[clangd] (DO NOT COMMIT) hovering on "md" raw strings displays those.

[sammccall]

Summary

This is useful for testing markdown rendering in hover of editors.

It shoudn't be checked in (it'd be a nice easter egg, but the implementation
is too messy).

[merge_guards_bot]

Unit tests: pass. 61742 tests passed, 0 failed and 780 were skipped.

clang-tidy: pass.

clang-format: fail. Please format your changes with clang-format by running git-clang-format HEAD^ or applying this patch.

Build artifacts: diff.json, clang-tidy.txt, clang-format.patch, CMakeCache.txt, console-log.txt, test-results.xml

clang-tools-extra/clangd/FormattedString.h

public:
   virtual void renderMarkdown(llvm::raw_ostream &OS) const = 0;
   virtual void renderPlainText(llvm::raw_ostream &OS) const = 0;
   std::string asMarkdown() const;
   std::string asPlainText() const;
 
   virtual ~Block() = default;
 };
 
+class RawBlock : public Block {
+ public:
+  RawBlock(std::string Text) : Text(std::move(Text)) {}
+  virtual void renderMarkdown(llvm::raw_ostream &OS) const override { OS << Text; }
+  virtual void renderPlainText(llvm::raw_ostream &OS) const override { OS << Text; }
+ private:
+  std::string Text;
+};
+
 /// Represents parts of the markup that can contain strings, like inline code,
 /// code block or plain text.
 /// One must introduce different paragraphs to create separate blocks.
 class Paragraph : public Block {
 public:
   void renderMarkdown(llvm::raw_ostream &OS) const override;
   void renderPlainText(llvm::raw_ostream &OS) const override;
 
public:
   Paragraph &addParagraph();
   /// Inserts a vertical space into the document.
   void addSpacer();
   /// Adds a block of code. This translates to a ``` block in markdown. In plain
   /// text representation, the code block will be surrounded by newlines.
   void addCodeBlock(std::string Code, std::string Language = "cpp");
 
   BulletList &addBulletList();
+  void addRaw(std::string Text) {
+    Children.push_back(std::make_unique<RawBlock>(std::move(Text)));
+  }
 
   /// Doesn't contain any trailing newlines.
   std::string asMarkdown() const;
   /// Doesn't contain any trailing newlines.
   std::string asPlainText() const;
 
 private:
   std::vector<std::unique_ptr<Block>> Children;
 };
 } // namespace markup
 } // namespace clangd
 } // namespace clang
 
 #endif

clang-tools-extra/clangd/Hover.h

struct HoverInfo {
   llvm::Optional<std::string> ReturnType;
   /// Set for functions, lambdas and macros with parameters.
   llvm::Optional<std::vector<Param>> Parameters;
   /// Set for all templates(function, class, variable).
   llvm::Optional<std::vector<Param>> TemplateParameters;
   /// Contains the evaluated value of the symbol if available.
   llvm::Optional<std::string> Value;
 
+  llvm::Optional<std::string> RawResponse;
+
   /// Produce a user-readable information.
   markup::Document present() const;
 };
 llvm::raw_ostream &operator<<(llvm::raw_ostream &, const HoverInfo::Param &);
 inline bool operator==(const HoverInfo::Param &LHS,
                        const HoverInfo::Param &RHS) {
   return std::tie(LHS.Type, LHS.Name, LHS.Default) ==
          std::tie(RHS.Type, RHS.Name, RHS.Default);

clang-tools-extra/clangd/Hover.cpp

if (auto Deduced = getDeducedType(AST.getASTContext(), SourceLocationBeg)) {
     std::vector<const Decl *> Result;
     if (const SelectionTree::Node *N = Selection.commonAncestor()) {
       auto Decls = explicitReferenceTargets(N->ASTNode, DeclRelation::Alias);
       if (!Decls.empty()) {
         HI = getHoverContents(Decls.front(), Index);
         // Look for a close enclosing expression to show the value of.
         if (!HI->Value)
           HI->Value = printExprValue(N, AST.getASTContext());
+      } else if (auto *SL = N->ASTNode.get<StringLiteral>()) {
+        if (SL->getBeginLoc().isFileID()) {
+          const char *Data = SM.getCharacterData(SL->getBeginLoc());
+          // safe because null-terminated
+          if (Data && !strncmp("R\"md(", Data, 5)) {
+            HI.emplace();
+            HI->RawResponse = SL->getString();
+          }
+        }
       }
       // FIXME: support hovers for other nodes?
       //  - certain expressions (sizeof etc)
       //  - built-in types
       //  - literals (esp user-defined)
     }
   }
 
   if (!HI)
     return llvm::None;
 
   auto Replacements = format::reformat(
       Style, HI->Definition, tooling::Range(0, HI->Definition.size()));
   if (auto Formatted =
           tooling::applyAllReplacements(HI->Definition, Replacements))
     HI->Definition = *Formatted;
 
   HI->SymRange = getTokenRange(AST.getSourceManager(), AST.getLangOpts(),
                                SourceLocationBeg);
   return HI;
 }
 
 markup::Document HoverInfo::present() const {
   markup::Document Output;
+  if (RawResponse) {
+    Output.addRaw(*RawResponse);
+    return Output;
+  }
   // Header contains a text of the form:
   // variable `var` : `int`
   //
   // class `X`
   //
   // function `foo` → `int`
   markup::Paragraph &Header = Output.addParagraph();
   Header.appendText(index::getSymbolKindString(Kind));