Installation already appears to support a couple modes:

• ESBUILD_BIN_PATH_FOR_TESTS which symlinks an esbuild binary into node_modules
• installBinaryFromPackage which either installs from a local cache or downloads the binary from npm (directly or via npm)

However, this doesn't match our needs exactly. In particular, we run yarn install in --offline mode inside a micro VM without network access. Thus, we need a way to tell the esbuild installer about a binary that we've already downloaded. Since we need the node_modules to be standalone, ESBUILD_BIN_PATH_FOR_TESTS doesn't work since it creates a symlink.

We handle a similar issue with node-sass by using npm_config_sass_binary_cache. However, the local caching logic in esbuild is a little more involved and I'm loathe to attempt replicating it our end (especially since we support both darwin and linux -- see the hack mentioned later).

So, there are two potential solutions:

• Support ESBUILD_CACHE_PATH which overrides the cache directly
• Support ESBUILD_BIN_PATH which acts just like ESBUILD_BIN_PATH_FOR_TESTS but copies the file instead

I decided on the latter since that resolves the problem directly (although I do need to test this change with our build system... opening the PR early to see if there's any appetite for this tweak).

For completeness, my current hack is:

mkdir -p ~/.cache/esbuild/bin/
cp external/esbuild/bin/esbuild ~/.cache/esbuild/bin/[email protected]

(within the yarn install Bazel action)