Add variable registration to ConfigVariableReader

Sources/DevConfiguration/Core/CodableValueRepresentation.swift

@@ -118,6 +118,28 @@ public struct CodableValueRepresentation: Sendable {
     }
 
 
+    /// Converts encoded `Data` into the appropriate ``ConfigContent`` for this representation.
+    ///
+    /// For string-backed representations, this converts the data to a string using the representation's encoding and
+    /// returns it as ``ConfigContent/string(_:)``. For data-backed representations, this returns the data's bytes as
+    /// ``ConfigContent/bytes(_:)``.
+    ///
+    /// - Parameter data: The encoded data to convert.
+    /// - Returns: The ``ConfigContent`` representing the encoded data.
+    /// - Throws: ``StringEncodingError`` if the data cannot be converted to a string using the expected encoding.
+    func encodeToContent(_ data: Data) throws -> ConfigContent {
+        switch kind {
+        case .string(let encoding):
+            guard let string = String(data: data, encoding: encoding) else {
+                throw StringEncodingError(encoding: encoding)
+            }
+            return .string(string)
+        case .data:
+            return .bytes(Array(data))
+        }
+    }
+
+
     /// Watches for raw data changes from the reader based on this representation.
     ///
     /// Each time the underlying configuration value changes, `onUpdate` is called with the new raw data (or `nil` if the
@@ -154,3 +176,10 @@ public struct CodableValueRepresentation: Sendable {
         }
     }
 }
+
+
+/// An error thrown when encoded data cannot be converted to a string using the expected encoding.
+struct StringEncodingError: Error {
+    /// The string encoding that failed.
+    let encoding: String.Encoding
+}

Sources/DevConfiguration/Core/ConfigVariableContent.swift

@@ -65,6 +65,9 @@ public struct ConfigVariableContent<Value>: Sendable where Value: Sendable {
             _ line: UInt,
             _ continuation: AsyncStream<Value>.Continuation
         ) async throws -> Void
+
+    /// Encodes a value into a ``ConfigContent`` for registration.
+    let encode: @Sendable (_ value: Value) throws -> ConfigContent
 }
 
 
@@ -99,7 +102,8 @@ extension ConfigVariableContent where Value == Bool {
                         continuation.yield(value)
                     }
                 }
-            }
+            },
+            encode: { .bool($0) }
         )
     }
 }
@@ -134,7 +138,8 @@ extension ConfigVariableContent where Value == [Bool] {
                         continuation.yield(value)
                     }
                 }
-            }
+            },
+            encode: { .boolArray($0) }
         )
     }
 }
@@ -169,7 +174,8 @@ extension ConfigVariableContent where Value == Float64 {
                         continuation.yield(value)
                     }
                 }
-            }
+            },
+            encode: { .double($0) }
         )
     }
 }
@@ -204,7 +210,8 @@ extension ConfigVariableContent where Value == [Float64] {
                         continuation.yield(value)
                     }
                 }
-            }
+            },
+            encode: { .doubleArray($0) }
         )
     }
 }
@@ -239,7 +246,8 @@ extension ConfigVariableContent where Value == Int {
                         continuation.yield(value)
                     }
                 }
-            }
+            },
+            encode: { .int($0) }
         )
     }
 }
@@ -274,7 +282,8 @@ extension ConfigVariableContent where Value == [Int] {
                         continuation.yield(value)
                     }
                 }
-            }
+            },
+            encode: { .intArray($0) }
         )
     }
 }
@@ -309,7 +318,8 @@ extension ConfigVariableContent where Value == String {
                         continuation.yield(value)
                     }
                 }
-            }
+            },
+            encode: { .string($0) }
         )
     }
 }
@@ -344,7 +354,8 @@ extension ConfigVariableContent where Value == [String] {
                         continuation.yield(value)
                     }
                 }
-            }
+            },
+            encode: { .stringArray($0) }
         )
     }
 }
@@ -379,7 +390,8 @@ extension ConfigVariableContent where Value == [UInt8] {
                         continuation.yield(value)
                     }
                 }
-            }
+            },
+            encode: { .bytes($0) }
         )
     }
 }
@@ -420,7 +432,8 @@ extension ConfigVariableContent where Value == [[UInt8]] {
                         continuation.yield(value)
                     }
                 }
-            }
+            },
+            encode: { .byteChunkArray($0) }
         )
     }
 }
@@ -467,7 +480,8 @@ extension ConfigVariableContent {
                         continuation.yield(value)
                     }
                 }
-            }
+            },
+            encode: { .string($0.rawValue) }
         )
     }
 
