From 77d1811e96e02164d40485e98369bdea44189855 Mon Sep 17 00:00:00 2001
From: Eric Liu <ioeric@google.com>
Date: Mon, 4 Jun 2018 11:31:55 +0000
Subject: [PATCH] [clangd] Avoid indexing decls associated with friend decls.

Summary:
These decls are sometime used as the canonical declarations (e.g. for go-to-def),
which seems to be bad.

- friend decls that are not definitions should be ignored for indexing purposes
- this means they should never be selected as canonical decl
- if the friend decl is the only decl, then the symbol should not be indexed

Reviewers: sammccall

Reviewed By: sammccall

Subscribers: mgorny, klimek, ilya-biryukov, MaskRay, jkorous, cfe-commits

Differential Revision: https://reviews.llvm.org/D47623

llvm-svn: 333885
---
 .../clangd/index/SymbolCollector.cpp          | 13 ++++++
 .../clangd/index/SymbolCollector.h            |  6 +++
 .../unittests/clangd/SymbolCollectorTests.cpp | 42 +++++++++++++++++++
 3 files changed, 61 insertions(+)

diff --git a/clang-tools-extra/clangd/index/SymbolCollector.cpp b/clang-tools-extra/clangd/index/SymbolCollector.cpp
index 482a4652fae0..261468d96c34 100644
--- a/clang-tools-extra/clangd/index/SymbolCollector.cpp
+++ b/clang-tools-extra/clangd/index/SymbolCollector.cpp
@@ -290,6 +290,19 @@ bool SymbolCollector::handleDeclOccurence(
     index::IndexDataConsumer::ASTNodeInfo ASTNode) {
   assert(ASTCtx && PP.get() && "ASTContext and Preprocessor must be set.");
   assert(CompletionAllocator && CompletionTUInfo);
+  assert(ASTNode.OrigD);
+  // If OrigD is an declaration associated with a friend declaration and it's
+  // not a definition, skip it. Note that OrigD is the occurrence that the
+  // collector is currently visiting.
+  if ((ASTNode.OrigD->getFriendObjectKind() !=
+       Decl::FriendObjectKind::FOK_None) &&
+      !(Roles & static_cast<unsigned>(index::SymbolRole::Definition)))
+    return true;
+  // A declaration created for a friend declaration should not be used as the
+  // canonical declaration in the index. Use OrigD instead, unless we've already
+  // picked a replacement for D
+  if (D->getFriendObjectKind() != Decl::FriendObjectKind::FOK_None)
+    D = CanonicalDecls.try_emplace(D, ASTNode.OrigD).first->second;
   const NamedDecl *ND = llvm::dyn_cast<NamedDecl>(D);
   if (!ND)
     return true;
diff --git a/clang-tools-extra/clangd/index/SymbolCollector.h b/clang-tools-extra/clangd/index/SymbolCollector.h
index 269c184baf27..dbbb6d7f11bf 100644
--- a/clang-tools-extra/clangd/index/SymbolCollector.h
+++ b/clang-tools-extra/clangd/index/SymbolCollector.h
@@ -80,6 +80,12 @@ private:
   Options Opts;
   // Decls referenced from the current TU, flushed on finish().
   llvm::DenseSet<const NamedDecl *> ReferencedDecls;
+  // Maps canonical declaration provided by clang to canonical declaration for
+  // an index symbol, if clangd prefers a different declaration than that
+  // provided by clang. For example, friend declaration might be considered
+  // canonical by clang but should not be considered canonical in the index
+  // unless it's a definition.
+  llvm::DenseMap<const Decl *, const Decl *> CanonicalDecls;
 };
 
 } // namespace clangd
diff --git a/clang-tools-extra/unittests/clangd/SymbolCollectorTests.cpp b/clang-tools-extra/unittests/clangd/SymbolCollectorTests.cpp
index 06a087cb80b9..587881182408 100644
--- a/clang-tools-extra/unittests/clangd/SymbolCollectorTests.cpp
+++ b/clang-tools-extra/unittests/clangd/SymbolCollectorTests.cpp
@@ -812,6 +812,48 @@ TEST_F(SymbolCollectorTest, DoubleCheckProtoHeaderComment) {
                                    QName("nx::Kind"), QName("nx::Kind_Fine")));
 }
 
+TEST_F(SymbolCollectorTest, DoNotIndexSymbolsInFriendDecl) {
+  Annotations Header(R"(
+    namespace nx {
+      class $z[[Z]] {};
+      class X {
+        friend class Y;
+        friend class Z;
+        friend void foo();
+        friend void $bar[[bar]]() {}
+      };
+      class $y[[Y]] {};
+      void $foo[[foo]]();
+    }
+  )");
+  runSymbolCollector(Header.code(), /*Main=*/"");
+
+  EXPECT_THAT(Symbols,
+              UnorderedElementsAre(
+                  QName("nx"), QName("nx::X"),
+                  AllOf(QName("nx::Y"), DeclRange(Header.range("y"))),
+                  AllOf(QName("nx::Z"), DeclRange(Header.range("z"))),
+                  AllOf(QName("nx::foo"), DeclRange(Header.range("foo"))),
+                  AllOf(QName("nx::bar"), DeclRange(Header.range("bar")))));
+}
+
+TEST_F(SymbolCollectorTest, ReferencesInFriendDecl) {
+  const std::string Header = R"(
+    class X;
+    class Y;
+  )";
+  const std::string Main = R"(
+    class C {
+      friend ::X;
+      friend class Y;
+    };
+  )";
+  CollectorOpts.CountReferences = true;
+  runSymbolCollector(Header, Main);
+  EXPECT_THAT(Symbols, UnorderedElementsAre(AllOf(QName("X"), Refs(1)),
+                                            AllOf(QName("Y"), Refs(1))));
+}
+
 } // namespace
 } // namespace clangd
 } // namespace clang
-- 
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