Add support for slash commands (under Feature Flag) (#6482)

* Add support for slash commands

* Update screenshots

* Rename module `slash` to `slashcommands`

* Rename `SlashCommand` to `SlashCommandService`

* Introduce MsgType in order to send text message with a different msgtype value.

* Format file and add parameter names, add default values and cleanup

* Add isSupported parameter to filter out unsupported yet commands.

* Slash commands: disable suggestions if the feature is disabled.

* Fix sending shrug command.

* Add missing test on SuggestionsProcessor

* Add tests on MessageComposerPresenter about slash command.

* Fix import ordering

* Add missing tests on CommandExecutor

* Add missing tests in MarkdownTextEditorStateTest

* Slash commands: Improve code when sending message with prefix.

* Slash commands: Add support for /unflip

---------

Co-authored-by: ElementBot <android@element.io>

libraries/slashcommands/api/build.gradle.kts

@@ -0,0 +1,17 @@
+/*
+ * Copyright (c) 2026 Element Creations Ltd.
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial.
+ * Please see LICENSE files in the repository root for full details.
+ */
+plugins {
+    id("io.element.android-library")
+}
+
+android {
+    namespace = "io.element.android.libraries.slashcommands.api"
+}
+
+dependencies {
+    implementation(projects.libraries.matrix.api)
+}

libraries/slashcommands/api/src/main/kotlin/io/element/android/libraries/slashcommands/api/ChatEffect.kt

@@ -0,0 +1,13 @@
+/*
+ * Copyright (c) 2026 Element Creations Ltd.
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial.
+ * Please see LICENSE files in the repository root for full details.
+ */
+
+package io.element.android.libraries.slashcommands.api
+
+enum class ChatEffect {
+    CONFETTI,
+    SNOWFALL
+}

libraries/slashcommands/api/src/main/kotlin/io/element/android/libraries/slashcommands/api/MessagePrefix.kt

@@ -0,0 +1,15 @@
+/*
+ * Copyright (c) 2026 Element Creations Ltd.
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial.
+ * Please see LICENSE files in the repository root for full details.
+ */
+
+package io.element.android.libraries.slashcommands.api
+
+enum class MessagePrefix {
+    Shrug,
+    TableFlip,
+    Unflip,
+    Lenny,
+}

libraries/slashcommands/api/src/main/kotlin/io/element/android/libraries/slashcommands/api/SlashCommand.kt

