Implement ProcessEnv.swift on Windows

Author: gmittert

Sources/Basic/ProcessEnv.swift

@@ -21,18 +21,34 @@ public enum ProcessEnv {
 
     /// Set the given key and value in the process's environment.
     public static func setVar(_ key: String, value: String) throws {
-        // FIXME: Need to handle Windows.
+      #if os(Windows)
+        guard 0 != key.withCString(encodedAs: UTF16.self, { keyStr in
+            value.withCString(encodedAs: UTF16.self) { valStr in
+                SetEnvironmentVariableW(keyStr, valStr)
+            }
+        }) else {
+            throw SystemError.setenv(Int32(GetLastError()), key)
+        }
+      #else
         guard SPMLibc.setenv(key, value, 1) == 0 else {
             throw SystemError.setenv(errno, key)
         }
+      #endif
     }
 
     /// Unset the give key in the process's environment.
     public static func unsetVar(_ key: String) throws {
-        // FIXME: Need to handle Windows.
+      #if os(Windows)
+        guard 0 != key.withCString(encodedAs: UTF16.self, { keyStr in
+            SetEnvironmentVariableW(keyStr, nil)
+        }) else {
+            throw SystemError.unsetenv(Int32(GetLastError()), key)
+        }
+      #else
         guard SPMLibc.unsetenv(key) == 0 else {
             throw SystemError.unsetenv(errno, key)
         }
+      #endif
     }
 
     /// The current working directory of the process.
@@ -42,10 +58,17 @@ public enum ProcessEnv {
 
     /// Change the current working directory of the process.
     public static func chdir(_ path: AbsolutePath) throws {
-        // FIXME: Need to handle Windows.
         let path = path.pathString
+      #if os(Windows)
+        guard 0 != path.withCString(encodedAs: UTF16.self, {
+            SetCurrentDirectoryW($0)
+        }) else {
+            throw SystemError.chdir(Int32(GetLastError()), path)
+        }
+      #else
         guard SPMLibc.chdir(path) == 0 else {
             throw SystemError.chdir(errno, path)
         }
+      #endif
     }
 }