[Macro] Do not drop in-process-plugin-server-path option

Fix a regression that `in-process-plugin-server-path` is accidentally
dropped in explicit module build.

rdar://154780122

Author: cachemeifyoucan

Sources/SwiftDriver/Jobs/FrontendJobHelpers.swift

@@ -566,23 +566,23 @@ extension Driver {
       .appending(components: frontendTargetInfo.target.triple.platformName() ?? "", "Swift.swiftmodule")
     let hasToolchainStdlib = try fileSystem.exists(toolchainStdlibPath)
 
-    let skipMacroOptions = isPlanJobForExplicitModule && isFrontendArgSupported(.loadResolvedPlugin)
+    let skipMacroSearchPath = isPlanJobForExplicitModule && isFrontendArgSupported(.loadResolvedPlugin)
     // If the resource directory has the standard library, prefer the toolchain's plugins
     // to the platform SDK plugins.
     // For explicit module build, the resolved plugins are provided by scanner.
-    if hasToolchainStdlib, !skipMacroOptions {
-      try addPluginPathArguments(commandLine: &commandLine)
+    if hasToolchainStdlib {
+      try addPluginPathArguments(commandLine: &commandLine, skipMacroSearchPath: skipMacroSearchPath)
     }
 
     try toolchain.addPlatformSpecificCommonFrontendOptions(commandLine: &commandLine,
                                                            inputs: &inputs,
                                                            frontendTargetInfo: frontendTargetInfo,
                                                            driver: &self,
-                                                           skipMacroOptions: skipMacroOptions)
+                                                           skipMacroOptions: skipMacroSearchPath)
 
     // Otherwise, prefer the platform's plugins.
-    if !hasToolchainStdlib, !skipMacroOptions {
-      try addPluginPathArguments(commandLine: &commandLine)
+    if !hasToolchainStdlib {
+      try addPluginPathArguments(commandLine: &commandLine, skipMacroSearchPath: skipMacroSearchPath)
     }
 
     if let passPluginPath = parsedOptions.getLastArgument(.loadPassPluginEQ),
@@ -923,7 +923,7 @@ extension Driver {
     entries[inputEntry, default: [:]][output.type] = output.fileHandle
   }
 
-  mutating func addPluginPathArguments(commandLine: inout [Job.ArgTemplate]) throws {
+  mutating func addPluginPathArguments(commandLine: inout [Job.ArgTemplate], skipMacroSearchPath: Bool) throws {
     guard isFrontendArgSupported(.pluginPath) else {
       return
     }
@@ -938,6 +938,10 @@ extension Driver {
 #endif
     }
 
+    guard !skipMacroSearchPath else {
+      return
+    }
+
     // Default paths for compiler plugins found within the toolchain
     // (loaded as shared libraries).
     commandLine.appendFlag(.pluginPath)

Tests/SwiftDriverTests/CachingBuildTests.swift

@@ -934,6 +934,9 @@ final class CachingBuildTests: XCTestCase {
         })
         /// command-line that compiles swift should contains -cache-replay-prefix-map
         XCTAssertTrue(command.contains { $0 == "-cache-replay-prefix-map" })
+        if job.kind == .compile {
+          XCTAssertTrue(command.contains { $0 == "-in-process-plugin-server-path" })
+        }
         XCTAssertFalse(command.contains { $0 == "-plugin-path" || $0 == "-external-plugin-path" ||
                                           $0 == "-load-plugin-library" || $0 == "-load-plugin-executable" })
       }

Tests/SwiftDriverTests/ExplicitModuleBuildTests.swift

@@ -2042,6 +2042,14 @@ final class ExplicitModuleBuildTests: XCTestCase {
       var scannerCommand = try driver.dependencyScannerInvocationCommand().1.map { try resolver.resolve($0) }
       XCTAssertTrue(scannerCommand.contains("-plugin-path"))
       XCTAssertTrue(scannerCommand.contains("-external-plugin-path"))
+      let jobs = try driver.planBuild()
+      for job in jobs {
+        if job.kind != .compile {
+          continue
+        }
+        let command = try job.commandLine.map { try resolver.resolve($0) }
+        XCTAssertTrue(command.contains { $0 == "-in-process-plugin-server-path" })
+      }
     }
   }