[clangd] Retrieve documentation for class member instance from index

Fixes clangd/clangd#2290

Author: HighCommander4

clang-tools-extra/clangd/CodeComplete.cpp

@@ -43,6 +43,7 @@
 #include "support/Trace.h"
 #include "clang/AST/Decl.h"
 #include "clang/AST/DeclBase.h"
+#include "clang/AST/DeclTemplate.h"
 #include "clang/Basic/CharInfo.h"
 #include "clang/Basic/LangOptions.h"
 #include "clang/Basic/SourceLocation.h"
@@ -1883,7 +1884,15 @@ class CodeCompleteFlow {
         for (auto &Cand : C.first) {
           if (Cand.SemaResult &&
               Cand.SemaResult->Kind == CodeCompletionResult::RK_Declaration) {
-            auto ID = clangd::getSymbolID(Cand.SemaResult->getDeclaration());
+            const NamedDecl *DeclToLookup = Cand.SemaResult->getDeclaration();
+            // For instantiations of members of class templates, the
+            // documentation will be stored at the member's original
+            // declaration.
+            if (const NamedDecl *Adjusted =
+                    dyn_cast<NamedDecl>(&adjustDeclToTemplate(*DeclToLookup))) {
+              DeclToLookup = Adjusted;
+            }
+            auto ID = clangd::getSymbolID(DeclToLookup);
             if (!ID)
               continue;
             Req.IDs.insert(ID);

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

@@ -1154,23 +1154,45 @@ TEST(CompletionTest, CommentsOnMembersFromHeader) {
       /// This is a member function.
       int delta();
     };
+
+    template <typename T>
+    struct beta {
+      /// This is a member field inside a template.
+      int omega;
+
+      /// This is a member function inside a template.
+      int epsilon();
+    };
   )cpp";
 
   auto File = testPath("foo.cpp");
   Annotations Test(R"cpp(
 #include "foo.h"
 alpha a;
-int x = a.^
+beta<int> b;
+int x = a.$p1^;
+int y = b.$p2^;
      )cpp");
   runAddDocument(Server, File, Test.code());
   auto CompletionList =
-      llvm::cantFail(runCodeComplete(Server, File, Test.point(), {}));
+      llvm::cantFail(runCodeComplete(Server, File, Test.point("p1"), {}));
 
   EXPECT_THAT(CompletionList.Completions,
               Contains(AllOf(named("gamma"), doc("This is a member field."))));
   EXPECT_THAT(
       CompletionList.Completions,
       Contains(AllOf(named("delta"), doc("This is a member function."))));
+
+  CompletionList =
+      llvm::cantFail(runCodeComplete(Server, File, Test.point("p2"), {}));
+
+  EXPECT_THAT(CompletionList.Completions,
+              Contains(AllOf(named("omega")
+                             /* FIXME: Doc retrieval does not work yet*/)));
+  EXPECT_THAT(
+      CompletionList.Completions,
+      Contains(AllOf(named("epsilon"),
+                     doc("This is a member function inside a template."))));
 }
 
 TEST(CompletionTest, CommentsOnMembersFromHeaderOverloadBundling) {

clang/include/clang/AST/DeclTemplate.h

@@ -3399,6 +3399,11 @@ inline UnsignedOrNone getExpandedPackSize(const NamedDecl *Param) {
 /// for their AssociatedDecl.
 TemplateParameterList *getReplacedTemplateParameterList(const Decl *D);
 
+/// If we have a 'templated' declaration for a template, adjust 'D' to
+/// refer to the actual template.
+/// If we have an implicit instantiation, adjust 'D' to refer to template.
+const Decl &adjustDeclToTemplate(const Decl &D);
+
 } // namespace clang
 
 #endif // LLVM_CLANG_AST_DECLTEMPLATE_H

clang/lib/AST/ASTContext.cpp

@@ -351,76 +351,6 @@ void ASTContext::addComment(const RawComment &RC) {
   Comments.addComment(RC, LangOpts.CommentOpts, BumpAlloc);
 }
 
