#18163 Document using `file://` URLs for external tools Issue created by danxmoran Is your feature request related to a problem? Please describe. We see our CI jobs fail semi-frequently on errors downloading external tools (i.e.

shfmt

or the Python GRPC plugin). The jobs run in containers where we could pre-install all of the tools we use to avoid these errors, but at the moment Pants only supports either finding a pre-installed binary (via

BinaryPathRequest

) or downloading the binary (via

ExternalToolRequest

), and the tools that give us trouble are all set up as `ExternalToolRequest`s. Describe the solution you'd like It would be nice if subsystems extending

ExternalTool

generically supported a boolean setting to flip from downloading the tool to finding the pre-downloaded tool. EDIT: Or maybe instead of a boolean setting, an optional string setting for the binary name to look up on the

PATH

. Describe alternatives you've considered We've considered self-hosting an S3 bucket, sticking all our binaries in it, and configuring our `default_url_template`s to point at it - but it sounds like binaries.pantsbuild.org is already effectively doing that for some binaries, and we still see flakiness pulling from it 😢 pantsbuild/pants