Verify FSEntry name

src/main/kotlin/filesystem/FSCreator.kt

@@ -1,6 +1,7 @@
 package filesystem
 
 import java.nio.file.FileAlreadyExistsException
+import java.nio.file.FileSystemException
 import java.nio.file.Path
 import kotlin.io.path.createDirectory
 import kotlin.io.path.createFile
@@ -9,24 +10,14 @@ import kotlin.io.path.writeText
 class FSCreator {
     /**
      * Create entry, leaving existing folders' contents, but overwriting existing files.
-     * @throws CyclicFolderException Cyclic folders cannot be created.
      */
-    @Throws(CyclicFolderException::class)
+    @Throws(FileSystemException::class)
     fun create(
         entryToCreate: FSEntry,
         destination: String,
     ) {
-        // No point in running anything if we know the input is invalid.
-        if (entryToCreate is FSFolder && entryToCreate.isCyclic()) {
-            throw CyclicFolderException()
-        }
-
-        val queue =
-            ArrayDeque(
-                listOf(
-                    entryToCreate to Path.of(destination),
-                ),
-            )
+        val queue = ArrayDeque<Pair<FSEntry, Path>>()
+        queue.add(entryToCreate to Path.of(destination))
 
         while (queue.isNotEmpty()) {
             val (entry, dest) = queue.removeFirst()
@@ -45,5 +36,3 @@ class FSCreator {
         }
     }
 }
-
-class CyclicFolderException : Exception("Cyclic FSFolders are not supported")

src/main/kotlin/filesystem/FSEntry.kt

@@ -16,24 +16,6 @@ sealed class FSEntry(val name: String) {
 
 class FSFile(name: String, val content: String) : FSEntry(name)
 
-class FSFolder(name: String, val entries: List<FSEntry>) : FSEntry(name) {
-    /**
-     * Check whether a folder is cyclic.
-     */
-    fun isCyclic(): Boolean {
-        val seen = listOf(this).toHashSet<FSEntry>()
-        val queue = ArrayDeque(entries)
-        while (queue.isNotEmpty()) {
-            val entry = queue.removeFirst()
-            if (!seen.add(entry)) {
-                return true
-            }
-            if (entry is FSFolder) {
-                queue.addAll(entry.entries)
-            }
-        }
-        return false
-    }
-}
+class FSFolder(name: String, val entries: List<FSEntry>) : FSEntry(name)
 
 class InvalidEntryNameException(name: String) : Exception("Invalid FSEntry name: '$name'")

src/test/kotlin/filesystem/FSCreatorTest.kt

@@ -2,6 +2,7 @@ package filesystem
 
 import org.junit.jupiter.api.*
 import java.io.File
+import java.nio.file.FileSystemException
 import java.util.concurrent.TimeUnit
 import kotlin.io.path.Path
 import kotlin.io.path.createDirectory
@@ -90,7 +91,7 @@ class FSCreatorTest {
                                 FSFile("hi", "hi"),
                             ),
                         ),
-                        FSFolder("folder", listOf()),
+                        FSFolder("another-folder", listOf()),
                         FSFile("1.txt", "One!"),
                         FSFile("2.txt", "Two!"),
                     ),
@@ -104,7 +105,7 @@ class FSCreatorTest {
                     "folder",
                     listOf(
                         FSFolder(
-                            "folder",
+                            "another-folder",
                             listOf(
                                 FSFolder(
                                     "secrets",
@@ -122,34 +123,20 @@ class FSCreatorTest {
             )
         }
         assertEquals("hi", File("_tmp/folder/sub-folder/hi").readText())
-        assertEquals("P4ssW0rd", File("_tmp/folder/folder/secrets/secret").readText())
+        assertEquals("P4ssW0rd", File("_tmp/folder/another-folder/secrets/secret").readText())
         assertEquals("One is a good number", File("_tmp/folder/1.txt").readText())
         assertEquals("Two!", File("_tmp/folder/2.txt").readText())
         assertEquals("Three!", File("_tmp/folder/3.txt").readText())
     }
 
     @Test
-    @Timeout(500, unit = TimeUnit.MILLISECONDS) // in case implementation starts trying to handle cyclic folders
-    fun `create throws on cyclic folder`() {
+    @Timeout(500, unit = TimeUnit.MILLISECONDS) // in case implementation starts trying to handle recursion
+    fun `create throws on recursive folder`() {
         val files = mutableListOf<FSEntry>()
         val folder = FSFolder("folder", files)
         files.add(folder)
-        assertThrows<CyclicFolderException> {
+        assertThrows<FileSystemException> {
             creator.create(folder, "_tmp")
         }
     }
-
-    @Test
-    @Timeout(500, unit = TimeUnit.MILLISECONDS)
-    fun `create throws on long cyclic folder`() {
-        val files = mutableListOf<FSEntry>()
-        val folder1 = FSFolder("folder", files)
-        val folder2 = FSFolder("folder2", listOf(folder1))
-        val folder3 = FSFolder("folder3", listOf(folder2))
-        val folder4 = FSFolder("folder4", listOf(folder3))
-        files.add(folder4)
-        assertThrows<CyclicFolderException> {
-            creator.create(folder4, "_tmp")
-        }
-    }
 }

src/test/kotlin/filesystem/FSEntryTest.kt

@@ -1,42 +0,0 @@
-package filesystem
-
-import org.junit.jupiter.api.Test
-import kotlin.test.assertFalse
-import kotlin.test.assertTrue
-
-class FSEntryTest {
-    @Test
-    fun `non-cyclic folder`() {
-        val folder =
-            FSFolder(
-                "folder",
-                listOf(
-                    FSFolder("folder", listOf()),
-                    FSFile("text.txt", "Hello!"),
-                ),
-            )
-        assertFalse(folder.isCyclic())
-    }
-
-    @Test
-    fun `cyclic folder`() {
-        val files = mutableListOf<FSEntry>()
-        val folder = FSFolder("folder", files)
-        files.add(folder)
-        assertTrue(folder.isCyclic())
-    }
-
-    @Test
-    fun `long cyclic folder`() {
-        val files = mutableListOf<FSEntry>()
-        val folder1 = FSFolder("folder", files)
-        val folder2 = FSFolder("folder2", listOf(folder1))
-        val folder3 = FSFolder("folder3", listOf(folder2))
-        val folder4 = FSFolder("folder4", listOf(folder3))
-        files.add(folder4)
-        assertTrue(folder1.isCyclic())
-        assertTrue(folder2.isCyclic())
-        assertTrue(folder3.isCyclic())
-        assertTrue(folder4.isCyclic())
-    }
-}