[clangd] Smarter hover on auto and decltype

[qchateau]

Summary

Only show the keyword as the hover "Name".

Show whether the type is deduced or undeduced as
the hover "Documentation".

Show the deduced type (if any) as the "Definition".

Don't show any hover information for:

• the "auto" word of "decltype(auto)"
• "auto" in lambda parameters
• "auto" in template arguments

---

This diff is a suggestion based on what @sammccall suggested in https://reviews.llvm.org/D92977 about hover on "auto". It somehow "hacks" onto the "Documentation" and "Definition" fields of HoverInfo. It sure looks good on VSCode, let me know if this seem acceptable to you.

[sammccall]

Thanks! This seems more consistent with our other hovers, but is going to be better-formatted/more attractive in VSCode.
There are a couple of wrinkles I'd like to discuss :-)

Brevity

This is clear and mostly consistent (documentation excepted), but uses three lines where clearly two would do - the "auto" title provides very little information, and the documentation only a bit more (pun intended!)

Can we combine them? The title has SymbolKind which normally holds the category. We can't easily add new SymbolKinds (it's an enum we don't own, which we should fix, but that's a yak-shave). But TypeAlias almost fits these roles for auto. What do you think about setting Kind/Name/Definition? This would give:

type-alias `auto`
const Foo&

This leaves the question of what to do with undeduced auto, maybe:

type-alias `auto`
/* not deduced */

(There are other cases: function parameter types void foo(auto X) and NTTP types template <auto X> class Y but we can punt on those)

this

D92041 recently added support for showing the type when hovering over this. It followed the existing auto behavior (put everything in Name) because that's the only place we were showing types per se.

So you're going to have a merge conflict, and we need to decide how to render it.

I don't really have a better idea than setting Name = "this", setting Definition, and leaving Kind=Unknown. Maybe we can do better once we can easily extend the SymbolKind enum.

[qchateau]

• Rebase on master after D92041
• Remove the usage of the "Documentation" field
• Use the TypeAlias Kind on auto and decltype
• Move code related to hover on this in a new function
• Update hover on this to be consistent with this change

[qchateau]

We can't easily add new SymbolKinds (it's an enum we don't own, which we should fix, but that's a yak-shave). But TypeAlias almost fits these roles for auto.

Yes I originally wanted to have "deduced-type auto" but I realized it would not be easy. I did not think of TypeAlias, let's use this until we can do better.

(There are other cases: function parameter types void foo(auto X) and NTTP types template <auto X> class Y but we can punt on those)

For now I disabled them (instead of displaying nonsense as we did before). Anyway as a user, I have zero useful information to get when hovering on these word, I prefer nothing rather than a useless pop-up.

[sammccall]

Agree with all the conclusions you've come to here. Main two issues are:

• the new traversal added to patch up some cases isn't the right approach IMO.
• some accidental regressions

I'd also like to distinguish decltype(auto) from other decltypes, but it's a problem with our existing helpers so let's not try that in this patch.

clang-tools-extra/clangd/Hover.cpp

618

You've rewritten this logic compared to the old getHoverContents(QualType), and I think there are regressions:

• We've dropped class documentation (see e.g. ac3f9e48421712168884d59cbfe8b294dd76a19b, this is visible in the tests)
• we're no longer using printName() to print tag-decls, which I expect changes e.g. the printing of anyonymous structs which is special-cased in that function (we have tests for this but probably not in combination with auto)
• we're no longer using the printing-policy to print non-tag types, which will lead to some random changes

I don't see a reason for these changes, can we revert them?

631

This functionality (reporting the auto type in structured bindings, and not reporting non-deduced uses of auto) belongs in the getDeducedType() helper rather than as a layer on top.
(Especially because it has to be done via an AST traversal rather than SelectionTree)

I'd suggest leaving it out of this patch to get this the original change landed quickly - this seems like a mostly-unrelated enhancement. But up to you.

880

decltype(auto) and decltype(expr) are fairly different things and ultimately we should be displaying them differently I think ("decltype(auto)" vs "decltype(...)").

Unfortunately it's awkward because our getDeducedType helper handles both at the moment (and so is misnamed, because decltype(expr) isn't deduced at all).

Can you add // FIXME: distinguish decltype(auto) vs decltype(expr) and I'll do some refactoring later?

clang-tools-extra/clangd/unittests/HoverTests.cpp

986

(not convinced this is fundamentally not useful - the fact that it's a template parameter means it's probably worth having a hover card for it at some point. But I agree with suppressing it for now)

1883

can we have a decltype test where the result is dependent?
e.g..

template <typename T>
struct X {
  using Y = ^decltype(T::Z);
};

should yield a definition of "<dependent type>" rather than "/* not deduced */".
(Since regular decltype() is not a deduced type)

[qchateau]

I updated this diff according to your review. There are a few things that may still need change but I need your input, see my other comments :)

[qchateau]

clang-tools-extra/clangd/Hover.cpp

618

• I can re-add class documentation, but should it work when auto is a pointer or a ref ? In that case, I'll need something like your unwrapType of https://reviews.llvm.org/D93314
• printName will print C instead of class C even if I hack around and give it the right PrintingPolicy. The problem is that IDE (at least VSCode) does not know what C is and cannot color it, which looks a nice less nice. Up to you !
• I can re-add the printing policy for non-tag types, and add it for tag-types if we chose not to use printName.

631

I'll remove this. I'll leave out the case of structured bindings for arrays (which is really weird and specific), but I guess I'll fix`getDeducedType` to return the undeduced QualType instead of None (which it already does but only for return types).

