feat(discovery): resolve message links into discoverable guilds (#3159)

fluxer_api/src/api/guild/controllers/GuildDiscoveryController.ts

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: AGPL-3.0-or-later
 
-import {createGuildID} from '@app/api/BrandedTypes';
+import {createChannelID, createGuildID} from '@app/api/BrandedTypes';
 import {Config} from '@app/api/Config';
 import type {GuildDiscoveryRow} from '@app/api/database/types/GuildDiscoveryTypes';
 import {DefaultUserOnly, LoginRequired} from '@app/api/middleware/AuthMiddleware';
@@ -15,12 +15,13 @@ import {GuildFeatures, JoinSourceTypes} from '@fluxer/constants/src/GuildConstan
 import {DiscoveryDisabledError} from '@fluxer/errors/src/domains/discovery/DiscoveryDisabledError';
 import {DiscoveryNotDiscoverableError} from '@fluxer/errors/src/domains/discovery/DiscoveryNotDiscoverableError';
 import {InvitesDisabledError} from '@fluxer/errors/src/domains/invite/InvitesDisabledError';
-import {GuildIdParam} from '@fluxer/schema/src/domains/common/CommonParamSchemas';
+import {GuildIdChannelIdParam, GuildIdParam} from '@fluxer/schema/src/domains/common/CommonParamSchemas';
 import {
 	DiscoveryApplicationPatchRequest,
 	DiscoveryApplicationRequest,
 	DiscoveryApplicationResponse,
 	DiscoveryCategoryListResponse,
+	DiscoveryChannelPreviewResponse,
 	DiscoveryGuildListResponse,
 	DiscoverySearchQuery,
 	DiscoveryStatusResponse,
@@ -100,6 +101,31 @@ export function GuildDiscoveryController(app: HonoApp) {
 			return ctx.json(categories);
 		},
 	);
+	app.get(
+		'/discovery/guilds/:guild_id/channels/:channel_id',
+		RateLimitMiddleware(RateLimitConfigs.DISCOVERY_CHANNEL_PREVIEW),
+		LoginRequired,
+		DefaultUserOnly,
+		Validator('param', GuildIdChannelIdParam),
+		OpenAPI({
+			operationId: 'get_discovery_channel_preview',
+			summary: 'Preview a channel in a discoverable guild',
+			description:
+				'Returns the guild and channel behind a channel or message link when the guild is listed in discovery and new members can read the channel.',
+			responseSchema: DiscoveryChannelPreviewResponse,
+			statusCode: 200,
+			security: ['sessionToken', 'bearerToken'],
+			tags: ['Discovery'],
+		}),
+		async (ctx) => {
+			ensureDiscoveryEnabled();
+			const {guild_id, channel_id} = ctx.req.valid('param');
+			const preview = await ctx
+				.get('discoveryService')
+				.getChannelPreview(createGuildID(guild_id), createChannelID(channel_id));
+			return ctx.json(preview);
+		},
+	);
 	app.post(
 		'/discovery/guilds/:guild_id/join',
 		RateLimitMiddleware(RateLimitConfigs.DISCOVERY_JOIN),

fluxer_api/src/api/guild/services/GuildDiscoveryService.ts

@@ -1,7 +1,8 @@
 // SPDX-License-Identifier: AGPL-3.0-or-later
 
-import type {GuildID, UserID} from '@app/api/BrandedTypes';
+import {type ChannelID, type GuildID, guildIdToRoleId, type UserID} from '@app/api/BrandedTypes';
 import {Config} from '@app/api/Config';
+import type {IChannelDataRepository} from '@app/api/channel/repositories/IChannelDataRepository';
 import type {GuildDiscoveryRow} from '@app/api/database/types/GuildDiscoveryTypes';
 import {mapGuildToGuildResponse} from '@app/api/guild/GuildModel';
 import type {IGuildDiscoveryRepository} from '@app/api/guild/repositories/GuildDiscoveryRepository';
@@ -10,6 +11,7 @@ import {contentModerationService} from '@app/api/infrastructure/ContentModeratio
 import type {IGatewayService} from '@app/api/infrastructure/IGatewayService';
 import {Logger} from '@app/api/Logger';
 import type {IGuildSearchService} from '@app/api/search/IGuildSearchService';
+import {Permissions} from '@fluxer/constants/src/ChannelConstants';
 import {
 	DISCOVERY_DEFAULT_LANGUAGE,
 	DISCOVERY_MAX_TAGS,
@@ -83,6 +85,8 @@ export abstract class IGuildDiscoveryService {
 
 	abstract listByStatus(params: {status: string}): Promise<Array<GuildDiscoveryRow>>;
 
