Update Dockerfile to work with 0.36 about semgrep-action

[mschwager]

From @mjambon:

the ocaml executables (semgrep-core and spacegrep) are compiled statically for linux but only "partially statically" for darwin i.e. only the libc is dynamically linked but the third-party libraries that we use are linked in statically.

I believe this means we can in fact simplify things by removing the PRECOMPILED_LOCATION, COPY --from=semgrep, and FROM ... AS semgrep from https://github.com/returntocorp/semgrep-action/blob/develop/Dockerfile.

cc @chmccreery who could do this with the v0.36.0 update, or we could do this separately.

[mschwager]

Looks like PRECOMPILED_LOCATION has been gone since semgrep/semgrep@4e97e83, which was included in the v0.31.0 release. Unless there's a specific reason for avoiding the binaries in the package I believe we simply remove the PRECOMPILED_LOCATION variable.

Is there a reason we were pulling the binaries from a separate Docker image rather than the Python package? If we can remove the PRECOMPILED_LOCATION I suspect we can remove the COPY --from=semgrep /usr/local/bin/semgrep-core /tmp/semgrep-core and FROM returntocorp/semgrep:0.35.0@sha256:... AS semgrep from the Dockerfile as well.

[underyx]

Is there a reason we were pulling the binaries from a separate Docker image rather than the Python package?

The python binaries don't work on alpine.

[mschwager]

Oh I see, it's because we're using Alpine. We could probably make our lives a lot easier by using python:3.7-slim instead of python:3.7-alpine. Regardless, I wonder how its continued with work without PRECOMPILED_LOCATION 🤷‍♂️

[chmccreery]

@mschwager let's do this separately. Let me know if you want to do it before this release, or if we can do it later this week.

[brendongo]

I think it's continued to work without PRECOMPILED_LOCATION because pipx install semgrep just works as expected comes with the spacegrep and semgrep binaries.

[mschwager]

Fixed by https://github.com/returntocorp/semgrep-action/pull/156.