revert: partially revert "ci: remove SwiftCompilerPlugin"

Package.swift

@@ -14,6 +14,7 @@ let package = Package(
   ],
   products: [
     .library(name: "SwiftBasicFormat", targets: ["SwiftBasicFormat"]),
+    .library(name: "SwiftCompilerPlugin", targets: ["SwiftCompilerPlugin"]),
     .library(name: "SwiftCompilerPluginMessageHandling", targets: ["SwiftCompilerPluginMessageHandling"]),
     .library(name: "SwiftDiagnostics", targets: ["SwiftDiagnostics"]),
     .library(name: "SwiftIDEUtils", targets: ["SwiftIDEUtils"]),
@@ -69,6 +70,19 @@ let package = Package(
       dependencies: ["_SwiftSyntaxTestSupport", "SwiftBasicFormat", "SwiftSyntaxBuilder"]
     ),
 
+    // MARK: SwiftCompilerPlugin
+
+    .target(
+      name: "SwiftCompilerPlugin",
+      dependencies: ["SwiftCompilerPluginMessageHandling", "SwiftSyntaxMacros"],
+      exclude: ["CMakeLists.txt"]
+    ),
+
+    .testTarget(
+      name: "SwiftCompilerPluginTest",
+      dependencies: ["SwiftCompilerPlugin"]
+    ),
+
     // MARK: SwiftCompilerPluginMessageHandling
 
     .target(

Sources/SwiftCompilerPlugin/CompilerPlugin.swift

@@ -12,6 +12,8 @@
 // NOTE: This basic plugin mechanism is mostly copied from
 // https://github.com/apple/swift-package-manager/blob/main/Sources/PackagePlugin/Plugin.swift
 
+#if !os(WASI)
+
 #if swift(>=6.0)
 public import SwiftSyntaxMacros
 private import Foundation
@@ -257,3 +259,5 @@ struct CompilerPluginError: Error, CustomStringConvertible {
     self.description = message
   }
 }
+
+#endif

Tests/SwiftCompilerPluginTest/CompilerPluginTests.swift

@@ -10,6 +10,8 @@
 //
 //===----------------------------------------------------------------------===//
 
+#if !os(WASI)
+
 @_spi(Testing) import SwiftCompilerPlugin
 import SwiftSyntax
 import SwiftSyntaxMacros
@@ -68,3 +70,5 @@ class CompilerPluginTests: XCTestCase {
 
   }
 }
+
+#endif