-/// If we have a 'templated' declaration for a template, adjust 'D' to
-/// refer to the actual template.
-/// If we have an implicit instantiation, adjust 'D' to refer to template.
-static const Decl &adjustDeclToTemplate(const Decl &D) {
-  if (const auto *FD = dyn_cast<FunctionDecl>(&D)) {
-    // Is this function declaration part of a function template?
-    if (const FunctionTemplateDecl *FTD = FD->getDescribedFunctionTemplate())
-      return *FTD;
-
-    // Nothing to do if function is not an implicit instantiation.
-    if (FD->getTemplateSpecializationKind() != TSK_ImplicitInstantiation)
-      return D;
-
-    // Function is an implicit instantiation of a function template?
-    if (const FunctionTemplateDecl *FTD = FD->getPrimaryTemplate())
-      return *FTD;
-
-    // Function is instantiated from a member definition of a class template?
-    if (const FunctionDecl *MemberDecl =
-            FD->getInstantiatedFromMemberFunction())
-      return *MemberDecl;
-
-    return D;
-  }
-  if (const auto *VD = dyn_cast<VarDecl>(&D)) {
-    // Static data member is instantiated from a member definition of a class
-    // template?
-    if (VD->isStaticDataMember())
-      if (const VarDecl *MemberDecl = VD->getInstantiatedFromStaticDataMember())
-        return *MemberDecl;
-
-    return D;
-  }
-  if (const auto *CRD = dyn_cast<CXXRecordDecl>(&D)) {
-    // Is this class declaration part of a class template?
-    if (const ClassTemplateDecl *CTD = CRD->getDescribedClassTemplate())
-      return *CTD;
-
-    // Class is an implicit instantiation of a class template or partial
-    // specialization?
-    if (const auto *CTSD = dyn_cast<ClassTemplateSpecializationDecl>(CRD)) {
-      if (CTSD->getSpecializationKind() != TSK_ImplicitInstantiation)
-        return D;
-      llvm::PointerUnion<ClassTemplateDecl *,
-                         ClassTemplatePartialSpecializationDecl *>
-          PU = CTSD->getSpecializedTemplateOrPartial();
-      return isa<ClassTemplateDecl *>(PU)
-                 ? *static_cast<const Decl *>(cast<ClassTemplateDecl *>(PU))
-                 : *static_cast<const Decl *>(
-                       cast<ClassTemplatePartialSpecializationDecl *>(PU));
-    }
-
-    // Class is instantiated from a member definition of a class template?
-    if (const MemberSpecializationInfo *Info =
-            CRD->getMemberSpecializationInfo())
-      return *Info->getInstantiatedFrom();
-
-    return D;
-  }
-  if (const auto *ED = dyn_cast<EnumDecl>(&D)) {
-    // Enum is instantiated from a member definition of a class template?
-    if (const EnumDecl *MemberDecl = ED->getInstantiatedFromMemberEnum())
-      return *MemberDecl;
-
-    return D;
-  }
-  // FIXME: Adjust alias templates?
-  return D;
-}
-
 const RawComment *ASTContext::getRawCommentForAnyRedecl(
                                                 const Decl *D,
                                                 const Decl **OriginalDecl) const {

clang/lib/AST/DeclTemplate.cpp

@@ -1706,3 +1706,70 @@ TemplateParameterList *clang::getReplacedTemplateParameterList(const Decl *D) {
     llvm_unreachable("Unhandled templated declaration kind");
   }
 }
+
+const Decl &clang::adjustDeclToTemplate(const Decl &D) {
+  if (const auto *FD = dyn_cast<FunctionDecl>(&D)) {
+    // Is this function declaration part of a function template?
+    if (const FunctionTemplateDecl *FTD = FD->getDescribedFunctionTemplate())
+      return *FTD;
+
+    // Nothing to do if function is not an implicit instantiation.
+    if (FD->getTemplateSpecializationKind() != TSK_ImplicitInstantiation)
+      return D;
+
+    // Function is an implicit instantiation of a function template?
+    if (const FunctionTemplateDecl *FTD = FD->getPrimaryTemplate())
+      return *FTD;
+
+    // Function is instantiated from a member definition of a class template?
+    if (const FunctionDecl *MemberDecl =
+            FD->getInstantiatedFromMemberFunction())
+      return *MemberDecl;
+
+    return D;
+  }
+  if (const auto *VD = dyn_cast<VarDecl>(&D)) {
+    // Static data member is instantiated from a member definition of a class
+    // template?
+    if (VD->isStaticDataMember())
+      if (const VarDecl *MemberDecl = VD->getInstantiatedFromStaticDataMember())
+        return *MemberDecl;
+
+    return D;
+  }
+  if (const auto *CRD = dyn_cast<CXXRecordDecl>(&D)) {
+    // Is this class declaration part of a class template?
+    if (const ClassTemplateDecl *CTD = CRD->getDescribedClassTemplate())
+      return *CTD;
+
+    // Class is an implicit instantiation of a class template or partial
+    // specialization?
+    if (const auto *CTSD = dyn_cast<ClassTemplateSpecializationDecl>(CRD)) {
+      if (CTSD->getSpecializationKind() != TSK_ImplicitInstantiation)
+        return D;
+      llvm::PointerUnion<ClassTemplateDecl *,
+                         ClassTemplatePartialSpecializationDecl *>
+          PU = CTSD->getSpecializedTemplateOrPartial();
+      return isa<ClassTemplateDecl *>(PU)
+                 ? *static_cast<const Decl *>(cast<ClassTemplateDecl *>(PU))
+                 : *static_cast<const Decl *>(
+                       cast<ClassTemplatePartialSpecializationDecl *>(PU));
+    }
+
+    // Class is instantiated from a member definition of a class template?
+    if (const MemberSpecializationInfo *Info =
+            CRD->getMemberSpecializationInfo())
+      return *Info->getInstantiatedFrom();
+
+    return D;
+  }
+  if (const auto *ED = dyn_cast<EnumDecl>(&D)) {
+    // Enum is instantiated from a member definition of a class template?
+    if (const EnumDecl *MemberDecl = ED->getInstantiatedFromMemberEnum())
+      return *MemberDecl;
+
+    return D;
+  }
+  // FIXME: Adjust alias templates?
+  return D;
+}