880

Sure, I'll add the comment. I'll leave that refactoring to you, I'm not quite sure how you intent to achieve it.

clang-tools-extra/clangd/unittests/HoverTests.cpp

986

As a user I'd prefer the hover to work over the whole decltype(auto) expression. But that does not seem quite compatible with the way tokens are parsed.

Are you suggesting I remove the test case or should I add a FIXME comment ?

[sammccall]

Thanks! I think this is in pretty good shape, remaining stuff is up to you.

Let me know if/when you want me to land this!

clang-tools-extra/clangd/Hover.cpp

618

should it work when auto is a pointer or a ref?

I think no need for now, I just want to avoid the regression.
(Nice to have, but at least in the codebases I work in, auto is much more common than decltype(auto) so it's rarely a reference, and pointers are idiomatically written auto*)

printName will print C instead of class C even if I hack around and give it the right PrintingPolicy.

Yeah... it's not supposed to, though the extra clarity is valuable here. You could just hack around this and prepend the TagTypeKind yourself :-)

clang-tools-extra/clangd/unittests/HoverTests.cpp

986

Sorry, I think we're talking about different examples.

(I agree decltype(auto) should ideally be a single thing and we should support hover on all of it, no need to address in this patch, FIXME would be nice).

But I was talking about the lambda auto parameter, where your comment says "not useful". Anyway, nothing to do here either except maybe soften the comment to "not supported at the moment".

1719

can you restore the comments to the original position above the struct, so we test that the documentation comment is included?

[qchateau]

• Verify documentation in hover test on 'auto'
• Fixed comments
• Converted raw string to string to avoid trailing whitespace

[qchateau]

You can land this if it is still fine after my final update.

email: [e-mail]

Thanks !

clang-tools-extra/clangd/unittests/HoverTests.cpp

986

Ahah yes my bad, I copy pasted the comment x)
I fixed it

2444–2454

I've also changed this raw string to a normal string (and another one line 2729) because they include whitespace at the end of the line. Git complains about it and my editor automatically trims trailing whitespace. I assume I'm not the only one using this setting and it annoyed me more than it should.

[qchateau]

Fix ExpandAutoType to not expand undeduced auto

[sammccall]

clang-tools-extra/clangd/AST.cpp

353

I added a comment to getDeducedType() - I think the intent here is that we return the AutoType itself if it's not deduced, right?

clang-tools-extra/clangd/Hover.cpp

591

I dropped this unused param

618

Hmm, it looks like this wasn't done. It's now printing e.g. class vector<class Foo> which seems more confusing than either class vector<Foo> or vector<Foo> (even if we lose some highlighting). I'll send a followup with proposed changes here.

[qchateau]

clang-tools-extra/clangd/AST.cpp

353

It is already the case for return types in VisitFunctionDecl, but not for types visited in in VisitDeclaratorDecl. I simply made it consistent. One could argue getDeducedType should return None when the type is not deduced, and I'd not argue against that. Though I have t admit this behavior makes things simpler for the hover feature.

clang-tools-extra/clangd/Hover.cpp

591

Good catch

618

We can probably use printDefinition for tag types and keep getAsString for non tag types. That would also make the definition close to what we get when hovering on an explicit type (as opposed to 'auto'). We'd probably need to set the scopes in HoverInfo as well, printDefinition does not print them.

clang-tools-extra/clangd/AST.cpp

 //===--- AST.cpp - Utility AST functions  -----------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
public:
   //- auto& i = 1;
   //- auto* i = &a;
   bool VisitDeclaratorDecl(DeclaratorDecl *D) {
     if (!D->getTypeSourceInfo() ||
         D->getTypeSourceInfo()->getTypeLoc().getBeginLoc() != SearchedLocation)
       return true;
 
     if (auto *AT = D->getType()->getContainedAutoType()) {
-      if (!AT->getDeducedType().isNull())
-        DeducedType = AT->getDeducedType();
+      DeducedType = AT->desugar();
     }
     return true;
   }
 
   // Handle auto return types:
   //- auto foo() {}
   //- auto& foo() {}
   //- auto foo() -> int {}

clang-tools-extra/clangd/Hover.cpp

 //===--- Hover.cpp - Information about code at the cursor location --------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 

 #include "clang/AST/Decl.h"
 #include "clang/AST/DeclBase.h"
 #include "clang/AST/DeclCXX.h"
 #include "clang/AST/DeclTemplate.h"
 #include "clang/AST/Expr.h"
 #include "clang/AST/ExprCXX.h"
 #include "clang/AST/OperationKinds.h"
 #include "clang/AST/PrettyPrinter.h"
+#include "clang/AST/RecursiveASTVisitor.h"
 #include "clang/AST/Type.h"
 #include "clang/Basic/SourceLocation.h"
 #include "clang/Basic/Specifiers.h"
 #include "clang/Basic/TokenKinds.h"
 #include "clang/Index/IndexSymbol.h"
 #include "clang/Tooling/Syntax/Tokens.h"
 #include "llvm/ADT/None.h"
 #include "llvm/ADT/Optional.h"
if (const auto *Var = dyn_cast<VarDecl>(D)) {
     if (!ECD->getType()->isDependentType())
       HI.Value = ECD->getInitVal().toString(10);
   }
 
