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In Clojure 1.9, if you throw an object that is not an instance of Throwable, you get the following error message:

user=> (try "something" (catch Object o "oops"))

VerifyError (class: user$eval1432, method: invokeStatic signature: ()Ljava/lang/Object;) catch_type not a subclass of Throwable java.lang.Class.getDeclaredConstructors0 (Class.java:-2)

The error message isn't too bad: it tells you most of what you want to know (except the actual class that you tried to catch).

But in a not to distant future Clojure might upgrade to Java 1.8 bytecode, and when that happens the error will look like this:

user=> (try "something" (catch Object o "oops"))

VerifyError Catch type is not a subclass of Throwable in exception handler 6
Exception Details:

user$eval1444.invokeStatic()Ljava/lang/Object; @6: astore_1


Type 'java/lang/Object' (constant pool 17) is not assignable to 'java/lang/Throwable'


0000000: 120d 4ba7 000a 4c12 0f4b a700 032a b0

Exception Handler Table:

bci [0, 3] => handler: 6

Stackmap Table:


java.lang.Class.getDeclaredConstructors0 (Class.java:-2)

To me this looks like an internal compiler error and I don't think it should be exposed to users.

The patch fixes the issue by adding a check at try expr parse time that the thing you are catching is a subclass of Throwable.

2 Answers

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Comment made by: alexmiller

The compiler should never produce byte code that has VerifyErrors so this is definitely a bug.

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Reference: https://clojure.atlassian.net/browse/CLJ-2345 (reported by schmee)