--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/clang-tools-extra/clangd/support/Markup.cpp	Mon May 25 11:55:54 2020 +0900
@@ -0,0 +1,504 @@
+//===--- Markup.cpp -----------------------------------------*- 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
+//
+//===----------------------------------------------------------------------===//
+#include "support/Markup.h"
+#include "llvm/ADT/ArrayRef.h"
+#include "llvm/ADT/STLExtras.h"
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/ADT/StringExtras.h"
+#include "llvm/ADT/StringRef.h"
+#include "llvm/Support/Compiler.h"
+#include "llvm/Support/ErrorHandling.h"
+#include "llvm/Support/FormatVariadic.h"
+#include "llvm/Support/raw_ostream.h"
+#include <cstddef>
+#include <iterator>
+#include <memory>
+#include <string>
+#include <vector>
+
+namespace clang {
+namespace clangd {
+namespace markup {
+namespace {
+
+// Is <contents a plausible start to an HTML tag?
+// Contents may not be the rest of the line, but it's the rest of the plain
+// text, so we expect to see at least the tag name.
+bool looksLikeTag(llvm::StringRef Contents) {
+  if (Contents.empty())
+    return false;
+  if (Contents.front() == '!' || Contents.front() == '?' ||
+      Contents.front() == '/')
+    return true;
+  // Check the start of the tag name.
+  if (!llvm::isAlpha(Contents.front()))
+    return false;
+  // Drop rest of the tag name, and following whitespace.
+  Contents = Contents
+                 .drop_while([](char C) {
+                   return llvm::isAlnum(C) || C == '-' || C == '_' || C == ':';
+                 })
+                 .drop_while(llvm::isSpace);
+  // The rest of the tag consists of attributes, which have restrictive names.
+  // If we hit '=', all bets are off (attribute values can contain anything).
+  for (; !Contents.empty(); Contents = Contents.drop_front()) {
+    if (llvm::isAlnum(Contents.front()) || llvm::isSpace(Contents.front()))
+      continue;
+    if (Contents.front() == '>' || Contents.startswith("/>"))
+      return true; // May close the tag.
+    if (Contents.front() == '=')
+      return true; // Don't try to parse attribute values.
+    return false;  // Random punctuation means this isn't a tag.
+  }
+  return true; // Potentially incomplete tag.
+}
+
+// Tests whether C should be backslash-escaped in markdown.
+// The string being escaped is Before + C + After. This is part of a paragraph.
+// StartsLine indicates whether `Before` is the start of the line.
+// After may not be everything until the end of the line.
+//
+// It's always safe to escape punctuation, but want minimal escaping.
+// The strategy is to escape the first character of anything that might start
+// a markdown grammar construct.
+bool needsLeadingEscape(char C, llvm::StringRef Before, llvm::StringRef After,
+                        bool StartsLine) {
+  assert(Before.take_while(llvm::isSpace).empty());
+  auto RulerLength = [&]() -> /*Length*/ unsigned {
+    if (!StartsLine || !Before.empty())
+      return false;
+    llvm::StringRef A = After.rtrim();
+    return llvm::all_of(A, [C](char D) { return C == D; }) ? 1 + A.size() : 0;
+  };
+  auto IsBullet = [&]() {
+    return StartsLine && Before.empty() &&
+           (After.empty() || After.startswith(" "));
+  };
+  auto SpaceSurrounds = [&]() {
+    return (After.empty() || llvm::isSpace(After.front())) &&
+           (Before.empty() || llvm::isSpace(Before.back()));
+  };
+  auto WordSurrounds = [&]() {
+    return (!After.empty() && llvm::isAlnum(After.front())) &&
+           (!Before.empty() && llvm::isAlnum(Before.back()));
+  };
+
+  switch (C) {
+  case '\\': // Escaped character.
+    return true;
+  case '`': // Code block or inline code
+    // Any number of backticks can delimit an inline code block that can end
+    // anywhere (including on another line). We must escape them all.
