command plugins: Inherit SwiftPM's --configuration flag in packageManager.build

This commit makes it possible for a build run on behalf of a command plugin to inherit the build configuration (debug or release) set for the whole `swift package` run using the `--configuration` flag.

 ### Motivation:

When a command plugin asks for a target to be built by calling packageManager.build, it must specify a release or debug build.  If no configuration is given, debug is the default.   This overrides any configuration specified by the user with `swift package -c <debug|release>`.

A command plugin might often be used as an alterative entry point to Swift PM, responsible for building a target and then processing it in some way to generate the final product.   The user might run `swift package -c release some-plugin --target some-target`, expecting a release build of target to be made, but currently the result will be a debug binary if the plugin uses the default options.

 ### Modifications:

* Added a new `.inherit` option for packageManager.build's `configuration` argument.;  .debug remains the default, as before.
* Added a test to verify that plugin-initiated builds are of the correct type.

 ### Result:

A command plugin can request a target build matching the configuration specified on the SwiftPM command line.   The default is still to make a debug build, however in future we might change this to inherit the overall SwiftPM configuration.

 ### Alternatives:

A command plugin does not currently seem to have access to SwiftPM's build configuration.   We could pass this information to the plugin, allowing the plugin author to pass it back in the packageManager.build() call.   This would be a less invasive change to SwiftPM, however the approach in this commit makes it easier to change the default to .inherit in the future.

Author: euanh

Fixtures/Miscellaneous/Plugins/CommandPluginTestStub/Package.swift

@@ -12,6 +12,13 @@ let package = Package(
                 description: "Writes diagnostic messages for testing"
             ))
         ),
+        .plugin(
+            name: "targetbuild-stub",
+            capability: .command(intent: .custom(
+                verb: "build-target",
+                description: "Build a target for testing"
+            ))
+        ),
         .executableTarget(
             name: "placeholder"
         ),

Fixtures/Miscellaneous/Plugins/CommandPluginTestStub/Plugins/targetbuild-stub/targetbuild_stub.swift

@@ -0,0 +1,25 @@
+import Foundation
+import PackagePlugin
+
+@main
+struct targetbuild_stub: CommandPlugin {
+    // This is a helper for testing target builds performed on behalf of plugins.
+    // It sends asks SwiftPM to build a target with different options depending on its arguments.
+    func performCommand(context: PluginContext, arguments: [String]) async throws {
+        // Build a target
+        var parameters = PackageManager.BuildParameters()
+        if arguments.contains("build-debug") {
+            parameters.configuration = .debug
+        } else if arguments.contains("build-release") {
+            parameters.configuration = .release
+        } else if arguments.contains("build-inherit") {
+            parameters.configuration = .inherit
+        }
+        // If no 'build-*' argument is present, the default (.debug) will be used.
+
+        let _ = try packageManager.build(
+            .product("placeholder"),
+            parameters: parameters
+        )
+    }
+}

Sources/Commands/Utilities/PluginDelegate.swift

@@ -77,6 +77,10 @@ final class PluginDelegate: PluginInvocationDelegate {
             buildParameters.configuration = .debug
         case .release:
             buildParameters.configuration = .release
+        case .inherit:
+            // The top level argument parser set buildParameters.configuration according to the
+            // --configuration command line parameter.   We don't need to do anything to inherit it.
+            break
         }
         buildParameters.flags.cCompilerFlags.append(contentsOf: parameters.otherCFlags)
         buildParameters.flags.cxxCompilerFlags.append(contentsOf: parameters.otherCxxFlags)

Sources/PackagePlugin/PackageManagerProxy.swift

@@ -81,7 +81,7 @@ public struct PackageManager {
     /// Represents an overall purpose of the build, which affects such things
     /// as optimization and generation of debug symbols.
     public enum BuildConfiguration: String {
-        case debug, release
+        case debug, release, inherit
     }
 
     /// Represents the amount of detail in a build log.
@@ -328,6 +328,8 @@ fileprivate extension PluginToHostMessage.BuildParameters.Configuration {
             self = .debug
         case .release:
             self = .release
+        case .inherit:
+            self = .inherit
         }
     }
 }

Sources/PackagePlugin/PluginMessages.swift

@@ -297,7 +297,7 @@ enum PluginToHostMessage: Codable {
         struct BuildParameters: Codable {
             var configuration: Configuration
             enum Configuration: String, Codable {
-                case debug, release
+                case debug, release, inherit
             }
             var logging: LogVerbosity
             enum LogVerbosity: String, Codable {