@@ -0,0 +1,71 @@
+/*
+ * Copyright (c) 2026 Element Creations Ltd.
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial.
+ * Please see LICENSE files in the repository root for full details.
+ */
+
+package io.element.android.libraries.slashcommands.api
+
+import io.element.android.libraries.matrix.api.core.RoomIdOrAlias
+import io.element.android.libraries.matrix.api.core.UserId
+
+/**
+ * Represent a slash command.
+ */
+sealed interface SlashCommand {
+    // This is not a Slash command
+    data object NotACommand : SlashCommand
+
+    // Slash command types:
+    sealed interface Error : SlashCommand
+    sealed interface SlashCommandSendMessage : SlashCommand
+    sealed interface SlashCommandAdmin : SlashCommand
+    sealed interface SlashCommandNavigation : SlashCommand
+
+    // Errors
+    data class ErrorEmptySlashCommand(val message: String) : Error
+    data class ErrorCommandNotSupportedInThreads(val message: String) : Error
+
+    // Unknown/Unsupported slash command
+    data class ErrorUnknownSlashCommand(val message: String) : Error
+
+    // A slash command is detected, but there is an error
+    data class ErrorSyntax(val message: String) : Error
+
+    // Valid commands:
+    data class SendPlainText(val message: CharSequence) : SlashCommandSendMessage
+    data class SendEmote(val message: CharSequence) : SlashCommandSendMessage
+    data class SendRainbow(val message: CharSequence) : SlashCommandSendMessage
+    data class SendRainbowEmote(val message: CharSequence) : SlashCommandSendMessage
+    data class BanUser(val userId: UserId, val reason: String?) : SlashCommandAdmin
+    data class UnbanUser(val userId: UserId, val reason: String?) : SlashCommandAdmin
+    data class IgnoreUser(val userId: UserId) : SlashCommandAdmin
+    data class UnignoreUser(val userId: UserId) : SlashCommandAdmin
+    data class SetUserPowerLevel(val userId: UserId, val powerLevel: Int?) : SlashCommandAdmin
+    data class ChangeRoomName(val name: String) : SlashCommandAdmin
+    data class Invite(val userId: UserId, val reason: String?) : SlashCommandAdmin
+    data class JoinRoom(val roomIdOrAlias: RoomIdOrAlias, val reason: String?) : SlashCommandAdmin
+    data class ChangeTopic(val topic: String) : SlashCommandAdmin
+    data class RemoveUser(val userId: UserId, val reason: String?) : SlashCommandAdmin
+    data class ChangeDisplayName(val displayName: String) : SlashCommandAdmin
+    data class ChangeDisplayNameForRoom(val displayName: String) : SlashCommandAdmin
+    data class ChangeRoomAvatar(val url: String) : SlashCommandAdmin
+    data class ChangeAvatarForRoom(val url: String) : SlashCommandAdmin
+    data class SendSpoiler(val message: String) : SlashCommandSendMessage
+    data class SendWithPrefix(val prefix: MessagePrefix, val message: CharSequence) : SlashCommandSendMessage
+    data object DiscardSession : SlashCommandAdmin
+    data class SendChatEffect(val chatEffect: ChatEffect, val message: String) : SlashCommandSendMessage
+    data object LeaveRoom : SlashCommandAdmin
+    data class UpgradeRoom(val newVersion: String) : SlashCommandAdmin
+
+    data object DevTools : SlashCommandNavigation
+    data class ShowUser(val userId: UserId) : SlashCommandNavigation
+}
+
+fun SlashCommand.Error.message() = when (this) {
+    is SlashCommand.ErrorEmptySlashCommand -> message
+    is SlashCommand.ErrorCommandNotSupportedInThreads -> message
+    is SlashCommand.ErrorUnknownSlashCommand -> message
+    is SlashCommand.ErrorSyntax -> message
+}

libraries/slashcommands/api/src/main/kotlin/io/element/android/libraries/slashcommands/api/SlashCommandService.kt

@@ -0,0 +1,41 @@
+/*
+ * Copyright (c) 2026 Element Creations Ltd.
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial.
+ * Please see LICENSE files in the repository root for full details.
+ */
+
+package io.element.android.libraries.slashcommands.api
+
+import io.element.android.libraries.matrix.api.timeline.Timeline
+
+interface SlashCommandService {
+    suspend fun getSuggestions(
+        text: String,
+        isInThread: Boolean,
+    ): List<SlashCommandSuggestion>
+
+    /**
+     * Parse the message and return a SlashCommand.
+     */
+    suspend fun parse(
+        textMessage: CharSequence,
+        formattedMessage: String?,
+        isInThreadTimeline: Boolean,
+    ): SlashCommand
+
+    /**
+     * Proceed a SlashCommandSendMessage.
+     */
+    suspend fun proceedSendMessage(
+        slashCommand: SlashCommand.SlashCommandSendMessage,
+        timeline: Timeline,
+    ): Result<Unit>
+
+    /**
+     * Proceed a SlashCommandAdmin.
+     */
+    suspend fun proceedAdmin(
+        slashCommand: SlashCommand.SlashCommandAdmin,
+    ): Result<Unit>
+}

libraries/slashcommands/api/src/main/kotlin/io/element/android/libraries/slashcommands/api/SlashCommandSuggestion.kt

@@ -0,0 +1,14 @@
+/*
+ * Copyright (c) 2026 Element Creations Ltd.
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial.
+ * Please see LICENSE files in the repository root for full details.
+ */
+
+package io.element.android.libraries.slashcommands.api
+
+data class SlashCommandSuggestion(
+    val command: String,
+    val parameters: String?,
+    val description: String,
+)