Hide build system internals with @_spi (#7365)

These details should not leak outside of the SwiftPM package. In the
(hopefully temporary) absence of `package` access control, we can hide
build system-related APIs with `@_spi` annotations.

Author: MaxDesiatov

Sources/Build/BuildOperation.swift

@@ -12,11 +12,18 @@
 
 @_spi(SwiftPMInternal)
 import Basics
+
+@_spi(SwiftPMInternal)
+import Build
+
 import LLBuildManifest
 import PackageGraph
 import PackageLoading
 import PackageModel
+
+@_spi(SwiftPMInternal)
 import SPMBuildCore
+
 import SPMLLBuild
 import Foundation
 
@@ -36,6 +43,7 @@ import DriverSupport
 import SwiftDriver
 #endif
 
+@_spi(SwiftPMInternal)
 public final class BuildOperation: PackageStructureDelegate, SPMBuildCore.BuildSystem, BuildErrorAdviceProvider {
     /// The delegate used by the build system.
     public weak var delegate: SPMBuildCore.BuildSystemDelegate?

Sources/Build/BuildOperationBuildSystemDelegateHandler.swift

@@ -16,7 +16,10 @@ import Dispatch
 import Foundation
 import LLBuildManifest
 import PackageModel
+
+@_spi(SwiftPMInternal)
 import SPMBuildCore
+
 import SPMLLBuild
 
 import struct TSCBasic.ByteString

Sources/Commands/CommandWorkspaceDelegate.swift

@@ -11,7 +11,10 @@
 //===----------------------------------------------------------------------===//
 
 import Basics
+
+@_spi(SwiftPMInternal)
 import CoreCommands
+
 import Dispatch
 import class Foundation.NSLock
 import struct Foundation.URL

Sources/Commands/PackageCommands/APIDiff.swift

@@ -12,12 +12,18 @@
 
 import ArgumentParser
 import Basics
+
+@_spi(SwiftPMInternal)
 import CoreCommands
+
 import Dispatch
 import PackageGraph
 import PackageModel
 import SourceControl
 
+@_spi(SwiftPMInternal)
+import SPMBuildCore
+
 struct DeprecatedAPIDiff: ParsableCommand {
     static let configuration = CommandConfiguration(commandName: "experimental-api-diff",
                                                     abstract: "Deprecated - use `swift package diagnose-api-breaking-changes` instead",

Sources/Commands/PackageCommands/ArchiveSource.swift

@@ -12,7 +12,10 @@
 
 import ArgumentParser
 import Basics
+
+@_spi(SwiftPMInternal)
 import CoreCommands
+
 import SourceControl
 
 extension SwiftPackageCommand {

Sources/Commands/PackageCommands/CompletionCommand.swift

@@ -11,6 +11,8 @@
 //===----------------------------------------------------------------------===//
 
 import ArgumentParser
+
+@_spi(SwiftPMInternal)
 import CoreCommands
 
 import var TSCBasic.stdoutStream

Sources/Commands/PackageCommands/ComputeChecksum.swift

@@ -12,7 +12,10 @@
 
 import ArgumentParser
 import Basics
+
+@_spi(SwiftPMInternal)
 import CoreCommands
+
 import Workspace
 
 import struct TSCBasic.SHA256

Sources/Commands/PackageCommands/Config.swift

@@ -12,7 +12,10 @@
 
 import ArgumentParser
 import Basics
+
+@_spi(SwiftPMInternal)
 import CoreCommands
+
 import Workspace
 
 import var TSCBasic.stderrStream

Sources/Commands/PackageCommands/Describe.swift

@@ -12,7 +12,10 @@
 
 import ArgumentParser
 import Basics
+
+@_spi(SwiftPMInternal)
 import CoreCommands
+
 import Foundation
 import PackageModel
 

Sources/Commands/PackageCommands/DumpCommands.swift

@@ -12,9 +12,16 @@
 
 import ArgumentParser
 import Basics
+
+@_spi(SwiftPMInternal)
 import CoreCommands
+
 import Foundation
 import PackageModel
+
+@_spi(SwiftPMInternal)
+import SPMBuildCore
+
 import XCBuildSupport
 
 struct DumpSymbolGraph: SwiftCommand {