   HI.Definition = printDefinition(D);
   return HI;
 }
 
-/// Generate a \p Hover object given the type \p T.
-HoverInfo getHoverContents(QualType T, ASTContext &ASTCtx,
-                           const SymbolIndex *Index,
-                           bool SuppressScope = false) {
-  HoverInfo HI;
-
-  if (const auto *D = T->getAsTagDecl()) {
-    HI.Name = printName(ASTCtx, *D);
-    HI.Kind = index::getSymbolInfo(D).Kind;
-
-    const auto *CommentD = getDeclForComment(D);
-    HI.Documentation = getDeclComment(ASTCtx, *CommentD);
-    enhanceFromIndex(HI, *CommentD, Index);
-  } else {
-    // Builtin types
-    auto Policy = printingPolicyForDecls(ASTCtx.getPrintingPolicy());
-    Policy.SuppressTagKeyword = true;
-    Policy.SuppressScope = SuppressScope;
-    HI.Name = T.getAsString(Policy);
-  }
-  return HI;
-}
-
 /// Generate a \p Hover object given the macro \p MacroDecl.
 HoverInfo getHoverContents(const DefinedMacro &Macro, ParsedAST &AST) {
   HoverInfo HI;
   SourceManager &SM = AST.getSourceManager();
   HI.Name = std::string(Macro.Name);
   HI.Kind = index::SymbolKind::Macro;
   // FIXME: Populate documentation
   // FIXME: Populate parameters
if (!Invalid) {
         HI.Definition =
             ("#define " + Buffer.substr(StartOffset, EndOffset - StartOffset))
                 .str();
     }
   }
   return HI;
 }
 
+llvm::Optional<HoverInfo> getThisExprHoverContents(const CXXThisExpr *CTE,
+                                                   ASTContext &ASTCtx,
+                                                   const SymbolIndex *Index) {
+  QualType OriginThisType = CTE->getType()->getPointeeType();
+  QualType ClassType = declaredType(OriginThisType->getAsTagDecl());
+  // For partial specialization class, origin `this` pointee type will be
+  // parsed as `InjectedClassNameType`, which will ouput template arguments
+  // like "type-parameter-0-0". So we retrieve user written class type in this
+  // case.
+  QualType PrettyThisType = ASTCtx.getPointerType(
+      QualType(ClassType.getTypePtr(), OriginThisType.getCVRQualifiers()));
+
+  auto Policy = printingPolicyForDecls(ASTCtx.getPrintingPolicy());
+  Policy.SuppressTagKeyword = true;
+  Policy.SuppressScope = true;
+  HoverInfo HI;
+  HI.Name = "this";
+  HI.Definition = PrettyThisType.getAsString(Policy);
+  return HI;
+}
+
+/// Generate a HoverInfo object given the deduced type \p QT
+HoverInfo getDeducedTypeHoverContents(QualType QT, const syntax::Token &Tok,
+                                      ASTContext &ASTCtx,
+                                      const SymbolIndex *Index) {
+  HoverInfo HI;
+  // FIXME: distinguish decltype(auto) vs decltype(expr)
+  HI.Name = tok::getTokenName(Tok.kind());
+  HI.Kind = index::SymbolKind::TypeAlias;
+
+  auto PP = printingPolicyForDecls(ASTCtx.getLangOpts());
+
+  if (QT->isUndeducedAutoType()) {
+    HI.Definition = "/* not deduced */";
+  } else {
+    HI.Definition = QT.getAsString(PP);
+
+    if (const auto *D = QT->getAsTagDecl()) {
+      const auto *CommentD = getDeclForComment(D);
+      HI.Documentation = getDeclComment(ASTCtx, *CommentD);
+      enhanceFromIndex(HI, *CommentD, Index);
+    }
+  }
+
+  return HI;
+}
+
 bool isLiteral(const Expr *E) {
   // Unfortunately there's no common base Literal classes inherits from
   // (apart from Expr), therefore these exclusions.
   return llvm::isa<CharacterLiteral>(E) || llvm::isa<CompoundLiteralExpr>(E) ||
          llvm::isa<CXXBoolLiteralExpr>(E) ||
          llvm::isa<CXXNullPtrLiteralExpr>(E) ||
          llvm::isa<FixedPointLiteral>(E) || llvm::isa<FloatingLiteral>(E) ||
          llvm::isa<ImaginaryLiteral>(E) || llvm::isa<IntegerLiteral>(E) ||
llvm::Optional<HoverInfo> getHoverContents(const Expr *E, ParsedAST &AST,
   // There's not much value in hovering over "42" and getting a hover card
   // saying "42 is an int", similar for other literals.
   if (isLiteral(E))
     return llvm::None;
 
   HoverInfo HI;
   // For `this` expr we currently generate hover with pointee type.
   if (const CXXThisExpr *CTE = dyn_cast<CXXThisExpr>(E)) {
-    QualType OriginThisType = CTE->getType()->getPointeeType();
-    QualType ClassType = declaredType(OriginThisType->getAsTagDecl());
-    // For partial specialization class, origin `this` pointee type will be
-    // parsed as `InjectedClassNameType`, which will ouput template arguments
-    // like "type-parameter-0-0". So we retrieve user written class type in this
-    // case.
-    QualType PrettyThisType = AST.getASTContext().getPointerType(
-        QualType(ClassType.getTypePtr(), OriginThisType.getCVRQualifiers()));
-    return getHoverContents(PrettyThisType, AST.getASTContext(), Index,
-                            /*SuppressScope=*/true);
+    return getThisExprHoverContents(CTE, AST.getASTContext(), Index);
   }
   // For expressions we currently print the type and the value, iff it is
   // evaluatable.
   if (auto Val = printExprValue(E, AST.getASTContext())) {
     auto Policy =
         printingPolicyForDecls(AST.getASTContext().getPrintingPolicy());
     Policy.SuppressTagKeyword = true;
     HI.Type = printType(E->getType(), Policy);
if (Tok.kind() == tok::identifier) {
       // Prefer the identifier token as a fallback highlighting range.
       HighlightRange = Tok.range(SM).toCharRange(SM);
       if (auto M = locateMacroAt(Tok, AST.getPreprocessor())) {
         HI = getHoverContents(*M, AST);
         break;
       }
     } else if (Tok.kind() == tok::kw_auto || Tok.kind() == tok::kw_decltype) {
       if (auto Deduced = getDeducedType(AST.getASTContext(), Tok.location())) {
-        HI = getHoverContents(*Deduced, AST.getASTContext(), Index);
+        HI = getDeducedTypeHoverContents(*Deduced, Tok, AST.getASTContext(),
+                                         Index);
         HighlightRange = Tok.range(SM).toCharRange(SM);
         break;
       }
+
+      // If we can't find interesting hover information for this
+      // auto/decltype keyword, return nothing to avoid showing
+      // irrelevant or incorrect informations.
+      return llvm::None;
     }
   }
 
