[clangd] Split CodeComplete into a separate file. NFC

Summary: Shared details of ClangdUnit and CodeComplete moved to a new Compiler file.

Reviewers: ilya-biryukov

Subscribers: klimek, mgorny, cfe-commits

Differential Revision: https://reviews.llvm.org/D40719

llvm-svn: 319655

1 files changed, 706 insertions, 0 deletions

diff --git a/clang-tools-extra/clangd/CodeComplete.cpp b/clang-tools-extra/clangd/CodeComplete.cpp
new file mode 100644
index 00000000000..04c2795a14e
--- /dev/null
+++ b/clang-tools-extra/clangd/CodeComplete.cpp
@@ -0,0 +1,706 @@
+//===--- CodeComplete.cpp ---------------------------------------*- C++-*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===---------------------------------------------------------------------===//
+//
+// AST-based completions are provided using the completion hooks in Sema.
+//
+// Signature help works in a similar way as code completion, but it is simpler
+// as there are typically fewer candidates.
+//
+//===---------------------------------------------------------------------===//
+
+#include "CodeComplete.h"
+#include "Compiler.h"
+#include "clang/Frontend/CompilerInstance.h"
+#include "clang/Frontend/FrontendActions.h"
+#include "clang/Sema/CodeCompleteConsumer.h"
+#include "clang/Sema/Sema.h"
+#include <queue>
+
+namespace clang {
+namespace clangd {
+namespace {
+
+CompletionItemKind getKindOfDecl(CXCursorKind CursorKind) {
+  switch (CursorKind) {
+  case CXCursor_MacroInstantiation:
+  case CXCursor_MacroDefinition:
+    return CompletionItemKind::Text;
+  case CXCursor_CXXMethod:
+    return CompletionItemKind::Method;
+  case CXCursor_FunctionDecl:
+  case CXCursor_FunctionTemplate:
+    return CompletionItemKind::Function;
+  case CXCursor_Constructor:
+  case CXCursor_Destructor:
+    return CompletionItemKind::Constructor;
+  case CXCursor_FieldDecl:
+    return CompletionItemKind::Field;
+  case CXCursor_VarDecl:
+  case CXCursor_ParmDecl:
+    return CompletionItemKind::Variable;
+  case CXCursor_ClassDecl:
+  case CXCursor_StructDecl:
+  case CXCursor_UnionDecl:
+  case CXCursor_ClassTemplate:
+  case CXCursor_ClassTemplatePartialSpecialization:
+    return CompletionItemKind::Class;
+  case CXCursor_Namespace:
+  case CXCursor_NamespaceAlias:
+  case CXCursor_NamespaceRef:
+    return CompletionItemKind::Module;
+  case CXCursor_EnumConstantDecl:
+    return CompletionItemKind::Value;
+  case CXCursor_EnumDecl:
+    return CompletionItemKind::Enum;
+  case CXCursor_TypeAliasDecl:
+  case CXCursor_TypeAliasTemplateDecl:
+  case CXCursor_TypedefDecl:
+  case CXCursor_MemberRef:
+  case CXCursor_TypeRef:
+    return CompletionItemKind::Reference;
+  default:
+    return CompletionItemKind::Missing;
+  }
+}
+
+CompletionItemKind getKind(CodeCompletionResult::ResultKind ResKind,
+                           CXCursorKind CursorKind) {
+  switch (ResKind) {
+  case CodeCompletionResult::RK_Declaration:
+    return getKindOfDecl(CursorKind);
+  case CodeCompletionResult::RK_Keyword:
+    return CompletionItemKind::Keyword;
+  case CodeCompletionResult::RK_Macro:
+    return CompletionItemKind::Text; // unfortunately, there's no 'Macro'
+                                     // completion items in LSP.
+  case CodeCompletionResult::RK_Pattern:
+    return CompletionItemKind::Snippet;
+  }
+  llvm_unreachable("Unhandled CodeCompletionResult::ResultKind.");
+}
+
+std::string escapeSnippet(const llvm::StringRef Text) {
+  std::string Result;
+  Result.reserve(Text.size()); // Assume '$', '}' and '\\' are rare.
