Problem

Using clojure.core/proxy to generate proxies for Java classes produces unpredictable method ordering in the generated class files.
This is a problem for repeatable builds (when doing AOT).

Context

Specifically, I'm running Clojure inside Docker, and I'd like my application image layer to be as small as those produced by Java developers (using Meta-inf classpaths and a lib directory). Anyway, to get this working properly so that all dependencies (including those compiled as part of AOT) are on a separate layer, I need the output of compiling my applications' dependencies' proxies to be the same each time I run the build. This reduces build time, image push time, image pull time and container scheduling time.

Some linux maintainers have also noted this (and other) compilation cases that can cause different class file output in their quest to make reproducible builds.

Example code that exhibits the problem (you'll need to run it a few times to see the issue).

https://github.com/kipz/predictable-proxies

Cause: In proxies, unsorted maps of methods are used in several places that affect the bytecode order of the emitted proxy.

Approach: In all places during proxy generation where an unordered map keyed by method are used, instead use a map sorted by a vector of method name, parameter type class names, and return type name.

Author: Ambrose Bonnaire-Sergeant

Patch: clj-1973-7.patch

Screened by: fogus