[clangd] Smarter hover on auto and decltype

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.

Reviewed By: sammccall

Differential Revision: https://reviews.llvm.org/D93227

Author: qchateau

clang-tools-extra/clangd/AST.cpp

@@ -350,8 +350,7 @@ class DeducedTypeVisitor : public RecursiveASTVisitor<DeducedTypeVisitor> {
       return true;
 
     if (auto *AT = D->getType()->getContainedAutoType()) {
-      if (!AT->getDeducedType().isNull())
-        DeducedType = AT->getDeducedType();
+      DeducedType = AT->desugar();
     }
     return true;
   }

clang-tools-extra/clangd/AST.h

@@ -109,6 +109,7 @@ QualType declaredType(const TypeDecl *D);
 
 /// Retrieves the deduced type at a given location (auto, decltype).
 /// It will return the underlying type.
+/// If the type is an undeduced auto, returns the type itself.
 llvm::Optional<QualType> getDeducedType(ASTContext &, SourceLocation Loc);
 
 /// Gets the nested name specifier necessary for spelling \p ND in \p

clang-tools-extra/clangd/Hover.cpp

@@ -27,6 +27,7 @@
 #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"
@@ -550,29 +551,6 @@ HoverInfo getHoverContents(const NamedDecl *D, const SymbolIndex *Index) {
   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;
@@ -608,6 +586,52 @@ HoverInfo getHoverContents(const DefinedMacro &Macro, ParsedAST &AST) {
   return HI;
 }
 
+llvm::Optional<HoverInfo> getThisExprHoverContents(const CXXThisExpr *CTE,
+                                                   ASTContext &ASTCtx) {
+  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.
@@ -641,18 +665,8 @@ llvm::Optional<HoverInfo> getHoverContents(const Expr *E, ParsedAST &AST,
 
   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);
-  }
+  if (const CXXThisExpr *CTE = dyn_cast<CXXThisExpr>(E))
+    return getThisExprHoverContents(CTE, AST.getASTContext());
   // For expressions we currently print the type and the value, iff it is
   // evaluatable.
   if (auto Val = printExprValue(E, AST.getASTContext())) {
@@ -849,10 +863,16 @@ llvm::Optional<HoverInfo> getHover(ParsedAST &AST, Position Pos,
       }
     } 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;
     }
   }
 

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

@@ -106,7 +106,7 @@ Expected<Tweak::Effect> ExpandAutoType::apply(const Selection& Inputs) {
       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