+  for (const auto Character : Text) {
+    if (Character == '$' || Character == '}' || Character == '\\')
+      Result.push_back('\\');
+    Result.push_back(Character);
+  }
+  return Result;
+}
+
+std::string getDocumentation(const CodeCompletionString &CCS) {
+  // Things like __attribute__((nonnull(1,3))) and [[noreturn]]. Present this
+  // information in the documentation field.
+  std::string Result;
+  const unsigned AnnotationCount = CCS.getAnnotationCount();
+  if (AnnotationCount > 0) {
+    Result += "Annotation";
+    if (AnnotationCount == 1) {
+      Result += ": ";
+    } else /* AnnotationCount > 1 */ {
+      Result += "s: ";
+    }
+    for (unsigned I = 0; I < AnnotationCount; ++I) {
+      Result += CCS.getAnnotation(I);
+      Result.push_back(I == AnnotationCount - 1 ? '\n' : ' ');
+    }
+  }
+  // Add brief documentation (if there is any).
+  if (CCS.getBriefComment() != nullptr) {
+    if (!Result.empty()) {
+      // This means we previously added annotations. Add an extra newline
+      // character to make the annotations stand out.
+      Result.push_back('\n');
+    }
+    Result += CCS.getBriefComment();
+  }
+  return Result;
+}
+
+/// Get the optional chunk as a string. This function is possibly recursive.
+///
+/// The parameter info for each parameter is appended to the Parameters.
+std::string
+getOptionalParameters(const CodeCompletionString &CCS,
+                      std::vector<ParameterInformation> &Parameters) {
+  std::string Result;
+  for (const auto &Chunk : CCS) {
+    switch (Chunk.Kind) {
+    case CodeCompletionString::CK_Optional:
+      assert(Chunk.Optional &&
+             "Expected the optional code completion string to be non-null.");
+      Result += getOptionalParameters(*Chunk.Optional, Parameters);
+      break;
+    case CodeCompletionString::CK_VerticalSpace:
+      break;
+    case CodeCompletionString::CK_Placeholder:
+      // A string that acts as a placeholder for, e.g., a function call
+      // argument.
+      // Intentional fallthrough here.
+    case CodeCompletionString::CK_CurrentParameter: {
+      // A piece of text that describes the parameter that corresponds to
+      // the code-completion location within a function call, message send,
+      // macro invocation, etc.
+      Result += Chunk.Text;
+      ParameterInformation Info;
+      Info.label = Chunk.Text;
+      Parameters.push_back(std::move(Info));
+      break;
+    }
+    default:
+      Result += Chunk.Text;
+      break;
+    }
+  }
+  return Result;
+}
+
+
+/// A scored code completion result.
+/// It may be promoted to a CompletionItem if it's among the top-ranked results.
+struct CompletionCandidate {
+  CompletionCandidate(CodeCompletionResult &Result)
+      : Result(&Result), Score(score(Result)) {}
+
+  CodeCompletionResult *Result;
+  float Score; // 0 to 1, higher is better.
+
+  // Comparison reflects rank: better candidates are smaller.
+  bool operator<(const CompletionCandidate &C) const {
+    if (Score != C.Score)
+      return Score > C.Score;
+    return *Result < *C.Result;
+  }
+
+  // Returns a string that sorts in the same order as operator<, for LSP.
+  // Conceptually, this is [-Score, Name]. We convert -Score to an integer, and
+  // hex-encode it for readability. Example: [0.5, "foo"] -> "41000000foo"
+  std::string sortText() const {
+    std::string S, NameStorage;
+    llvm::raw_string_ostream OS(S);
+    write_hex(OS, encodeFloat(-Score), llvm::HexPrintStyle::Lower,
+              /*Width=*/2 * sizeof(Score));
+    OS << Result->getOrderedName(NameStorage);
+    return OS.str();
+  }
+
+private:
+  static float score(const CodeCompletionResult &Result) {
+    // Priority 80 is a really bad score.
+    float Score = 1 - std::min<float>(80, Result.Priority) / 80;
+
+    switch (static_cast<CXAvailabilityKind>(Result.Availability)) {
+    case CXAvailability_Available:
+      // No penalty.
+      break;
+    case CXAvailability_Deprecated:
+      Score *= 0.1f;
+      break;
+    case CXAvailability_NotAccessible:
+    case CXAvailability_NotAvailable:
+      Score = 0;
+      break;
+    }
+    return Score;
+  }
+
+  // Produces an integer that sorts in the same order as F.
