feat: implement repo-mode (#290)

(cherry picked from commit 9073748)

Author: mafredri

README.md

@@ -388,5 +388,6 @@ On MacOS or Windows systems, we recommend either using a VM or the provided `.de
 | `--coder-agent-subsystem` | `CODER_AGENT_SUBSYSTEM` |  | Coder agent subsystems to report when forwarding logs. The envbuilder subsystem is always included. |
 | `--push-image` | `ENVBUILDER_PUSH_IMAGE` |  | Push the built image to a remote registry. This option forces a reproducible build. |
 | `--get-cached-image` | `ENVBUILDER_GET_CACHED_IMAGE` |  | Print the digest of the cached image, if available. Exits with an error if not found. |
+| `--remote-repo-build-mode` | `ENVBUILDER_REMOTE_REPO_BUILD_MODE` | `false` | Use the remote repository as the source of truth when building the image. Enabling this option ignores user changes to local files and they will not be reflected in the image. This can be used to improving cache utilization when multiple users are building working on the same repository. |
 | `--verbose` | `ENVBUILDER_VERBOSE` |  | Enable verbose logging. |
 <!--- END docsgen --->

constants/constants.go

@@ -28,4 +28,8 @@ var (
 	// to skip building when a container is restarting.
 	// e.g. docker stop -> docker start
 	MagicFile = filepath.Join(MagicDir, "built")
+
+	// MagicFile is the location of the build context when
+	// using remote build mode.
+	MagicRemoteRepoDir = filepath.Join(MagicDir, "repo")
 )