feat: add ContainerBlock layout block support

slack-api-model-kotlin-extension/src/main/kotlin/com/slack/api/model/kotlin_extension/block/ContainerBlockBuilder.kt

@@ -0,0 +1,86 @@
+package com.slack.api.model.kotlin_extension.block
+
+import com.slack.api.model.block.ContainerBlock
+import com.slack.api.model.block.LayoutBlock
+import com.slack.api.model.block.RichTextBlock
+import com.slack.api.model.block.composition.PlainTextObject
+import com.slack.api.model.block.composition.TextObject
+import com.slack.api.model.block.element.ImageElement
+import com.slack.api.model.kotlin_extension.block.container.MultiLayoutBlockContainer
+
+@BlockLayoutBuilder
+class ContainerBlockBuilder : Builder<ContainerBlock> {
+    private var blockId: String? = null
+    private var title: PlainTextObject? = null
+    private var richTextTitle: RichTextBlock? = null
+    private var subtitle: TextObject? = null
+    private var childBlocks: List<LayoutBlock>? = null
+    private var width: String? = null
+    private var icon: ImageElement? = null
+    private var isCollapsible: Boolean? = null
+    private var defaultCollapsed: Boolean? = null
+    private var hasHeaderDivider: Boolean? = null
+
+    fun blockId(id: String) {
+        blockId = id
+    }
+
+    fun title(text: String, emoji: Boolean? = null) {
+        title = PlainTextObject(text, emoji)
+    }
+
+    fun title(textObject: PlainTextObject) {
+        title = textObject
+    }
+
+    fun richTextTitle(richText: RichTextBlock) {
+        richTextTitle = richText
+    }
+
+    fun subtitle(text: String, emoji: Boolean? = null) {
+        subtitle = PlainTextObject(text, emoji)
+    }
+
+    fun subtitle(textObject: TextObject) {
+        subtitle = textObject
+    }
+
+    fun childBlocks(builder: MultiLayoutBlockContainer.() -> Unit) {
+        childBlocks = MultiLayoutBlockContainer().apply(builder).underlying
+    }
+
+    fun width(width: String) {
+        this.width = width
+    }
+
+    fun icon(imageUrl: String, altText: String) {
+        icon = ImageElement.builder().imageUrl(imageUrl).altText(altText).build()
+    }
+
+    fun isCollapsible(collapsible: Boolean) {
+        isCollapsible = collapsible
+    }
+
+    fun defaultCollapsed(collapsed: Boolean) {
+        defaultCollapsed = collapsed
+    }
+
+    fun hasHeaderDivider(divider: Boolean) {
+        hasHeaderDivider = divider
+    }
+
+    override fun build(): ContainerBlock {
+        return ContainerBlock.builder()
+            .blockId(blockId)
+            .title(title)
+            .richTextTitle(richTextTitle)
+            .subtitle(subtitle)
+            .childBlocks(childBlocks ?: ArrayList())
+            .width(width)
+            .icon(icon)
+            .isCollapsible(isCollapsible)
+            .defaultCollapsed(defaultCollapsed)
+            .hasHeaderDivider(hasHeaderDivider)
+            .build()
+    }
+}

slack-api-model-kotlin-extension/src/main/kotlin/com/slack/api/model/kotlin_extension/block/container/MultiLayoutBlockContainer.kt

@@ -67,4 +67,8 @@ class MultiLayoutBlockContainer : LayoutBlockDsl {
     override fun shareShortcut(builder: ShareShortcutBlockBuilder.() -> Unit) {
         underlying += ShareShortcutBlockBuilder().apply(builder).build()
     }
+
+    override fun container(builder: ContainerBlockBuilder.() -> Unit) {
+        underlying += ContainerBlockBuilder().apply(builder).build()
+    }
 }

slack-api-model-kotlin-extension/src/main/kotlin/com/slack/api/model/kotlin_extension/block/dsl/LayoutBlockDsl.kt

