feat(microservices): Allow custom exchangeType as string for plugin compatibility

[ChangmoKang]

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• The commit message follows our guidelines: https://github.com/nestjs/nest/blob/master/CONTRIBUTING.md
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Other... Please describe:

What is the current behavior?

Currently, only the default exchange types can be used.

Issue Number: N/A

What is the new behavior?

Make exchangeType configurable as a generic string instead of strict union, enabling support for plugins like rabbitmq-delayed-message-exchange which use non-standard types (e.g., x-delayed-message, x-local-random).

#	Exchange Type	Plugin	Key Features	Min. RabbitMQ
1	x‑delayed-message	rabbitmq_delayed_message_exchange	Schedules or retries messages via the x-delay header—removes the need for TTL‑DLX stacks	3.6.0+
2	x‑consistent-hash	rabbitmq_consistent_hash_exchange	Consistent‑hash key‑to‑queue load‑balancing with minimal key relocation when consumers scale	3.7.0+
3	x‑modulus-hash	rabbitmq_sharding	Simple hash(key) mod N sharding for linear throughput growth	3.8.0+
4	x‑random	rabbitmq_random_exchange	Picks one queue at random among those bound with the same routing key—lightweight load spread	3.6.0+
5	x‑local-random	Local Random Exchange Docs	Routes only to queues on the publisher’s node, then random‑selects—cuts network hops	4.0.0+
6	x‑lvc (Last Value Cache)	rabbitmq_lvc_exchange	Stores the latest message per routing key; new bindings receive that snapshot instantly	3.6.0+
7	x‑recent-history	rabbitmq_recent_history_exchange	Keeps the last N (default 20) messages and replays them—ideal for chat or log viewers	3.6.0+
8	x‑rtopic (Reverse Topic)	rabbitmq_rtopic_exchange	Lets publishers use wildcards (*, #) while bindings stay static—publisher‑driven multicast	3.6.0+
9	x‑management	rabbitmq_management_exchange	Invokes the Management HTTP API via pure AMQP frames—handy behind firewalls	3.6.0+

Does this PR introduce a breaking change?

• Yes
• No

Other information

[coveralls]

Pull Request Test Coverage Report for Build db5aa2fa-ca53-4757-a161-3dca69eec471

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 88.923%

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Totals
Change from base Build c99d332b-8204-48ec-bc18-15971298dd6e:	0.0%
Covered Lines:	7177
Relevant Lines:	8071

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💛 - Coveralls

[kamilmysliwiec]

Suggested change

	exchangeType?: string;
	exchangeType?: 'direct' | 'fanout' | 'topic' | 'headers' | string & {};

with this (ugly) hack we'd be able to preserve type intelisense

[ChangmoKang]

@kamilmysliwiec That would also be good. pragmatic way to preserve Intellisense while keeping flexibility.

Maybe we could define a type and use it explicitly to make things even clearer.

// packages/microservices/external/rmq-url.interface.ts:71
type AmqpMainExchangeType = 'direct' | 'fanout' | 'topic' | 'headers';

/**
 * @publicApi
 */
export type AmqpExchangeType = AmqpMainExchangeType | (string & {});

// packages/microservices/interfaces/microservice-configuration.interface.ts:289
exchangeType?: AmqpExchangeType;

[kamilmysliwiec]

external is supposed to hold files (types) that are copied from the original package, so adding a new custom type there might cause unexpected issues later on

[ChangmoKang]

@kamilmysliwiec I’ve removed the custom type and updated the code as initially suggested to preserve IntelliSense.
Please feel free to leave a comment if there’s anything else that needs to be addressed.

[kamilmysliwiec]

LGTM