+	abstract getChannelPreview(guildId: GuildID, channelId: ChannelID): Promise<DiscoveryChannelPreview>;
+
 	abstract searchDiscoverable(params: {
 		query?: string;
 		categoryId?: number;
@@ -118,7 +122,13 @@ interface DiscoveryGuildResult {
 	verification_level: number;
 }
 
+interface DiscoveryChannelPreview {
+	guild: {id: string; name: string; icon: string | null};
+	channel: {id: string; name: string | null; type: number};
+}
+
 const DISCOVERY_CATEGORY_FACET = 'discoveryCategory';
+const PUBLIC_CHANNEL_PERMISSIONS = Permissions.VIEW_CHANNEL | Permissions.READ_MESSAGE_HISTORY;
 
 function toDiscoveryCategoryCounts(
 	counts: Readonly<Record<string, number>> | undefined,
@@ -143,6 +153,7 @@ export class GuildDiscoveryService extends IGuildDiscoveryService {
 		private readonly guildRepository: IGuildRepositoryAggregate,
 		private readonly gatewayService: IGatewayService,
 		private readonly guildSearchService: IGuildSearchService | null,
+		private readonly channelDataRepository: IChannelDataRepository,
 	) {
 		super();
 	}
@@ -382,6 +393,38 @@ export class GuildDiscoveryService extends IGuildDiscoveryService {
 		return this.discoveryRepository.listFullByStatus(params.status);
 	}
 
+	async getChannelPreview(guildId: GuildID, channelId: ChannelID): Promise<DiscoveryChannelPreview> {
+		const [status, guild, channel, everyoneRole] = await Promise.all([
+			this.discoveryRepository.findByGuildId(guildId),
+			this.guildRepository.findUnique(guildId),
+			this.channelDataRepository.findUnique(channelId),
+			this.guildRepository.getRole(guildIdToRoleId(guildId), guildId),
+		]);
+		if (
+			status?.status !== DiscoveryApplicationStatus.APPROVED ||
+			!guild ||
+			guild.features.has(GuildFeatures.INVITES_DISABLED) ||
+			!channel ||
+			channel.guildId !== guildId ||
+			!everyoneRole
+		) {
+			throw new DiscoveryNotDiscoverableError();
+		}
+		if ((everyoneRole.permissions & Permissions.ADMINISTRATOR) === 0n) {
+			const overwrite = channel.permissionOverwrites.get(everyoneRole.id);
+			const permissions = overwrite
+				? (everyoneRole.permissions & ~overwrite.deny) | overwrite.allow
+				: everyoneRole.permissions;
+			if ((permissions & PUBLIC_CHANNEL_PERMISSIONS) !== PUBLIC_CHANNEL_PERMISSIONS) {
+				throw new DiscoveryNotDiscoverableError();
+			}
+		}
+		return {
+			guild: {id: guild.id.toString(), name: guild.name, icon: guild.iconHash},
+			channel: {id: channel.id.toString(), name: channel.name, type: channel.type},
+		};
+	}
+
 	async searchDiscoverable(params: {
 		query?: string;
 		categoryId?: number;

