Replace scattered defaults subcommands with system property. (apple#604)

Common subcommands for all defaults.

- Closes apple#384.
- Replaces `registry default` and `system dns default` subcommands with
`system property`.
- Users can use `system property ls` to see details about each supported
default value.
- `system property set` implements reasonable validation for all
properties.
- NOTE: Probing of the registry for `registry default set` was removed,
which means users will find out about a botched setting when pulling or
pushing.
- Updates docs.

## Type of Change
- [ ] Bug fix
- [x] New feature  
- [x] Breaking change
- [x] Documentation update

## Motivation and Context
See apple#384.

## Testing
- [x] Tested locally
- [x] Added/updated tests
- [x] Added/updated docs

Author: jglogan

Sources/CLI/Registry/RegistryCommand.swift

@@ -24,7 +24,6 @@ extension Application {
             subcommands: [
                 Login.self,
                 Logout.self,
-                RegistryDefault.self,
             ],
             aliases: ["r"]
         )

Sources/CLI/Registry/RegistryDefault.swift

@@ -0,0 +1,44 @@
+//===----------------------------------------------------------------------===//
+// Copyright © 2025 Apple Inc. and the container project authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//   https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//===----------------------------------------------------------------------===//
+
+import ArgumentParser
+import ContainerClient
+import ContainerPersistence
+import ContainerizationError
+import Foundation
+
+extension Application {
+    struct PropertyClear: AsyncParsableCommand {
+        static let configuration = CommandConfiguration(
+            commandName: "clear",
+            abstract: "Clear a property value"
+        )
+
+        @OptionGroup
+        var global: Flags.Global
+
+        @Argument(help: "the property ID")
+        var id: String
+
+        func run() async throws {
+            guard let key = DefaultsStore.Keys(rawValue: id) else {
+                throw ContainerizationError(.invalidArgument, message: "invalid property ID: \(id)")
+            }
+
+            DefaultsStore.unset(key: key)
+        }
+    }
+}

Sources/CLI/System/DNS/DNSDefault.swift

@@ -0,0 +1,51 @@
+//===----------------------------------------------------------------------===//
+// Copyright © 2025 Apple Inc. and the container project authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//   https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//===----------------------------------------------------------------------===//
+
+import ArgumentParser
+import ContainerClient
+import ContainerPersistence
+import ContainerizationError
+import Foundation
+
+extension Application {
+    struct PropertyGet: AsyncParsableCommand {
+        static let configuration = CommandConfiguration(
+            commandName: "get",
+            abstract: "Retrieve a property value"
+        )
+
+        @OptionGroup
+        var global: Flags.Global
+
+        @Argument(help: "the property ID")
+        var id: String
+
+        func run() async throws {
+            let value = DefaultsStore.allValues()
+                .filter { id == $0.id }
+                .first
+            guard let value else {
+                throw ContainerizationError(.invalidArgument, message: "property ID \(id) not found")
+            }
+
+            guard let val = value.value?.description else {
+                return
+            }
+
+            print(val)
+        }
+    }
+}

Sources/CLI/System/Property/PropertyClear.swift

@@ -0,0 +1,93 @@
+//===----------------------------------------------------------------------===//
+// Copyright © 2025 Apple Inc. and the container project authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//   https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//===----------------------------------------------------------------------===//
+
+import ArgumentParser
+import ContainerClient
+import ContainerPersistence
+import Foundation
+
+extension Application {
+    struct PropertyList: AsyncParsableCommand {
+        static let configuration = CommandConfiguration(
+            commandName: "list",
+            abstract: "List system properties",
+            aliases: ["ls"]
+        )
+
+        @Flag(name: .shortAndLong, help: "Only output the network name")
+        var quiet = false
+
+        @Option(name: .long, help: "Format of the output")
+        var format: ListFormat = .table
+
+        @OptionGroup
+        var global: Flags.Global
+
+        func run() async throws {
+            let vals = DefaultsStore.allValues()
+            try printValues(vals, format: format)
+        }
+
+        private func createHeader() -> [[String]] {
+            [["ID", "TYPE", "VALUE", "DESCRIPTION"]]
+        }
+
+        private func printValues(_ vals: [DefaultsStoreValue], format: ListFormat) throws {
+            if format == .json {
+                let data = try JSONEncoder().encode(vals)
+                print(String(data: data, encoding: .utf8)!)
+                return
+            }
+
+            if self.quiet {
+                vals.forEach {
+                    print($0.id)
+                }
+                return
+            }
+
+            var rows = createHeader()
+            for property in vals {
+                rows.append(property.asRow)
+            }
+
+            let formatter = TableOutput(rows: rows)
+            print(formatter.format())
+        }
+    }
+}
+
+extension DefaultsStoreValue {
+    var asRow: [String] {
+        [id, String(describing: type), value?.description.elided(to: 40) ?? "*undefined*", description]
+    }
+}
+
+extension String {
+    func elided(to maxCount: Int) -> String {
+        let ellipsis = "..."
+        guard self.count > maxCount else {
+            return self
+        }
+
+        if maxCount < ellipsis.count {
+            return ellipsis
+        }
+
+        let prefixCount = maxCount - ellipsis.count
+        return self.prefix(prefixCount) + ellipsis
+    }
+}