[clang-tools-extra] [clangd] Improve Markup Rendering (PR #140498)

[Maksim Ivanov via cfe-commits]

================
@@ -370,40 +497,128 @@ std::unique_ptr<Block> Paragraph::clone() const {
 
 /// 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) {
+llvm::StringRef Paragraph::chooseMarker(llvm::ArrayRef<llvm::StringRef> Options,
+                                        llvm::StringRef Text) const {
   // 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();
 }
 
+bool Paragraph::punctuationIndicatesLineBreak(llvm::StringRef Line) const {
+  constexpr llvm::StringLiteral Punctuation = R"txt(.:,;!?)txt";
+
+  Line = Line.rtrim();
+  return !Line.empty() && Punctuation.contains(Line.back());
+}
+
+bool Paragraph::isHardLineBreakIndicator(llvm::StringRef Rest) const {
+  // '-'/'*' md list, '@'/'\' documentation command, '>' md blockquote,
+  // '#' headings, '`' code blocks, two spaces (markdown force newline)
+  constexpr llvm::StringLiteral LinebreakIndicators = R"txt(-*@\>#`)txt";
+
+  Rest = Rest.ltrim(" \t");
+  if (Rest.empty())
+    return false;
+
+  if (LinebreakIndicators.contains(Rest.front()))
+    return true;
+
+  if (llvm::isDigit(Rest.front())) {
+    llvm::StringRef AfterDigit = Rest.drop_while(llvm::isDigit);
+    if (AfterDigit.starts_with(".") || AfterDigit.starts_with(")"))
+      return true;
+  }
+  return false;
+}
+
+bool Paragraph::isHardLineBreakAfter(llvm::StringRef Line,
+                                     llvm::StringRef Rest) const {
+  // In Markdown, 2 spaces before a line break forces a line break.
+  // Add a line break for plaintext in this case too.
+  // Should we also consider whether Line is short?
+  return Line.ends_with("  ") || punctuationIndicatesLineBreak(Line) ||
+         isHardLineBreakIndicator(Rest);
+}
+
 void Paragraph::renderPlainText(llvm::raw_ostream &OS) const {
   bool NeedsSpace = false;
+  std::string ConcatenatedText;
+  llvm::raw_string_ostream ConcatenatedOS(ConcatenatedText);
+
   for (auto &C : Chunks) {
+
+    if (C.Kind == ChunkKind::PlainText) {
+      if (C.SpaceBefore || NeedsSpace)
+        ConcatenatedOS << ' ';
+
+      ConcatenatedOS << C.Contents;
+      NeedsSpace = llvm::isSpace(C.Contents.back()) || C.SpaceAfter;
+      continue;
+    }
+
     if (C.SpaceBefore || NeedsSpace)
-      OS << " ";
+      ConcatenatedOS << ' ';
     llvm::StringRef Marker = "";
-    if (C.Preserve && C.Kind == Chunk::InlineCode)
+    if (C.Preserve && C.Kind == ChunkKind::InlineCode)
       Marker = chooseMarker({"`", "'", "\""}, C.Contents);
-    OS << Marker << C.Contents << Marker;
+    else if (C.Kind == ChunkKind::Bold)
+      Marker = "**";
+    else if (C.Kind == ChunkKind::Emphasized)
+      Marker = "*";
+    ConcatenatedOS << Marker << C.Contents << Marker;
     NeedsSpace = C.SpaceAfter;
   }
-  OS << '\n';
+
+  // We go through the contents line by line to handle the newlines
+  // and required spacing correctly.
+  llvm::StringRef Line, Rest;
+
+  for (std::tie(Line, Rest) =
+           llvm::StringRef(ConcatenatedText).trim().split('\n');
+       !(Line.empty() && Rest.empty());
+       std::tie(Line, Rest) = Rest.split('\n')) {
+
+    Line = Line.ltrim();
+    if (Line.empty())
+      continue;
+
+    OS << canonicalizeSpaces(Line);
+
+    if (isHardLineBreakAfter(Line, Rest))
+      OS << '\n';
+    else if (!Rest.empty())
+      OS << ' ';
----------------
emaxx-google wrote:

Can this result in an unnecessary trailing space if the next line is empty?

https://github.com/llvm/llvm-project/pull/140498