@@ -510,7 +524,8 @@ extension ConfigVariableContent {
                         continuation.yield(value)
                     }
                 }
-            }
+            },
+            encode: { .stringArray($0.map(\.rawValue)) }
         )
     }
 
@@ -552,7 +567,8 @@ extension ConfigVariableContent {
                         continuation.yield(value)
                     }
                 }
-            }
+            },
+            encode: { .string($0.description) }
         )
     }
 
@@ -595,7 +611,8 @@ extension ConfigVariableContent {
                         continuation.yield(value)
                     }
                 }
-            }
+            },
+            encode: { .stringArray($0.map(\.description)) }
         )
     }
 }
@@ -642,7 +659,8 @@ extension ConfigVariableContent {
                         continuation.yield(value)
                     }
                 }
-            }
+            },
+            encode: { .int($0.rawValue) }
         )
     }
 
@@ -685,7 +703,8 @@ extension ConfigVariableContent {
                         continuation.yield(value)
                     }
                 }
-            }
+            },
+            encode: { .intArray($0.map(\.rawValue)) }
         )
     }
 
@@ -727,7 +746,8 @@ extension ConfigVariableContent {
                         continuation.yield(value)
                     }
                 }
-            }
+            },
+            encode: { .int($0.configInt) }
         )
     }
 
@@ -770,7 +790,8 @@ extension ConfigVariableContent {
                         continuation.yield(value)
                     }
                 }
-            }
+            },
+            encode: { .intArray($0.map(\.configInt)) }
         )
     }
 }
@@ -905,6 +926,11 @@ extension ConfigVariableContent {
                     }
                     continuation.yield(defaultValue)
                 }
+            },
+            encode: { (value) in
+                let resolvedEncoder = encoder ?? JSONEncoder()
+                let data = try resolvedEncoder.encode(value)
+                return try representation.encodeToContent(data)
             }
         )
     }

Sources/DevConfiguration/Core/ConfigVariableReader.swift

@@ -7,6 +7,7 @@
 
 import Configuration
 import DevFoundation
+import OSLog
 
 /// Provides access to configuration values queried by a `ConfigVariable`.
 ///
@@ -53,6 +54,12 @@ public struct ConfigVariableReader {
     /// The event bus used to post diagnostic events like ``ConfigVariableDecodingFailedEvent``.
     public let eventBus: EventBus
 
+    /// The variables that have been registered with this reader, keyed by their configuration key.
+    private(set) var registeredVariables: [ConfigKey: RegisteredConfigVariable] = [:]
+
+    /// The logger used for registration diagnostics.
+    private static let logger = Logger(subsystem: "DevConfiguration", category: "ConfigVariableReader")
+
 
     /// Creates a new `ConfigVariableReader` with the specified providers and the default telemetry access reporter.
     ///
@@ -87,6 +94,44 @@ public struct ConfigVariableReader {
 }
 
