Class/forName considered as function name (proposal: say that it must be a simple symbol)

[arichiardi]

• I have read the Clojure etiquette and will respect it when communicating on this platform.

version
2024.02.12

platform
linux - native binary

problem
I have the following in a file (for extending XTDB's handler):

(extend-protocol pedestal.servlet-interceptor/WriteableBody
           (Class/forName "[B") ;; This errors out
           (write-body-to-stream [^InputStream input-stream ^OutputStream output-stream]
             (with-open [out output-stream] (.write out ^bytes input-stream)))
           juxt.clojars_mirrors.muuntaja.v0v6v8.muuntaja.protocols.StreamableResponse
           (write-body-to-stream [^InputStream input-stream ^OutputStream output-stream]
             (with-open [out output-stream] ((.f input-stream) ^OutputStream out))))

The highlighter line is reported as:

src/web2/server.clj:53:27: error: Function name must be simple symbol but got: "[B"

I don't think it's a configuration error and it only happens with the latest version of clj-kondo.

expected behavior

It should not error out as above.

[borkdude]

You can't officially use (Class/forName "[B") with extend-protocol.
Only class names are allowed, not expressions. That it works is accidental. In this case it's better to write the extend call manually. I can give links where this is discussed later on. One of the issues with doing what you do above is that it becomes unreliable when you have multiple expressions like that.

[arichiardi]

I see, did not know that!

better to write the extend call or simply (?)

I'd like to know what "simply" is here cause I like simple :)

[borkdude]

That was a typo. Writing extend is simple.

[borkdude]

In Clojure 1.12 you will be able to write (extend-protocol IFoo byte* ...)

[borkdude]

Here is the relevant JIRA: https://clojure.atlassian.net/browse/CLJ-1381
Slack discussion: https://clojurians.slack.com/archives/CHY97NXE2/p1677266201633939

[borkdude]

I think we could improve the error message to say that the class name must be a simple symbol

[borkdude]

Also see https://clojure.atlassian.net/browse/CLJ-2836

[borkdude]

I'll leave this issue open until CLJ-2836 is resolved.