+  // That is: a < b <==> encodeFloat(a) < encodeFloat(b).
+  static uint32_t encodeFloat(float F) {
+    static_assert(std::numeric_limits<float>::is_iec559, "");
+    static_assert(sizeof(float) == sizeof(uint32_t), "");
+    constexpr uint32_t TopBit = ~(~uint32_t{0} >> 1);
+
+    // Get the bits of the float. Endianness is the same as for integers.
+    uint32_t U;
+    memcpy(&U, &F, sizeof(float));
+    // IEEE 754 floats compare like sign-magnitude integers.
+    if (U & TopBit)    // Negative float.
+      return 0 - U;    // Map onto the low half of integers, order reversed.
+    return U + TopBit; // Positive floats map onto the high half of integers.
+  }
+};
+
+class CompletionItemsCollector : public CodeCompleteConsumer {
+public:
+  CompletionItemsCollector(const CodeCompleteOptions &CodeCompleteOpts,
+                           CompletionList &Items)
+      : CodeCompleteConsumer(CodeCompleteOpts.getClangCompleteOpts(),
+                             /*OutputIsBinary=*/false),
+        ClangdOpts(CodeCompleteOpts), Items(Items),
+        Allocator(std::make_shared<clang::GlobalCodeCompletionAllocator>()),
+        CCTUInfo(Allocator) {}
+
+  void ProcessCodeCompleteResults(Sema &S, CodeCompletionContext Context,
+                                  CodeCompletionResult *Results,
+                                  unsigned NumResults) override final {
+    StringRef Filter = S.getPreprocessor().getCodeCompletionFilter();
+    std::priority_queue<CompletionCandidate> Candidates;
+    for (unsigned I = 0; I < NumResults; ++I) {
+      auto &Result = Results[I];
+      if (!ClangdOpts.IncludeIneligibleResults &&
+          (Result.Availability == CXAvailability_NotAvailable ||
+           Result.Availability == CXAvailability_NotAccessible))
+        continue;
+      if (!Filter.empty() && !fuzzyMatch(S, Context, Filter, Result))
+        continue;
+      Candidates.emplace(Result);
+      if (ClangdOpts.Limit && Candidates.size() > ClangdOpts.Limit) {
+        Candidates.pop();
+        Items.isIncomplete = true;
+      }
+    }
+    while (!Candidates.empty()) {
+      auto &Candidate = Candidates.top();
+      const auto *CCS = Candidate.Result->CreateCodeCompletionString(
+          S, Context, *Allocator, CCTUInfo,
+          CodeCompleteOpts.IncludeBriefComments);
+      assert(CCS && "Expected the CodeCompletionString to be non-null");
+      Items.items.push_back(ProcessCodeCompleteResult(Candidate, *CCS));
+      Candidates.pop();
+    }
+    std::reverse(Items.items.begin(), Items.items.end());
+  }
+
+  GlobalCodeCompletionAllocator &getAllocator() override { return *Allocator; }
+
+  CodeCompletionTUInfo &getCodeCompletionTUInfo() override { return CCTUInfo; }
+
+private:
+  bool fuzzyMatch(Sema &S, const CodeCompletionContext &CCCtx, StringRef Filter,
+                  CodeCompletionResult Result) {
+    switch (Result.Kind) {
+    case CodeCompletionResult::RK_Declaration:
+      if (auto *ID = Result.Declaration->getIdentifier())
+        return fuzzyMatch(Filter, ID->getName());
+      break;
+    case CodeCompletionResult::RK_Keyword:
+      return fuzzyMatch(Filter, Result.Keyword);
+    case CodeCompletionResult::RK_Macro:
+      return fuzzyMatch(Filter, Result.Macro->getName());
+    case CodeCompletionResult::RK_Pattern:
+      return fuzzyMatch(Filter, Result.Pattern->getTypedText());
+    }
+    auto *CCS = Result.CreateCodeCompletionString(
+        S, CCCtx, *Allocator, CCTUInfo, /*IncludeBriefComments=*/false);
+    return fuzzyMatch(Filter, CCS->getTypedText());
+  }
+
+  // Checks whether Target matches the Filter.
+  // Currently just requires a case-insensitive subsequence match.