 
+// MARK: - Registration
+
+extension ConfigVariableReader {
+    /// Registers a configuration variable with this reader.
+    ///
+    /// Registration records the variable's key, default value, secrecy, and metadata in a non-generic form so that the
+    /// reader can provide information about all registered variables without needing their generic type parameters.
+    ///
+    /// Registration is intended to be performed during setup, before the reader is shared with other components. If a
+    /// variable with the same key has already been registered, the new registration overwrites the previous one, a
+    /// warning is logged, and an assertion failure is triggered.
+    ///
+    /// - Parameter variable: The configuration variable to register.
+    public mutating func register<Value>(_ variable: ConfigVariable<Value>) {
+        let defaultContent: ConfigContent
+        do {
+            defaultContent = try variable.content.encode(variable.defaultValue)
+        } catch {
+            assertionFailure("Failed to encode default value for config variable '\(variable.key)': \(error)")
+            Self.logger.error("Failed to encode default value for config variable '\(variable.key)': \(error)")
+            return
+        }
+
+        if registeredVariables[variable.key] != nil {
+            assertionFailure("Config variable '\(variable.key)' is already registered")
+            Self.logger.error("Config variable '\(variable.key)' is already registered; overwriting")
+        }
+
+        registeredVariables[variable.key] = RegisteredConfigVariable(
+            key: variable.key,
+            defaultContent: defaultContent,
+            secrecy: variable.secrecy,
+            metadata: variable.metadata
+        )
+    }
+}
+
+
 // MARK: - Value Access
 
 extension ConfigVariableReader {

Sources/DevConfiguration/Core/RegisteredConfigVariable.swift

@@ -0,0 +1,42 @@
+//
+//  RegisteredConfigVariable.swift
+//  DevConfiguration
+//
+//  Created by Prachi Gauriar on 3/5/2026.
+//
+
+import Configuration
+
+/// A non-generic representation of a registered ``ConfigVariable``.
+///
+/// `RegisteredConfigVariable` stores the type-erased information from a ``ConfigVariable`` so that registered variables
+/// can be stored in homogeneous collections. It captures the variable's key, its default value as a ``ConfigContent``,
+/// its secrecy setting, and any attached metadata.
+@dynamicMemberLookup
+struct RegisteredConfigVariable: Sendable {
+    /// The configuration key used to look up this variable's value.
+    let key: ConfigKey
+
+    /// The variable's default value represented as a ``ConfigContent``.
+    let defaultContent: ConfigContent
+
+    /// Whether this value should be treated as a secret.
+    let secrecy: ConfigVariableSecrecy
+
+    /// The configuration variable's metadata.
+    let metadata: ConfigVariableMetadata
+
+
+    /// Provides dynamic member lookup access to metadata properties.
+    ///
+    /// This subscript enables dot-syntax access to metadata properties, mirroring the access pattern on
+    /// ``ConfigVariable``.
+    ///
+    /// - Parameter keyPath: A keypath to a property on `ConfigVariableMetadata`.
+    /// - Returns: The value of the metadata property.
+    subscript<MetadataValue>(
+        dynamicMember keyPath: KeyPath<ConfigVariableMetadata, MetadataValue>
+    ) -> MetadataValue {
+        metadata[keyPath: keyPath]
+    }
+}

Tests/DevConfigurationTests/Testing Support/MockCodableConfig.swift

@@ -0,0 +1,11 @@
+//
+//  MockCodableConfig.swift
+//  DevConfiguration
+//
+//  Created by Prachi Gauriar on 3/5/2026.
+//
+
+struct MockCodableConfig: Codable, Hashable, Sendable {
+    let variant: String
+    let count: Int
+}

Tests/DevConfigurationTests/Testing Support/MockConfigIntValue.swift

@@ -0,0 +1,18 @@
+//
+//  MockConfigIntValue.swift
+//  DevConfiguration
+//
+//  Created by Prachi Gauriar on 3/5/2026.
+//
+
+import Configuration
+
+struct MockConfigIntValue: ExpressibleByConfigInt, Hashable, Sendable {
+    let intValue: Int
+    var configInt: Int { intValue }
+    var description: String { "\(intValue)" }
+
+    init?(configInt: Int) {
+        self.intValue = configInt
+    }
+}

Tests/DevConfigurationTests/Testing Support/MockConfigStringValue.swift

@@ -0,0 +1,17 @@
+//
+//  MockConfigStringValue.swift
+//  DevConfiguration
+//
+//  Created by Prachi Gauriar on 3/5/2026.
+//
+
+import Configuration
+
+struct MockConfigStringValue: ExpressibleByConfigString, Hashable, Sendable {
+    let stringValue: String
+    var description: String { stringValue }
+
+    init?(configString: String) {
+        self.stringValue = configString
+    }
+}