Sources/SPMBuildCore/Plugins/PluginInvocation.swift

@@ -861,7 +861,7 @@ public enum PluginInvocationBuildSubset {
 public struct PluginInvocationBuildParameters {
     public var configuration: Configuration
     public enum Configuration: String {
-        case debug, release
+        case debug, release, inherit
     }
     public var logging: LogVerbosity
     public enum LogVerbosity: String {
@@ -993,6 +993,8 @@ fileprivate extension PluginInvocationBuildParameters.Configuration {
             self = .debug
         case .release:
             self = .release
+        case .inherit:
+            self = .inherit
         }
     }
 }

Tests/CommandsTests/PackageToolTests.swift

@@ -1983,6 +1983,68 @@ final class PackageToolTests: CommandsTestCase {
         }
     }
 
+    // Test target builds requested by a command plugin
+    func testCommandPluginTargetBuilds() throws {
+        // Only run the test if the environment in which we're running actually supports Swift concurrency (which the plugin APIs require).
+        try XCTSkipIf(!UserToolchain.default.supportsSwiftConcurrency(), "skipping because test environment doesn't support concurrency")
+
+        let debugTarget = [".build", "debug", "placeholder"]
+        let releaseTarget = [".build", "release", "placeholder"]
+
+        func AssertIsExecutableFile(_ fixturePath: AbsolutePath, file: StaticString = #filePath, line: UInt = #line) {
+            XCTAssert(
+                localFileSystem.isExecutableFile(fixturePath),
+                "\(fixturePath) does not exist",
+                file: file,
+                line: line
+            )
+        }
+
+        func AssertNotExists(_ fixturePath: AbsolutePath, file: StaticString = #filePath, line: UInt = #line) {
+            XCTAssertFalse(
+                localFileSystem.exists(fixturePath),
+                "\(fixturePath) should not exist",
+                file: file,
+                line: line
+            )
+        }
+
+        // By default, a plugin-requested build produces a debug binary
+        try fixture(name: "Miscellaneous/Plugins/CommandPluginTestStub") { fixturePath in
+            let _ = try SwiftPM.Package.execute(["-c", "release", "build-target"], packagePath: fixturePath)
+            AssertIsExecutableFile(fixturePath.appending(components: debugTarget))
+            AssertNotExists(fixturePath.appending(components: releaseTarget))
+        }
+
+        // If the plugin specifies a debug binary, that is what will be built, regardless of overall configuration
+        try fixture(name: "Miscellaneous/Plugins/CommandPluginTestStub") { fixturePath in
+            let _ = try SwiftPM.Package.execute(["-c", "release", "build-target", "build-debug"], packagePath: fixturePath)
+            AssertIsExecutableFile(fixturePath.appending(components: debugTarget))
+            AssertNotExists(fixturePath.appending(components: releaseTarget))
+        }
+
+        // If the plugin requests a release binary, that is what will be built, regardless of overall configuration
+        try fixture(name: "Miscellaneous/Plugins/CommandPluginTestStub") { fixturePath in
+            let _ = try SwiftPM.Package.execute(["-c", "debug", "build-target", "build-release"], packagePath: fixturePath)
+            AssertNotExists(fixturePath.appending(components: debugTarget))
+            AssertIsExecutableFile(fixturePath.appending(components: releaseTarget))
+        }
+
+        // If the plugin inherits the overall build configuration, that is what will be built
+        try fixture(name: "Miscellaneous/Plugins/CommandPluginTestStub") { fixturePath in
+            let _ = try SwiftPM.Package.execute(["-c", "debug", "build-target", "build-inherit"], packagePath: fixturePath)
+            AssertIsExecutableFile(fixturePath.appending(components: debugTarget))
+            AssertNotExists(fixturePath.appending(components: releaseTarget))
+        }
+
+        // If the plugin inherits the overall build configuration, that is what will be built
+        try fixture(name: "Miscellaneous/Plugins/CommandPluginTestStub") { fixturePath in
+            let _ = try SwiftPM.Package.execute(["-c", "release", "build-target", "build-inherit"], packagePath: fixturePath)
+            AssertNotExists(fixturePath.appending(components: debugTarget))
+            AssertIsExecutableFile(fixturePath.appending(components: releaseTarget))
+        }
+    }
+
     func testCommandPluginNetworkingPermissions(permissionsManifestFragment: String, permissionError: String, reason: String, remedy: [String]) throws {
         // Only run the test if the environment in which we're running actually supports Swift concurrency (which the plugin APIs require).
         try XCTSkipIf(!UserToolchain.default.supportsSwiftConcurrency(), "skipping because test environment doesn't support concurrency")