[clang-tools-extra] clangd: Extend index references with constructor calls through forwarding (PR #169742)
via cfe-commits
cfe-commits at lists.llvm.org
Fri Nov 28 10:34:44 PST 2025
https://github.com/timon-ul updated https://github.com/llvm/llvm-project/pull/169742
>From 44ebad6933fccab5bcfc866ee56dd5381da5f452 Mon Sep 17 00:00:00 2001
From: Timon Ulrich <timon.ulrich at advantest.com>
Date: Mon, 10 Nov 2025 10:40:14 +0100
Subject: [PATCH 1/8] clangd: make forwarding heuristic available for more
locations
---
clang-tools-extra/clangd/AST.cpp | 21 +++++++++++++++++++++
clang-tools-extra/clangd/AST.h | 4 ++++
clang-tools-extra/clangd/Preamble.cpp | 22 +---------------------
3 files changed, 26 insertions(+), 21 deletions(-)
diff --git a/clang-tools-extra/clangd/AST.cpp b/clang-tools-extra/clangd/AST.cpp
index 0dcff2eae05e7..4b73bdba8aaa9 100644
--- a/clang-tools-extra/clangd/AST.cpp
+++ b/clang-tools-extra/clangd/AST.cpp
@@ -1040,5 +1040,26 @@ bool isExpandedFromParameterPack(const ParmVarDecl *D) {
return getUnderlyingPackType(D) != nullptr;
}
+bool isLikelyForwardingFunction(FunctionTemplateDecl *FT) {
+ const auto *FD = FT->getTemplatedDecl();
+ const auto NumParams = FD->getNumParams();
+ // Check whether its last parameter is a parameter pack...
+ if (NumParams > 0) {
+ const auto *LastParam = FD->getParamDecl(NumParams - 1);
+ if (const auto *PET = dyn_cast<PackExpansionType>(LastParam->getType())) {
+ // ... of the type T&&... or T...
+ const auto BaseType = PET->getPattern().getNonReferenceType();
+ if (const auto *TTPT =
+ dyn_cast<TemplateTypeParmType>(BaseType.getTypePtr())) {
+ // ... whose template parameter comes from the function directly
+ if (FT->getTemplateParameters()->getDepth() == TTPT->getDepth()) {
+ return true;
+ }
+ }
+ }
+ }
+ return false;
+}
+
} // namespace clangd
} // namespace clang
diff --git a/clang-tools-extra/clangd/AST.h b/clang-tools-extra/clangd/AST.h
index 2b83595e5b8e9..af45ae2d9022d 100644
--- a/clang-tools-extra/clangd/AST.h
+++ b/clang-tools-extra/clangd/AST.h
@@ -253,6 +253,10 @@ resolveForwardingParameters(const FunctionDecl *D, unsigned MaxDepth = 10);
/// reference to one (e.g. `Args&...` or `Args&&...`).
bool isExpandedFromParameterPack(const ParmVarDecl *D);
+/// Heuristic that checks if FT is forwarding a parameter pack to another
+/// function. (e.g. `make_unique`).
+bool isLikelyForwardingFunction(FunctionTemplateDecl *FT);
+
} // namespace clangd
} // namespace clang
diff --git a/clang-tools-extra/clangd/Preamble.cpp b/clang-tools-extra/clangd/Preamble.cpp
index 8af9e4649218d..09aaf3290b585 100644
--- a/clang-tools-extra/clangd/Preamble.cpp
+++ b/clang-tools-extra/clangd/Preamble.cpp
@@ -7,6 +7,7 @@
//===----------------------------------------------------------------------===//
#include "Preamble.h"
+#include "AST.h"
#include "CollectMacros.h"
#include "Compiler.h"
#include "Config.h"
@@ -166,27 +167,6 @@ class CppFilePreambleCallbacks : public PreambleCallbacks {
collectPragmaMarksCallback(*SourceMgr, Marks));
}
- static bool isLikelyForwardingFunction(FunctionTemplateDecl *FT) {
- const auto *FD = FT->getTemplatedDecl();
- const auto NumParams = FD->getNumParams();
- // Check whether its last parameter is a parameter pack...
- if (NumParams > 0) {
- const auto *LastParam = FD->getParamDecl(NumParams - 1);
- if (const auto *PET = dyn_cast<PackExpansionType>(LastParam->getType())) {
- // ... of the type T&&... or T...
- const auto BaseType = PET->getPattern().getNonReferenceType();
- if (const auto *TTPT =
- dyn_cast<TemplateTypeParmType>(BaseType.getTypePtr())) {
- // ... whose template parameter comes from the function directly
- if (FT->getTemplateParameters()->getDepth() == TTPT->getDepth()) {
- return true;
- }
- }
- }
- }
- return false;
- }
-
bool shouldSkipFunctionBody(Decl *D) override {
// Usually we don't need to look inside the bodies of header functions
// to understand the program. However when forwarding function like
>From f0d886eecf613bbf913629acd8951ee9ac8ab242 Mon Sep 17 00:00:00 2001
From: Timon Ulrich <timon.ulrich at advantest.com>
Date: Tue, 18 Nov 2025 14:07:14 +0100
Subject: [PATCH 2/8] clangd: Added new unittest for finding more refs to
constructors
Constructor calls hidden behind make_unique are currently not found, but
very useful, this test expects to find them in the main index.