+    return true;
+  case '~': // Code block
+    return StartsLine && Before.empty() && After.startswith("~~");
+  case '#': { // ATX heading.
+    if (!StartsLine || !Before.empty())
+      return false;
+    llvm::StringRef Rest = After.ltrim(C);
+    return Rest.empty() || Rest.startswith(" ");
+  }
+  case ']': // Link or link reference.
+    // We escape ] rather than [ here, because it's more constrained:
+    //   ](...) is an in-line link
+    //   ]: is a link reference
+    // The following are only links if the link reference exists:
+    //   ] by itself is a shortcut link
+    //   ][...] is an out-of-line link
+    // Because we never emit link references, we don't need to handle these.
+    return After.startswith(":") || After.startswith("(");
+  case '=': // Setex heading.
+    return RulerLength() > 0;
+  case '_': // Horizontal ruler or matched delimiter.
+    if (RulerLength() >= 3)
+      return true;
+    // Not a delimiter if surrounded by space, or inside a word.
+    // (The rules at word boundaries are subtle).
+    return !(SpaceSurrounds() || WordSurrounds());
+  case '-': // Setex heading, horizontal ruler, or bullet.
+    if (RulerLength() > 0)
+      return true;
+    return IsBullet();
+  case '+': // Bullet list.
+    return IsBullet();
+  case '*': // Bullet list, horizontal ruler, or delimiter.
+    return IsBullet() || RulerLength() >= 3 || !SpaceSurrounds();
+  case '<': // HTML tag (or autolink, which we choose not to escape)
+    return looksLikeTag(After);
+  case '>': // Quote marker. Needs escaping at start of line.
+    return StartsLine && Before.empty();
+  case '&': { // HTML entity reference
+    auto End = After.find(';');
+    if (End == llvm::StringRef::npos)
+      return false;
+    llvm::StringRef Content = After.substr(0, End);
+    if (Content.consume_front("#")) {
+      if (Content.consume_front("x") || Content.consume_front("X"))
+        return llvm::all_of(Content, llvm::isHexDigit);
+      return llvm::all_of(Content, llvm::isDigit);
+    }
+    return llvm::all_of(Content, llvm::isAlpha);
+  }
+  case '.': // Numbered list indicator. Escape 12. -> 12\. at start of line.
+  case ')':
+    return StartsLine && !Before.empty() &&
+           llvm::all_of(Before, llvm::isDigit) && After.startswith(" ");
+  default:
+    return false;
+  }
+}
+
+/// Escape a markdown text block. Ensures the punctuation will not introduce
+/// any of the markdown constructs.
+std::string renderText(llvm::StringRef Input, bool StartsLine) {
+  std::string R;
+  for (unsigned I = 0; I < Input.size(); ++I) {
+    if (needsLeadingEscape(Input[I], Input.substr(0, I), Input.substr(I + 1),
+                           StartsLine))
+      R.push_back('\\');
+    R.push_back(Input[I]);
+  }
+  return R;
+}
+
+/// Renders \p Input as an inline block of code in markdown. The returned value
+/// is surrounded by backticks and the inner contents are properly escaped.
+std::string renderInlineBlock(llvm::StringRef Input) {
+  std::string R;
+  // Double all backticks to make sure we don't close the inline block early.
+  for (size_t From = 0; From < Input.size();) {
+    size_t Next = Input.find("`", From);
+    R += Input.substr(From, Next - From);
+    if (Next == llvm::StringRef::npos)
+      break;
+    R += "``"; // double the found backtick.
+
+    From = Next + 1;
+  }
+  // If results starts with a backtick, add spaces on both sides. The spaces
+  // are ignored by markdown renderers.
+  if (llvm::StringRef(R).startswith("`") || llvm::StringRef(R).endswith("`"))
+    return "` " + std::move(R) + " `";
+  // Markdown render should ignore first and last space if both are there. We
+  // add an extra pair of spaces in that case to make sure we render what the
+  // user intended.