fluxer_api/src/api/guild/tests/DiscoverySearchAndJoin.test.ts

@@ -3,7 +3,8 @@
 import {createTestAccount, setUserACLs} from '@app/api/auth/tests/AuthTestUtils';
 import type {GuildID} from '@app/api/BrandedTypes';
 import {createTestBotAccount} from '@app/api/bot/tests/BotTestUtils';
-import {createGuild, getUserGuilds} from '@app/api/guild/tests/GuildTestUtils';
+import {createPermissionOverwrite} from '@app/api/channel/tests/ChannelTestUtils';
+import {createChannel, createGuild, getUserGuilds} from '@app/api/guild/tests/GuildTestUtils';
 import {setInjectedGatewayService} from '@app/api/middleware/ServiceRegistry';
 import {getGuildRepository} from '@app/api/middleware/ServiceSingletons';
 import {banUser} from '@app/api/moderation/tests/ModerationTestUtils';
@@ -15,11 +16,13 @@ import {createBuilder, createBuilderWithoutAuth} from '@app/api/test/TestRequest
 import syncDiscoveryIndex from '@app/api/worker/tasks/SyncDiscoveryIndex';
 import {clearWorkerDependencies, setWorkerDependenciesForTest} from '@app/api/worker/WorkerContext';
 import {APIErrorCodes} from '@fluxer/constants/src/ApiErrorCodes';
+import {Permissions} from '@fluxer/constants/src/ChannelConstants';
 import {DiscoveryCategories, DiscoveryCategoryLabels} from '@fluxer/constants/src/DiscoveryConstants';
 import {GuildVerificationLevel} from '@fluxer/constants/src/GuildConstants';
 import type {
 	DiscoveryApplicationResponse,
 	DiscoveryCategoryResponse,
+	DiscoveryChannelPreviewResponse,
 	DiscoveryGuildListResponse,
 } from '@fluxer/schema/src/domains/guild/GuildDiscoverySchemas';
 import type {WorkerTaskHelpers} from '@pkgs/worker/src/contracts/WorkerTask';
@@ -507,4 +510,65 @@ describe('Discovery Search and Join', () => {
 				.execute();
 		});
 	});
+	describe('channel preview', () => {
+		async function createListedGuild(name: string): Promise<{ownerToken: string; guildId: string; channelId: string}> {
+			const owner = await createTestAccount(harness);
+			const guild = await createGuild(harness, owner.token, name);
+			await setGuildMemberCount(harness, guild.id, 10);
+			const admin = await createTestAccount(harness);
+			await setUserACLs(harness, admin, ['admin:authenticate', 'discovery:review']);
+			await applyAndApprove(
+				harness,
+				owner.token,
+				admin.token,
+				guild.id,
+				`${name} welcomes everyone`,
+				DiscoveryCategories.GAMING,
+			);
+			return {ownerToken: owner.token, guildId: guild.id, channelId: guild.system_channel_id!};
+		}
+		test('should preview a channel that new members can read', async () => {
+			const {guildId, channelId} = await createListedGuild('Preview Guild');
+			const viewer = await createTestAccount(harness);
+			const preview = await createBuilder<DiscoveryChannelPreviewResponse>(harness, viewer.token)
+				.get(`/discovery/guilds/${guildId}/channels/${channelId}`)
+				.expect(HTTP_STATUS.OK)
+				.execute();
+			expect(preview.guild.id).toBe(guildId);
+			expect(preview.guild.name).toBe('Preview Guild');
+			expect(preview.channel.id).toBe(channelId);
+		});
+		test('should not preview a channel hidden from everyone', async () => {
+			const {ownerToken, guildId} = await createListedGuild('Hidden Channel Guild');
+			const hidden = await createChannel(harness, ownerToken, guildId, 'staff');
+			await createPermissionOverwrite(harness, ownerToken, hidden.id, guildId, {
+				type: 0,
+				allow: '0',
+				deny: Permissions.VIEW_CHANNEL.toString(),
+			});
+			const viewer = await createTestAccount(harness);
+			await createBuilder(harness, viewer.token)
+				.get(`/discovery/guilds/${guildId}/channels/${hidden.id}`)
+				.expect(HTTP_STATUS.BAD_REQUEST, APIErrorCodes.DISCOVERY_NOT_DISCOVERABLE)
+				.execute();
+		});
+		test('should not preview a channel from another guild', async () => {
+			const {guildId} = await createListedGuild('Listed Guild');
+			const other = await createListedGuild('Other Listed Guild');
+			const viewer = await createTestAccount(harness);
+			await createBuilder(harness, viewer.token)
+				.get(`/discovery/guilds/${guildId}/channels/${other.channelId}`)
+				.expect(HTTP_STATUS.BAD_REQUEST, APIErrorCodes.DISCOVERY_NOT_DISCOVERABLE)
+				.execute();
+		});
+		test('should not preview a guild that is not listed', async () => {
+			const owner = await createTestAccount(harness);
+			const guild = await createGuild(harness, owner.token, 'Unlisted Guild');
+			const viewer = await createTestAccount(harness);
+			await createBuilder(harness, viewer.token)
+				.get(`/discovery/guilds/${guild.id}/channels/${guild.system_channel_id}`)
+				.expect(HTTP_STATUS.BAD_REQUEST, APIErrorCodes.DISCOVERY_NOT_DISCOVERABLE)
+				.execute();
+		});
+	});
 });

fluxer_api/src/api/middleware/ServiceSingletons.ts

@@ -463,6 +463,7 @@ export const getGuildDiscoveryService = singleton(
 			getGuildRepository(),
 			getGatewayService(),
 			getGuildSearchService(),
+			getChannelRepository().channelData,
 		),
 );
 export const getReadStateRequestService = singleton(() => new ReadStateRequestService(getReadStateService()));

