[clangd] clangd-indexer: Drop support for MR-via-YAML

[sammccall]

Summary

It's slow, and the open-source reduce implementation doesn't scale properly.
While here, tidy up some dead headers and comments.

[sammccall]

This was previously in D52465, but I reduced the scope of that patch to make it easier to land.

[sammccall]

Remove unused function.

[kadircet]

LGTM

clangd/indexer/IndexerMain.cpp

 //===--- IndexerMain.cpp -----------------------------------------*- C++-*-===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 //
 // GlobalSymbolBuilder is a tool to extract symbols from a whole project.
 // This tool is **experimental** only. Don't use it in production code.
 //
 //===----------------------------------------------------------------------===//
 
-#include "RIFF.h"
-#include "index/CanonicalIncludes.h"
 #include "index/Index.h"
 #include "index/IndexAction.h"
 #include "index/Merge.h"
 #include "index/Serialization.h"
 #include "index/SymbolCollector.h"
-#include "clang/Frontend/CompilerInstance.h"
-#include "clang/Frontend/FrontendActions.h"
-#include "clang/Index/IndexDataConsumer.h"
-#include "clang/Index/IndexingAction.h"
 #include "clang/Tooling/CommonOptionsParser.h"
 #include "clang/Tooling/Execution.h"
 #include "clang/Tooling/Tooling.h"
 #include "llvm/Support/CommandLine.h"
-#include "llvm/Support/MemoryBuffer.h"
 #include "llvm/Support/Path.h"
 #include "llvm/Support/Signals.h"
-#include "llvm/Support/ThreadPool.h"
-#include "llvm/Support/YAMLTraits.h"
 
 using namespace llvm;
 using namespace clang::tooling;
 using clang::clangd::SymbolSlab;
 
 namespace clang {
 namespace clangd {
 namespace {
 
 static llvm::cl::opt<std::string> AssumedHeaderDir(
     "assume-header-dir",
     llvm::cl::desc("The index includes header that a symbol is defined in. "
                    "If the absolute path cannot be determined (e.g. an "
                    "in-memory VFS) then the relative path is resolved against "
                    "this directory, which must be absolute. If this flag is "
                    "not given, such headers will have relative paths."),
     llvm::cl::init(""));
 
-static llvm::cl::opt<bool> MergeOnTheFly(
-    "merge-on-the-fly",
-    llvm::cl::desc(
-        "Merges symbols for each processed translation unit as soon "
-        "they become available. This results in a smaller memory "
-        "usage and an almost instant reduce stage. Optimal for running as a "
-        "standalone tool, but cannot be used with multi-process executors like "
-        "MapReduce."),
-    llvm::cl::init(true), llvm::cl::Hidden);
-
 static llvm::cl::opt<IndexFileFormat>
     Format("format", llvm::cl::desc("Format of the index to be written"),
            llvm::cl::values(clEnumValN(IndexFileFormat::YAML, "yaml",
                                        "human-readable YAML format"),
                             clEnumValN(IndexFileFormat::RIFF, "binary",
                                        "binary RIFF format")),
            llvm::cl::init(IndexFileFormat::YAML));
 
-/// Responsible for aggregating symbols from each processed file and producing
-/// the final results. All methods in this class must be thread-safe,
-/// 'consumeSymbols' may be called from multiple threads.
-class SymbolsConsumer {
+class IndexActionFactory : public tooling::FrontendActionFactory {
 public:
-  virtual ~SymbolsConsumer() = default;
-
-  /// Consume a SymbolSlab build for a file.
-  virtual void consumeSymbols(SymbolSlab Symbols) = 0;
-  /// Produce a resulting symbol slab, by combining  occurrences of the same
-  /// symbols across translation units.
-  virtual SymbolSlab mergeResults() = 0;
-};
-
-class SymbolIndexActionFactory : public tooling::FrontendActionFactory {
-public:
-  SymbolIndexActionFactory(SymbolsConsumer &Consumer) : Consumer(Consumer) {}
+  IndexActionFactory(IndexFileIn &Result) : Result(Result) {}
 