   // If it wasn't auto/decltype or macro, look for decls and expressions.
   if (!HI) {
     auto Offset = SM.getFileOffset(*CurLoc);
     // Editors send the position on the left of the hovered character.
     // So our selection tree should be biased right. (Tested with VSCode).
     SelectionTree ST =
         SelectionTree::createRight(AST.getASTContext(), TB, Offset, Offset);
     std::vector<const Decl *> Result;

clang-tools-extra/clangd/refactor/tweaks/ExpandAutoType.cpp

 //===--- ExpandAutoType.cpp --------------------------------------*- C++-*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 #include "refactor/Tweak.h"

 
 Expected<Tweak::Effect> ExpandAutoType::apply(const Selection& Inputs) {
   auto &SrcMgr = Inputs.AST->getSourceManager();
 
   llvm::Optional<clang::QualType> DeducedType = getDeducedType(
       Inputs.AST->getASTContext(), CachedLocation->getBeginLoc());
 
   // if we can't resolve the type, return an error message
-  if (DeducedType == llvm::None)
+  if (DeducedType == llvm::None || (*DeducedType)->isUndeducedAutoType())
     return error("Could not deduce type for 'auto' type");
 
   // if it's a lambda expression, return an error message
   if (isa<RecordType>(*DeducedType) &&
       dyn_cast<RecordType>(*DeducedType)->getDecl()->isLambda()) {
     return error("Could not expand type of lambda expression");
   }
 

clang-tools-extra/clangd/unittests/HoverTests.cpp

 //===-- HoverTests.cpp ----------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
class Foo {})cpp";
       {"class X { operator [[^X]](); };",
        [](HoverInfo &HI) {
          HI.NamespaceScope = "";
          HI.Name = "X";
          HI.Kind = index::SymbolKind::Class;
          HI.Definition = "class X {}";
        }},
 
+      // auto on structured bindings
+      {R"cpp(
+        void foo() {
+          struct S { int x; float y; };
+          [[au^to]] [x, y] = S();
+        }
+        )cpp",
+       [](HoverInfo &HI) {
+         HI.Name = "auto";
+         HI.Kind = index::SymbolKind::TypeAlias;
+         HI.Definition = "struct S";
+       }},
+      // undeduced auto
+      {R"cpp(
+        template<typename T>
+        void foo() {
+          [[au^to]] x = T{};
+        }
+        )cpp",
+       [](HoverInfo &HI) {
+         HI.Name = "auto";
+         HI.Kind = index::SymbolKind::TypeAlias;
+         HI.Definition = "/* not deduced */";
+       }},
       // auto on lambda
       {R"cpp(
         void foo() {
           [[au^to]] lamb = []{};
         }
         )cpp",
        [](HoverInfo &HI) {
-         HI.Name = "(lambda)";
-         HI.Kind = index::SymbolKind::Class;
+         HI.Name = "auto";
+         HI.Kind = index::SymbolKind::TypeAlias;
+         HI.Definition = "class(lambda)";
        }},
       // auto on template instantiation
       {R"cpp(
         template<typename T> class Foo{};
         void foo() {
           [[au^to]] x = Foo<int>();
         }
         )cpp",
        [](HoverInfo &HI) {
-         HI.Name = "Foo<int>";
-         HI.Kind = index::SymbolKind::Class;
+         HI.Name = "auto";
+         HI.Kind = index::SymbolKind::TypeAlias;
+         HI.Definition = "class Foo<int>";
        }},
       // auto on specialized template
       {R"cpp(
         template<typename T> class Foo{};
         template<> class Foo<int>{};
         void foo() {
           [[au^to]] x = Foo<int>();
         }
         )cpp",
        [](HoverInfo &HI) {
-         HI.Name = "Foo<int>";
-         HI.Kind = index::SymbolKind::Class;
+         HI.Name = "auto";
+         HI.Kind = index::SymbolKind::TypeAlias;
+         HI.Definition = "class Foo<int>";
        }},
 
       // macro
       {R"cpp(
         // Best MACRO ever.
         #define MACRO(x,y,z) void foo(x, y, z);
         [[MAC^RO]](int, double d, bool z = false);
         )cpp",
class Foo {})cpp";
           R"cpp(
           template <typename T> class Foo {};
           class X;
           void foo() {
             [[^auto]] x = Foo<X>();
           }
           )cpp",
           [](HoverInfo &HI) {
-            HI.Name = "Foo<X>";
-            HI.Kind = index::SymbolKind::Class;
+            HI.Name = "auto";
+            HI.Kind = index::SymbolKind::TypeAlias;
+            HI.Definition = "class Foo<class X>";
           }},
       {// Falls back to primary template, when the type is not instantiated.
        R"cpp(
           // comment from primary
           template <typename T> class Foo {};
           // comment from specialization
           template <typename T> class Foo<T*> {};
           void foo() {
for (const auto &Test : Tests) {
     EXPECT_EQ(H->CallPassType->Converted, Test.Converted);
   }
 }
 