fluxer_api/src/api/openapi/openapi.json

@@ -5541,6 +5541,77 @@
 				]
 			}
 		},
+		"/discovery/guilds/{guild_id}/channels/{channel_id}": {
+			"get": {
+				"operationId": "get_discovery_channel_preview",
+				"summary": "Preview a channel in a discoverable guild",
+				"tags": ["Discovery"],
+				"responses": {
+					"200": {
+						"description": "Success",
+						"content": {
+							"application/json": {"schema": {"$ref": "#/components/schemas/DiscoveryChannelPreviewResponse"}}
+						}
+					},
+					"400": {
+						"description": "Bad Request - The request was malformed or contained invalid data",
+						"content": {"application/json": {"schema": {"$ref": "#/components/schemas/Error"}}}
+					},
+					"401": {
+						"description": "Unauthorized - Authentication is required or the token is invalid",
+						"content": {"application/json": {"schema": {"$ref": "#/components/schemas/Error"}}}
+					},
+					"403": {
+						"description": "Forbidden - You do not have permission to perform this action",
+						"content": {"application/json": {"schema": {"$ref": "#/components/schemas/Error"}}}
+					},
+					"429": {
+						"description": "Too Many Requests - You are being rate limited",
+						"content": {"application/json": {"schema": {"$ref": "#/components/schemas/ThrottledError"}}},
+						"headers": {
+							"Retry-After": {
+								"description": "Number of seconds to wait before retrying (only on 429)",
+								"schema": {"type": "integer"}
+							},
+							"X-RateLimit-Limit": {
+								"description": "The number of requests that can be made in the current window",
+								"schema": {"type": "integer"}
+							},
+							"X-RateLimit-Remaining": {
+								"description": "The number of remaining requests that can be made",
+								"schema": {"type": "integer"}
+							},
+							"X-RateLimit-Reset": {
+								"description": "Unix timestamp when the rate limit resets",
+								"schema": {"type": "integer"}
+							}
+						}
+					},
+					"500": {
+						"description": "Internal Server Error - An unexpected error occurred",
+						"content": {"application/json": {"schema": {"$ref": "#/components/schemas/Error"}}}
+					}
+				},
+				"description": "Returns the guild and channel behind a channel or message link when the guild is listed in discovery and new members can read the channel.",
+				"security": [{"sessionToken": []}],
+				"parameters": [
+					{
+						"name": "guild_id",
+						"in": "path",
+						"required": true,
+						"schema": {"description": "The ID of the guild", "$ref": "#/components/schemas/SnowflakeType"},
+						"description": "The ID of the guild"
+					},
+					{
+						"name": "channel_id",
+						"in": "path",
+						"required": true,
+						"schema": {"description": "The ID of the channel", "$ref": "#/components/schemas/SnowflakeType"},
+						"description": "The ID of the channel"
+					}
+				]
+			}
+		},
 		"/discovery/guilds/{guild_id}/join": {
 			"post": {
 				"operationId": "join_discovery_guild",
@@ -28579,6 +28650,35 @@
 				"required": ["url"],
 				"additionalProperties": false
 			},
+			"DiscoveryChannelPreviewResponse": {
+				"type": "object",
+				"properties": {
+					"guild": {
+						"type": "object",
+						"properties": {
+							"id": {"description": "Guild ID", "$ref": "#/components/schemas/SnowflakeStringType"},
+							"name": {"type": "string", "description": "Guild name"},
+							"icon": {"description": "Guild icon hash", "type": ["string", "null"]}
+						},
+						"required": ["id", "name", "icon"],
+						"additionalProperties": false,
+						"description": "The discoverable guild the channel belongs to"
+					},
+					"channel": {
+						"type": "object",
+						"properties": {
+							"id": {"description": "Channel ID", "$ref": "#/components/schemas/SnowflakeStringType"},
+							"name": {"description": "Channel name", "type": ["string", "null"]},
+							"type": {"type": "number", "description": "Channel type"}
+						},
+						"required": ["id", "name", "type"],
+						"additionalProperties": false,
+						"description": "A channel that new members can view"
+					}
+				},
+				"required": ["guild", "channel"],
+				"additionalProperties": false
+			},
 			"DiscoveryGuildListResponse": {
 				"type": "object",
 				"properties": {

