Allow mrkdwn descriptions on OptionObject (fixes #1471)

`OptionObject.description` was hard-typed to `PlainTextObject`, so a
`mrkdwn` description on a radio-button or checkbox option was coerced to
plain_text on deserialize, losing the markdown. The option-object docs
state that radio buttons and checkboxes can use mrkdwn text objects for
the description.

Widen the field to `TextObject` (the same type already used for
`OptionObject.text`), which routes deserialization through the existing
polymorphic text-object factory so `mrkdwn` round-trips as a
`MarkdownTextObject` and `plain_text` still returns a `PlainTextObject`.
The Kotlin DSL gains a `markdownDescription(...)` overload alongside the
existing plain_text `description(...)`. Source-compatible: all call
sites pass plain_text and the getter's declared type only broadens.

Ref: https://docs.slack.dev/reference/block-kit/composition-objects/option-object

Co-Authored-By: Claude <svc-devxp-claude@slack-corp.com>

Author: zimeg

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

@@ -1,7 +1,9 @@
 package com.slack.api.model.kotlin_extension.block.composition
 
+import com.slack.api.model.block.composition.MarkdownTextObject
 import com.slack.api.model.block.composition.OptionObject
 import com.slack.api.model.block.composition.PlainTextObject
+import com.slack.api.model.block.composition.TextObject
 import com.slack.api.model.kotlin_extension.block.BlockLayoutBuilder
 import com.slack.api.model.kotlin_extension.block.Builder
 import com.slack.api.model.kotlin_extension.block.composition.container.SingleTextObjectContainer
@@ -14,7 +16,7 @@ class OptionObjectBuilder private constructor(
 ) : Builder<OptionObject>, TextObjectDsl by textContainer {
     private var value: String? = null
     private var url: String? = null
-    private var description: PlainTextObject? = null
+    private var description: TextObject? = null
 
     constructor() : this(SingleTextObjectContainer())
 
@@ -40,15 +42,25 @@ class OptionObjectBuilder private constructor(
     }
 
     /**
-     * a line of descriptive text shown below the text field beside the radio button. Maximum length for the text
-     * object within this field is 75 characters.
+     * A plain_text line of descriptive text shown below the text field beside the radio button. Maximum length for the
+     * text object within this field is 75 characters.
      *
      * @see <a href="https://docs.slack.dev/reference/block-kit/composition-objects/option-object">Option object documentation</a>
      */
     fun description(text: String, emoji: Boolean? = null) {
         description = PlainTextObject(text, emoji)
     }
 
+    /**
+     * A mrkdwn line of descriptive text shown below the text field beside the radio button. Only radio buttons and
+     * checkboxes can use mrkdwn descriptions. Maximum length for the text object within this field is 75 characters.
+     *
+     * @see <a href="https://docs.slack.dev/reference/block-kit/composition-objects/option-object">Option object documentation</a>
+     */
+    fun markdownDescription(text: String, verbatim: Boolean? = null) {
+        description = MarkdownTextObject(text, verbatim)
+    }
+
     override fun build(): OptionObject {
         return OptionObject.builder()
             .description(description)

slack-api-model/src/main/java/com/slack/api/model/block/composition/OptionObject.java

@@ -29,11 +29,13 @@ public class OptionObject {
     private String value;
 
     /**
-     * A plain_text only text object that defines a line of descriptive text shown
-     * below the text field beside the radio button.
+     * A text object that defines a line of descriptive text shown below the text
+     * field beside the radio button. Overflow, select, and multi-select menus can
+     * only use plain_text objects, while radio buttons and checkboxes can use
+     * mrkdwn text objects.
      * Maximum length for the text object within this field is 75 characters.
      */
-    private PlainTextObject description;
+    private TextObject description;
 
     /**
      * A URL to load in the user's browser when the option is clicked.

slack-api-model/src/test/java/test_locally/api/model/block/BlockKitTest.java

@@ -5,6 +5,9 @@
 import com.slack.api.model.Message;
 import com.slack.api.model.block.*;
 import com.slack.api.model.block.composition.ConfirmationDialogObject;
+import com.slack.api.model.block.composition.MarkdownTextObject;
+import com.slack.api.model.block.composition.OptionObject;
+import com.slack.api.model.block.composition.PlainTextObject;
 import com.slack.api.model.block.element.*;
 import com.slack.api.model.view.View;
 import org.junit.Test;
@@ -2426,4 +2429,62 @@ public void buildTaskCardBlock() {
         assertThat(taskCard.getStatus(), is("in_progress"));
         assertThat(taskCard.getSources().size(), is(1));
     }
+
+    @Test
+    public void parseCheckboxesWithMrkdwnOptionDescription() {
+        String json = "{" +
+                "  \"blocks\": [\n" +
+                "    {\n" +
+                "      \"type\": \"actions\",\n" +
+                "      \"elements\": [\n" +
+                "        {\n" +
+                "          \"type\": \"checkboxes\",\n" +
+                "          \"action_id\": \"this_is_an_action_id\",\n" +
+                "          \"options\": [\n" +
+                "            {\n" +
+                "              \"value\": \"A1\",\n" +
+                "              \"text\": {\n" +
+                "                \"type\": \"plain_text\",\n" +
+                "                \"text\": \"Checkbox 1\"\n" +
+                "              },\n" +
+                "              \"description\": {\n" +
+                "                \"type\": \"mrkdwn\",\n" +
+                "                \"text\": \"*bold* description\"\n" +
+                "              }\n" +
+                "            },\n" +
+                "            {\n" +
+                "              \"value\": \"A2\",\n" +
+                "              \"text\": {\n" +
+                "                \"type\": \"plain_text\",\n" +
+                "                \"text\": \"Checkbox 2\"\n" +
+                "              },\n" +
+                "              \"description\": {\n" +
+                "                \"type\": \"plain_text\",\n" +
+                "                \"text\": \"plain description\"\n" +
+                "              }\n" +
+                "            }\n" +
+                "          ]\n" +
+                "        }\n" +
+                "      ]\n" +
+                "    }\n" +
+                "  ]\n" +
+                "}";
+        Message message = GsonFactory.createSnakeCase().fromJson(json, Message.class);
+        assertThat(message, is(notNullValue()));
+        ActionsBlock block = (ActionsBlock) message.getBlocks().get(0);
+        CheckboxesElement checkboxes = (CheckboxesElement) block.getElements().get(0);
+
+        // A mrkdwn description must round-trip as a MarkdownTextObject, not be
+        // coerced to plain_text (regression test for slackapi/java-slack-sdk#1471).
+        OptionObject mrkdwnOption = checkboxes.getOptions().get(0);
+        assertThat(mrkdwnOption.getDescription(), instanceOf(MarkdownTextObject.class));
+        assertThat(mrkdwnOption.getDescription().getType(), is("mrkdwn"));
+        assertThat(((MarkdownTextObject) mrkdwnOption.getDescription()).getText(), is("*bold* description"));
+
+        // A plain_text description still deserializes as PlainTextObject.
+        OptionObject plainOption = checkboxes.getOptions().get(1);
+        assertThat(plainOption.getDescription(), instanceOf(PlainTextObject.class));
+        assertThat(plainOption.getDescription().getType(), is("plain_text"));
+        assertThat(((PlainTextObject) plainOption.getDescription()).getText(), is("plain description"));
+    }
 }