[clang][ExtractAPI] Complete declaration fragments for TagDecl types defined in a typedef

enums and structs declared inside typedefs have incorrect declaration fragments, where the typedef keyword and other syntax is missing.

For the following struct:

typedef struct Test {
    int hello;
} Test;
The produced declaration is:

"declarationFragments": [
  {
    "kind": "keyword",
    "spelling": "struct"
  },
  {
    "kind": "text",
    "spelling": " "
  },
  {
    "kind": "identifier",
    "spelling": "Test"
  }
],
instead the declaration fragments should represent the following

typedef struct Test {
    …
} Test;

This patch removes the condition in SymbolGraphSerializer.cpp file and completes declaration fragments

Reviewed By: dang

Differential Revision: https://reviews.llvm.org/D146385

Author: Ruturaj4

clang/include/clang/ExtractAPI/DeclarationFragments.h

@@ -99,6 +99,25 @@ class DeclarationFragments {
 
   const std::vector<Fragment> &getFragments() const { return Fragments; }
 
+  // Add a new Fragment to the beginning of the Fragments.
+  DeclarationFragments &appendFront(StringRef Spelling, FragmentKind Kind,
+                                    StringRef PreciseIdentifier = "",
+                                    const Decl *Declaration = nullptr) {
+    Fragments.emplace(Fragments.begin(), Spelling, Kind, PreciseIdentifier,
+                      Declaration);
+    return *this;
+  }
+
+  DeclarationFragments &appendFront(DeclarationFragments &&Other) {
+    Fragments.insert(Fragments.begin(),
+                     std::make_move_iterator(Other.Fragments.begin()),
+                     std::make_move_iterator(Other.Fragments.end()));
+    Other.Fragments.clear();
+    return *this;
+  }
+
+  void removeLast() { Fragments.pop_back(); }
+
   /// Append a new Fragment to the end of the Fragments.
   ///
   /// \returns a reference to the DeclarationFragments object itself after

clang/include/clang/ExtractAPI/ExtractAPIVisitor.h

@@ -22,6 +22,7 @@
 #include "clang/Basic/SourceManager.h"
 #include "clang/ExtractAPI/API.h"
 #include "clang/ExtractAPI/TypedefUnderlyingTypeResolver.h"
+#include "llvm/ADT/StringRef.h"
 #include <type_traits>
 
 namespace clang {
@@ -105,6 +106,24 @@ class ExtractAPIVisitorBase : public RecursiveASTVisitor<Derived> {
   }
 };
 
+template <typename T>
+static void modifyRecords(const T &Records, const StringRef &Name) {
+  for (const auto &Record : Records) {
+    if (Name == Record.second.get()->Name) {
+      Record.second.get()->Declaration.removeLast();
+      Record.second.get()
+          ->Declaration
+          .appendFront(" ", DeclarationFragments::FragmentKind::Text)
+          .appendFront("typedef", DeclarationFragments::FragmentKind::Keyword,
+                       "", nullptr)
+          .append(" { ... } ", DeclarationFragments::FragmentKind::Text)
+          .append(Name, DeclarationFragments::FragmentKind::Identifier)
+          .append(";", DeclarationFragments::FragmentKind::Text);
+      break;
+    }
+  }
+}
+
 template <typename Derived>
 bool ExtractAPIVisitorBase<Derived>::VisitVarDecl(const VarDecl *Decl) {
   // skip function parameters.
@@ -401,6 +420,21 @@ bool ExtractAPIVisitorBase<Derived>::VisitTypedefNameDecl(
   if (!getDerivedExtractAPIVisitor().shouldDeclBeIncluded(Decl))
     return true;
 
+  // Add the notion of typedef for tag type (struct or enum) of the same name.
+  if (const ElaboratedType *ET =
+          dyn_cast<ElaboratedType>(Decl->getUnderlyingType())) {
+    if (const TagType *TagTy = dyn_cast<TagType>(ET->desugar())) {
+      if (Decl->getName() == TagTy->getDecl()->getName()) {
+        if (TagTy->getDecl()->isStruct()) {
+          modifyRecords(API.getStructs(), Decl->getName());
+        }
+        if (TagTy->getDecl()->isEnum()) {
+          modifyRecords(API.getEnums(), Decl->getName());
+        }
+      }
+    }
+  }
+
   PresumedLoc Loc =
       Context.getSourceManager().getPresumedLoc(Decl->getLocation());
   StringRef Name = Decl->getName();