fluxer_api/src/api/rate_limit_configs/DiscoveryRateLimitConfig.ts

@@ -16,6 +16,10 @@ export const DiscoveryRateLimitConfigs = {
 		bucket: 'discovery:join',
 		config: {limit: 10, windowMs: ms('1 minute')},
 	} as RouteRateLimitConfig,
+	DISCOVERY_CHANNEL_PREVIEW: {
+		bucket: 'discovery:channel_preview',
+		config: {limit: 60, windowMs: ms('10 seconds')},
+	} as RouteRateLimitConfig,
 	DISCOVERY_APPLY: {
 		bucket: 'discovery:apply::guild_id',
 		config: {limit: 5, windowMs: ms('1 minute')},

fluxer_app/src/features/app/constants/Endpoints.ts

@@ -245,6 +245,8 @@ export const Endpoints = {
 	DISCOVERY_GUILDS: '/discovery/guilds',
 	DISCOVERY_CATEGORIES: '/discovery/categories',
 	DISCOVERY_JOIN: (guildId: string) => `/discovery/guilds/${guildId}/join`,
+	DISCOVERY_CHANNEL_PREVIEW: (guildId: string, channelId: string) =>
+		`/discovery/guilds/${guildId}/channels/${channelId}`,
 	GUILD_DISCOVERY: (guildId: string) => `/guilds/${guildId}/discovery`,
 	CONNECTIONS: '/users/@me/connections',
 	CONNECTIONS_VERIFY_AND_CREATE: '/users/@me/connections/verify',

fluxer_app/src/features/discovery/commands/DiscoveryCommands.ts

@@ -23,6 +23,11 @@ export interface DiscoveryGuild {
 
 type DiscoveryGuildPayload = Omit<DiscoveryGuild, 'banner'> & {banner?: string | null};
 
+export interface DiscoveryChannelPreview {
+	guild: {id: string; name: string; icon: string | null};
+	channel: {id: string; name: string | null; type: number};
+}
+
 interface DiscoveryCategoryCountPayload {
 	category_type: number;
 	count: number;
@@ -115,6 +120,11 @@ export async function getCategories(): Promise<Array<DiscoveryCategory>> {
 	return requestDiscoveryCategories();
 }
 
+export async function getChannelPreview(guildId: string, channelId: string): Promise<DiscoveryChannelPreview> {
+	const response = await http.get<DiscoveryChannelPreview>(Endpoints.DISCOVERY_CHANNEL_PREVIEW(guildId, channelId));
+	return response.body;
+}
+
 export async function joinGuild(guildId: string): Promise<void> {
 	await http.post(Endpoints.DISCOVERY_JOIN(guildId));
 	logger.info('Joined guild via discovery', {guildId});

fluxer_app/src/features/discovery/commands/DiscoveryJoinCommands.tsx

@@ -112,10 +112,17 @@ function showJoinGuildErrorModal(error: unknown): void {
 	);
 }
 
-export async function joinDiscoveryGuild(guildId: string): Promise<boolean> {
+export async function joinDiscoveryGuild(
+	guildId: string,
+	target?: {channelId: string; messageId?: string},
+): Promise<boolean> {
 	try {
 		await DiscoveryCommands.joinGuild(guildId);
+		if (target) {
+			NavigationCommands.selectChannel(guildId, target.channelId, target.messageId);
+		} else {
 			NavigationCommands.selectGuild(guildId);
+		}
 		return true;
 	} catch (error) {
 		showJoinGuildErrorModal(error);

