// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
// Exceptions. See /LICENSE for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception

#ifndef CARBON_TOOLCHAIN_DRIVER_CLANG_RUNNER_H_
#define CARBON_TOOLCHAIN_DRIVER_CLANG_RUNNER_H_

#include <filesystem>
#include <optional>

#include "common/error.h"
#include "common/ostream.h"
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/IntrusiveRefCntPtr.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/Support/ThreadPool.h"
#include "llvm/Support/VirtualFileSystem.h"
#include "llvm/TargetParser/Triple.h"
#include "toolchain/driver/runtimes_cache.h"
#include "toolchain/driver/tool_runner_base.h"
#include "toolchain/install/install_paths.h"

namespace Carbon {

// Runs Clang in a similar fashion to invoking it with the provided arguments on
// the command line. We use a textual command line interface to allow easily
// incorporating custom command line flags from user invocations that we don't
// parse, but will pass transparently along to Clang itself.
//
// This class is thread safe, allowing multiple threads to share a single runner
// and concurrently invoke Clang.
//
// This doesn't literally use a subprocess to invoke Clang; it instead tries to
// directly use the Clang command line driver library. We also work to simplify
// how that driver operates and invoke it in an opinionated way to get the best
// behavior for our expected use cases in the Carbon driver:
//
// - Ensure thread-safe invocation of Clang to enable concurrent usage.
// - Minimize canonicalization of file names to try to preserve the paths as
//   users type them.
// - Minimize the use of subprocess invocations which are expensive on some
//   operating systems. To the extent possible, we try to directly invoke the
//   Clang logic within this process.
// - Provide programmatic API to control defaults of Clang. For example, causing
//   verbose output.
//
// Note that this makes the current process behave like running Clang -- it uses
// standard output and standard error, and otherwise can only read and write
// files based on their names described in the arguments. It doesn't provide any
// higher-level abstraction such as streams for inputs or outputs.
//
// TODO: Switch the diagnostic machinery to buffer and do locked output so that
// concurrent invocations of Clang don't intermingle their diagnostic output.
//
// TODO: If support for thread-local overrides of `llvm::errs` and `llvm::outs`
// becomes available upstream, also buffer and synchronize those streams to
// further improve the behavior of concurrent invocations.
class ClangRunner : ToolRunnerBase {
 public:
  // Build a Clang runner that uses the provided installation and filesystem.
  //
  // Optionally accepts a `vlog_stream` to enable verbose logging from Carbon to
  // that stream. The verbose output from Clang goes to stderr regardless.
  ClangRunner(const InstallPaths* install_paths,
              llvm::IntrusiveRefCntPtr<llvm::vfs::FileSystem> fs,
              llvm::raw_ostream* vlog_stream = nullptr);

  // Run Clang with the provided arguments and a runtime cache for on-demand
  // runtime building.
  //
  // This works to support all of the Clang commandline, including commands that
  // use target-dependent resources like linking. When it detects such commands,
  // it will use runtimes from the provided cache. If not available in the
  // cache, it will build the necessary runtimes using the provided thread pool
  // both to use and incorporate into the cache.
  //
  // Returns an error only if unable to successfully run Clang with the
  // arguments. If able to run Clang, no error is returned a bool indicating
  // whether than Clang invocation succeeded is returned.
  auto Run(llvm::ArrayRef<llvm::StringRef> args,
           Runtimes::Cache& runtimes_cache,
           llvm::ThreadPoolInterface& runtimes_build_thread_pool,
           bool enable_leaking = false) -> ErrorOr<bool>;

  // Run Clang with the provided arguments and prebuilt runtimes.
  //
  // Similar to `Run`, but requires and uses pre-built runtimes rather than a
  // cache or building them on demand.
  auto RunWithPrebuiltRuntimes(llvm::ArrayRef<llvm::StringRef> args,
                               Runtimes& prebuilt_runtimes,
                               bool enable_leaking = false) -> ErrorOr<bool>;

  // Run Clang with the provided arguments and without any target runtimes.
  //
  // This method can be used to avoid building target-dependent resources when
  // unnecessary, but not all Clang command lines will work correctly.
  // Specifically, compile-only commands will typically work, while linking will
  // not.
  //
  // This function simply returns true or false depending on whether Clang runs
  // successfully, as it should display any needed error messages.
  auto RunWithNoRuntimes(llvm::ArrayRef<llvm::StringRef> args,
                         bool enable_leaking = false) -> bool;

 private:
  friend class ClangRuntimesBuilderBase;

  // Handles building the Clang driver and passing the arguments down to it.
  auto RunInternal(llvm::ArrayRef<llvm::StringRef> args, llvm::StringRef target,
                   std::optional<llvm::StringRef> target_resource_dir_path,
                   bool enable_leaking) -> bool;

  // Returns the target-specific source files for the builtins runtime library.
  auto CollectBuiltinsSrcFiles(const llvm::Triple& target_triple)
      -> llvm::SmallVector<llvm::StringRef>;

  // Builds the builtins runtime library into the provided archive file path,
  // using the provided objects path for intermediate object files.
  auto BuildBuiltinsLib(llvm::StringRef target,
                        const llvm::Triple& target_triple,
                        const std::filesystem::path& runtimes_path,
                        llvm::ThreadPoolTaskGroup& threads) -> ErrorOr<Success>;

  llvm::IntrusiveRefCntPtr<llvm::vfs::FileSystem> fs_;
};

}  // namespace Carbon

#endif  // CARBON_TOOLCHAIN_DRIVER_CLANG_RUNNER_H_
