diff --git a/clang/include/clang/AST/DeclBase.h b/clang/include/clang/AST/DeclBase.h
--- a/clang/include/clang/AST/DeclBase.h
+++ b/clang/include/clang/AST/DeclBase.h
@@ -238,6 +238,9 @@
   /// The extra two bits are used for the ModuleOwnershipKind.
   llvm::PointerIntPair<Decl *, 2, ModuleOwnershipKind> NextInContextAndBits;
 
+  /// The previous declaration within the same lexical DeclContext.
+  Decl *PreviousInContext;
+
 private:
   friend class DeclContext;
 
@@ -374,21 +377,23 @@
 protected:
   Decl(Kind DK, DeclContext *DC, SourceLocation L)
       : NextInContextAndBits(nullptr, getModuleOwnershipKindForChildOf(DC)),
-        DeclCtx(DC), Loc(L), DeclKind(DK), InvalidDecl(false), HasAttrs(false),
-        Implicit(false), Used(false), Referenced(false),
-        TopLevelDeclInObjCContainer(false), Access(AS_none), FromASTFile(0),
-        IdentifierNamespace(getIdentifierNamespaceForKind(DK)),
+        PreviousInContext(nullptr), DeclCtx(DC), Loc(L), DeclKind(DK),
+        InvalidDecl(false), HasAttrs(false), Implicit(false), Used(false),
+        Referenced(false), TopLevelDeclInObjCContainer(false), Access(AS_none),
+        FromASTFile(0), IdentifierNamespace(getIdentifierNamespaceForKind(DK)),
         CacheValidAndLinkage(0) {
-    if (StatisticsEnabled) add(DK);
+    if (StatisticsEnabled)
+      add(DK);
   }
 
   Decl(Kind DK, EmptyShell Empty)
-      : DeclKind(DK), InvalidDecl(false), HasAttrs(false), Implicit(false),
-        Used(false), Referenced(false), TopLevelDeclInObjCContainer(false),
-        Access(AS_none), FromASTFile(0),
+      : PreviousInContext(nullptr), DeclKind(DK), InvalidDecl(false),
+        HasAttrs(false), Implicit(false), Used(false), Referenced(false),
+        TopLevelDeclInObjCContainer(false), Access(AS_none), FromASTFile(0),
         IdentifierNamespace(getIdentifierNamespaceForKind(DK)),
         CacheValidAndLinkage(0) {
-    if (StatisticsEnabled) add(DK);
+    if (StatisticsEnabled)
+      add(DK);
   }
 
   virtual ~Decl();
@@ -431,6 +436,9 @@
   Decl *getNextDeclInContext() { return NextInContextAndBits.getPointer(); }
   const Decl *getNextDeclInContext() const {return NextInContextAndBits.getPointer();}
 
+  Decl *getPreviousDeclInContext() { return PreviousInContext; }
+  const Decl *getPreviousDeclInContext() const { return PreviousInContext; }
+
   DeclContext *getDeclContext() {
     if (isInSemaDC())
       return getSemanticDC();
diff --git a/clang/lib/AST/ASTContext.cpp b/clang/lib/AST/ASTContext.cpp
--- a/clang/lib/AST/ASTContext.cpp
+++ b/clang/lib/AST/ASTContext.cpp
@@ -258,6 +258,44 @@
       CommentBeforeDecl->isTrailingComment())
     return nullptr;
 