+  if (llvm::StringRef(R).startswith(" ") && llvm::StringRef(R).endswith(" "))
+    return "` " + std::move(R) + " `";
+  return "`" + std::move(R) + "`";
+}
+
+/// Get marker required for \p Input to represent a markdown codeblock. It
+/// consists of at least 3 backticks(`). Although markdown also allows to use
+/// tilde(~) for code blocks, they are never used.
+std::string getMarkerForCodeBlock(llvm::StringRef Input) {
+  // Count the maximum number of consecutive backticks in \p Input. We need to
+  // start and end the code block with more.
+  unsigned MaxBackticks = 0;
+  unsigned Backticks = 0;
+  for (char C : Input) {
+    if (C == '`') {
+      ++Backticks;
+      continue;
+    }
+    MaxBackticks = std::max(MaxBackticks, Backticks);
+    Backticks = 0;
+  }
+  MaxBackticks = std::max(Backticks, MaxBackticks);
+  // Use the corresponding number of backticks to start and end a code block.
+  return std::string(/*Repeat=*/std::max(3u, MaxBackticks + 1), '`');
+}
+
+// Trims the input and concatenates whitespace blocks into a single ` `.
+std::string canonicalizeSpaces(llvm::StringRef Input) {
+  llvm::SmallVector<llvm::StringRef, 4> Words;
+  llvm::SplitString(Input, Words);
+  return llvm::join(Words, " ");
+}
+
+std::string renderBlocks(llvm::ArrayRef<std::unique_ptr<Block>> Children,
+                         void (Block::*RenderFunc)(llvm::raw_ostream &) const) {
+  std::string R;
+  llvm::raw_string_ostream OS(R);
+
+  // Trim rulers.
+  Children = Children.drop_while(
+      [](const std::unique_ptr<Block> &C) { return C->isRuler(); });
+  auto Last = llvm::find_if(
+      llvm::reverse(Children),
+      [](const std::unique_ptr<Block> &C) { return !C->isRuler(); });
+  Children = Children.drop_back(Children.end() - Last.base());
+
+  bool LastBlockWasRuler = true;
+  for (const auto &C : Children) {
+    if (C->isRuler() && LastBlockWasRuler)
+      continue;
+    LastBlockWasRuler = C->isRuler();
+    ((*C).*RenderFunc)(OS);
+  }
+
+  // Get rid of redundant empty lines introduced in plaintext while imitating
+  // padding in markdown.
+  std::string AdjustedResult;
+  llvm::StringRef TrimmedText(OS.str());
+  TrimmedText = TrimmedText.trim();
+
+  llvm::copy_if(TrimmedText, std::back_inserter(AdjustedResult),
+                [&TrimmedText](const char &C) {
+                  return !llvm::StringRef(TrimmedText.data(),
+                                          &C - TrimmedText.data() + 1)
+                              // We allow at most two newlines.
+                              .endswith("\n\n\n");
+                });
+
+  return AdjustedResult;
+}
+
+// Separates two blocks with extra spacing. Note that it might render strangely
+// in vscode if the trailing block is a codeblock, see
+// https://github.com/microsoft/vscode/issues/88416 for details.
+class Ruler : public Block {
+public:
+  void renderMarkdown(llvm::raw_ostream &OS) const override {
+    // Note that we need an extra new line before the ruler, otherwise we might
+    // make previous block a title instead of introducing a ruler.
+    OS << "\n---\n";
+  }
+  void renderPlainText(llvm::raw_ostream &OS) const override { OS << '\n'; }
+  std::unique_ptr<Block> clone() const override {
+    return std::make_unique<Ruler>(*this);
+  }
+  bool isRuler() const override { return true; }
+};
+
+class CodeBlock : public Block {
+public:
+  void renderMarkdown(llvm::raw_ostream &OS) const override {
+    std::string Marker = getMarkerForCodeBlock(Contents);
+    // No need to pad from previous blocks, as they should end with a new line.