fluxer_app/src/features/discovery/state/DiscoveryChannelPreviews.ts

@@ -0,0 +1,55 @@
+// SPDX-License-Identifier: AGPL-3.0-or-later
+
+import type {DiscoveryChannelPreview} from '@app/features/discovery/commands/DiscoveryCommands';
+import * as DiscoveryCommands from '@app/features/discovery/commands/DiscoveryCommands';
+import {failureCode} from '@app/features/platform/utils/ResponseInspection';
+import {APIErrorCodes} from '@fluxer/constants/src/ApiErrorCodes';
+import {makeAutoObservable, observable, runInAction} from 'mobx';
+
+type DiscoveryChannelPreviewEntry =
+	| {status: 'loading'}
+	| {status: 'ready'; preview: DiscoveryChannelPreview}
+	| {status: 'unavailable'};
+
+function entryKey(guildId: string, channelId: string): string {
+	return `${guildId}:${channelId}`;
+}
+
+class DiscoveryChannelPreviews {
+	private entries = observable.map<string, DiscoveryChannelPreviewEntry>();
+	private discoveryDisabled = false;
+
+	constructor() {
+		makeAutoObservable(this, {}, {autoBind: true});
+	}
+
+	get(guildId: string, channelId: string): DiscoveryChannelPreviewEntry | undefined {
+		return this.entries.get(entryKey(guildId, channelId));
+	}
+
+	request(guildId: string, channelId: string): void {
+		const key = entryKey(guildId, channelId);
+		if (this.discoveryDisabled || this.entries.has(key)) return;
+		this.entries.set(key, {status: 'loading'});
+		DiscoveryCommands.getChannelPreview(guildId, channelId).then(
+			(preview) => {
+				runInAction(() => this.entries.set(key, {status: 'ready', preview}));
+			},
+			(error: unknown) => {
+				const code = failureCode(error);
+				runInAction(() => {
+					if (code === APIErrorCodes.DISCOVERY_DISABLED) {
+						this.discoveryDisabled = true;
+						this.entries.set(key, {status: 'unavailable'});
+					} else if (code === APIErrorCodes.DISCOVERY_NOT_DISCOVERABLE) {
+						this.entries.set(key, {status: 'unavailable'});
+					} else {
+						this.entries.delete(key);
+					}
+				});
+			},
+		);
+	}
+}
+
+export default new DiscoveryChannelPreviews();

fluxer_app/src/features/messaging/components/markdown/renderers/LinkRenderer.tsx

@@ -11,6 +11,8 @@ import type {Channel} from '@app/features/channel/models/Channel';
 import Channels from '@app/features/channel/state/Channels';
 import {getDMDisplayName, getIcon, getName} from '@app/features/channel/utils/ChannelUtils';
 import DeveloperMode from '@app/features/devtools/state/DeveloperMode';
+import {joinDiscoveryGuild} from '@app/features/discovery/commands/DiscoveryJoinCommands';
+import DiscoveryChannelPreviews from '@app/features/discovery/state/DiscoveryChannelPreviews';
 import type {Guild} from '@app/features/guild/models/Guild';
 import Guilds from '@app/features/guild/state/Guilds';
 import {getGuildIconDisplayInitials} from '@app/features/guild/utils/GuildInitialsUtils';
@@ -75,6 +77,7 @@ import type {UserSettingsDeepLinkTarget} from '@app/features/user/components/set
 import * as AvatarUtils from '@app/features/user/utils/AvatarUtils';
 import * as StringUtils from '@app/lib/strings';
 import {ME} from '@fluxer/constants/src/AppConstants';
+import {isProbablyAValidSnowflake} from '@fluxer/snowflake/src/SnowflakeUtils';
 import type {I18n} from '@lingui/core';
 import {msg} from '@lingui/core/macro';
 import {useLingui} from '@lingui/react';
@@ -82,7 +85,7 @@ import {CaretRightIcon, ChatTeardropIcon, LockIcon} from '@phosphor-icons/react'
 import {clsx} from 'clsx';
 import {observer} from 'mobx-react-lite';
 import type React from 'react';
-import {useCallback} from 'react';
+import {useCallback, useEffect, useState} from 'react';
 
 const LINK_CONTENT_OPTION_OVERRIDES: Partial<MarkdownRenderOptions> = {disableEmojiInteractions: true};
 
@@ -201,7 +204,7 @@ type CompactGuildMentionIconStyle = React.CSSProperties & {
 	'--jump-link-guild-icon-image'?: string;
 };
 
-function CompactGuildMentionIcon({guild}: {guild: Guild}) {
+function CompactGuildMentionIcon({guild}: {guild: Pick<Guild, 'id' | 'name' | 'icon'>}) {
 	const iconUrl = guild.icon ? AvatarUtils.getGuildIconURL({id: guild.id, icon: guild.icon}) : '';
 	const style: CompactGuildMentionIconStyle | undefined = iconUrl
 		? {'--jump-link-guild-icon-image': `url(${iconUrl})`}
@@ -514,6 +517,143 @@ function InaccessibleJumpLinkMention({url, i18n, interactive = true}: Inaccessib
 	);
 }
 