+  // FIXME: make stricter and word-based: 'unique_ptr' should not match 'que'.
+  // FIXME: return a score to be incorporated into ranking.
+  static bool fuzzyMatch(StringRef Filter, StringRef Target) {
+    size_t TPos = 0;
+    for (char C : Filter) {
+      TPos = Target.find_lower(C, TPos);
+      if (TPos == StringRef::npos)
+        return false;
+    }
+    return true;
+  }
+
+  CompletionItem
+  ProcessCodeCompleteResult(const CompletionCandidate &Candidate,
+                            const CodeCompletionString &CCS) const {
+
+    // Adjust this to InsertTextFormat::Snippet iff we encounter a
+    // CK_Placeholder chunk in SnippetCompletionItemsCollector.
+    CompletionItem Item;
+    Item.insertTextFormat = InsertTextFormat::PlainText;
+
+    Item.documentation = getDocumentation(CCS);
+    Item.sortText = Candidate.sortText();
+
+    // Fill in the label, detail, insertText and filterText fields of the
+    // CompletionItem.
+    ProcessChunks(CCS, Item);
+
+    // Fill in the kind field of the CompletionItem.
+    Item.kind = getKind(Candidate.Result->Kind, Candidate.Result->CursorKind);
+
+    return Item;
+  }
+
+  virtual void ProcessChunks(const CodeCompletionString &CCS,
+                             CompletionItem &Item) const = 0;
+
+  CodeCompleteOptions ClangdOpts;
+  CompletionList &Items;
+  std::shared_ptr<clang::GlobalCodeCompletionAllocator> Allocator;
+  CodeCompletionTUInfo CCTUInfo;
+
+}; // CompletionItemsCollector
+
+bool isInformativeQualifierChunk(CodeCompletionString::Chunk const &Chunk) {
+  return Chunk.Kind == CodeCompletionString::CK_Informative &&
+         StringRef(Chunk.Text).endswith("::");
+}
+
+class PlainTextCompletionItemsCollector final
+    : public CompletionItemsCollector {
+
+public:
+  PlainTextCompletionItemsCollector(
+      const CodeCompleteOptions &CodeCompleteOpts,
+      CompletionList &Items)
+      : CompletionItemsCollector(CodeCompleteOpts, Items) {}
+
+private:
+  void ProcessChunks(const CodeCompletionString &CCS,
+                     CompletionItem &Item) const override {
+    for (const auto &Chunk : CCS) {
+      // Informative qualifier chunks only clutter completion results, skip
+      // them.
+      if (isInformativeQualifierChunk(Chunk))
+        continue;
+
+      switch (Chunk.Kind) {
+      case CodeCompletionString::CK_TypedText:
+        // There's always exactly one CK_TypedText chunk.
+        Item.insertText = Item.filterText = Chunk.Text;
+        Item.label += Chunk.Text;
+        break;
+      case CodeCompletionString::CK_ResultType:
+        assert(Item.detail.empty() && "Unexpected extraneous CK_ResultType");
+        Item.detail = Chunk.Text;
+        break;
+      case CodeCompletionString::CK_Optional:
+        break;
+      default:
+        Item.label += Chunk.Text;
+        break;
+      }
+    }
+  }
+}; // PlainTextCompletionItemsCollector
+
+class SnippetCompletionItemsCollector final : public CompletionItemsCollector {
+
+public:
+  SnippetCompletionItemsCollector(
+      const CodeCompleteOptions &CodeCompleteOpts,
+      CompletionList &Items)
+      : CompletionItemsCollector(CodeCompleteOpts, Items) {}
+
+private:
+  void ProcessChunks(const CodeCompletionString &CCS,
+                     CompletionItem &Item) const override {
+    unsigned ArgCount = 0;
+    for (const auto &Chunk : CCS) {
+      // Informative qualifier chunks only clutter completion results, skip
+      // them.
+      if (isInformativeQualifierChunk(Chunk))
+        continue;
+
+      switch (Chunk.Kind) {
+      case CodeCompletionString::CK_TypedText:
+        // The piece of text that the user is expected to type to match
+        // the code-completion string, typically a keyword or the name of
+        // a declarator or macro.
+        Item.filterText = Chunk.Text;
+        LLVM_FALLTHROUGH;
+      case CodeCompletionString::CK_Text:
+        // A piece of text that should be placed in the buffer,
+        // e.g., parentheses or a comma in a function call.