+    OS << Marker << Language << '\n' << Contents << '\n' << Marker << '\n';
+  }
+
+  void renderPlainText(llvm::raw_ostream &OS) const override {
+    // In plaintext we want one empty line before and after codeblocks.
+    OS << '\n' << Contents << "\n\n";
+  }
+
+  std::unique_ptr<Block> clone() const override {
+    return std::make_unique<CodeBlock>(*this);
+  }
+
+  CodeBlock(std::string Contents, std::string Language)
+      : Contents(std::move(Contents)), Language(std::move(Language)) {}
+
+private:
+  std::string Contents;
+  std::string Language;
+};
+
+// Inserts two spaces after each `\n` to indent each line. First line is not
+// indented.
+std::string indentLines(llvm::StringRef Input) {
+  assert(!Input.endswith("\n") && "Input should've been trimmed.");
+  std::string IndentedR;
+  // We'll add 2 spaces after each new line.
+  IndentedR.reserve(Input.size() + Input.count('\n') * 2);
+  for (char C : Input) {
+    IndentedR += C;
+    if (C == '\n')
+      IndentedR.append("  ");
+  }
+  return IndentedR;
+}
+
+class Heading : public Paragraph {
+public:
+  Heading(size_t Level) : Level(Level) {}
+  void renderMarkdown(llvm::raw_ostream &OS) const override {
+    OS << std::string(Level, '#') << ' ';
+    Paragraph::renderMarkdown(OS);
+  }
+
+private:
+  size_t Level;
+};
+
+} // namespace
+
+std::string Block::asMarkdown() const {
+  std::string R;
+  llvm::raw_string_ostream OS(R);
+  renderMarkdown(OS);
+  return llvm::StringRef(OS.str()).trim().str();
+}
+
+std::string Block::asPlainText() const {
+  std::string R;
+  llvm::raw_string_ostream OS(R);
+  renderPlainText(OS);
+  return llvm::StringRef(OS.str()).trim().str();
+}
+
+void Paragraph::renderMarkdown(llvm::raw_ostream &OS) const {
+  bool NeedsSpace = false;
+  bool HasChunks = false;
+  for (auto &C : Chunks) {
+    if (C.SpaceBefore || NeedsSpace)
+      OS << " ";
+    switch (C.Kind) {
+    case Chunk::PlainText:
+      OS << renderText(C.Contents, !HasChunks);
+      break;
+    case Chunk::InlineCode:
+      OS << renderInlineBlock(C.Contents);
+      break;
+    }
+    HasChunks = true;
+    NeedsSpace = C.SpaceAfter;
+  }
+  // Paragraphs are translated into markdown lines, not markdown paragraphs.
+  // Therefore it only has a single linebreak afterwards.
+  // VSCode requires two spaces at the end of line to start a new one.
+  OS << "  \n";
+}
+
+std::unique_ptr<Block> Paragraph::clone() const {
+  return std::make_unique<Paragraph>(*this);
+}
+
+/// Choose a marker to delimit `Text` from a prioritized list of options.
+/// This is more readable than escaping for plain-text.
+llvm::StringRef chooseMarker(llvm::ArrayRef<llvm::StringRef> Options,
+                             llvm::StringRef Text) {
+  // Prefer a delimiter whose characters don't appear in the text.
+  for (llvm::StringRef S : Options)
+    if (Text.find_first_of(S) == llvm::StringRef::npos)
+      return S;
+  return Options.front();
+}
+
+void Paragraph::renderPlainText(llvm::raw_ostream &OS) const {
+  bool NeedsSpace = false;
+  for (auto &C : Chunks) {
+    if (C.SpaceBefore || NeedsSpace)
+      OS << " ";
+    llvm::StringRef Marker = "";
+    if (C.Preserve && C.Kind == Chunk::InlineCode)
+      Marker = chooseMarker({"`", "'", "\""}, C.Contents);
+    OS << Marker << C.Contents << Marker;
+    NeedsSpace = C.SpaceAfter;
+  }
+  OS << '\n';
+}
+
+void BulletList::renderMarkdown(llvm::raw_ostream &OS) const {
+  for (auto &D : Items) {
+    // Instead of doing this we might prefer passing Indent to children to get
+    // rid of the copies, if it turns out to be a bottleneck.
