Basic implementation of document formatting

Still some important TODOs to address:

- Improve the algorithm that converts between offsets and line/column
  pairs. Right now it's extremely naive.
- Add proper support for a .clang-format file that specifies
  the coding style.

src/clang_format.cc

@@ -0,0 +1,26 @@
+#include "clang_format.h"
+
+using namespace clang::format;
+using namespace clang::tooling;
+
+ClangFormat::ClangFormat(llvm::StringRef document_filename,
+                         llvm::StringRef document,
+                         llvm::ArrayRef<clang::tooling::Range> ranges,
+                         int tab_size,
+                         bool insert_spaces)
+    : document_filename_(document_filename),
+      document_(document),
+      ranges_(ranges),
+      tab_size_(tab_size),
+      insert_spaces_(insert_spaces) {}
+ClangFormat::~ClangFormat(){};
+
+std::vector<Replacement> ClangFormat::FormatWholeDocument() {
+  // TODO: Construct a valid style.
+  FormatStyle style = getChromiumStyle(FormatStyle::LK_Cpp);
+  style.UseTab = insert_spaces_ ? FormatStyle::UseTabStyle::UT_Never
+                                : FormatStyle::UseTabStyle::UT_Always;
+  style.IndentWidth = tab_size_;
+  auto format_result = reformat(style, document_, ranges_, document_filename_);
+  return std::vector<Replacement>(format_result.begin(), format_result.end());
+}

src/clang_format.h

@@ -0,0 +1,20 @@
+#include <clang/Format/Format.h>
+
+#include <vector>
+
+struct ClangFormat {
+  llvm::StringRef document_filename_;
+  llvm::StringRef document_;
+  llvm::ArrayRef<clang::tooling::Range> ranges_;
+  int tab_size_;
+  bool insert_spaces_;
+
+  ClangFormat(llvm::StringRef document_filename,
+              llvm::StringRef document,
+              llvm::ArrayRef<clang::tooling::Range> ranges,
+              int tab_size,
+              bool insert_spaces);
+  ~ClangFormat();
+
+  std::vector<clang::tooling::Replacement> FormatWholeDocument();
+};

src/clang_utils.cc

@@ -104,6 +104,28 @@ optional<lsDiagnostic> BuildAndDisposeDiagnostic(CXDiagnostic diagnostic,
   return ls_diagnostic;
 }
 
+static lsPosition OffsetToRange(llvm::StringRef document, size_t offset) {
+  // TODO: Support Windows line endings, etc.
+  llvm::StringRef text_before = document.substr(0, offset);
+  int num_line = text_before.count('\n');
+  int num_column = text_before.size() - text_before.rfind('\n') - 1;
+  return {num_line, num_column};
+}
+
+std::vector<lsTextEdit> ConvertClangReplacementsIntoTextEdits(
+    llvm::StringRef document,
+    const std::vector<clang::tooling::Replacement>& clang_replacements) {
+  std::vector<lsTextEdit> text_edits_result;
+  for (const auto& replacement : clang_replacements) {
+    const auto startPosition = OffsetToRange(document, replacement.getOffset());
+    const auto endPosition = OffsetToRange(
+        document, replacement.getOffset() + replacement.getLength());
+    text_edits_result.push_back(
+        {{startPosition, endPosition}, replacement.getReplacementText()});
+  }
+  return text_edits_result;
+}
+
 std::string FileName(CXFile file) {
   CXString cx_name = clang_getFileName(file);
   std::string name = ToString(cx_name);

src/clang_utils.h

@@ -3,6 +3,7 @@
 #include "language_server_api.h"
 
 #include <clang-c/Index.h>
+#include <clang/Format/Format.h>
 #include <optional.h>
 
 #include <vector>
@@ -18,3 +19,8 @@ std::string FileName(CXFile file);
 std::string ToString(CXString cx_string);
 
 std::string ToString(CXCursorKind cursor_kind);
+
+// Converts Clang formatting replacement operations into LSP text edits.
+std::vector<lsTextEdit> ConvertClangReplacementsIntoTextEdits(
+     llvm::StringRef document,
+     const std::vector<clang::tooling::Replacement>& clang_replacements);

src/messages/text_document_formatting.cc

@@ -1,3 +1,4 @@
+#include "clang_format.h"
 #include "message_handler.h"
 
 namespace {
@@ -14,7 +15,38 @@ REGISTER_IPC_MESSAGE(Ipc_TextDocumentFormatting);
 struct Out_TextDocumentFormatting
     : public lsOutMessage<Out_TextDocumentFormatting> {
   lsRequestId id;
-  std::vector<lsTextEdit> edits;
+  std::vector<lsTextEdit> result;
 };
-MAKE_REFLECT_STRUCT(Out_TextDocumentFormatting, jsonrpc, id, edits);
+MAKE_REFLECT_STRUCT(Out_TextDocumentFormatting, jsonrpc, id, result);
+
+struct TextDocumentFormattingHandler
+    : BaseMessageHandler<Ipc_TextDocumentFormatting> {
+  void Run(Ipc_TextDocumentFormatting* request) override {
+    QueryFile* file;
+    if (!FindFileOrFail(db, project, request->id,
+                        request->params.textDocument.uri.GetPath(), &file)) {
+      return;
+    }
+
+    WorkingFile* working_file =
+        working_files->GetFileByFilename(file->def->path);
+
+    int tab_size = request->params.formattingOptions.tabSize;
+    bool insert_spaces = request->params.formattingOptions.insertSpaces;
+
+    Out_TextDocumentFormatting response;
+    response.id = request->id;
+
+    const auto clang_format = std::unique_ptr<ClangFormat>(new ClangFormat(
+        working_file->filename, working_file->buffer_content,
+        {clang::tooling::Range(0, working_file->buffer_content.size())},
+        tab_size, insert_spaces));
+    const auto replacements = clang_format->FormatWholeDocument();
+    response.result = ConvertClangReplacementsIntoTextEdits(
+        working_file->buffer_content, replacements);
+
+    QueueManager::WriteStdout(IpcId::TextDocumentFormatting, response);
+  }
+};
+REGISTER_MESSAGE_HANDLER(TextDocumentFormattingHandler);
 }  // namespace

wscript

@@ -234,6 +234,16 @@ def build(bld):
     cc_files += bld.path.ant_glob(['src/clang_cxx/*.cc'])
 
   lib = []
+  # clang-format support
+  lib.append('clangBasic')
+  lib.append('clangFormat')
+  lib.append('clangLex')
+  lib.append('clangRewrite')
+  lib.append('clangToolingCore')
+  lib.append('LLVMCore')
+  lib.append('LLVMDemangle')
+  lib.append('LLVMSupport')
+  lib.append('ncurses')
   if sys.platform.startswith('linux'):
     lib.append('rt')
     lib.append('pthread')