+        Item.label += Chunk.Text;
+        Item.insertText += Chunk.Text;
+        break;
+      case CodeCompletionString::CK_Optional:
+        // A code completion string that is entirely optional.
+        // For example, an optional code completion string that
+        // describes the default arguments in a function call.
+
+        // FIXME: Maybe add an option to allow presenting the optional chunks?
+        break;
+      case CodeCompletionString::CK_Placeholder:
+        // A string that acts as a placeholder for, e.g., a function call
+        // argument.
+        ++ArgCount;
+        Item.insertText += "${" + std::to_string(ArgCount) + ':' +
+                           escapeSnippet(Chunk.Text) + '}';
+        Item.label += Chunk.Text;
+        Item.insertTextFormat = InsertTextFormat::Snippet;
+        break;
+      case CodeCompletionString::CK_Informative:
+        // A piece of text that describes something about the result
+        // but should not be inserted into the buffer.
+        // For example, the word "const" for a const method, or the name of
+        // the base class for methods that are part of the base class.
+        Item.label += Chunk.Text;
+        // Don't put the informative chunks in the insertText.
+        break;
+      case CodeCompletionString::CK_ResultType:
+        // A piece of text that describes the type of an entity or,
+        // for functions and methods, the return type.
+        assert(Item.detail.empty() && "Unexpected extraneous CK_ResultType");
+        Item.detail = Chunk.Text;
+        break;
+      case CodeCompletionString::CK_CurrentParameter:
+        // A piece of text that describes the parameter that corresponds to
+        // the code-completion location within a function call, message send,
+        // macro invocation, etc.
+        //
+        // This should never be present while collecting completion items,
+        // only while collecting overload candidates.
+        llvm_unreachable("Unexpected CK_CurrentParameter while collecting "
+                         "CompletionItems");
+        break;
+      case CodeCompletionString::CK_LeftParen:
+        // A left parenthesis ('(').
+      case CodeCompletionString::CK_RightParen:
+        // A right parenthesis (')').
+      case CodeCompletionString::CK_LeftBracket:
+        // A left bracket ('[').
+      case CodeCompletionString::CK_RightBracket:
+        // A right bracket (']').
+      case CodeCompletionString::CK_LeftBrace:
+        // A left brace ('{').
+      case CodeCompletionString::CK_RightBrace:
+        // A right brace ('}').
+      case CodeCompletionString::CK_LeftAngle:
+        // A left angle bracket ('<').
+      case CodeCompletionString::CK_RightAngle:
+        // A right angle bracket ('>').
+      case CodeCompletionString::CK_Comma:
+        // A comma separator (',').
+      case CodeCompletionString::CK_Colon:
+        // A colon (':').
+      case CodeCompletionString::CK_SemiColon:
+        // A semicolon (';').
+      case CodeCompletionString::CK_Equal:
+        // An '=' sign.
+      case CodeCompletionString::CK_HorizontalSpace:
+        // Horizontal whitespace (' ').
+        Item.insertText += Chunk.Text;
+        Item.label += Chunk.Text;
+        break;
+      case CodeCompletionString::CK_VerticalSpace:
+        // Vertical whitespace ('\n' or '\r\n', depending on the
+        // platform).
+        Item.insertText += Chunk.Text;
+        // Don't even add a space to the label.
+        break;
+      }
+    }
+  }
+}; // SnippetCompletionItemsCollector
+
+class SignatureHelpCollector final : public CodeCompleteConsumer {
+
+public:
+  SignatureHelpCollector(const clang::CodeCompleteOptions &CodeCompleteOpts,
+                         SignatureHelp &SigHelp)
+      : CodeCompleteConsumer(CodeCompleteOpts, /*OutputIsBinary=*/false),
+        SigHelp(SigHelp),
+        Allocator(std::make_shared<clang::GlobalCodeCompletionAllocator>()),
+        CCTUInfo(Allocator) {}
+
+  void ProcessOverloadCandidates(Sema &S, unsigned CurrentArg,
+                                 OverloadCandidate *Candidates,
+                                 unsigned NumCandidates) override {
+    SigHelp.signatures.reserve(NumCandidates);
+    // FIXME(rwols): How can we determine the "active overload candidate"?