+  const SourceLocation &CommentEndLoc = CommentBeforeDecl->getEndLoc();
+  if (CommentEndLoc.isInvalid())
+    return nullptr;
+
+  // Check if there's any other declaration in between the end of the comment
+  // and the current declaration.
+  if (const Decl *PreviousInContext = D->getPreviousDeclInContext()) {
+    // Use the previous decl's declaration location if the previous declaration
+    // is the lexical declaration context of the current declaration, and the
+    // end location otherwise. For example:
+    //
+    // ```
+    //   /// Doc for struct s
+    //   struct s {          // <- declaration location for `s`
+    //
+    //     int i;            // Both the PreviousDeclInContext and the
+    //                       // LexicalDeclContext of `i` is `s`
+    //
+    //     /// Doc for func
+    //     void func();
+    //   };                  // <- end location for `s`
+    //
+    //   bool b;             // The PreviousDeclInContext of `b` is `s`
+    // ```
+    //
+    // In this case, `Doc for struct s` shouldn't be attached to `i`; and
+    // `Doc for func` shouldn't be attached to `b`.
+    const DeclContext *DC = dyn_cast<DeclContext>(PreviousInContext);
+    const SourceLocation &PreviousDeclLoc =
+        DC && D->getLexicalDeclContext() == DC
+            ? PreviousInContext->getLocation()
+            : PreviousInContext->getEndLoc();
+    if (PreviousDeclLoc.isValid() && PreviousDeclLoc.isFileID() &&
+        SourceMgr.isPointWithin(PreviousDeclLoc, CommentEndLoc,
+                                RepresentativeLocForDecl))
+      return nullptr;
+  }
+
   // Decompose the end of the comment.
   const unsigned CommentEndOffset =
       Comments.getCommentEndOffset(CommentBeforeDecl);
@@ -273,9 +311,8 @@
   StringRef Text(Buffer + CommentEndOffset,
                  DeclLocDecomp.second - CommentEndOffset);
 
-  // There should be no other declarations or preprocessor directives between
-  // comment and declaration.
-  if (Text.find_first_of(";{}#@") != StringRef::npos)
+  // There should be no preprocessor directives between comment and declaration.
+  if (Text.find_first_of("#@") != StringRef::npos)
     return nullptr;
 
   return CommentBeforeDecl;
diff --git a/clang/lib/AST/DeclBase.cpp b/clang/lib/AST/DeclBase.cpp
--- a/clang/lib/AST/DeclBase.cpp
+++ b/clang/lib/AST/DeclBase.cpp
@@ -1344,6 +1344,7 @@
     else
       FirstNewDecl = D;
 
+    D->PreviousInContext = PrevDecl;
     PrevDecl = D;
   }
 
@@ -1392,6 +1393,8 @@
   std::tie(ExternalFirst, ExternalLast) =
       BuildDeclChain(Decls, FieldsAlreadyLoaded);
   ExternalLast->NextInContextAndBits.setPointer(FirstDecl);
+  if (FirstDecl)
+    FirstDecl->PreviousInContext = ExternalLast;
   FirstDecl = ExternalFirst;
   if (!LastDecl)
     LastDecl = ExternalLast;
@@ -1498,25 +1501,26 @@
   assert((D->NextInContextAndBits.getPointer() || D == LastDecl) &&
          "decl is not in decls list");
 
-  // Remove D from the decl chain.  This is O(n) but hopefully rare.
+  // Remove D from the decl chain.
   if (D == FirstDecl) {
     if (D == LastDecl)
       FirstDecl = LastDecl = nullptr;
     else
       FirstDecl = D->NextInContextAndBits.getPointer();
-  } else {
-    for (Decl *I = FirstDecl; true; I = I->NextInContextAndBits.getPointer()) {
-      assert(I && "decl not found in linked list");
-      if (I->NextInContextAndBits.getPointer() == D) {
-        I->NextInContextAndBits.setPointer(D->NextInContextAndBits.getPointer());
-        if (D == LastDecl) LastDecl = I;
-        break;
-      }
-    }
+  }
+
+  if (auto *Next = D->NextInContextAndBits.getPointer())
+    Next->PreviousInContext = D->PreviousInContext;
+
+  if (auto *Prev = D->PreviousInContext) {
+    Prev->NextInContextAndBits.setPointer(D->NextInContextAndBits.getPointer());
+    if (D == LastDecl)
+      LastDecl = Prev;
   }
 
   // Mark that D is no longer in the decl chain.
   D->NextInContextAndBits.setPointer(nullptr);
+  D->PreviousInContext = nullptr;
 
