lein uberjar results in "Method code too large!"

Question

I have a clojure project that runs fine using lein run, but lein uberjar results in

java.lang.RuntimeException: Method code too large!, compiling:(some_file.clj:1:1)

for the same project. I could trace it down to some_file.clj using a large vector of more than 2000 entries that is defined something like this:

(def x
  [[1 :qwre :asdf]
   [2 :zxcv :fafa]
   ...
])

When removing enough entries from that vector, lein uberjar compiles without issues. How can I make uberjar do its job, leaving all entries in the vector?

N.B. When changing x to a constant a la (def ^:const x, lein run will also throw a Method too large! error. And btw, that error occurs in the place where x is used, so just defining the constant is fine, if it is not being used.

Answer 1

There is a 64kb limit on the size of the method in Java. It seems that in your case the method that creates the big vector literal exceeds this limit.

Actually, you can check it by yourself, using a fancy library called clj-java-decompiler. Here's a short example using boot:

(set-env!
 :dependencies '[[com.clojure-goes-fast/clj-java-decompiler "0.1.0"]])

(require '[clj-java-decompiler.core :as d])

(d/decompile-form
 {}
 [[1 :qwre :asdf]
  [2 :zxcv :fafa]
  [3 :zxcv :fafa]])

;; ==> prints:
;;
;; // Decompiling class: cjd__init
;; import clojure.lang.*;
;; 
;; public class cjd__init
;; {
;;  public static final AFn const__10;
;;  
;;  public static void load() {
;;                             const__10;
;;                             }
;;  
;;  public static void __init0() {
;;                                const__10 = (AFn)Tuple.create((Object)Tuple.create((Object)1L, (Object)RT.keyword((String)null, "qwre"), (Object)RT.keyword((String)null, "asdf")), (Object)Tuple.create((Object)2L, (Object)RT.keyword((String)null, "zxcv"), (Object)RT.keyword((String)null, "fafa")), (Object)Tuple.create((Object)3L, (Object)RT.keyword((String)null, "zxcv"), (Object)RT.keyword((String)null, "fafa")));
;;                                }
;;  
;;  static {
;;          __init0();
;;          Compiler.pushNSandLoader(RT.classForName("cjd__init").getClassLoader());
;;          try {
;;               load();
;;               Var.popThreadBindings();
;;               }
;;          finally {
;;                   Var.popThreadBindings();
;;                   }
;;          }
;;  }
;; 

As you can see, there's a method __init0 that creates the actual Java object for the vector literal. Given enough elements in the vector, size of the method can easily exceed the 64kb limit.

I think, in your case, the easiest solution to this problem will be to put your vector to the file and then slurp+read this file. Something, like this:

file vector.edn:

[[1 :qwre :asdf]
 [2 :zxcv :fafa]
 ...
 ]

and then in your code:

(def x (clojure.edn/read-string (slurp "vector.edn"))