+    // Right now the overloaded candidates seem to be provided in a "best fit"
+    // order, so I'm not too worried about this.
+    SigHelp.activeSignature = 0;
+    assert(CurrentArg <= (unsigned)std::numeric_limits<int>::max() &&
+           "too many arguments");
+    SigHelp.activeParameter = static_cast<int>(CurrentArg);
+    for (unsigned I = 0; I < NumCandidates; ++I) {
+      const auto &Candidate = Candidates[I];
+      const auto *CCS = Candidate.CreateSignatureString(
+          CurrentArg, S, *Allocator, CCTUInfo, true);
+      assert(CCS && "Expected the CodeCompletionString to be non-null");
+      SigHelp.signatures.push_back(ProcessOverloadCandidate(Candidate, *CCS));
+    }
+  }
+
+  GlobalCodeCompletionAllocator &getAllocator() override { return *Allocator; }
+
+  CodeCompletionTUInfo &getCodeCompletionTUInfo() override { return CCTUInfo; }
+
+private:
+  SignatureInformation
+  ProcessOverloadCandidate(const OverloadCandidate &Candidate,
+                           const CodeCompletionString &CCS) const {
+    SignatureInformation Result;
+    const char *ReturnType = nullptr;
+
+    Result.documentation = getDocumentation(CCS);
+
+    for (const auto &Chunk : CCS) {
+      switch (Chunk.Kind) {
+      case CodeCompletionString::CK_ResultType:
+        // A piece of text that describes the type of an entity or,
+        // for functions and methods, the return type.
+        assert(!ReturnType && "Unexpected CK_ResultType");
+        ReturnType = Chunk.Text;
+        break;
+      case CodeCompletionString::CK_Placeholder:
+        // A string that acts as a placeholder for, e.g., a function call
+        // argument.
+        // Intentional fallthrough here.
+      case CodeCompletionString::CK_CurrentParameter: {
+        // A piece of text that describes the parameter that corresponds to
+        // the code-completion location within a function call, message send,
+        // macro invocation, etc.
+        Result.label += Chunk.Text;
+        ParameterInformation Info;
+        Info.label = Chunk.Text;
+        Result.parameters.push_back(std::move(Info));
+        break;
+      }
+      case CodeCompletionString::CK_Optional: {
+        // The rest of the parameters are defaulted/optional.
+        assert(Chunk.Optional &&
+               "Expected the optional code completion string to be non-null.");
+        Result.label +=
+            getOptionalParameters(*Chunk.Optional, Result.parameters);
+        break;
+      }
+      case CodeCompletionString::CK_VerticalSpace:
+        break;
+      default:
+        Result.label += Chunk.Text;
+        break;
+      }
+    }
+    if (ReturnType) {
+      Result.label += " -> ";
+      Result.label += ReturnType;
+    }
+    return Result;
+  }
+
+  SignatureHelp &SigHelp;
+  std::shared_ptr<clang::GlobalCodeCompletionAllocator> Allocator;
+  CodeCompletionTUInfo CCTUInfo;
+
+}; // SignatureHelpCollector
+
+bool invokeCodeComplete(std::unique_ptr<CodeCompleteConsumer> Consumer,
+                        const clang::CodeCompleteOptions &Options,
+                        PathRef FileName,
+                        const tooling::CompileCommand &Command,
+                        PrecompiledPreamble const *Preamble, StringRef Contents,
+                        Position Pos, IntrusiveRefCntPtr<vfs::FileSystem> VFS,
+                        std::shared_ptr<PCHContainerOperations> PCHs,
+                        Logger &Logger) {
+  std::vector<const char *> ArgStrs;
+  for (const auto &S : Command.CommandLine)
+    ArgStrs.push_back(S.c_str());
+
+  VFS->setCurrentWorkingDirectory(Command.Directory);
+
+  IgnoreDiagnostics DummyDiagsConsumer;
+  auto CI = createInvocationFromCommandLine(
+      ArgStrs,
+      CompilerInstance::createDiagnostics(new DiagnosticOptions,
+                                          &DummyDiagsConsumer, false),
+      VFS);
+  assert(CI && "Couldn't create CompilerInvocation");
+
+  std::unique_ptr<llvm::MemoryBuffer> ContentsBuffer =
+      llvm::MemoryBuffer::getMemBufferCopy(Contents, FileName);
+
+  // Attempt to reuse the PCH from precompiled preamble, if it was built.
