feat(tools/depot-scanner): init project

depot-scanner is a tool that runs Nix and parses the --trace-file-access output to deduce what files are necessary to evaluate a derivation.

Take DEPOT_ROOT from the environment. If depotRoot doesn't exist, print an error early.

Fix the build of the protobuf library. Switch to the GRPC build rule, as a service is in this proto file.

Create the PathType enum and parse it from cmdline flags.

Change-Id: I537b5c6bceecf76ca510f7ac04ab9dad7785feb1
Reviewed-on: https://cl.tvl.fyi/c/depot/+/1769
Tested-by: BuildkiteCI
Reviewed-by: tazjin <mail@tazj.in>
Reviewed-by: lukegb <lukegb@tvl.fyi>

nix/buildGo/default.nix

@@ -110,14 +110,14 @@ let
   };
 
   # Build a Go library out of the specified protobuf definition.
-  proto = { name, proto, path ? name, extraDeps ? [] }: (makeOverridable package) {
+  proto = { name, proto, path ? name, goPackage ? name, extraDeps ? [] }: (makeOverridable package) {
     inherit name path;
     deps = [ protoLibs.goProto.proto.gopkg ] ++ extraDeps;
     srcs = lib.singleton (runCommand "goproto-${name}.pb.go" {} ''
       cp ${proto} ${baseNameOf proto}
       ${protobuf}/bin/protoc --plugin=${protoLibs.goProto.protoc-gen-go.gopkg}/bin/protoc-gen-go \
         --go_out=plugins=grpc,import_path=${baseNameOf path}:. ${baseNameOf proto}
-      mv *.pb.go $out
+      mv ./${goPackage}/*.pb.go $out
     '');
   };