+interface DiscoverableJumpLinkMentionProps {
+	guildId: string;
+	channelId: string;
+	messageId?: string;
+	url: string;
+	i18n: I18n;
+	interactive?: boolean;
+}
+
+const DiscoverableJumpLinkMention = observer(function DiscoverableJumpLinkMention({
+	guildId,
+	channelId,
+	messageId,
+	url,
+	i18n,
+	interactive = true,
+}: DiscoverableJumpLinkMentionProps) {
+	useLingui();
+	const [joining, setJoining] = useState(false);
+	useEffect(() => {
+		DiscoveryChannelPreviews.request(guildId, channelId);
+	}, [guildId, channelId]);
+	const handleClick = useCallback(
+		(event: React.MouseEvent<HTMLButtonElement | HTMLSpanElement>) => {
+			if (!interactive) return;
+			event.preventDefault();
+			event.stopPropagation();
+			if (joining) return;
+			setJoining(true);
+			void joinDiscoveryGuild(guildId, {channelId, messageId}).finally(() => setJoining(false));
+		},
+		[channelId, guildId, interactive, joining, messageId],
+	);
+	const handleAuxClick = useCallback(
+		(event: React.MouseEvent<HTMLButtonElement | HTMLSpanElement>) => {
+			if (!interactive) return;
+			if (event.button !== 1) return;
+			event.preventDefault();
+			event.stopPropagation();
+			void openExternalUrl(url);
+		},
+		[interactive, url],
+	);
+	const handleContextMenu = useCallback(
+		(event: React.MouseEvent<HTMLButtonElement | HTMLSpanElement>) => {
+			if (!interactive) return;
+			ContextMenuCommands.openFromEvent(event, ({onClose}) => (
+				<JumpLinkContextMenu
+					url={url}
+					i18n={i18n}
+					onClose={onClose}
+					data-flx="messaging.markdown.renderers.link-renderer.discoverable-jump-link-mention.context-menu"
+				/>
+			));
+		},
+		[interactive, i18n, url],
+	);
+	const entry = DiscoveryChannelPreviews.get(guildId, channelId);
+	if (entry?.status !== 'ready') {
+		return (
+			<InaccessibleJumpLinkMention
+				url={url}
+				i18n={i18n}
+				interactive={interactive}
+				data-flx="messaging.markdown.renderers.link-renderer.discoverable-jump-link-mention.inaccessible"
+			/>
+		);
+	}
+	const {guild, channel} = entry.preview;
+	const ariaLabel = messageId
+		? i18n._(JUMP_TO_THE_MESSAGE_IN_DESCRIPTOR, {labelText: guild.name})
+		: i18n._(JUMP_TO_DESCRIPTOR, {labelText: guild.name});
+	const Component = interactive ? 'button' : 'span';
+	return (
+		<Component
+			data-flx="messaging.markdown.renderers.link-renderer.discoverable-jump-link-mention.component.click"
+			{...(interactive ? {type: 'button'} : {})}
+			className={clsx(markupStyles.mention, interactive && markupStyles.interactive, jumpLinkStyles.jumpLinkButton)}
+			onClick={handleClick}
+			onAuxClick={handleAuxClick}
+			onContextMenu={handleContextMenu}
+			aria-label={ariaLabel}
+			aria-busy={joining || undefined}
+			{...(interactive
+				? {'aria-roledescription': i18n._(messageId ? MESSAGE_LINK_DESCRIPTOR : CHANNEL_LINK_DESCRIPTOR)}
+				: {})}
+			tabIndex={interactive ? 0 : -1}
+		>
+			<span
+				className={jumpLinkStyles.part}
+				data-flx="messaging.markdown.renderers.link-renderer.discoverable-jump-link-mention.part--guild"
+			>
+				<CompactGuildMentionIcon
+					guild={guild}
+					data-flx="messaging.markdown.renderers.link-renderer.discoverable-jump-link-mention.guild-icon"
+				/>
+				<span
+					className={jumpLinkStyles.name}
+					data-flx="messaging.markdown.renderers.link-renderer.discoverable-jump-link-mention.guild-name"
+				>
+					{guild.name}
+				</span>
+			</span>
+			<span
+				className={jumpLinkStyles.divider}
+				aria-hidden="true"
+				data-flx="messaging.markdown.renderers.link-renderer.discoverable-jump-link-mention.divider"
+			>
+				<CaretRightIcon
+					weight="bold"
+					data-flx="messaging.markdown.renderers.link-renderer.discoverable-jump-link-mention.caret-right-icon"
+				/>
+			</span>
+			{messageId ? (
+				<ChatTeardropIcon
+					className={jumpLinkStyles.icon}
+					weight="fill"
+					data-flx="messaging.markdown.renderers.link-renderer.discoverable-jump-link-mention.chat-teardrop-icon"
+				/>
+			) : (
+				<span
+					className={jumpLinkStyles.part}
+					data-flx="messaging.markdown.renderers.link-renderer.discoverable-jump-link-mention.part--channel"
+				>
+					{getIcon({type: channel.type}, {className: jumpLinkStyles.icon})}
+					<span
+						className={jumpLinkStyles.name}
+						data-flx="messaging.markdown.renderers.link-renderer.discoverable-jump-link-mention.channel-name"
+					>
+						{channel.name ?? channel.id}
+					</span>
+				</span>
+			)}
+		</Component>
+	);
+});
+
 interface SettingsJumpLinkMentionProps {
 	target: UserSettingsDeepLinkTarget;
 	url: string;
@@ -740,6 +880,14 @@ export const LinkRenderer = observer(function LinkRenderer({
 	const jumpTarget = messageJumpTarget ?? channelJumpTarget;
 	const jumpChannel = jumpTarget ? (Channels.getChannel(jumpTarget.channelId) ?? null) : null;
 	const jumpGuild = jumpChannel?.guildId ? (Guilds.getGuild(jumpChannel.guildId) ?? null) : null;
+	const discoverableGuildId =
+		jumpTarget &&
+		!jumpChannel &&
+		jumpTarget.scope !== ME &&
+		isProbablyAValidSnowflake(jumpTarget.scope) &&
+		!Guilds.getGuild(jumpTarget.scope)
+			? jumpTarget.scope
+			: null;
 	const settingsTarget = isAppProtocolUrl(url) ? parseUserSettingsDeepLink(url) : null;
 	const appPage = settingsTarget ? null : parseAppPageLink(url);
 	const isInlineReplyContext = isRestrictedInlineContext(options.context);
@@ -810,11 +958,22 @@ export const LinkRenderer = observer(function LinkRenderer({
 		);
 	}
 	if (jumpTarget && !jumpChannel && !text) {
-		const mention = (
+		const interactive = !isInlineReplyContext && !shouldDisableInteractions;
+		const mention = discoverableGuildId ? (
+			<DiscoverableJumpLinkMention
+				guildId={discoverableGuildId}
+				channelId={jumpTarget.channelId}
+				messageId={messageJumpTarget?.messageId}
+				url={url}
+				i18n={i18n}
+				interactive={interactive}
+				data-flx="messaging.markdown.renderers.link-renderer.discoverable-jump-link-mention"
+			/>
+		) : (
 			<InaccessibleJumpLinkMention
 				url={url}
 				i18n={i18n}
-				interactive={!isInlineReplyContext && !shouldDisableInteractions}
+				interactive={interactive}
 				data-flx="messaging.markdown.renderers.link-renderer.inaccessible-jump-link-mention"
 			/>
 		);

