[Runtime] Include partial errors in oneOf/anyOf decoding errors

Sources/OpenAPIRuntime/Conversion/ErrorExtensions.swift

@@ -22,16 +22,19 @@ extension DecodingError {
     ///   occurred.
     ///   - codingPath: The coding path to the decoder that attempted to decode
     ///   the type.
+    ///   - errors: The errors encountered when decoding individual cases.
     /// - Returns: A decoding error.
     static func failedToDecodeAnySchema(
         type: Any.Type,
-        codingPath: [any CodingKey]
+        codingPath: [any CodingKey],
+        errors: [any Error]
     ) -> Self {
         DecodingError.valueNotFound(
             type,
             DecodingError.Context.init(
                 codingPath: codingPath,
-                debugDescription: "The anyOf structure did not decode into any child schema."
+                debugDescription: "The anyOf structure did not decode into any child schema.",
+                underlyingError: MultiError(errors: errors)
             )
         )
     }
@@ -43,24 +46,47 @@ extension DecodingError {
     ///   occurred.
     ///   - codingPath: The coding path to the decoder that attempted to decode
     ///   the type.
+    ///   - errors: The errors encountered when decoding individual cases.
     /// - Returns: A decoding error.
     @_spi(Generated)
     public static func failedToDecodeOneOfSchema(
         type: Any.Type,
-        codingPath: [any CodingKey]
+        codingPath: [any CodingKey],
+        errors: [any Error]
     ) -> Self {
         DecodingError.valueNotFound(
             type,
             DecodingError.Context.init(
                 codingPath: codingPath,
-                debugDescription: "The oneOf structure did not decode into any child schema."
+                debugDescription: "The oneOf structure did not decode into any child schema.",
+                underlyingError: MultiError(errors: errors)
             )
         )
     }
-}
 
-@_spi(Generated)
-extension DecodingError {
+    /// Returns a decoding error used by the oneOf decoder when
+    /// the discriminator property contains an unknown schema name.
+    /// - Parameters:
+    ///   - discriminatorKey: The discriminator coding key.
+    ///   - discriminatorValue: The unknown value of the discriminator.
+    ///   - codingPath: The coding path to the decoder that attempted to decode
+    ///   the type, with the discriminator value as the last component.
+    /// - Returns: A decoding error.
+    @_spi(Generated)
+    public static func unknownOneOfDiscriminator(
+        discriminatorKey: any CodingKey,
+        discriminatorValue: String,
+        codingPath: [any CodingKey]
+    ) -> Self {
+        return DecodingError.keyNotFound(
+            discriminatorKey,
+            DecodingError.Context.init(
+                codingPath: codingPath,
+                debugDescription:
+                    "The oneOf structure does not contain the provided discriminator value '\(discriminatorValue)'."
+            )
+        )
+    }
 
     /// Verifies that the anyOf decoder successfully decoded at least one
     /// child schema, and throws an error otherwise.
@@ -70,17 +96,49 @@ extension DecodingError {
     ///   occurred.
     ///   - codingPath: The coding path to the decoder that attempted to decode
     ///   the type.
+    ///   - errors: The errors encountered when decoding individual cases.
     /// - Throws: An error of type `DecodingError.failedToDecodeAnySchema` if none of the child schemas were successfully decoded.
+    @_spi(Generated)
     public static func verifyAtLeastOneSchemaIsNotNil(
         _ values: [Any?],
         type: Any.Type,
-        codingPath: [any CodingKey]
+        codingPath: [any CodingKey],
+        errors: [any Error]
     ) throws {
         guard values.contains(where: { $0 != nil }) else {
             throw DecodingError.failedToDecodeAnySchema(
                 type: type,
-                codingPath: codingPath
+                codingPath: codingPath,
+                errors: errors
             )
         }
     }
 }
+
+/// A wrapper of multiple errors, for example collected during a parallelized
+/// operation from the individual subtasks.
+struct MultiError: Swift.Error, LocalizedError, CustomStringConvertible {
+
+    /// The multiple underlying errors.
+    var errors: [any Error]
+
+    var description: String {
+        let combinedDescription =
+            errors
+            .map { error in
+                guard let error = error as? (any PrettyStringConvertible) else {
+                    return error.localizedDescription
+                }
+                return error.prettyDescription
+            }
+            .enumerated()
+            .map { ($0.offset + 1, $0.element) }
+            .map { "Error \($0.0): [\($0.1)]" }
+            .joined(separator: ", ")
+        return "MultiError (contains \(errors.count) error\(errors.count == 1 ? "" : "s")): \(combinedDescription)"
+    }
+
+    var errorDescription: String? {
+        description
+    }
+}

