Fix CRT support for Windows

Author: stevapple

Sources/SwiftDriver/Driver/Driver.swift

@@ -370,6 +370,9 @@ public struct Driver {
     self.numParallelJobs = Self.determineNumParallelJobs(&parsedOptions, diagnosticsEngine: diagnosticEngine, env: env)
 
     Self.validateWarningControlArgs(&parsedOptions, diagnosticEngine: diagnosticEngine)
+    Self.validateCRuntimeArgs(&parsedOptions,
+                              diagnosticEngine: diagnosticsEngine,
+                              targetTriple: self.frontendTargetInfo.target.triple)
     Self.validateProfilingArgs(&parsedOptions,
                                fileSystem: fileSystem,
                                workingDirectory: workingDirectory,
@@ -1660,6 +1663,14 @@ extension Driver {
     }
   }
 
+  static func validateCRuntimeArgs(_ parsedOptions: inout ParsedOptions,
+                                   diagnosticEngine: DiagnosticsEngine,
+                                   targetTriple: Triple) {
+    if parsedOptions.hasArgument(.libc) && !targetTriple.isWindows {
+      diagnosticEngine.emit(.error_unsupported_opt_for_target(arg: "-libc", target: targetTriple))
+    }
+  }
+
   static func validateProfilingArgs(_ parsedOptions: inout ParsedOptions,
                                     fileSystem: FileSystem,
                                     workingDirectory: AbsolutePath?,

Sources/SwiftDriver/Jobs/WindowsToolchain+LinkerSupport.swift

@@ -75,6 +75,20 @@ extension WindowsToolchain {
       }
       commandLine.appendFlag("-fuse-ld=\(linker)")
 
+      // FIXME: Do we really need `oldnames`?
+      commandLine.appendFlags("-autolink-library", "oldnames")
+      if let crt = parsedOptions.getLastArgument(.libc) {
+        switch crt.asSingle {
+        case "MT": commandLine.appendFlags("-autolink-library", "libcmt")
+        case "MTd": commandLine.appendFlags("-autolink-library", "libcmtd")
+        case "MD": commandLine.appendFlags("-autolink-library", "msvcrt")
+        case "MDd": commandLine.appendFlags("-autolink-library", "msvcrtd")
+        default: fatalError("Invalid C runtime value should be filtered")
+        }
+      } else {
+        commandLine.appendFlags("-autolink-library", "msvcrt")
+      }
+
       let staticStdlib = parsedOptions.hasFlag(positive: .staticStdlib,
                                                negative: .noStaticStdlib,
                                                 default: false)
@@ -152,11 +166,6 @@ extension WindowsToolchain {
         }
       }
 
-      if parsedOptions.hasArgument(.profileGenerate) {
-        // Profiling support for Windows isn't ready yet. It should have been disabled.
-        fatalError("Profiling support should have been disabled on Windows.")
-      }
-
       // Run clang++ in verbose mode if "-v" is set
       try commandLine.appendLast(.v, from: &parsedOptions)
 

Sources/SwiftDriver/Toolchains/WindowsToolchain.swift

@@ -117,16 +117,25 @@ extension WindowsToolchain {
     if parsedOptions.hasArgument(.profileUse) {
       throw ToolchainValidationError.argumentNotSupported("-profile-use=")
     }
+    
+    if let crt = parsedOptions.getLastArgument(.libc) {
+      if !["MT", "MTd", "MD", "MDd"].contains(crt.asSingle) {
+        throw ToolchainValidationError.illegalCrtName(crt.asSingle)
+      }
+    }
   }
-}
-
-public enum ToolchainValidationError: Error, DiagnosticData {
-  case argumentNotSupported(String)
 
-  public var description: String {
-    switch self {
-    case .argumentNotSupported(let argument):
-      return "\(argument) is not supported for Windows"
+  public enum ToolchainValidationError: Error, DiagnosticData {
+    case argumentNotSupported(String)
+    case illegalCrtName(String)
+
+    public var description: String {
+      switch self {
+      case .argumentNotSupported(let argument):
+        return "\(argument) is not supported for Windows"
+      case .illegalCrtName(let argument):
+        return "\(argument) is not a valid C Runtime for Windows"
+      }
     }
   }
 }