This folder contains cached wasm binaries for emscripten (C++ wasm compiler).

Caching these standard libraries saves significant amount of time for clean builds (1-3 min).

These cached libraries shouldn't change, unless we update the version of emscripten. Instructions for updating emsdk/emscripten are in build_defs/emscripten/repo.bzl.

To update the cache:

1. Delete everything in emscripten_cache/asmjs.
2. Update comment out the line that says rm -rf "$EM_CACHE" at the bottom of build_defs/emscripten/emsdk_wrapper.sh
3. Build a C++ wasm binary via bazel build.
4. Look at your bazel build output, and find a line that says something like (this will be cached in "/tmp/emscripten-cache-UcBjY7Unpg/is_vanilla.txt.
5. Copy everything from that tmp folder (e.g. /tmp/emscripten-cache-UcBjY7Unpg) into the emscripten_cache folder in your repo. Don't copy the is_vanilla.txt file.
6. Check in those new files, and revert the other changes.