packages/schema/src/domains/common/CommonParamSchemas.ts

@@ -50,6 +50,10 @@ export const GuildIdUserIdParam = GuildIdParam.extend(UserIdParam.shape);
 
 export type GuildIdUserIdParam = z.infer<typeof GuildIdUserIdParam>;
 
+export const GuildIdChannelIdParam = GuildIdParam.extend(ChannelIdParam.shape);
+
+export type GuildIdChannelIdParam = z.infer<typeof GuildIdChannelIdParam>;
+
 export const GuildIdRoleIdParam = GuildIdParam.extend({
 	role_id: SnowflakeType.describe('The ID of the role'),
 });

packages/schema/src/domains/guild/GuildDiscoverySchemas.ts

@@ -100,6 +100,25 @@ export const DiscoveryGuildListResponse = z.object({
 
 export type DiscoveryGuildListResponse = z.infer<typeof DiscoveryGuildListResponse>;
 
+export const DiscoveryChannelPreviewResponse = z.object({
+	guild: z
+		.object({
+			id: SnowflakeStringType.describe('Guild ID'),
+			name: z.string().describe('Guild name'),
+			icon: z.string().nullable().describe('Guild icon hash'),
+		})
+		.describe('The discoverable guild the channel belongs to'),
+	channel: z
+		.object({
+			id: SnowflakeStringType.describe('Channel ID'),
+			name: z.string().nullable().describe('Channel name'),
+			type: z.number().describe('Channel type'),
+		})
+		.describe('A channel that new members can view'),
+});
+
+export type DiscoveryChannelPreviewResponse = z.infer<typeof DiscoveryChannelPreviewResponse>;
+
 export const DiscoveryApplicationResponse = z.object({
 	guild_id: SnowflakeStringType.describe('Guild ID'),
 	guild_nsfw_level: NSFWLevelSchema.nullable().optional().describe('NSFW level of the guild'),