preps for CESID

Summary:
# Context
We want to experiment on EdenFS using Meta's mature stack of data analysis and experimentation that is QE + Deltoid. To do this, we need an ID we can join against in data land so we can define a population unit. We're using the [CESID](https://fb.workplace.com/groups/301619822315138/permalink/528321876311597/) for this purpose, which uniquely identifies a dev server, sandcastle instance, ondemand, and laptop/PC.

# This Diff
Adding the new field and function that will be populated later in the stack

# Technical Details
This code leverages 2 things:
- The previously-introduced CESID getter API ported over with cxx.rs
- Conditional compilation to obscure away Meta-only logic from the OSS project (using a header file introduced in this stack)

Reviewed By: genevievehelsel

Differential Revision: D62343641

fbshipit-source-id: 2a70ee00c1a57204c83ffe0c8974dfc92fd3da67

eden/common/eden-config.h

@@ -0,0 +1,12 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+// This configuration file is used by the Buck build.
+
+#pragma once
+
+#define LOGGER_FB_SESSION_INFO 1

eden/common/telemetry/SessionInfo.cpp

@@ -6,9 +6,9 @@
  */
 
 #include "eden/common/telemetry/SessionInfo.h"
-
 #include <folly/Conv.h>
 #include <folly/Exception.h>
+#include "eden/common/eden-config.h"
 
 #if defined(__linux__) || defined(__APPLE__)
 #include <folly/portability/Unistd.h>
@@ -56,6 +56,7 @@ SessionInfo makeSessionInfo(
   env.os = getOperatingSystemName();
   env.osVersion = getOperatingSystemVersion();
   env.appVersion = std::move(appVersion);
+  env.crossEnvSessionId = getCrossEnvSessionId();
 #if defined(__APPLE__)
   env.systemArchitecture = getOperatingSystemArchitecture();
 #endif
@@ -113,6 +114,7 @@ std::string getHostname() {
 }
 
 std::optional<uint64_t> getCiInstanceId() {
+#if defined(LOGGER_FB_SESSION_INFO)
   auto str = std::getenv("SANDCASTLE_INSTANCE_ID");
   if (!str) {
     return std::nullopt;
@@ -123,6 +125,13 @@ std::optional<uint64_t> getCiInstanceId() {
   } catch (const folly::ConversionError&) {
     return std::nullopt;
   }
+#else
+  return std::nullopt;
+#endif
+}
+
+std::string getCrossEnvSessionId() {
+  return std::string();
 }
 
 } // namespace facebook::eden

eden/common/telemetry/SessionInfo.h

@@ -22,6 +22,7 @@ struct SessionInfo {
   std::string os;
   std::string osVersion;
   std::string appVersion;
+  std::string crossEnvSessionId;
 #ifdef __APPLE__
   std::string systemArchitecture;
 #endif
@@ -50,4 +51,11 @@ std::string getHostname();
  */
 std::optional<uint64_t> getCiInstanceId();
 
+/**
+ * Returns the Cross Environment Session Id, which uniquely identifies the host.
+ * This function returns an empty string if the Cross Environment Session Id is
+ * not unknown.
+ */
+std::string getCrossEnvSessionId();
+
 } // namespace facebook::eden