+  if (Preamble) {
+    auto Bounds =
+        ComputePreambleBounds(*CI->getLangOpts(), ContentsBuffer.get(), 0);
+    if (!Preamble->CanReuse(*CI, ContentsBuffer.get(), Bounds, VFS.get()))
+      Preamble = nullptr;
+  }
+
+  auto Clang = prepareCompilerInstance(
+      std::move(CI), Preamble, std::move(ContentsBuffer), std::move(PCHs),
+      std::move(VFS), DummyDiagsConsumer);
+  auto &DiagOpts = Clang->getDiagnosticOpts();
+  DiagOpts.IgnoreWarnings = true;
+
+  auto &FrontendOpts = Clang->getFrontendOpts();
+  FrontendOpts.SkipFunctionBodies = true;
+  FrontendOpts.CodeCompleteOpts = Options;
+  FrontendOpts.CodeCompletionAt.FileName = FileName;
+  FrontendOpts.CodeCompletionAt.Line = Pos.line + 1;
+  FrontendOpts.CodeCompletionAt.Column = Pos.character + 1;
+
+  Clang->setCodeCompletionConsumer(Consumer.release());
+
+  SyntaxOnlyAction Action;
+  if (!Action.BeginSourceFile(*Clang, Clang->getFrontendOpts().Inputs[0])) {
+    Logger.log("BeginSourceFile() failed when running codeComplete for " +
+               FileName);
+    return false;
+  }
+  if (!Action.Execute()) {
+    Logger.log("Execute() failed when running codeComplete for " + FileName);
+    return false;
+  }
+
+  Action.EndSourceFile();
+
+  return true;
+}
+
+} // namespace
+
+clang::CodeCompleteOptions CodeCompleteOptions::getClangCompleteOpts() const {
+  clang::CodeCompleteOptions Result;
+  Result.IncludeCodePatterns = EnableSnippets && IncludeCodePatterns;
+  Result.IncludeMacros = IncludeMacros;
+  Result.IncludeGlobals = IncludeGlobals;
+  Result.IncludeBriefComments = IncludeBriefComments;
+
+  return Result;
+}
+
+CompletionList codeComplete(PathRef FileName,
+                            const tooling::CompileCommand &Command,
+                            PrecompiledPreamble const *Preamble,
+                            StringRef Contents, Position Pos,
+                            IntrusiveRefCntPtr<vfs::FileSystem> VFS,
+                            std::shared_ptr<PCHContainerOperations> PCHs,
+                            CodeCompleteOptions Opts, Logger &Logger) {
+  CompletionList Results;
+  std::unique_ptr<CodeCompleteConsumer> Consumer;
+  if (Opts.EnableSnippets) {
+    Consumer =
+        llvm::make_unique<SnippetCompletionItemsCollector>(Opts, Results);
+  } else {
+    Consumer =
+        llvm::make_unique<PlainTextCompletionItemsCollector>(Opts, Results);
+  }
+  invokeCodeComplete(std::move(Consumer), Opts.getClangCompleteOpts(), FileName,
+                     Command, Preamble, Contents, Pos, std::move(VFS),
+                     std::move(PCHs), Logger);
+  return Results;
+}
+
+SignatureHelp
+signatureHelp(PathRef FileName, const tooling::CompileCommand &Command,
+              PrecompiledPreamble const *Preamble, StringRef Contents,
+              Position Pos, IntrusiveRefCntPtr<vfs::FileSystem> VFS,
+              std::shared_ptr<PCHContainerOperations> PCHs, Logger &Logger) {
+  SignatureHelp Result;
+  clang::CodeCompleteOptions Options;
+  Options.IncludeGlobals = false;
+  Options.IncludeMacros = false;
+  Options.IncludeCodePatterns = false;
+  Options.IncludeBriefComments = true;
+  invokeCodeComplete(llvm::make_unique<SignatureHelpCollector>(Options, Result),
+                     Options, FileName, Command, Preamble, Contents, Pos,
+                     std::move(VFS), std::move(PCHs), Logger);
+  return Result;
+}
+
+} // namespace clangd
+} // namespace clang