 TEST(Hover, NoHover) {
   llvm::StringRef Tests[] = {
       "^int main() {}",
       "void foo() {^}",
-      R"cpp(// structured binding. Not supported yet
-            struct Bar {};
-            void foo() {
-              Bar a[2];
-              ^auto [x,y] = a;
-            }
-          )cpp",
-      R"cpp(// Template auto parameter. Nothing (Not useful).
-            template<a^uto T>
-            void func() {
-            }
-            void foo() {
-               func<1>();
-            }
+      // FIXME: "decltype(auto)" should be a single hover
+      "decltype(au^to) x = 0;",
+      // FIXME: not supported yet
+      R"cpp(// Lambda auto parameter
+            auto lamb = [](a^uto){};
           )cpp",
       R"cpp(// non-named decls don't get hover. Don't crash!
             ^static_assert(1, "");
           )cpp",
       R"cpp(// non-evaluatable expr
           template <typename T> void foo() {
             (void)[[size^of]](T);
           })cpp",
const std::function<void(HoverInfo &)> ExpectedBuilder;
           }},
       {
           R"cpp(// Simple initialization with auto
             void foo() {
               ^[[auto]] i = 1;
             }
           )cpp",
           [](HoverInfo &HI) {
-            HI.Name = "int";
-            // FIXME: Should be Builtin/Integral.
-            HI.Kind = index::SymbolKind::Unknown;
+            HI.Name = "auto";
+            HI.Kind = index::SymbolKind::TypeAlias;
+            HI.Definition = "int";
           }},
       {
           R"cpp(// Simple initialization with const auto
             void foo() {
               const ^[[auto]] i = 1;
             }
           )cpp",
-          [](HoverInfo &HI) { HI.Name = "int"; }},
+          [](HoverInfo &HI) {
+            HI.Name = "auto";
+            HI.Kind = index::SymbolKind::TypeAlias;
+            HI.Definition = "int";
+          }},
       {
           R"cpp(// Simple initialization with const auto&
             void foo() {
               const ^[[auto]]& i = 1;
             }
           )cpp",
-          [](HoverInfo &HI) { HI.Name = "int"; }},
+          [](HoverInfo &HI) {
+            HI.Name = "auto";
+            HI.Kind = index::SymbolKind::TypeAlias;
+            HI.Definition = "int";
+          }},
       {
           R"cpp(// Simple initialization with auto&
             void foo() {
               int x;
               ^[[auto]]& i = x;
             }
           )cpp",
-          [](HoverInfo &HI) { HI.Name = "int"; }},
+          [](HoverInfo &HI) {
+            HI.Name = "auto";
+            HI.Kind = index::SymbolKind::TypeAlias;
+            HI.Definition = "int";
+          }},
       {
           R"cpp(// Simple initialization with auto*
             void foo() {
               int a = 1;
               ^[[auto]]* i = &a;
             }
           )cpp",
-          [](HoverInfo &HI) { HI.Name = "int"; }},
+          [](HoverInfo &HI) {
+            HI.Name = "auto";
+            HI.Kind = index::SymbolKind::TypeAlias;
+            HI.Definition = "int";
+          }},
+      {
+          R"cpp(// Simple initialization with auto from pointer
+            void foo() {
+              int a = 1;
+              ^[[auto]] i = &a;
+            }
+          )cpp",
+          [](HoverInfo &HI) {
+            HI.Name = "auto";
+            HI.Kind = index::SymbolKind::TypeAlias;
+            HI.Definition = "int *";
+          }},
       {
           R"cpp(// Auto with initializer list.
             namespace std
             {
               template<class _E>
               class initializer_list {};
             }
             void foo() {
               ^[[auto]] i = {1,2};
             }
           )cpp",
           [](HoverInfo &HI) {
-            HI.Name = "initializer_list<int>";
-            HI.Kind = index::SymbolKind::Class;
+            HI.Name = "auto";
+            HI.Kind = index::SymbolKind::TypeAlias;
+            HI.Definition = "class std::initializer_list<int>";
           }},
       {
           R"cpp(// User defined conversion to auto
             struct Bar {
               operator ^[[auto]]() const { return 10; }
             };
           )cpp",
-          [](HoverInfo &HI) { HI.Name = "int"; }},
+          [](HoverInfo &HI) {
+            HI.Name = "auto";
+            HI.Kind = index::SymbolKind::TypeAlias;
+            HI.Definition = "int";
+          }},
       {
           R"cpp(// Simple initialization with decltype(auto)
             void foo() {
               ^[[decltype]](auto) i = 1;
             }
           )cpp",
-          [](HoverInfo &HI) { HI.Name = "int"; }},
+          [](HoverInfo &HI) {
+            HI.Name = "decltype";
+            HI.Kind = index::SymbolKind::TypeAlias;
+            HI.Definition = "int";
+          }},
       {
           R"cpp(// Simple initialization with const decltype(auto)
             void foo() {
               const int j = 0;
               ^[[decltype]](auto) i = j;
             }
           )cpp",
-          [](HoverInfo &HI) { HI.Name = "const int"; }},
+          [](HoverInfo &HI) {
+            HI.Name = "decltype";
+            HI.Kind = index::SymbolKind::TypeAlias;
+            HI.Definition = "const int";
+          }},
       {
           R"cpp(// Simple initialization with const& decltype(auto)
             void foo() {
               int k = 0;
               const int& j = k;
               ^[[decltype]](auto) i = j;
             }
           )cpp",
-          [](HoverInfo &HI) { HI.Name = "const int &"; }},
+          [](HoverInfo &HI) {
+            HI.Name = "decltype";
+            HI.Kind = index::SymbolKind::TypeAlias;
+            HI.Definition = "const int &";
+          }},
       {
           R"cpp(// Simple initialization with & decltype(auto)
             void foo() {
               int k = 0;
               int& j = k;
               ^[[decltype]](auto) i = j;
             }
           )cpp",
-          [](HoverInfo &HI) { HI.Name = "int &"; }},
+          [](HoverInfo &HI) {
+            HI.Name = "decltype";
+            HI.Kind = index::SymbolKind::TypeAlias;
+            HI.Definition = "int &";
+          }},
       {
           R"cpp(// simple trailing return type
             ^[[auto]] main() -> int {
               return 0;
             }
           )cpp",
-          [](HoverInfo &HI) { HI.Name = "int"; }},
+          [](HoverInfo &HI) {
+            HI.Name = "auto";
+            HI.Kind = index::SymbolKind::TypeAlias;
+            HI.Definition = "int";
+          }},
       {
           R"cpp(// auto function return with trailing type
             struct Bar {};
             ^[[auto]] test() -> decltype(Bar()) {
               return Bar();
             }
           )cpp",
           [](HoverInfo &HI) {
-            HI.Name = "Bar";
-            HI.Kind = index::SymbolKind::Struct;
+            HI.Name = "auto";
+            HI.Kind = index::SymbolKind::TypeAlias;
+            HI.Definition = "struct Bar";
             HI.Documentation = "auto function return with trailing type";
           }},
       {
           R"cpp(// trailing return type
             struct Bar {};
             auto test() -> ^[[decltype]](Bar()) {
               return Bar();
             }
           )cpp",
           [](HoverInfo &HI) {
-            HI.Name = "Bar";
-            HI.Kind = index::SymbolKind::Struct;
+            HI.Name = "decltype";
+            HI.Kind = index::SymbolKind::TypeAlias;
+            HI.Definition = "struct Bar";
             HI.Documentation = "trailing return type";
           }},
       {
           R"cpp(// auto in function return
             struct Bar {};
             ^[[auto]] test() {
               return Bar();
             }
           )cpp",
           [](HoverInfo &HI) {
-            HI.Name = "Bar";
-            HI.Kind = index::SymbolKind::Struct;
+            HI.Name = "auto";
+            HI.Kind = index::SymbolKind::TypeAlias;
+            HI.Definition = "struct Bar";
             HI.Documentation = "auto in function return";
           }},
       {
           R"cpp(// auto& in function return
             struct Bar {};
             ^[[auto]]& test() {
               static Bar x;
               return x;
             }
           )cpp",
           [](HoverInfo &HI) {
-            HI.Name = "Bar";
-            HI.Kind = index::SymbolKind::Struct;
+            HI.Name = "auto";
+            HI.Kind = index::SymbolKind::TypeAlias;
+            HI.Definition = "struct Bar";
             HI.Documentation = "auto& in function return";
           }},
       {
           R"cpp(// auto* in function return
             struct Bar {};
             ^[[auto]]* test() {
               Bar* bar;
               return bar;
             }
           )cpp",
           [](HoverInfo &HI) {
-            HI.Name = "Bar";
-            HI.Kind = index::SymbolKind::Struct;
+            HI.Name = "auto";
+            HI.Kind = index::SymbolKind::TypeAlias;
+            HI.Definition = "struct Bar";