+    OS << "- " << indentLines(D.asMarkdown()) << '\n';
+  }
+  // We need a new line after list to terminate it in markdown.
+  OS << '\n';
+}
+
+void BulletList::renderPlainText(llvm::raw_ostream &OS) const {
+  for (auto &D : Items) {
+    // Instead of doing this we might prefer passing Indent to children to get
+    // rid of the copies, if it turns out to be a bottleneck.
+    OS << "- " << indentLines(D.asPlainText()) << '\n';
+  }
+}
+
+Paragraph &Paragraph::appendSpace() {
+  if (!Chunks.empty())
+    Chunks.back().SpaceAfter = true;
+  return *this;
+}
+
+Paragraph &Paragraph::appendText(llvm::StringRef Text) {
+  std::string Norm = canonicalizeSpaces(Text);
+  if (Norm.empty())
+    return *this;
+  Chunks.emplace_back();
+  Chunk &C = Chunks.back();
+  C.Contents = std::move(Norm);
+  C.Kind = Chunk::PlainText;
+  C.SpaceBefore = llvm::isSpace(Text.front());
+  C.SpaceAfter = llvm::isSpace(Text.back());
+  return *this;
+}
+
+Paragraph &Paragraph::appendCode(llvm::StringRef Code, bool Preserve) {
+  bool AdjacentCode =
+      !Chunks.empty() && Chunks.back().Kind == Chunk::InlineCode;
+  std::string Norm = canonicalizeSpaces(std::move(Code));
+  if (Norm.empty())
+    return *this;
+  Chunks.emplace_back();
+  Chunk &C = Chunks.back();
+  C.Contents = std::move(Norm);
+  C.Kind = Chunk::InlineCode;
+  C.Preserve = Preserve;
+  // Disallow adjacent code spans without spaces, markdown can't render them.
+  C.SpaceBefore = AdjacentCode;
+  return *this;
+}
+
+std::unique_ptr<Block> BulletList::clone() const {
+  return std::make_unique<BulletList>(*this);
+}
+
+class Document &BulletList::addItem() {
+  Items.emplace_back();
+  return Items.back();
+}
+
+Document &Document::operator=(const Document &Other) {
+  Children.clear();
+  for (const auto &C : Other.Children)
+    Children.push_back(C->clone());
+  return *this;
+}
+
+void Document::append(Document Other) {
+  std::move(Other.Children.begin(), Other.Children.end(),
+            std::back_inserter(Children));
+}
+
+Paragraph &Document::addParagraph() {
+  Children.push_back(std::make_unique<Paragraph>());
+  return *static_cast<Paragraph *>(Children.back().get());
+}
+
+void Document::addRuler() { Children.push_back(std::make_unique<Ruler>()); }
+
+void Document::addCodeBlock(std::string Code, std::string Language) {
+  Children.emplace_back(
+      std::make_unique<CodeBlock>(std::move(Code), std::move(Language)));
+}
+
+std::string Document::asMarkdown() const {
+  return renderBlocks(Children, &Block::renderMarkdown);
+}
+
+std::string Document::asPlainText() const {
+  return renderBlocks(Children, &Block::renderPlainText);
+}
+
+BulletList &Document::addBulletList() {
+  Children.emplace_back(std::make_unique<BulletList>());
+  return *static_cast<BulletList *>(Children.back().get());
+}
+
+Paragraph &Document::addHeading(size_t Level) {
+  assert(Level > 0);
+  Children.emplace_back(std::make_unique<Heading>(Level));
+  return *static_cast<Paragraph *>(Children.back().get());
+}
+} // namespace markup
+} // namespace clangd
+} // namespace clang