Do not append line separator on empty stream.

typelevel · Dec 7, 2023 · 9f9fc1e · 9f9fc1e
1 parent 43572fd
commit 9f9fc1e
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Showing 2 changed files with 21 additions and 2 deletions.
diff --git a/io/shared/src/main/scala/fs2/io/file/Files.scala b/io/shared/src/main/scala/fs2/io/file/Files.scala
@@ -443,8 +443,13 @@ sealed trait Files[F[_]] extends FilesPlatform[F] {
     * using the specified flags to open the file.
     */
   def writeUtf8Lines(path: Path, flags: Flags): Pipe[F, String, Nothing] = in =>
-    in.intersperse(lineSeparator)
-      .append(Stream[F, String](lineSeparator))
+    in.pull.uncons
+      .flatMap {
+        case Some(_) =>
+          in.intersperse(lineSeparator).append(Stream[F, String](lineSeparator)).underlying
+        case None => Pull.done
+      }
+      .stream
       .through(writeUtf8(path, flags))
 }
 

diff --git a/io/shared/src/test/scala/fs2/io/file/FilesSuite.scala b/io/shared/src/test/scala/fs2/io/file/FilesSuite.scala
@@ -169,6 +169,20 @@ class FilesSuite extends Fs2IoSuite with BaseFileSuite {
                          |bar
                          |""".stripMargin)
     }
+
+    test("writeUtf8Lines - empty stream") {
+      Stream
+        .resource(tempFile)
+        .flatMap { path =>
+          Stream.empty
+            .covary[IO]
+            .through(Files[IO].writeUtf8Lines(path)) ++ Files[IO]
+            .readUtf8(path)
+        }
+        .compile
+        .foldMonoid
+        .assertEquals("")
+    }
   }
 
   group("tail") {