             HI.Documentation = "auto* in function return";
           }},
       {
           R"cpp(// const auto& in function return
             struct Bar {};
             const ^[[auto]]& test() {
               static Bar x;
               return x;
             }
           )cpp",
           [](HoverInfo &HI) {
-            HI.Name = "Bar";
-            HI.Kind = index::SymbolKind::Struct;
+            HI.Name = "auto";
+            HI.Kind = index::SymbolKind::TypeAlias;
+            HI.Definition = "struct Bar";
             HI.Documentation = "const auto& in function return";
           }},
       {
           R"cpp(// decltype(auto) in function return
             struct Bar {};
             ^[[decltype]](auto) test() {
               return Bar();
             }
           )cpp",
           [](HoverInfo &HI) {
-            HI.Name = "Bar";
-            HI.Kind = index::SymbolKind::Struct;
+            HI.Name = "decltype";
+            HI.Kind = index::SymbolKind::TypeAlias;
+            HI.Definition = "struct Bar";
             HI.Documentation = "decltype(auto) in function return";
           }},
       {
           R"cpp(// decltype(auto) reference in function return
             ^[[decltype]](auto) test() {
               static int a;
               return (a);
             }
           )cpp",
-          [](HoverInfo &HI) { HI.Name = "int &"; }},
+          [](HoverInfo &HI) {
+            HI.Name = "decltype";
+            HI.Kind = index::SymbolKind::TypeAlias;
+            HI.Definition = "int &";
+          }},
       {
           R"cpp(// decltype lvalue reference
             void foo() {
               int I = 0;
               ^[[decltype]](I) J = I;
             }
           )cpp",
-          [](HoverInfo &HI) { HI.Name = "int"; }},
+          [](HoverInfo &HI) {
+            HI.Name = "decltype";
+            HI.Kind = index::SymbolKind::TypeAlias;
+            HI.Definition = "int";
+          }},
       {
           R"cpp(// decltype lvalue reference
             void foo() {
               int I= 0;
               int &K = I;
               ^[[decltype]](K) J = I;
             }
           )cpp",
-          [](HoverInfo &HI) { HI.Name = "int &"; }},
+          [](HoverInfo &HI) {
+            HI.Name = "decltype";
+            HI.Kind = index::SymbolKind::TypeAlias;
+            HI.Definition = "int &";
+          }},
       {
           R"cpp(// decltype lvalue reference parenthesis
             void foo() {
               int I = 0;
               ^[[decltype]]((I)) J = I;
             }
           )cpp",
-          [](HoverInfo &HI) { HI.Name = "int &"; }},
+          [](HoverInfo &HI) {
+            HI.Name = "decltype";
+            HI.Kind = index::SymbolKind::TypeAlias;
+            HI.Definition = "int &";
+          }},
       {
           R"cpp(// decltype rvalue reference
             void foo() {
               int I = 0;
               ^[[decltype]](static_cast<int&&>(I)) J = static_cast<int&&>(I);
             }
           )cpp",
-          [](HoverInfo &HI) { HI.Name = "int &&"; }},
+          [](HoverInfo &HI) {
+            HI.Name = "decltype";
+            HI.Kind = index::SymbolKind::TypeAlias;
+            HI.Definition = "int &&";
+          }},
       {
           R"cpp(// decltype rvalue reference function call
             int && bar();
             void foo() {
               int I = 0;
               ^[[decltype]](bar()) J = bar();
             }
           )cpp",
-          [](HoverInfo &HI) { HI.Name = "int &&"; }},
+          [](HoverInfo &HI) {
+            HI.Name = "decltype";
+            HI.Kind = index::SymbolKind::TypeAlias;
+            HI.Definition = "int &&";
+          }},
       {
           R"cpp(// decltype of function with trailing return type.
             struct Bar {};
             auto test() -> decltype(Bar()) {
               return Bar();
             }
             void foo() {
               ^[[decltype]](test()) i = test();
             }
           )cpp",
           [](HoverInfo &HI) {
-            HI.Name = "Bar";
-            HI.Kind = index::SymbolKind::Struct;
+            HI.Name = "decltype";
+            HI.Kind = index::SymbolKind::TypeAlias;
+            HI.Definition = "struct Bar";
             HI.Documentation =
                 "decltype of function with trailing return type.";
           }},
       {
           R"cpp(// decltype of var with decltype.
             void foo() {
               int I = 0;
               decltype(I) J = I;
               ^[[decltype]](J) K = J;
             }
           )cpp",
-          [](HoverInfo &HI) { HI.Name = "int"; }},
+          [](HoverInfo &HI) {
+            HI.Name = "decltype";
+            HI.Kind = index::SymbolKind::TypeAlias;
+            HI.Definition = "int";
+          }},
+      {
+          R"cpp(// decltype of dependent type
+            template <typename T>
+            struct X {
+              using Y = ^[[decltype]](T::Z);
+            };
+          )cpp",
+          [](HoverInfo &HI) {
+            HI.Name = "decltype";
+            HI.Kind = index::SymbolKind::TypeAlias;
+            HI.Definition = "<dependent type>";
+          }},
       {
           R"cpp(// More complicated structured types.
             int bar();
             ^[[auto]] (*foo)() = bar;
           )cpp",
-          [](HoverInfo &HI) { HI.Name = "int"; }},
+          [](HoverInfo &HI) {
+            HI.Name = "auto";
+            HI.Kind = index::SymbolKind::TypeAlias;
+            HI.Definition = "int";
+          }},
       {
           R"cpp(// Should not crash when evaluating the initializer.
             struct Test {};
             void test() { Test && [[te^st]] = {}; }
           )cpp",
           [](HoverInfo &HI) {
             HI.Name = "test";
             HI.Kind = index::SymbolKind::Variable;
             HI.NamespaceScope = "";
             HI.LocalScope = "test::";
             HI.Type = "struct Test &&";
             HI.Definition = "Test &&test = {}";
           }},
       {
           R"cpp(// auto on alias
           typedef int int_type;
           ^[[auto]] x = int_type();
           )cpp",
-          [](HoverInfo &HI) { HI.Name = "int"; }},
+          [](HoverInfo &HI) {
+            HI.Name = "auto";
+            HI.Kind = index::SymbolKind::TypeAlias;
+            HI.Definition = "int";
+          }},
       {
           R"cpp(// auto on alias
           struct cls {};
           typedef cls cls_type;
           ^[[auto]] y = cls_type();
           )cpp",
           [](HoverInfo &HI) {
-            HI.Name = "cls";
-            HI.Kind = index::SymbolKind::Struct;
+            HI.Name = "auto";
+            HI.Kind = index::SymbolKind::TypeAlias;
+            HI.Definition = "struct cls";
             HI.Documentation = "auto on alias";
           }},
       {
           R"cpp(// auto on alias
           template <class>
           struct templ {};
           ^[[auto]] z = templ<int>();
           )cpp",
           [](HoverInfo &HI) {
-            HI.Name = "templ<int>";
-            HI.Kind = index::SymbolKind::Struct;
+            HI.Name = "auto";
+            HI.Kind = index::SymbolKind::TypeAlias;
+            HI.Definition = "struct templ<int>";
             HI.Documentation = "auto on alias";
           }},
       {
+          R"cpp(// Undeduced auto declaration
+            template<typename T>
+            void foo() {
+              ^[[auto]] x = T();
+            }
+          )cpp",
+          [](HoverInfo &HI) {
+            HI.Name = "auto";
+            HI.Kind = index::SymbolKind::TypeAlias;
+            HI.Definition = "/* not deduced */";
+          }},
+      {
+          R"cpp(// Undeduced auto return type
+            template<typename T>
+            ^[[auto]] foo() {
+              return T();
+            }
+          )cpp",
+          [](HoverInfo &HI) {
+            HI.Name = "auto";
+            HI.Kind = index::SymbolKind::TypeAlias;
+            HI.Definition = "/* not deduced */";
+          }},
+      {
+          R"cpp(// Template auto parameter
+            template<[[a^uto]] T>
+              void func() {
+            }
+          )cpp",
+          [](HoverInfo &HI) {
+            // FIXME: not sure this is what we want, but this
+            // is what we currently get with getDeducedType
+            HI.Name = "auto";
+            HI.Kind = index::SymbolKind::TypeAlias;
+            HI.Definition = "/* not deduced */";
+          }},
+      {
+          R"cpp(// Undeduced decltype(auto) return type
+            template<typename T>
+            ^[[decltype]](auto) foo() {
+              return T();
+            }
+          )cpp",
+          [](HoverInfo &HI) {
+            HI.Name = "decltype";
+            HI.Kind = index::SymbolKind::TypeAlias;
+            HI.Definition = "/* not deduced */";
+          }},
+      {
           R"cpp(// should not crash.
           template <class T> struct cls {
             int method();
           };
 
