Introduce overwrite parameter to File.copyRecursively.

#KT-8924 Fixed

libraries/stdlib/src/kotlin/io/files/Utils.kt

@@ -218,7 +218,7 @@ public enum class OnErrorAction {
 private class TerminateException(file: File) : FileSystemException(file) {}
 
 /**
- * Copies this file with all its children to the specified destination [dst] path.
+ * Copies this file with all its children to the specified destination [target] path.
  * If some directories on the way to the destination are missing, then they will be created.
  *
  * If any errors occur during the copying, then further actions will depend on the result of the call
@@ -231,11 +231,13 @@ private class TerminateException(file: File) : FileSystemException(file) {}
  * AccessDeniedException - if there was an attempt to open a directory that didn't succeed.
  * IOException - if some problems occur when copying.
  *
+ * @param overwrite `true` if it is allowed to overwrite existing destination files and directories.
  * @return `false` if the copying was terminated, `true` otherwise.
 *
 * Note that if this function fails, then partial copying may have taken place.
  */
-public fun File.copyRecursively(dst: File,
+public fun File.copyRecursively(target: File,
+                                overwrite: Boolean = false,
                                 onError: (File, IOException) -> OnErrorAction =
                                 { file, exception -> throw exception }
 ): Boolean {
@@ -252,16 +254,29 @@ public fun File.copyRecursively(dst: File,
                     return false
             } else {
                 val relPath = src.toRelativeString(this)
-                val dstFile = File(dst, relPath)
+                val dstFile = File(target, relPath)
                 if (dstFile.exists() && !(src.isDirectory && dstFile.isDirectory)) {
-                    if (onError(dstFile, FileAlreadyExistsException(file = src,
-                            other = dstFile,
-                            reason = "The destination file already exists")) == OnErrorAction.TERMINATE)
-                        return false
-                } else if (src.isDirectory) {
+                    val stillExists = if (!overwrite) true else {
+                        if (dstFile.isDirectory)
+                            !dstFile.deleteRecursively()
+                        else
+                            !dstFile.delete()
+                    }
+
+                    if (stillExists) {
+                        if (onError(dstFile, FileAlreadyExistsException(file = src,
+                                    other = dstFile,
+                                    reason = "The destination file already exists")) == OnErrorAction.TERMINATE)
+                                return false
+
+                        continue
+                    }
+                }
+
+                if (src.isDirectory) {
                     dstFile.mkdirs()
                 } else {
-                    if (src.copyTo(dstFile, true) != src.length()) {
+                    if (src.copyTo(dstFile, overwrite) != src.length()) {
                         if (onError(src, IOException("src.length() != dst.length()")) == OnErrorAction.TERMINATE)
                             return false
                     }

libraries/stdlib/test/io/Files.kt

@@ -451,20 +451,22 @@ class FilesTest {
         }
     }
 
+    fun compareDirectories(src: File, dst: File) {
+        for (file in src.walkTopDown()) {
+            val dstFile = dst.resolve(file.relativeTo(src))
+            assertTrue(dstFile.exists())
+            assertEquals(file.isFile, dstFile.isFile)
+            if (dstFile.isFile) {
+                assertEquals(file.readText(), dstFile.readText())
+            }
+        }
+    }
+
     @test fun copyRecursively() {
         val src = createTempDir()
         val dst = createTempDir()
         dst.delete()
-        fun check() {
-            for (file in src.walkTopDown()) {
-                val dstFile = dst.resolve(file.relativeTo(src))
-                assertTrue(dstFile.exists())
-                if (dstFile.isFile) {
-                    assertEquals(file.readText(), dstFile.readText())
-                }
-
-            }
-        }
+        fun check() = compareDirectories(src, dst)
 
         try {
             val subDir1 = createTempDir(prefix = "d1_", directory = src)
@@ -531,6 +533,40 @@ class FilesTest {
         }
     }
 
+    @test fun copyRecursivelyWithOverwrite() {
+        val src = createTempDir()
+        val dst = createTempDir()
+        fun check() = compareDirectories(src, dst)
+
+        try {
+            val srcFile = src.resolve("test")
+            val dstFile = dst.resolve("test")
+            srcFile.writeText("text1")
+
+            src.copyRecursively(dst)
+
+            srcFile.writeText("text1 modified")
+            src.copyRecursively(dst, overwrite = true)
+            check()
+
+            dstFile.delete()
+            dstFile.mkdir()
+            dstFile.resolve("subFile").writeText("subfile")
+            src.copyRecursively(dst, overwrite = true)
+            check()
+
+            srcFile.delete()
+            srcFile.mkdir()
+            srcFile.resolve("subFile").writeText("text2")
+            src.copyRecursively(dst, overwrite = true)
+            check()
+        }
+        finally {
+            src.deleteRecursively()
+            dst.deleteRecursively()
+        }
+    }
+
     @test fun helpers1() {
         val str = "123456789\n"
         System.setIn(str.byteInputStream())