@@ -95,4 +95,11 @@ interface LayoutBlockDsl {
      * @see <a href="https://tools.slack.dev/deno-slack-sdk/">Next generation platform</a>
      */
     fun shareShortcut(builder: ShareShortcutBlockBuilder.() -> Unit)
+
+    /**
+     * A container block groups related blocks together into a visually distinct section.
+     *
+     * @see <a href="https://docs.slack.dev/reference/block-kit/blocks/container-block">Container documentation</a>
+     */
+    fun container(builder: ContainerBlockBuilder.() -> Unit)
 }

slack-api-model-kotlin-extension/src/test/kotlin/test_locally/block/ContainerBlockTest.kt

@@ -0,0 +1,160 @@
+package test_locally.block
+
+import com.slack.api.model.block.ContainerBlock
+import com.slack.api.model.block.DividerBlock
+import com.slack.api.model.block.SectionBlock
+import com.slack.api.model.block.composition.MarkdownTextObject
+import com.slack.api.model.block.composition.PlainTextObject
+import com.slack.api.model.kotlin_extension.block.withBlocks
+import com.slack.api.util.json.GsonFactory
+import org.junit.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertNotNull
+import kotlin.test.assertNull
+import kotlin.test.assertTrue
+
+class ContainerBlockTest {
+
+    @Test
+    fun constructBasicContainer() {
+        val gson = GsonFactory.createSnakeCase()
+        val blocks = withBlocks {
+            container {
+                blockId("container-1")
+                title("Container Title")
+                width("wide")
+                isCollapsible(true)
+                defaultCollapsed(false)
+                hasHeaderDivider(true)
+                icon("https://example.com/icon.png", "icon")
+                childBlocks {
+                    divider()
+                }
+            }
+        }
+        assertEquals(1, blocks.size)
+        val container = blocks[0] as ContainerBlock
+        assertEquals("container", container.type)
+        assertEquals("container-1", container.blockId)
+        assertEquals("Container Title", container.title.text)
+        assertEquals("wide", container.width)
+        assertEquals(true, container.isCollapsible)
+        assertEquals(false, container.defaultCollapsed)
+        assertEquals(true, container.hasHeaderDivider)
+        assertNotNull(container.icon)
+        assertEquals(1, container.childBlocks.size)
+        assertTrue(container.childBlocks[0] is DividerBlock)
+
+        val json = gson.toJson(blocks)
+        assertTrue(json.contains("\"type\":\"container\""))
+        assertTrue(json.contains("\"block_id\":\"container-1\""))
+    }
+
+    @Test
+    fun constructContainerWithPlainTextObject() {
+        val titleObj = PlainTextObject.builder().text("Title with emoji").emoji(true).build()
+        val blocks = withBlocks {
+            container {
+                title(titleObj)
+                childBlocks {
+                    divider()
+                }
+            }
+        }
+        val container = blocks[0] as ContainerBlock
+        assertEquals("Title with emoji", container.title.text)
+    }
+
+    @Test
+    fun constructContainerWithSubtitle() {
+        val blocks = withBlocks {
+            container {
+                title("Title")
+                subtitle("Plain subtitle")
+                childBlocks {
+                    divider()
+                }
+            }
+        }
+        val container = blocks[0] as ContainerBlock
+        assertNotNull(container.subtitle)
+        assertEquals("Plain subtitle", container.subtitle.text)
+    }
+
+    @Test
+    fun constructContainerWithMarkdownSubtitle() {
+        val blocks = withBlocks {
+            container {
+                title("Title")
+                subtitle(MarkdownTextObject.builder().text("*Bold* subtitle").build())
+                childBlocks {
+                    divider()
+                }
+            }
+        }
+        val container = blocks[0] as ContainerBlock
+        assertNotNull(container.subtitle)
+        assertEquals("mrkdwn", container.subtitle.type)
+    }
+
+    @Test
+    fun constructContainerWithMultipleChildBlocks() {
+        val blocks = withBlocks {
+            container {
+                title("Title")
+                childBlocks {
+                    section {
+                        markdownText("Section inside container")
+                    }
+                    divider()
+                }
+            }
+        }
+        val container = blocks[0] as ContainerBlock
+        assertEquals(2, container.childBlocks.size)
+        assertTrue(container.childBlocks[0] is SectionBlock)
+        assertTrue(container.childBlocks[1] is DividerBlock)
+    }
+
+    @Test
+    fun constructContainerWithoutOptionalFields() {
+        val blocks = withBlocks {
+            container {
+                title("Minimal")
+                childBlocks {
+                    divider()
+                }
+            }
+        }
+        val container = blocks[0] as ContainerBlock
+        assertNull(container.blockId)
+        assertNull(container.width)
+        assertNull(container.isCollapsible)
+        assertNull(container.defaultCollapsed)
+        assertNull(container.hasHeaderDivider)
+        assertNull(container.icon)
+        assertNull(container.richTextTitle)
+    }
+
+    @Test
+    fun roundTripSerialization() {
+        val gson = GsonFactory.createSnakeCase()
+        val blocks = withBlocks {
+            container {
+                blockId("rt-1")
+                title("Round trip")
+                subtitle("Sub")
+                width("wide")
+                isCollapsible(true)
+                childBlocks {
+                    divider()
+                }
+            }
+        }
+        val json = gson.toJson(blocks)
+        val reparsed = gson.fromJson(json, Array<ContainerBlock>::class.java)
+        assertEquals("rt-1", reparsed[0].blockId)
+        assertEquals("Round trip", reparsed[0].title.text)
+        assertEquals("wide", reparsed[0].width)
+    }
+}