   // Remove D from the lookup table if necessary.
   if (isa<NamedDecl>(D)) {
@@ -1551,6 +1555,7 @@
 
   if (FirstDecl) {
     LastDecl->NextInContextAndBits.setPointer(D);
+    D->PreviousInContext = LastDecl;
     LastDecl = D;
   } else {
     FirstDecl = LastDecl = D;
diff --git a/clang/test/Index/annotate-comments-enum-constant.c b/clang/test/Index/annotate-comments-enum-constant.c
new file mode 100644
--- /dev/null
+++ b/clang/test/Index/annotate-comments-enum-constant.c
@@ -0,0 +1,16 @@
+// RUN: rm -rf %t
+// RUN: mkdir %t
+// RUN: c-index-test -test-load-source all -comments-xml-schema=%S/../../bindings/xml/comment-xml-schema.rng %s > %t/out
+// RUN: FileCheck %s --dump-input always < %t/out
+
+enum {
+  /// Documentation for Foo
+  Foo,
+  Bar, // No documentation for Bar
+  /// Documentation for Baz
+  Baz,
+};
+// CHECK: EnumConstantDecl=Foo:[[@LINE-5]]:3 (Definition) {{.*}} BriefComment=[Documentation for Foo] FullCommentAsHTML=[<p class="para-brief"> Documentation for Foo</p>] FullCommentAsXML=[<Variable file="{{[^"]+}}annotate-comments-enum-constant.c" line="[[@LINE-5]]" column="3"><Name>Foo</Name><USR>c:@Ea@Foo@Foo</USR><Declaration>Foo</Declaration><Abstract><Para> Documentation for Foo</Para></Abstract></Variable>]
+// CHECK: EnumConstantDecl=Bar:[[@LINE-5]]:3 (Definition)
+// CHECK-NOT: BriefComment=[Documentation for Foo]
+// CHECK: EnumConstantDecl=Baz:[[@LINE-5]]:3 (Definition) {{.*}} BriefComment=[Documentation for Baz] FullCommentAsHTML=[<p class="para-brief"> Documentation for Baz</p>] FullCommentAsXML=[<Variable file="{{[^"]+}}annotate-comments-enum-constant.c" line="[[@LINE-5]]" column="3"><Name>Baz</Name><USR>c:@Ea@Foo@Baz</USR><Declaration>Baz</Declaration><Abstract><Para> Documentation for Baz</Para></Abstract></Variable>]
diff --git a/clang/test/Index/annotate-comments.cpp b/clang/test/Index/annotate-comments.cpp
--- a/clang/test/Index/annotate-comments.cpp
+++ b/clang/test/Index/annotate-comments.cpp
@@ -254,6 +254,14 @@
 MYMAC(0,0)
 void isdoxy54(int);
 
+/// IS_DOXYGEN_SINGLE
+struct isdoxy55 {
+  int notdoxy48;
+  /// IS_DOXYGEN_SINGLE
+  int isdoxy56;
+};
+bool notdoxy49;
+
 #endif
 
 // RUN: rm -rf %t
@@ -337,3 +345,6 @@
 // CHECK: annotate-comments.cpp:241:6: FunctionDecl=isdoxy52:{{.*}} BriefComment=[Aaa. IS_DOXYGEN_START Bbb.]
 // CHECK: annotate-comments.cpp:248:6: FunctionDecl=isdoxy53:{{.*}} BriefComment=[Aaa. IS_DOXYGEN_START IS_DOXYGEN_END]
 // CHECK: annotate-comments.cpp:255:6: FunctionDecl=isdoxy54:{{.*}} BriefComment=[Aaa. IS_DOXYGEN_START IS_DOXYGEN_END]
+
+// CHECK: annotate-comments.cpp:258:8: StructDecl=isdoxy55:{{.*}} IS_DOXYGEN_SINGLE
+// CHECK: annotate-comments.cpp:261:7: FieldDecl=isdoxy56:{{.*}} IS_DOXYGEN_SINGLE