Sources/OpenAPIRuntime/Deprecated/Deprecated.swift

@@ -143,3 +143,74 @@ extension Converter {
         }
     }
 }
+
+extension DecodingError {
+    /// Returns a decoding error used by the oneOf decoder when not a single
+    /// child schema decodes the received payload.
+    /// - Parameters:
+    ///   - type: The type representing the oneOf schema in which the decoding
+    ///   occurred.
+    ///   - codingPath: The coding path to the decoder that attempted to decode
+    ///   the type.
+    /// - Returns: A decoding error.
+    @_spi(Generated)
+    @available(*, deprecated)
+    public static func failedToDecodeOneOfSchema(
+        type: Any.Type,
+        codingPath: [any CodingKey]
+    ) -> Self {
+        DecodingError.valueNotFound(
+            type,
+            DecodingError.Context.init(
+                codingPath: codingPath,
+                debugDescription: "The oneOf structure did not decode into any child schema."
+            )
+        )
+    }
+
+    /// Returns a decoding error used by the anyOf decoder when not a single
+    /// child schema decodes the received payload.
+    /// - Parameters:
+    ///   - type: The type representing the anyOf schema in which the decoding
+    ///   occurred.
+    ///   - codingPath: The coding path to the decoder that attempted to decode
+    ///   the type.
+    /// - Returns: A decoding error.
+    @available(*, deprecated)
+    static func failedToDecodeAnySchema(
+        type: Any.Type,
+        codingPath: [any CodingKey]
+    ) -> Self {
+        DecodingError.valueNotFound(
+            type,
+            DecodingError.Context.init(
+                codingPath: codingPath,
+                debugDescription: "The anyOf structure did not decode into any child schema."
+            )
+        )
+    }
+
+    /// Verifies that the anyOf decoder successfully decoded at least one
+    /// child schema, and throws an error otherwise.
+    /// - Parameters:
+    ///   - values: An array of optional values to check.
+    ///   - type: The type representing the anyOf schema in which the decoding
+    ///   occurred.
+    ///   - codingPath: The coding path to the decoder that attempted to decode
+    ///   the type.
+    /// - Throws: An error of type `DecodingError.failedToDecodeAnySchema` if none of the child schemas were successfully decoded.
+    @_spi(Generated)
+    @available(*, deprecated)
+    public static func verifyAtLeastOneSchemaIsNotNil(
+        _ values: [Any?],
+        type: Any.Type,
+        codingPath: [any CodingKey]
+    ) throws {
+        guard values.contains(where: { $0 != nil }) else {
+            throw DecodingError.failedToDecodeAnySchema(
+                type: type,
+                codingPath: codingPath
+            )
+        }
+    }
+}

Tests/OpenAPIRuntimeTests/URICoder/Test_URICodingRoundtrip.swift

@@ -50,22 +50,30 @@ final class Test_URICodingRoundtrip: Test_Runtime {
                 self.value3 = value3
             }
             init(from decoder: any Decoder) throws {
+                var errors: [any Error] = []
                 do {
                     let container = try decoder.singleValueContainer()
-                    value1 = try? container.decode(Foundation.Date.self)
+                    value1 = try container.decode(Foundation.Date.self)
+                } catch {
+                    errors.append(error)
                 }
                 do {
                     let container = try decoder.singleValueContainer()
-                    value2 = try? container.decode(SimpleEnum.self)
+                    value2 = try container.decode(SimpleEnum.self)
+                } catch {
+                    errors.append(error)
                 }
                 do {
                     let container = try decoder.singleValueContainer()
-                    value3 = try? container.decode(TrivialStruct.self)
+                    value3 = try container.decode(TrivialStruct.self)
+                } catch {
+                    errors.append(error)
                 }
                 try DecodingError.verifyAtLeastOneSchemaIsNotNil(
                     [value1, value2, value3],
                     type: Self.self,
-                    codingPath: decoder.codingPath
+                    codingPath: decoder.codingPath,
+                    errors: errors
                 )
             }
             func encode(to encoder: any Encoder) throws {