           auto test = cls<int>().[[m^ethod]]();
           )cpp",
           [](HoverInfo &HI) {

           namespace ns {
             class Foo {
               Foo* bar() {
                 return [[t^his]];
               }
             };
           }
           )cpp",
-          [](HoverInfo &HI) { HI.Name = "Foo *"; }},
+          [](HoverInfo &HI) {
+            HI.Name = "this";
+            HI.Definition = "Foo *";
+          }},
       {
           R"cpp(// this expr for template class
           namespace ns {
             template <typename T>
             class Foo {
               Foo* bar() const {
                 return [[t^his]];
               }
             };
           }
           )cpp",
-          [](HoverInfo &HI) { HI.Name = "const Foo<T> *"; }},
+          [](HoverInfo &HI) {
+            HI.Name = "this";
+            HI.Definition = "const Foo<T> *";
+          }},
       {
           R"cpp(// this expr for specialization class
           namespace ns {
             template <typename T> class Foo {};
             template <>
             struct Foo<int> {
               Foo* bar() {
                 return [[thi^s]];
               }
             };
           }
           )cpp",
-          [](HoverInfo &HI) { HI.Name = "Foo<int> *"; }},
+          [](HoverInfo &HI) {
+            HI.Name = "this";
+            HI.Definition = "Foo<int> *";
+          }},
       {
           R"cpp(// this expr for partial specialization struct
           namespace ns {
             template <typename T, typename F> struct Foo {};
             template <typename F>
             struct Foo<int, F> {
               Foo* bar() const {
                 return [[thi^s]];
               }
             };
           }
           )cpp",
-          [](HoverInfo &HI) { HI.Name = "const Foo<int, F> *"; }},
+          [](HoverInfo &HI) {
+            HI.Name = "this";
+            HI.Definition = "const Foo<int, F> *";
+          }},
   };
 
