fix modulemap generation on window using swift-build

- Windows paths need to be escaped

Author: daveinglis

Sources/PackageLoading/ModuleMapGenerator.swift

@@ -18,12 +18,6 @@ import TSCBasic
 /// Name of the module map file recognized by the Clang and Swift compilers.
 public let moduleMapFilename = "module.modulemap"
 
-extension Basics.AbsolutePath {
-  fileprivate var moduleEscapedPathString: String {
-    return self.pathString.replacing("\\", with: "\\\\")
-  }
-}
-
 /// A protocol for targets which might have a modulemap.
 protocol ModuleMapProtocol {
     var moduleMapPath: Basics.AbsolutePath { get }
@@ -179,9 +173,9 @@ public struct ModuleMapGenerator {
         var moduleMap = "module \(moduleName) {\n"
         switch type {
         case .umbrellaHeader(let hdr):
-            moduleMap.append("    umbrella header \"\(hdr.moduleEscapedPathString)\"\n")
+            moduleMap.append("    umbrella header \"\(hdr.escapedPathString)\"\n")
         case .umbrellaDirectory(let dir):
-            moduleMap.append("    umbrella \"\(dir.moduleEscapedPathString)\"\n")
+            moduleMap.append("    umbrella \"\(dir.escapedPathString)\"\n")
         }
         moduleMap.append(
             """

Sources/SwiftBuildSupport/PackagePIFProjectBuilder+Modules.swift

@@ -14,6 +14,7 @@ import Foundation
 import TSCUtility
 
 import struct Basics.AbsolutePath
+import struct Basics.RelativePath
 import class Basics.ObservabilitySystem
 import func Basics.resolveSymlinks
 import struct Basics.SourceControlURL
@@ -366,7 +367,7 @@ extension PackagePIFProjectBuilder {
             export *
             }
             """
-            moduleMapFile = "\(generatedModuleMapDir)/\(sourceModule.name).modulemap"
+            moduleMapFile = try RelativePath(validating:"\(generatedModuleMapDir)/\(sourceModule.name).modulemap").pathString
 
             // We only need to impart this to C clients.
             impartedSettings[.OTHER_CFLAGS] = ["-fmodule-map-file=\(moduleMapFile)", "$(inherited)"]
@@ -376,15 +377,15 @@ extension PackagePIFProjectBuilder {
                 log(.debug, "\(package.name).\(sourceModule.name) generated umbrella header")
                 moduleMapFileContents = """
                 module \(sourceModule.c99name) {
-                umbrella header "\(path)"
+                umbrella header "\(path.escapedPathString)"
                 export *
                 }
                 """
             } else if case .umbrellaDirectory(let path) = sourceModule.moduleMapType {
                 log(.debug, "\(package.name).\(sourceModule.name) generated umbrella directory")
                 moduleMapFileContents = """
                 module \(sourceModule.c99name) {
-                umbrella "\(path)"
+                umbrella "\(path.escapedPathString)"
                 export *
                 }
                 """