   clang::FrontendAction *create() override {
-    auto CollectorOpts = SymbolCollector::Options();
-    CollectorOpts.FallbackDir = AssumedHeaderDir;
+    SymbolCollector::Options Opts;
+    Opts.FallbackDir = AssumedHeaderDir;
     return createStaticIndexingAction(
-               CollectorOpts,
-               [&](SymbolSlab S) { Consumer.consumeSymbols(std::move(S)); })
-        .release();
-  }
-
-  SymbolsConsumer &Consumer;
-};
-
-/// Stashes per-file results inside ExecutionContext, merges all of them at the
-/// end. Useful for running on MapReduce infrastructure to avoid keeping symbols
-/// from multiple files in memory.
-class ToolExecutorConsumer : public SymbolsConsumer {
-public:
-  ToolExecutorConsumer(ToolExecutor &Executor) : Executor(Executor) {}
-
-  void consumeSymbols(SymbolSlab Symbols) override {
-    for (const auto &Sym : Symbols)
-      Executor.getExecutionContext()->reportResult(Sym.ID.str(), toYAML(Sym));
-  }
-
-  SymbolSlab mergeResults() override {
-    SymbolSlab::Builder UniqueSymbols;
-    Executor.getToolResults()->forEachResult(
-        [&](llvm::StringRef Key, llvm::StringRef Value) {
-          llvm::yaml::Input Yin(Value);
-          auto Sym = cantFail(clang::clangd::symbolFromYAML(Yin));
-          auto ID = cantFail(clang::clangd::SymbolID::fromStr(Key));
-          if (const auto *Existing = UniqueSymbols.find(ID))
-            UniqueSymbols.insert(mergeSymbol(*Existing, Sym));
-          else
-            UniqueSymbols.insert(Sym);
-        });
-    return std::move(UniqueSymbols).build();
-  }
-
-private:
-  ToolExecutor &Executor;
-};
-
-/// Merges symbols for each translation unit as soon as the file is processed.
-/// Optimal choice for standalone tools.
-class OnTheFlyConsumer : public SymbolsConsumer {
-public:
-  void consumeSymbols(SymbolSlab Symbols) override {
-    std::lock_guard<std::mutex> Lock(Mut);
-    for (auto &&Sym : Symbols) {
-      if (const auto *Existing = Result.find(Sym.ID))
-        Result.insert(mergeSymbol(*Existing, Sym));
+               Opts,
+               [&](SymbolSlab S) {
+                 // Merge as we go.
+                 std::lock_guard<std::mutex> Lock(SymbolsMu);
+                 for (const auto &Sym : S) {
+                   if (const auto *Existing = Symbols.find(Sym.ID))
+                     Symbols.insert(mergeSymbol(*Existing, Sym));
                    else
-        Result.insert(Sym);
+                     Symbols.insert(Sym);
                  }
+               })
+        .release();
   }
 
-  SymbolSlab mergeResults() override {
-    std::lock_guard<std::mutex> Lock(Mut);
-    return std::move(Result).build();
-  }
+  // Awkward: we write the result in the destructor, because the executor
+  // takes ownership so it's the easiest way to get our data back out.
+  ~IndexActionFactory() { Result.Symbols = std::move(Symbols).build(); }
 
 private:
-  std::mutex Mut;
-  SymbolSlab::Builder Result;
+  IndexFileIn &Result;
+  std::mutex SymbolsMu;
+  SymbolSlab::Builder Symbols;
 };
 
 } // namespace
 } // namespace clangd
 } // namespace clang
 
 int main(int argc, const char **argv) {
   llvm::sys::PrintStackTraceOnErrorSignal(argv[0]);
 
   const char *Overview = R"(
-  This is an **experimental** tool to extract symbols from a whole project
-  for clangd (global code completion). It will be changed and deprecated
-  eventually. Don't use it in production code!
+  Creates an index of symbol information etc in a whole project.
+  This is **experimental** and not production-ready!
 
-  Example usage for building index for the whole project using CMake compile
-  commands:
+  Example usage for a project using CMake compile commands:
 
   $ clangd-indexer --executor=all-TUs compile_commands.json > index.yaml
 
   Example usage for file sequence index without flags:
 
   $ clangd-indexer File1.cpp File2.cpp ... FileN.cpp > index.yaml
 
-  Note: only symbols from header files will be collected.
+  Note: only symbols from header files will be indexed.
   )";
 
   auto Executor = clang::tooling::createExecutorFromCommandLineArgs(
       argc, argv, cl::GeneralCategory, Overview);
 
   if (!Executor) {
     llvm::errs() << llvm::toString(Executor.takeError()) << "\n";
     return 1;
   }
 
   if (!clang::clangd::AssumedHeaderDir.empty() &&
       !llvm::sys::path::is_absolute(clang::clangd::AssumedHeaderDir)) {
     llvm::errs() << "--assume-header-dir must be an absolute path.\n";
     return 1;
   }
 
-  if (clang::clangd::MergeOnTheFly && !Executor->get()->isSingleProcess()) {
-    llvm::errs()
-        << "Found multi-process executor, forcing the use of intermediate YAML "
-           "serialization instead of the on-the-fly merge.\n";
-    clang::clangd::MergeOnTheFly = false;
-  }
-
-  std::unique_ptr<clang::clangd::SymbolsConsumer> Consumer;
-  if (clang::clangd::MergeOnTheFly)
-    Consumer = llvm::make_unique<clang::clangd::OnTheFlyConsumer>();
-  else
-    Consumer =
-        llvm::make_unique<clang::clangd::ToolExecutorConsumer>(**Executor);
-
-  // Map phase: emit symbols found in each translation unit.
+  // Collect symbols found in each translation unit, merging as we go.
+  clang::clangd::IndexFileIn Data;
   auto Err = Executor->get()->execute(
-      llvm::make_unique<clang::clangd::SymbolIndexActionFactory>(*Consumer));
+      llvm::make_unique<clang::clangd::IndexActionFactory>(Data));
   if (Err) {
     llvm::errs() << llvm::toString(std::move(Err)) << "\n";
   }
-  // Reduce phase: combine symbols with the same IDs.
-  auto UniqueSymbols = Consumer->mergeResults();
-  // Output phase: emit result symbols.
-  clang::clangd::IndexFileOut Out;
-  Out.Symbols = &UniqueSymbols;
+
+  // Emit collected data.
+  clang::clangd::IndexFileOut Out(Data);
   Out.Format = clang::clangd::Format;
   llvm::outs() << Out;
   return 0;
 }