Add -no-whole-module-optimization flag

This mirrors this change swiftlang/swift#29362

Author: keith

Sources/SwiftDriver/Driver/Driver.swift

@@ -721,7 +721,7 @@ extension Driver {
     // Some output flags affect the compiler mode.
     if let outputOption = parsedOptions.getLast(in: .modes) {
       switch outputOption.option {
-      case .emitPch, .emitImportedModules, .indexFile:
+      case .emitPch, .emitImportedModules:
         return .singleCompile
 
       case .repl, .deprecatedIntegratedRepl, .lldbRepl:
@@ -740,13 +740,13 @@ extension Driver {
       return parsedOptions.hasAnyInput ? .immediate : .repl
     }
 
-    let requiresSingleCompile = parsedOptions.hasArgument(.wholeModuleOptimization, .indexFile)
-
+    let useWMO = parsedOptions.hasFlag(positive: .wholeModuleOptimization, negative: .noWholeModuleOptimization, default: false)
+    let hasIndexFile = parsedOptions.hasArgument(.indexFile)
     let wantBatchMode = parsedOptions.hasFlag(positive: .enableBatchMode, negative: .disableBatchMode, default: false)
 
-    if requiresSingleCompile {
+    if useWMO || hasIndexFile {
       if wantBatchMode {
-        let disablingOption: Option = parsedOptions.hasArgument(.wholeModuleOptimization) ? .wholeModuleOptimization : .indexFile
+        let disablingOption: Option = useWMO ? .wholeModuleOptimization : .indexFile
         diagnosticsEngine.emit(.warn_ignoring_batch_mode(disablingOption))
       }
 

Sources/SwiftDriver/Options/Options.swift

@@ -428,6 +428,7 @@ extension Option {
   public static let warnSwift3ObjcInference: Option = Option("-warn-swift3-objc-inference", .flag, alias: Option.warnSwift3ObjcInferenceComplete, attributes: [.helpHidden, .frontend, .doesNotAffectIncrementalBuild])
   public static let warningsAsErrors: Option = Option("-warnings-as-errors", .flag, attributes: [.frontend], helpText: "Treat warnings as errors")
   public static let wholeModuleOptimization: Option = Option("-whole-module-optimization", .flag, attributes: [.frontend, .noInteractive], helpText: "Optimize input files together instead of individually")
+  public static let noWholeModuleOptimization: Option = Option("-no-whole-module-optimization", .flag, attributes: [.frontend, .noInteractive], helpText: "Disable optimizing input files together instead of individually")
   public static let wmo: Option = Option("-wmo", .flag, alias: Option.wholeModuleOptimization, attributes: [.helpHidden, .frontend, .noInteractive])
   public static let workingDirectoryEQ: Option = Option("-working-directory=", .joined, alias: Option.workingDirectory)
   public static let workingDirectory: Option = Option("-working-directory", .separate, metaVar: "<path>", helpText: "Resolve file paths relative to the specified directory")
@@ -723,6 +724,7 @@ extension Option {
       Option.noStdlibRpath,
       Option.noToolchainStdlibRpath,
       Option.nostdimport,
+      Option.noWholeModuleOptimization,
       Option.numThreads,
       Option.Onone,
       Option.Oplayground,

Tests/SwiftDriverTests/SwiftDriverTests.swift

@@ -152,11 +152,44 @@ final class SwiftDriverTests: XCTestCase {
       let driver1 = try Driver(args: ["swiftc", "main.swift", "-whole-module-optimization"])
       XCTAssertEqual(driver1.compilerMode, .singleCompile)
 
-      let driver2 = try Driver(args: ["swiftc", "main.swift", "-g"])
+      let driver2 = try Driver(args: ["swiftc", "main.swift", "-whole-module-optimization", "-no-whole-module-optimization"])
       XCTAssertEqual(driver2.compilerMode, .standardCompile)
+
+      let driver3 = try Driver(args: ["swiftc", "main.swift", "-g"])
+      XCTAssertEqual(driver3.compilerMode, .standardCompile)
     }
   }
 
+  func testBatchModeDiagnostics() throws {
+      try assertNoDriverDiagnostics(args: "swiftc", "-enable-batch-mode") { driver in
+        switch driver.compilerMode {
+        case .batchCompile:
+          break
+        default:
+          XCTFail("Expected batch compile, got \(driver.compilerMode)")
+        }
+      }
+
+      try assertDriverDiagnostics(args: "swiftc", "-enable-batch-mode", "-whole-module-optimization") { driver, diagnostics in
+        XCTAssertEqual(driver.compilerMode, .singleCompile)
+        diagnostics.expect(.warning("ignoring '-enable-batch-mode' because '-whole-module-optimization' was also specified"))
+      }
+
+      try assertDriverDiagnostics(args: "swiftc", "-enable-batch-mode", "-whole-module-optimization", "-no-whole-module-optimization", "-index-file", "-module-name", "foo") { driver, diagnostics in
+        XCTAssertEqual(driver.compilerMode, .singleCompile)
+        diagnostics.expect(.warning("ignoring '-enable-batch-mode' because '-index-file' was also specified"))
+      }
+
+      try assertNoDriverDiagnostics(args: "swiftc", "-enable-batch-mode", "-whole-module-optimization", "-no-whole-module-optimization") { driver in
+        switch driver.compilerMode {
+        case .batchCompile:
+          break
+        default:
+          XCTFail("Expected batch compile, got \(driver.compilerMode)")
+        }
+      }
+  }
+
   func testInputFiles() throws {
     let driver1 = try Driver(args: ["swiftc", "a.swift", "/tmp/b.swift"])
     XCTAssertEqual(driver1.inputFiles,