[clang-tools-extra] [clang-doc] add Markdown parser (PR #155887)

[Paul Kirth via cfe-commits]

================
@@ -0,0 +1,229 @@
+#include "MDParser.h"
+#include "clang/Basic/CharInfo.h"
+#include "llvm/ADT/AllocatorList.h"
+
+namespace clang {
+namespace doc {
+namespace {
+bool isEmphasisDelimiter(char &Token) {
+  // TODO: support '_'
+  if (Token == '*')
+    return true;
+  return false;
+}
+} // namespace
+
+std::pair<std::optional<DelimiterContext>, size_t>
+MarkdownParser::processDelimiters(SmallString<64> &Line, const size_t &Origin) {
+  size_t Idx = Origin;
+  while (Idx < Line.size() && Line[Idx] == Line[Origin]) {
+    ++Idx;
+  }
+
+  char Preceeding = (Origin == 0) ? ' ' : Line[Origin - 1];
+  char Proceeding = (Idx >= Line.size()) ? ' ' : Line[Idx];
+
+  bool LeftFlanking = !isWhitespace(Proceeding) &&
+                      (!isPunctuation(Proceeding) || isWhitespace(Preceeding) ||
+                       isPunctuation(Preceeding));
+  bool RightFlanking = !isWhitespace(Preceeding) &&
+                       (!isPunctuation(Preceeding) || isWhitespace(Proceeding) ||
+                        isPunctuation(Proceeding));
+
+  if (LeftFlanking && RightFlanking)
+    return {DelimiterContext{LeftFlanking, RightFlanking, true, true}, Idx};
+  if (LeftFlanking)
+    return {DelimiterContext{LeftFlanking, RightFlanking, true, false}, Idx};
+  if (RightFlanking)
+    return {DelimiterContext{LeftFlanking, RightFlanking, false, true}, Idx};
+  return {std::nullopt, 0};
+}
+
+Node *MarkdownParser::createTextNode(const std::list<LineNode *> &Text) {
+  Node *TextNode = new (Arena) Node();
+  for (const auto *Node : Text) {
+    TextNode->Content.append(Node->Content);
+  }
+  TextNode->Type = MDType::Text;
+  return TextNode;
+}
+
+Node *MarkdownParser::reverseIterateLine(std::list<LineNode *> &Stack,
+                                         std::list<LineNode *>::iterator &It) {
+  auto ReverseIt = std::make_reverse_iterator(It);
+  std::list<LineNode *> Text;
+  while (ReverseIt != Stack.rend()) {
+    auto *ReverseCurrent = *ReverseIt;
+    if (!ReverseCurrent->DelimiterContext && !ReverseCurrent->Content.empty()) {
+      Text.push_back(ReverseCurrent);
+      ReverseIt++;
+      continue;
+    }
+
+    if (ReverseCurrent->DelimiterContext &&
+        ReverseCurrent->DelimiterContext->CanOpen) {
+      if (Text.empty()) {
+        // If there is no text between the runs, there is no emphasis, so both
+        // delimiter runs are literal text.
+        auto *DelimiterTextNode = new (Arena) Node();
+        DelimiterTextNode->Content =
+            Saver.save((*It)->Content + ReverseCurrent->Content);
+        DelimiterTextNode->Type = MDType::Text;
+        return DelimiterTextNode;
+      }
+      Node *Emphasis = nullptr;
+
+      auto &Closer = (*It)->DelimiterContext;
+      auto &Opener = ReverseCurrent->DelimiterContext;
+
+      if (Closer->Length >= 2 && Opener->Length >= 2) {
+        // We have at least one strong node.
+        Closer->Length -= 2;
+        Opener->Length -= 2;
+        Emphasis = new (Arena) Node();
+        Emphasis->Type = MDType::Strong;
+        auto *Child = createTextNode(Text);
+        Child->Parent = Emphasis;
+        Emphasis->Children.push_back(Child);
+      } else if (Closer->Length == 1 && Opener->Length == 1) {
+        Closer->Length -= 1;
+        Opener->Length -= 1;
+        Emphasis = new (Arena) Node();
+        Emphasis->Type = MDType::Emphasis;
+        auto *Child = createTextNode(Text);
+        Child->Parent = Emphasis;
+        Emphasis->Children.push_back(Child);
+      }
+
+      if (Closer->Length == 0)
+        It = Stack.erase(It);
+      if (Opener->Length == 0)
+        ReverseIt = std::make_reverse_iterator(Stack.erase(ReverseIt.base()));
+      if (!Text.empty())
+        for (auto *Node : Text)
+          Stack.remove(Node);
+      return Emphasis;
+    }
+    ReverseIt++;
+  }
+  return nullptr;
+}
+
+std::list<Node *>
+MarkdownParser::processEmphasis(std::list<LineNode *> &Stack) {
+  std::list<Node *> Result;
+  auto It = Stack.begin();
+  while (It != Stack.end()) {
+    LineNode *Current = *It;
+    if (Current->DelimiterContext && Current->DelimiterContext->CanClose) {
+      auto *NewNode = reverseIterateLine(Stack, It);
+      if (NewNode) {
+        Result.push_back(NewNode);
+        It = Stack.begin();
+        continue;
+      }
+    }
+    ++It;
+  }
+
+  return Result;
+}
+
+void MarkdownParser::parseLine(SmallString<64> &Line, Node *Current) {
+  std::list<LineNode *> Stack;
+  BumpPtrAllocator LineArena;
+  size_t StrCount = 0;
+  size_t Idx = 0;
+  for (; Idx < Line.size(); ++Idx) {
+    if (isEmphasisDelimiter(Line[Idx])) {
+      auto DelimiterResult = processDelimiters(Line, Idx);
+      if (DelimiterResult.first != std::nullopt) {
+        if (StrCount > 0) {
+          auto *TextNode = new (LineArena) LineNode();
+          TextNode->Content = Line.substr(Idx - StrCount, StrCount);
+          Stack.push_back(TextNode);
+          StrCount = 0;
+        }
+        auto *NewNode = new (LineArena) LineNode();
+        NewNode->Content = Line.substr(Idx, DelimiterResult.second - Idx);
+        NewNode->DelimiterContext = std::move(DelimiterResult.first);
+        NewNode->DelimiterContext->Length = NewNode->Content.size();
+        Stack.push_back(NewNode);
+        Idx = DelimiterResult.second - 1;
+        continue;
+      }
+    }
+    // Not any emphasis delimiter, so it will be appended as a string later
+    StrCount += 1;
----------------
ilovepi wrote:

if you reverse the condition above, you can have an early continue and remove a level of indentation.

```
if (!isEmphasisDelimiter(Line[Idx])){
 ++StrCount;
 continue;
}
```


https://github.com/llvm/llvm-project/pull/155887