charleskorn · charleskorn · Aug 15, 2022 · Aug 12, 2022 · Aug 12, 2022 · Aug 14, 2022
diff --git a/src/commonMain/kotlin/com/charleskorn/kaml/YamlConfiguration.kt b/src/commonMain/kotlin/com/charleskorn/kaml/YamlConfiguration.kt
@@ -31,6 +31,7 @@ package com.charleskorn.kaml
  * * [encodingIndentationSize]: number of spaces to use as indentation when encoding objects as YAML
  * * [breakScalarsAt]: maximum length of scalars when encoding objects as YAML (scalars exceeding this length will be split into multiple lines)
  * * [sequenceStyle]: how sequences (aka lists and arrays) should be formatted. See [SequenceStyle] for an example of each
+ * * [sequenceBlockIndent]: number of spaces to use as indentation for sequences, if [sequenceStyle] set to [SequenceStyle.Block]
  */
 public data class YamlConfiguration constructor(
     internal val encodeDefaults: Boolean = true,
@@ -42,7 +43,8 @@ public data class YamlConfiguration constructor(
     internal val breakScalarsAt: Int = 80,
     internal val sequenceStyle: SequenceStyle = SequenceStyle.Block,
     internal val singleLineStringStyle: SingleLineStringStyle = SingleLineStringStyle.DoubleQuoted,
-    internal val multiLineStringStyle: MultiLineStringStyle = singleLineStringStyle.multiLineStringStyle
+    internal val multiLineStringStyle: MultiLineStringStyle = singleLineStringStyle.multiLineStringStyle,
+    internal val sequenceBlockIndent: Int = 0
 )
 
 public enum class PolymorphismStyle {

diff --git a/src/commonTest/kotlin/com/charleskorn/kaml/YamlWritingTest.kt b/src/commonTest/kotlin/com/charleskorn/kaml/YamlWritingTest.kt
@@ -245,6 +245,58 @@ class YamlWritingTest : DescribeSpec({
                 }
             }
 
+            context("serializing a list of integers in flow form with sequence block indent") {
+                val output = Yaml(configuration = YamlConfiguration(sequenceStyle = SequenceStyle.Flow, sequenceBlockIndent = 2))
+                    .encodeToString(ListSerializer(Int.serializer()), listOf(1, 2, 3))
+
+                it("returns the value serialized in the expected YAML form") {
+                    output shouldBe "[1, 2, 3]"
+                }
+            }
+
+            context("serializing a list of integers without sequence block indent") {
+                val output = Yaml(configuration = YamlConfiguration(sequenceBlockIndent = 0))
+                    .encodeToString(ListSerializer(Int.serializer()), listOf(1, 2, 3))
+
+                it("returns the value serialized in the expected YAML form") {
+                    output shouldBe
+                        """
+                        |- 1
+                        |- 2
+                        |- 3
+                        """.trimMargin()
+                }
+            }
+
+            context("serializing a list of integers with sequence block indent") {
+                val output = Yaml(configuration = YamlConfiguration(sequenceBlockIndent = 2))
+                    .encodeToString(ListSerializer(Int.serializer()), listOf(1, 2, 3))
+
+                it("returns the value serialized in the expected YAML form") {
+                    output shouldBe
+                        """
+                        |  - 1
+                        |  - 2
+                        |  - 3
+                        """.trimMargin()
+                }
+            }
+
+            context("serializing a list of objects with sequence block indent") {
+                @Serializable
+                data class Foo(val bar: String)
+
+                val output = Yaml(configuration = YamlConfiguration(sequenceBlockIndent = 2))
+                    .encodeToString(ListSerializer(Foo.serializer()), listOf(Foo("baz")))
+
+                it("returns the value serialized in the expected YAML form") {
+                    output shouldBe
+                        """
+                        |  - bar: "baz"
+                        """.trimMargin()
+                }
+            }
+
             context("serializing a list of nullable integers in flow form") {
                 val output = Yaml(configuration = YamlConfiguration(sequenceStyle = SequenceStyle.Flow))
                     .encodeToString(ListSerializer(Int.serializer().nullable), listOf(1, null, 3))

diff --git a/src/jvmMain/kotlin/com/charleskorn/kaml/YamlOutput.kt b/src/jvmMain/kotlin/com/charleskorn/kaml/YamlOutput.kt
@@ -51,7 +51,13 @@ internal class YamlOutput(
     private val configuration: YamlConfiguration
 ) : AbstractEncoder(), AutoCloseable {
     private val settings = DumpSettings.builder()
+        // SnakeYAML validates that this value must be at least 1
         .setIndent(configuration.encodingIndentationSize)
+        // SnakeYAML helps to validate that this value must be non-negative
+        .setIndicatorIndent(configuration.sequenceBlockIndent)
+        // No special reason why true is conditional. Designed to be consistent with 0.46.0 of kaml
+        .setIndentWithIndicator(configuration.sequenceBlockIndent > 0)
+        // Unclear if this value is validated
         .setWidth(configuration.breakScalarsAt)
         .build()
 
@@ -149,11 +155,7 @@ internal class YamlOutput(
     private fun encodeComment(descriptor: SerialDescriptor, index: Int) {
         val commentAnno = descriptor.getElementAnnotations(index)
             .filterIsInstance<YamlComment>()
-            .firstOrNull()
-
-        if (commentAnno == null) {
-            return
-        }
+            .firstOrNull() ?: return
 
         for (line in commentAnno.lines) {
             emitter.emit(CommentEvent(CommentType.BLOCK, " $line", Optional.empty(), Optional.empty()))