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$eval1432, method: invokeStatic signature: ()Ljava/lang/Object;) catch_type not a subclass of Throwable java.lang.Class.getDeclaredConstructors0 (Class.java:-2)
`
The error message isn't too bad: it tells you most of what you want to know (except the actual class that you tried to catch).
But in a not to distant future Clojure might upgrade to Java 1.8 bytecode, and when that happens the error will look like this:
`
user=> (try "something" (catch Object o "oops"))
VerifyError Catch type is not a subclass of Throwable in exception handler 6
Exception Details:
Location:
user$eval1444.invokeStatic()Ljava/lang/Object; @6: astore_1
Reason:
Type 'java/lang/Object' (constant pool 17) is not assignable to 'java/lang/Throwable'
Bytecode:
0000000: 120d 4ba7 000a 4c12 0f4b a700 032a b0
Exception Handler Table:
bci [0, 3] => handler: 6
Stackmap Table:
same_locals_1_stack_item_frame(@6,Object[#17])
append_frame(@13,Object[#21])
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.
