From a31a61dafeaa9110687110fc127ea6f7c91dd3e6 Mon Sep 17 00:00:00 2001
From: Kadir Cetinkaya <kadircet@google.com>
Date: Fri, 24 Jan 2020 13:04:00 +0100
Subject: [PATCH] [clangd][Hover] Handle uninstantiated templates

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

Reviewers: hokein, sammccall

Subscribers: ilya-biryukov, MaskRay, jkorous, arphaman, usaxena95, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D73344
---
 clang-tools-extra/clangd/Hover.cpp                | 27 +++++++++++++++--------
 clang-tools-extra/clangd/unittests/HoverTests.cpp | 19 ++++++++++++++++
 2 files changed, 37 insertions(+), 9 deletions(-)

diff --git a/clang-tools-extra/clangd/Hover.cpp b/clang-tools-extra/clangd/Hover.cpp
index 26b6cf4..834c9d0 100644
--- a/clang-tools-extra/clangd/Hover.cpp
+++ b/clang-tools-extra/clangd/Hover.cpp
@@ -26,6 +26,7 @@
 #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"
@@ -205,15 +206,23 @@ const FunctionDecl *getUnderlyingFunction(const Decl *D) {
 // 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;
 }
 
diff --git a/clang-tools-extra/clangd/unittests/HoverTests.cpp b/clang-tools-extra/clangd/unittests/HoverTests.cpp
index bb14ede..758c642 100644
--- a/clang-tools-extra/clangd/unittests/HoverTests.cpp
+++ b/clang-tools-extra/clangd/unittests/HoverTests.cpp
@@ -554,6 +554,25 @@ class Foo {})cpp";
             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);
-- 
2.7.4