Add In-process plugin server path

Author: rintaro

Sources/SwiftDriver/Jobs/FrontendJobHelpers.swift

@@ -781,10 +781,19 @@ extension Driver {
     guard isFrontendArgSupported(.pluginPath) else {
       return
     }
+    let pluginPathRoot = VirtualPath.absolute(try toolchain.executableDir.parentDirectory)
+
+    if isFrontendArgSupported(.inProcessPluginServerPath) {
+      commandLine.appendFlag(.inProcessPluginServerPath)
+#if os(Windows)
+      commandLine.appendPath(pluginPathRoot.appending(components: "bin", sharedLibraryName("SwiftInProcPluginServer")))
+#else
+      commandLine.appendPath(pluginPathRoot.appending(components: "lib", "swift", "host", sharedLibraryName("libSwiftInProcPluginServer")))
+#endif
+    }
 
     // Default paths for compiler plugins found within the toolchain
     // (loaded as shared libraries).
-    let pluginPathRoot = VirtualPath.absolute(try toolchain.executableDir.parentDirectory)
     commandLine.appendFlag(.pluginPath)
     commandLine.appendPath(pluginPathRoot.pluginPath)
 

Sources/SwiftOptions/Options.swift

@@ -546,6 +546,7 @@ extension Option {
   public static let importPrescan: Option = Option("-import-prescan", .flag, attributes: [.frontend, .noDriver], helpText: "When performing a dependency scan, only identify all imports of the main Swift module sources")
   public static let importUnderlyingModule: Option = Option("-import-underlying-module", .flag, attributes: [.frontend, .noInteractive], helpText: "Implicitly imports the Objective-C half of a module")
   public static let inPlace: Option = Option("-in-place", .flag, attributes: [.noInteractive, .noBatch, .indent], helpText: "Overwrite input file with formatted file.", group: .codeFormatting)
+  public static let inProcessPluginServerPath: Option = Option("-in-process-plugin-server-path", .separate, attributes: [.frontend, .argumentIsPath], helpText: "Path to dynamic library plugin server")
   public static let includeSpiSymbols: Option = Option("-include-spi-symbols", .flag, attributes: [.helpHidden, .frontend, .noInteractive, .supplementaryOutput], helpText: "Add symbols with SPI information to the symbol graph")
   public static let incremental: Option = Option("-incremental", .flag, attributes: [.helpHidden, .noInteractive, .doesNotAffectIncrementalBuild], helpText: "Perform an incremental build if possible")
   public static let indentSwitchCase: Option = Option("-indent-switch-case", .flag, attributes: [.noInteractive, .noBatch, .indent], helpText: "Indent cases in switch statements.", group: .codeFormatting)
@@ -1399,6 +1400,7 @@ extension Option {
       Option.importPrescan,
       Option.importUnderlyingModule,
       Option.inPlace,
+      Option.inProcessPluginServerPath,
       Option.includeSpiSymbols,
       Option.incremental,
       Option.indentSwitchCase,