available(Configuration 1.0, *)
 extension ConfigProvider {
 
     /// Implements `watchValue` by getting the current value and emitting it immediately.
@@ -116,6 +117,7 @@ extension ConfigProvider {
 ///   - work: A closure that performs the value lookup and returns the result.
 /// - Returns: A lookup result containing the encoded key and the value from the closure.
 /// - Throws: Rethrows any errors thrown by the provided closure.
+@available(Configuration 1.0, *)
 package func withConfigValueLookup<Failure: Error>(
     encodedKey: String,
     work: () throws(Failure) -> ConfigValue?
@@ -147,6 +149,7 @@ package func withConfigValueLookup<Failure: Error>(
 ///   - work: An async closure that performs the value lookup and returns the result.
 /// - Returns: A lookup result containing the encoded key and the value from the closure.
 /// - Throws: Rethrows any errors thrown by the provided closure.
+@available(Configuration 1.0, *)
 package func withConfigValueLookup<Failure: Error>(
     encodedKey: String,
     work: () async throws(Failure) -> ConfigValue?

Sources/Configuration/ConfigReader+internalHelpers.swift

@@ -18,6 +18,7 @@ import FoundationEssentials
 import Foundation
 #endif
 
+@available(Configuration 1.0, *)
 extension ConfigValue {
     /// Returns a copy of the config value marked as secret.
     ///
@@ -29,6 +30,7 @@ extension ConfigValue {
     }
 }
 
+@available(Configuration 1.0, *)
 extension Result<ConfigValue?, any Error> {
     /// Returns a copy of the result with the value marked as secret.
     ///
@@ -38,6 +40,7 @@ extension Result<ConfigValue?, any Error> {
     }
 }
 
+@available(Configuration 1.0, *)
 extension LookupResult {
     /// Returns a copy of the config value marked as secret.
     ///
@@ -49,6 +52,7 @@ extension LookupResult {
     }
 }
 
+@available(Configuration 1.0, *)
 extension Result<LookupResult, any Error> {
     /// Returns a copy of the result with the value marked as secret.
     ///
@@ -58,6 +62,7 @@ extension Result<LookupResult, any Error> {
     }
 }
 
+@available(Configuration 1.0, *)
 extension AccessEvent.ProviderResult {
     /// Returns a copy of the result marked as secret.
     ///
@@ -80,6 +85,7 @@ extension AccessEvent.ProviderResult {
 ///   - isSecret: Whether to mark the values as secret.
 ///   - tuple: A tuple containing provider results and a configuration value result.
 /// - Returns: The tuple with values marked as secret if the flag is true, otherwise unchanged.
+@available(Configuration 1.0, *)
 private func mergingIsSecret(
     _ isSecret: Bool,
     _ tuple: ([AccessEvent.ProviderResult], Result<ConfigValue?, any Error>)
@@ -121,6 +127,7 @@ private func mergingIsSecret(
 ///   - fileID: Source file identifier for access event metadata.
 ///   - line: Source line number for access event metadata.
 /// - Returns: The converted configuration value, or `nil` if not found or conversion fails.
+@available(Configuration 1.0, *)
 internal func valueFromReader<Value>(
     forKey key: ConfigKey,
     type: ConfigType,
@@ -193,6 +200,7 @@ internal func valueFromReader<Value>(
 ///   - fileID: Source file identifier used for event reporting.
 ///   - line: Source line number used for event reporting.
 /// - Returns: The configuration value converted to the requested type.
+@available(Configuration 1.0, *)
 internal func valueFromReader<Value>(
     forKey key: ConfigKey,
     type: ConfigType,
@@ -269,6 +277,7 @@ internal func valueFromReader<Value>(
 /// - Throws: `ConfigError.missingRequiredConfigValue` if the configuration value is not found, or any error thrown
 ///   by the `unwrap` closure if conversion fails.
 /// - Returns: The configuration value converted to the requested type.
+@available(Configuration 1.0, *)
 internal func requiredValueFromReader<Value>(
     forKey key: ConfigKey,
     type: ConfigType,
@@ -324,6 +333,7 @@ internal func requiredValueFromReader<Value>(
     return try finalResult.get().0
 }
 
+@available(Configuration 1.0, *)
 extension ConfigReader {
 
     /// Gets a config value synchronously.

Sources/Configuration/ConfigReader+methods.swift

@@ -18,6 +18,7 @@
 // #                                                                           #
 // #############################################################################
 
+@available(Configuration 1.0, *)
 extension ConfigReader {
 
     // MARK: - Get