Wrote 2 test cases, modified writeAll function to stop unwanted file …

build.sbt

@@ -2,7 +2,7 @@ import com.typesafe.tools.mima.core._
 
 Global / onChangedBuildSource := ReloadOnSourceChanges
 
-ThisBuild / tlBaseVersion := "3.12"
+ThisBuild / tlBaseVersion := "3.13"
 
 ThisBuild / organization := "co.fs2"
 ThisBuild / organizationName := "Functional Streams for Scala"

io/js/src/main/scala/fs2/io/file/FilesPlatform.scala

@@ -416,36 +416,44 @@ private[fs2] trait FilesCompanionPlatform {
         .chunkN(options.chunkSize)
         .flatMap(Stream.chunk)
     }
-
     override def writeAll(path: Path, _flags: Flags): Pipe[F, Byte, Nothing] =
       in =>
-        in.through {
-          writeWritable(
-            F.async_[Writable] { cb =>
-              val ws = facade.fs
-                .createWriteStream(
-                  path.toString,
-                  new facade.fs.WriteStreamOptions {
-                    flags = combineFlags(_flags)
+        in.pull.stepLeg.flatMap {
+          case None      => Pull.done
+          case Some(leg) =>
+            Stream
+              .eval(F.async_[Writable] { cb =>
+                val ws = facade.fs
+                  .createWriteStream(
+                    path.toString,
+                    new facade.fs.WriteStreamOptions {
+                      flags = combineFlags(_flags)
+                    }
+                  )
+                ws.once[Unit](
+                  "ready",
+                  _ => {
+                    ws.removeAllListeners()
+                    cb(Right(ws))
                   }
                 )
-              ws.once[Unit](
-                "ready",
-                _ => {
-                  ws.removeAllListeners()
-                  cb(Right(ws))
-                }
-              )
-              ws.once[js.Error](
-                "error",
-                error => {
-                  ws.removeAllListeners()
-                  cb(Left(js.JavaScriptException(error)))
-                }
-              )
-              ()
-            }
-          )
-        }
+                ws.once[js.Error](
+                  "error",
+                  error => {
+                    ws.removeAllListeners()
+                    cb(Left(js.JavaScriptException(error)))
+                  }
+                )
+                ()
+              })
+              .flatMap { ws =>
+                leg.stream
+                  .cons(leg.head)
+                  .through(writeWritable(F.pure(ws)))
+              }
+              .pull
+              .echo
+        }.stream
+
   }
 }

io/shared/src/main/scala/fs2/io/file/Files.scala

@@ -534,9 +534,17 @@ object Files extends FilesCompanionPlatform with FilesLowPriority {
         flags: Flags
     ): Pipe[F, Byte, Nothing] =
       in =>
-        Stream
-          .resource(writeCursor(path, flags))
-          .flatMap(_.writeAll(in).void.stream)
+        in.pull.stepLeg.flatMap {
+          case None      => Pull.done
+          case Some(leg) =>
+            Stream
+              .resource(writeCursor(path, flags))
+              .flatMap { cursor =>
+                cursor.writeAll(leg.stream.cons(leg.head)).void.stream
+              }
+              .pull
+              .echo
+        }.stream
 
     def writeCursor(
         path: Path,

io/shared/src/test/scala/fs2/io/file/FilesSuite.scala

@@ -166,8 +166,8 @@ class FilesSuite extends Fs2Suite with BaseFileSuite {
         .compile
         .foldMonoid
         .assertEquals("""|foo
-                         |bar
-                         |""".stripMargin)
+             |bar
+             |""".stripMargin)
     }
 
     test("writeUtf8Lines - side effect") {
@@ -200,6 +200,32 @@ class FilesSuite extends Fs2Suite with BaseFileSuite {
         .foldMonoid
         .assertEquals("")
     }
+    test("empty stream does not create file") {
+      Files[IO].tempDirectory.use { dir =>
+        val path = dir / "should-not-exist.txt"
+        Stream.empty
+          .covary[IO]
+          .through(Files[IO].writeAll(path))
+          .compile
+          .drain
+          .flatMap(_ => Files[IO].exists(path))
+          .assertEquals(false)
+      }
+    }
+
+    test("error stream does not create file") {
+      Files[IO].tempDirectory.use { dir =>
+        val path = dir / "should-not-exist.txt"
+        Stream
+          .raiseError[IO](new RuntimeException("boom"))
+          .through(Files[IO].writeAll(path))
+          .compile
+          .drain
+          .attempt
+          .flatMap(_ => Files[IO].exists(path))
+          .assertEquals(false)
+      }
+    }
   }
 
   group("tail") {