[clangd][Hover] Handle uninstantiated templates

[kadircet]

Summary

Fixes https://github.com/clangd/clangd/issues/263

[merge_guards_bot]

Unit tests: unknown.

clang-tidy: unknown.

clang-format: unknown.

Build artifacts: diff.json, console-log.txt

Pre-merge checks is in beta. Report issue. Please join beta or enable it for your project.

[sammccall]

Can you file a new bug or modify the upstream one to audit existing uses of getTemplateInstantiationPattern() (and maybe related functions)?

getSpecializedTemplate() is used with no null check in findTarget and xrefs, and I'm sure related cases are around too.

clang-tools-extra/clangd/Hover.cpp

209

I think "Template may not be instantiated e.g. if the type didn't need to be complete; fallback to primary template." might be enough of a comment here

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

557

make these comments meaningful

557

Can you add a comment about what specifically this is testing?
(Type isn't instantiated, we fall back to primary template)

[kadircet]

• Address comments

[merge_guards_bot]

Unit tests: fail. 62158 tests passed, 5 failed and 811 were skipped.

failed: libc++.std/language_support/cmp/cmp_partialord/partialord.pass.cpp
failed: libc++.std/language_support/cmp/cmp_strongeq/cmp.strongeq.pass.cpp
failed: libc++.std/language_support/cmp/cmp_strongord/strongord.pass.cpp
failed: libc++.std/language_support/cmp/cmp_weakeq/cmp.weakeq.pass.cpp
failed: libc++.std/language_support/cmp/cmp_weakord/weakord.pass.cpp

clang-tidy: pass.

clang-format: pass.

Build artifacts: diff.json, clang-tidy.txt, clang-format.patch, CMakeCache.txt, console-log.txt, test-results.xml

Pre-merge checks is in beta. Report issue. Please join beta or enable it for your project.

clang-tools-extra/clangd/Hover.cpp

 #include "clang/AST/ASTTypeTraits.h"
 #include "clang/AST/Decl.h"
 #include "clang/AST/DeclBase.h"
 #include "clang/AST/DeclTemplate.h"
 #include "clang/AST/Expr.h"
 #include "clang/AST/ExprCXX.h"
 #include "clang/AST/PrettyPrinter.h"
 #include "clang/AST/Type.h"
+#include "clang/Basic/Specifiers.h"
 #include "clang/Index/IndexSymbol.h"
 #include "llvm/ADT/None.h"
 #include "llvm/ADT/Optional.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/StringExtras.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/Support/Casting.h"
const FunctionDecl *getUnderlyingFunction(const Decl *D) {
 
   // Non-lambda functions.
   return D->getAsFunction();
 }
 
 // Returns the decl that should be used for querying comments, either from index
 // or AST.
 const NamedDecl *getDeclForComment(const NamedDecl *D) {
-  if (auto *CTSD = llvm::dyn_cast<ClassTemplateSpecializationDecl>(D))
-    if (!CTSD->isExplicitInstantiationOrSpecialization())
-      return CTSD->getTemplateInstantiationPattern();
-  if (auto *VTSD = llvm::dyn_cast<VarTemplateSpecializationDecl>(D))
-    if (!VTSD->isExplicitInstantiationOrSpecialization())
-      return VTSD->getTemplateInstantiationPattern();
-  if (auto *FD = D->getAsFunction())
-    if (FD->isTemplateInstantiation())
-      return FD->getTemplateInstantiationPattern();
+  if (const auto *TSD = llvm::dyn_cast<ClassTemplateSpecializationDecl>(D)) {
+    // Template may not be instantiated e.g. if the type didn't need to be
+    // complete; fallback to primary template.
+    if (TSD->getTemplateSpecializationKind() == TSK_Undeclared)
+      return TSD->getSpecializedTemplate();
+    if (const auto *TIP = TSD->getTemplateInstantiationPattern())
+      return TIP;
+  }
+  if (const auto *TSD = llvm::dyn_cast<VarTemplateSpecializationDecl>(D)) {
+    if (TSD->getTemplateSpecializationKind() == TSK_Undeclared)
+      return TSD->getSpecializedTemplate();
+    if (const auto *TIP = TSD->getTemplateInstantiationPattern())
+      return TIP;
+  }
+  if (const auto *FD = D->getAsFunction())
+    if (const auto *TIP = FD->getTemplateInstantiationPattern())
+      return TIP;
   return D;
 }
 
 // Look up information about D from the index, and add it to Hover.
 void enhanceFromIndex(HoverInfo &Hover, const NamedDecl &ND,
                       const SymbolIndex *Index) {
   assert(&ND == getDeclForComment(&ND));
   // We only add documentation, so don't bother if we already have some.

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

class Foo {})cpp";
           void foo() {
             [[^auto]] x = Foo<X>();
           }
           )cpp",
           [](HoverInfo &HI) {
             HI.Name = "Foo<X>";
             HI.Kind = index::SymbolKind::Class;
           }},
+      {// 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() {
+            [[Fo^o]]<int*> *x = nullptr;
+          }
+          )cpp",
+       [](HoverInfo &HI) {
+         HI.Name = "Foo<int *>";
+         HI.Kind = index::SymbolKind::Class;
+         HI.NamespaceScope = "";
+         HI.Definition = "template <> class Foo<int *>";
+         // FIXME: Maybe force instantiation to make use of real template
+         // pattern.
+         HI.Documentation = "comment from primary";
+       }},
   };
   for (const auto &Case : Cases) {
     SCOPED_TRACE(Case.Code);
 
     Annotations T(Case.Code);
     TestTU TU = TestTU::withCode(T.code());
     TU.ExtraArgs.push_back("-std=c++17");
     TU.ExtraArgs.push_back("-fno-delayed-template-parsing");