Revert inadvertent pull platform filtering from apple#545. (apple#593)

- Reverts an inadvertent "fix" from apple#545.
- Closes apple#592.

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

## Motivation and Context
See apple#592 

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

Author: jglogan

Sources/CLI/Image/ImagePull.swift

@@ -45,13 +45,13 @@ extension Application {
         @Option(
             help: "Set OS if image can target multiple operating systems"
         )
-        var os: String = "linux"
+        var os: String?
 
         @Option(
             name: [.customLong("arch"), .customShort("a")],
             help: "Set arch if image can target multiple architectures"
         )
-        var arch: String = Arch.hostArchitecture().rawValue
+        var arch: String?
 
         @Argument var reference: String
 
@@ -69,8 +69,10 @@ extension Application {
             var p: Platform?
             if let platform {
                 p = try Platform(from: platform)
-            } else {
-                p = try Platform(from: "\(os)/\(arch)")
+            } else if let arch {
+                p = try Platform(from: "\(os ?? "linux")/\(arch)")
+            } else if let os {
+                p = try Platform(from: "\(os)/\(arch ?? Arch.hostArchitecture().rawValue)")
             }
 
             let scheme = try RequestScheme(registry.scheme)

Sources/CLI/Image/ImageSave.swift

@@ -40,13 +40,13 @@ extension Application {
         @Option(
             help: "Set OS if image can target multiple operating systems"
         )
-        var os: String = "linux"
+        var os: String?
 
         @Option(
             name: [.customLong("arch"), .customShort("a")],
             help: "Set arch if image can target multiple architectures"
         )
-        var arch: String = Arch.hostArchitecture().rawValue
+        var arch: String?
 
         @Option(
             name: .shortAndLong, help: "Path to save the image tar archive", completion: .file(),
@@ -61,8 +61,10 @@ extension Application {
             var p: Platform?
             if let platform {
                 p = try Platform(from: platform)
-            } else {
-                p = try Platform(from: "\(os)/\(arch)")
+            } else if let arch {
+                p = try Platform(from: "\(os ?? "linux")/\(arch)")
+            } else if let os {
+                p = try Platform(from: "\(os)/\(arch ?? Arch.hostArchitecture().rawValue)")
             }
 
             let progressConfig = try ProgressConfig(

Tests/CLITests/Subcommands/Images/TestCLIImages.swift

@@ -14,6 +14,7 @@
 // limitations under the License.
 //===----------------------------------------------------------------------===//
 
+import ContainerClient
 import ContainerizationOCI
 import Foundation
 import Testing
@@ -167,6 +168,60 @@ extension TestCLIImagesCommand {
         }
     }
 
+    @Test func testPullOs() throws {
+        do {
+            let os = "linux"
+            let arch = Arch.hostArchitecture().rawValue
+            let pullArgs = [
+                "--os",
+                os,
+            ]
+
+            try doPull(imageName: alpine318, args: pullArgs)
+
+            let output = try doInspectImages(image: alpine318)
+            #expect(output.count == 1, "expected a single image inspect output, got \(output)")
+
+            var found = false
+            for v in output[0].variants {
+                if v.platform.os == os && v.platform.architecture == arch {
+                    found = true
+                }
+            }
+            #expect(found, "expected to find image with os \(os) and architecture \(arch), instead got \(output[0])")
+        } catch {
+            Issue.record("failed to pull and inspect image \(error)")
+            return
+        }
+    }
+
+    @Test func testPullArch() throws {
+        do {
+            let os = "linux"
+            let arch = "amd64"
+            let pullArgs = [
+                "--arch",
+                arch,
+            ]
+
+            try doPull(imageName: alpine318, args: pullArgs)
+
+            let output = try doInspectImages(image: alpine318)
+            #expect(output.count == 1, "expected a single image inspect output, got \(output)")
+
+            var found = false
+            for v in output[0].variants {
+                if v.platform.os == os && v.platform.architecture == arch {
+                    found = true
+                }
+            }
+            #expect(found, "expected to find image with os \(os) and architecture \(arch), instead got \(output[0])")
+        } catch {
+            Issue.record("failed to pull and inspect image \(error)")
+            return
+        }
+    }
+
     @Test func testPullRemoveSingle() throws {
         do {
             try doPull(imageName: alpine)