slack-api-model/src/main/java/com/slack/api/model/block/Blocks.java

@@ -147,6 +147,12 @@ public static CarouselBlock carousel(ModelConfigurator<CarouselBlock.CarouselBlo
         return configurator.configure(CarouselBlock.builder()).build();
     }
 
+    // ContainerBlock
+
+    public static ContainerBlock container(ModelConfigurator<ContainerBlock.ContainerBlockBuilder> configurator) {
+        return configurator.configure(ContainerBlock.builder()).build();
+    }
+
     // TaskCardBlock
 
     public static TaskCardBlock taskCard(ModelConfigurator<TaskCardBlock.TaskCardBlockBuilder> configurator) {

slack-api-model/src/main/java/com/slack/api/model/block/ContainerBlock.java

@@ -0,0 +1,45 @@
+package com.slack.api.model.block;
+
+import com.slack.api.model.block.composition.PlainTextObject;
+import com.slack.api.model.block.composition.TextObject;
+import com.slack.api.model.block.element.ImageElement;
+import lombok.AllArgsConstructor;
+import lombok.Builder;
+import lombok.Data;
+import lombok.NoArgsConstructor;
+
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * https://docs.slack.dev/reference/block-kit/blocks/container-block
+ */
+@Data
+@Builder
+@NoArgsConstructor
+@AllArgsConstructor
+public class ContainerBlock implements LayoutBlock {
+    public static final String TYPE = "container";
+    private final String type = TYPE;
+
+    private PlainTextObject title;
+
+    private RichTextBlock richTextTitle;
+
+    private TextObject subtitle;
+
+    @Builder.Default
+    private List<LayoutBlock> childBlocks = new ArrayList<>();
+
+    private String width;
+
+    private ImageElement icon;
+
+    private Boolean isCollapsible;
+
+    private Boolean defaultCollapsed;
+
+    private Boolean hasHeaderDivider;
+
+    private String blockId;
+}

slack-api-model/src/main/java/com/slack/api/util/json/GsonLayoutBlockFactory.java

@@ -43,6 +43,8 @@ private Class<? extends LayoutBlock> getLayoutClassInstance(String typeName) {
                 return CardBlock.class;
             case CarouselBlock.TYPE:
                 return CarouselBlock.class;
+            case ContainerBlock.TYPE:
+                return ContainerBlock.class;
             case ContextActionsBlock.TYPE:
                 return ContextActionsBlock.class;
             case ContextBlock.TYPE: