Announce Buildbarn as supporting REv2.0 to REv2.3.

All of the features that have been added since that are dependent on a
given version number have been implemented:

- REv2.1: Command.output_paths instead of output_{files,directories}.
- REv2.2: Platform properties in the Action message.
- REv2.3: Resolving argv[0] relative to the working directory.
- REv2.3: Virtual execution duration.

Newer versions of Bazel now also support output_paths, but they will
only start to use it if the remote execution service announces the right
version number. This means we'd better get this correct going forward.

Details: bazelbuild/remote-apis#253

pkg/capabilities/server.go

@@ -33,13 +33,13 @@ func (s *server) GetCapabilities(ctx context.Context, in *remoteexecution.GetCap
 		return nil, err
 	}
 
-	// TODO: Set these version numbers properly; including
-	// DeprecatedApiVersion. Instead of setting these here, should
+	// TODO: Instead of setting these version numbers here, should
 	// we let providers set these and have MergingProvider merge
 	// those as well?
 	capabilitiesWithVersion := remoteexecution.ServerCapabilities{
-		LowApiVersion:  &semver.SemVer{Major: 2},
-		HighApiVersion: &semver.SemVer{Major: 2},
+		DeprecatedApiVersion: &semver.SemVer{Major: 2, Minor: 0},
+		LowApiVersion:        &semver.SemVer{Major: 2, Minor: 0},
+		HighApiVersion:       &semver.SemVer{Major: 2, Minor: 3},
 	}
 	proto.Merge(&capabilitiesWithVersion, capabilities)
 	return &capabilitiesWithVersion, nil

pkg/capabilities/server_test.go

@@ -60,8 +60,9 @@ func TestServer(t *testing.T) {
 				DigestFunctions: digest.SupportedDigestFunctions,
 				ExecEnabled:     true,
 			},
-			LowApiVersion:  &semver.SemVer{Major: 2},
-			HighApiVersion: &semver.SemVer{Major: 2},
+			DeprecatedApiVersion: &semver.SemVer{Major: 2, Minor: 0},
+			LowApiVersion:        &semver.SemVer{Major: 2, Minor: 0},
+			HighApiVersion:       &semver.SemVer{Major: 2, Minor: 3},
 		}, serverCapabilities)
 	})
 }