[llvm] [llvm]Add a simple Telemetry framework (PR #102323)

[Vy Nguyen via llvm-commits]

================
@@ -0,0 +1,136 @@
+//===- llvm/Telemetry/Telemetry.h - Telemetry -------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+///
+/// \file
+/// This file provides the basic framework for Telemetry
+///
+/// It comprises of three important structs/classes:
+///
+/// - Telemeter: The class responsible for collecting and forwarding
+///              telemery data.
+/// - TelemetryInfo: data courier
+/// - TelemetryConfig: this stores configurations on Telemeter.
+///
+/// Refer to its documentation at llvm/docs/Telemetry.rst for more details.
+//===---------------------------------------------------------------------===//
+
+#ifndef LLVM_TELEMETRY_TELEMETRY_H
+#define LLVM_TELEMETRY_TELEMETRY_H
+
+#include <chrono>
+#include <ctime>
+#include <memory>
+#include <optional>
+#include <string>
+
+#include "llvm/ADT/StringExtras.h"
+#include "llvm/ADT/StringRef.h"
+#include "llvm/Support/Error.h"
+#include "llvm/Support/JSON.h"
+
+namespace llvm {
+namespace telemetry {
+
+/// Configuration for the Telemeter class.
+/// This stores configurations from both users and vendors and is passed
+/// to the Telemeter upon construction. (Any changes to the config after
+/// the Telemeter's construction will not have effect on it).
+///
+/// This struct can be extended as needed to add additional configuration
+/// points specific to a vendor's implementation.
+struct Config {
+  // If true, telemetry will be enabled.
+  bool EnableTelemetry;
----------------
oontvoo wrote:

1. We can make `EnableTelemetry` a const variable.
2. I'm not sure I understand the issue here. In my mind, the functin's impl can read from the commandline variable if it wants.

Eg.:

```
// Upstream (ie., default) impl
std::unique_ptr<Config> llvm::telemetry::makeConfig() {
return std::Make_unique<Config>{/*EnableTelemetry*/false};
}

// In some tool specific sub-directory:
std::unique_ptr<Config> mytool::telemetry::makeConfig() {
  InputArgList args = ....;
  bool enableTelemetry =  args.getLastArgValue(OPT_EnableTelemetry);
  return std::make_unique<Config>{enableTelemetry);
}


```

https://github.com/llvm/llvm-project/pull/102323