   // Create a tiny index, so tests above can verify documentation is fetched.
   Symbol IndexSym = func("indexSymbol");
   IndexSym.Documentation = "comment from index";
   SymbolSlab::Builder Symbols;
   Symbols.insert(IndexSym);
   auto Index =
for (const auto &Case : Cases) {
     EXPECT_EQ(H->Value, Expected.Value);
   }
 }
 
 TEST(Hover, DocsFromIndex) {
   Annotations T(R"cpp(
   template <typename T> class X {};
   void foo() {
-    au^to t = X<int>();
+    auto t = X<int>();
     X^<int> w;
     (void)w;
   })cpp");
 
   TestTU TU = TestTU::withCode(T.code());
   auto AST = TU.build();
   Symbol IndexSym;
   IndexSym.ID = getSymbolID(&findDecl(AST, "X"));
template <typename T, typename C = bool> class Foo {})",
             HI.Parameters->push_back(P);
             P.Name = "foo";
             HI.Parameters->push_back(P);
             P.Default = "default";
             HI.Parameters->push_back(P);
             HI.NamespaceScope = "ns::";
             HI.Definition = "ret_type foo(params) {}";
           },
-          R"(function foo
-
-→ ret_type
-Parameters:
-- 
-- type
-- type foo
-- type foo = default
-
-// In namespace ns
-ret_type foo(params) {})",
+          "function foo\n"
+          "\n"
+          "→ ret_type\n"
+          "Parameters:\n"
+          "- \n"
+          "- type\n"
+          "- type foo\n"
+          "- type foo = default\n"
+          "\n"
+          "// In namespace ns\n"
+          "ret_type foo(params) {}",
       },
       {
           [](HoverInfo &HI) {
             HI.Kind = index::SymbolKind::Field;
             HI.LocalScope = "test::Bar::";
             HI.Value = "value";
             HI.Name = "foo";
             HI.Type = "type";

 // plaintext.
 TEST(Hover, PresentRulers) {
   HoverInfo HI;
   HI.Kind = index::SymbolKind::Variable;
   HI.Name = "foo";
   HI.Value = "val";
   HI.Definition = "def";
 
-  llvm::StringRef ExpectedMarkdown = R"md(### variable `foo`  
-
----
-Value = `val`  
-
----
-```cpp
-def
-```)md";
+  llvm::StringRef ExpectedMarkdown = //
+      "### variable `foo`  \n"
+      "\n"
+      "---\n"
+      "Value = `val`  \n"
+      "\n"
+      "---\n"
+      "```cpp\n"
+      "def\n"
+      "```";
   EXPECT_EQ(HI.present().asMarkdown(), ExpectedMarkdown);
 
   llvm::StringRef ExpectedPlaintext = R"pt(variable foo
 
 Value = val
 
 def)pt";
   EXPECT_EQ(HI.present().asPlainText(), ExpectedPlaintext);
 }
 } // namespace
 } // namespace clangd
 } // namespace clang