NPE when using :handlers instead of meaningful error message

[borkdude]

It seems transit is giving an NPE instead of a meaningful error message when using :handlers and you give it a type it can't handle:

clojure -Sdeps '{:deps {com.cognitect/transit-clj {:mvn/version "RELEASE"}}}' -M /tmp/transit.clj

(require '[cognitect.transit :as transit])

(def ldt-write-handler (transit/write-handler "pod.babashka.sql/local-date-time" str))

(defn write-transit [v]
  (let [baos (java.io.ByteArrayOutputStream.)]
    (transit/write (transit/writer baos :json {:handlers {java.time.LocalDateTime ldt-write-handler}}) v)
    (.toString baos "utf-8")))

(write-transit (into-array String ["foo"]))

Syntax error (NullPointerException) compiling at (/tmp/transit.clj:19:1).
null

[puredanger]

Can you drop (pst *e) at that point too?

[borkdude]

user=> (load-file "/tmp/array.clj")
"[\"~#pod.babashka.sql/array\",[\"foo\"]]"
Syntax error (NullPointerException) compiling at (/tmp/array.clj:10:51).
null
user=> (pst *e)
Note: The following stack trace applies to the reader or compiler, your code was not executed.
CompilerException Syntax error compiling at (/tmp/array.clj:10:51). #:clojure.error{:phase :compile-syntax-check, :line 10, :column 51, :source "/tmp/array.clj"}
	clojure.lang.Compiler.load (Compiler.java:7648)
	clojure.lang.Compiler.loadFile (Compiler.java:7574)
	clojure.lang.RT$3.invoke (RT.java:327)
	user/eval5 (NO_SOURCE_FILE:1)
	user/eval5 (NO_SOURCE_FILE:1)
	clojure.lang.Compiler.eval (Compiler.java:7177)
	clojure.lang.Compiler.eval (Compiler.java:7132)
	clojure.core/eval (core.clj:3214)
	clojure.core/eval (core.clj:3210)
	clojure.main/repl/read-eval-print--9086/fn--9089 (main.clj:437)
	clojure.main/repl/read-eval-print--9086 (main.clj:437)
	clojure.main/repl/fn--9095 (main.clj:458)
Caused by:
RuntimeException java.lang.NullPointerException
	com.cognitect.transit.impl.WriterFactory$1.write (WriterFactory.java:65)
	cognitect.transit/write (transit.clj:171)
	cognitect.transit/write (transit.clj:168)
	user/write-transit (array.clj:7)
	user/write-transit (array.clj:5)
	user/eval294 (array.clj:11)
	user/eval294 (array.clj:11)
	clojure.lang.Compiler.eval (Compiler.java:7177)
	clojure.lang.Compiler.load (Compiler.java:7636)
	clojure.lang.Compiler.loadFile (Compiler.java:7574)
Caused by:
NullPointerException
	com.cognitect.transit.impl.AbstractEmitter.marshalTop (AbstractEmitter.java:203)
	com.cognitect.transit.impl.JsonEmitter.emit (JsonEmitter.java:41)
	com.cognitect.transit.impl.WriterFactory$1.write (WriterFactory.java:62)
	cognitect.transit/write (transit.clj:171)

[myguidingstar]

@borkdude the above code will work if you provide the a default handler like this:

(deftype DefaultHandler []
  WriteHandler
  (tag [this v] "unknown")
  (rep [this v] (pr-str v)))

(defn write-transit [v]
  (let [baos (java.io.ByteArrayOutputStream.)
        default-handler (transit/write-handler
                          (fn [_] "atom")
                          (fn [a] @a))]
    (transit/write (transit/writer baos :json {:default-handler (DefaultHandler.)
                                               :handlers {java.time.LocalDateTime ldt-write-handler}}) v)
    (.toString baos "utf-8")))

(write-transit (into-array String ["foo"]))
;; => ["~#unknown" "#object[\"[Ljava.lang.String;\" 0x711ae4e6 \"[Ljava.lang.String;@711ae4e6\"]"]

I guess by design you have to provide :default-handler to writer for now. That being said I agree that NPE is bad dev experience.