---
.../clangd/unittests/XRefsTests.cpp | 31 +++++++++++++++++++
1 file changed, 31 insertions(+)
diff --git a/clang-tools-extra/clangd/unittests/XRefsTests.cpp b/clang-tools-extra/clangd/unittests/XRefsTests.cpp
index 7ed08d7cce3d3..51e29f5f1af43 100644
--- a/clang-tools-extra/clangd/unittests/XRefsTests.cpp
+++ b/clang-tools-extra/clangd/unittests/XRefsTests.cpp
@@ -13,6 +13,7 @@
#include "SyncAPI.h"
#include "TestFS.h"
#include "TestTU.h"
+#include "TestWorkspace.h"
#include "XRefs.h"
#include "index/MemIndex.h"
#include "clang/AST/Decl.h"
@@ -2713,6 +2714,36 @@ TEST(FindReferences, NoQueryForLocalSymbols) {
}
}
+TEST(FindReferences, ForwardingInIndex) {
+ Annotations Header(R"cpp(
+ namespace std {
+ template <class T> T &&forward(T &t);
+ template <class T, class... Args> T *make_unique(Args &&...args) {
+ return new T(std::forward<Args>(args)...);
+ }
+ }
+ struct Test {
+ [[T^est]](){}
+ };
+ )cpp");
+ Annotations Main(R"cpp(
+ #include "header.hpp"
+ int main() {
+ auto a = std::[[make_unique]]<Test>();
+ }
+ )cpp");
+ TestWorkspace TW;
+ TW.addMainFile("header.hpp", Header.code());
+ TW.addMainFile("main.cpp", Main.code());
+ auto AST = TW.openFile("header.hpp").value();
+ auto Index = TW.index();
+
+ EXPECT_THAT(findReferences(AST, Header.point(), 0, Index.get(),
+ /*AddContext*/ true)
+ .References,
+ ElementsAre(rangeIs(Header.range()), rangeIs(Main.range())));
+}
+
TEST(GetNonLocalDeclRefs, All) {
struct Case {
llvm::StringRef AnnotatedCode;
>From 36972c5dab08029a3fc71e7730d26c5df4333cd3 Mon Sep 17 00:00:00 2001
From: Timon Ulrich <timon.ulrich at advantest.com>
Date: Wed, 26 Nov 2025 23:38:11 +0100
Subject: [PATCH 3/8] clangd: Collecting constructor references through
forwarding in index
---
.../clangd/index/SymbolCollector.cpp | 36 +++++++++++++++++++
1 file changed, 36 insertions(+)
diff --git a/clang-tools-extra/clangd/index/SymbolCollector.cpp b/clang-tools-extra/clangd/index/SymbolCollector.cpp
index 39c479b5f4d5b..aed74ddac1f46 100644
--- a/clang-tools-extra/clangd/index/SymbolCollector.cpp
+++ b/clang-tools-extra/clangd/index/SymbolCollector.cpp
@@ -29,6 +29,7 @@
#include "clang/AST/DeclTemplate.h"
#include "clang/AST/DeclarationName.h"
#include "clang/AST/Expr.h"
+#include "clang/AST/RecursiveASTVisitor.h"
#include "clang/Basic/FileEntry.h"
#include "clang/Basic/LangOptions.h"
#include "clang/Basic/SourceLocation.h"
@@ -576,6 +577,21 @@ SymbolCollector::getRefContainer(const Decl *Enclosing,
return Enclosing;
}
+class ForwardVisitor : public RecursiveASTVisitor<ForwardVisitor> {
+public:
+ ForwardVisitor() {}
+
+ bool VisitCXXConstructExpr(CXXConstructExpr *E) {
+ if (auto *Callee = E->getConstructor()) {
+ Constructors.push_back(Callee);
+ }
+ return true;
+ }
+
+ // Output of this visitor
+ std::vector<CXXConstructorDecl *> Constructors{};
+};
+
// Always return true to continue indexing.
bool SymbolCollector::handleDeclOccurrence(
const Decl *D, index::SymbolRoleSet Roles,
@@ -654,6 +670,26 @@ bool SymbolCollector::handleDeclOccurrence(
// occurrence inside the base-specifier.
processRelations(*ND, ID, Relations);
+ if (auto *FD = llvm::dyn_cast<clang::FunctionDecl>(D)) {
+ if (auto *FT = FD->getDescribedFunctionTemplate();
+ FT && isLikelyForwardingFunction(FT)) {
+ ForwardVisitor FS{};
+ for (auto *Specialized : FT->specializations()) {
+ FS.TraverseStmt(Specialized->getBody());
+ }
+ auto FileLoc = SM.getFileLoc(Loc);
+ auto FID = SM.getFileID(FileLoc);
+ if (Opts.RefsInHeaders || FID == SM.getMainFileID()) {
+ for (auto *Constructor : FS.Constructors) {
+ addRef(getSymbolIDCached(Constructor),
+ SymbolRef{FileLoc, FID, Roles, index::getSymbolInfo(ND).Kind,
+ getRefContainer(ASTNode.Parent, Opts),
+ isSpelled(FileLoc, *ND)});
+ }
+ }
+ }
+ }
+
bool CollectRef = static_cast<bool>(Opts.RefFilter & toRefKind(Roles));
// Unlike other fields, e.g. Symbols (which use spelling locations), we use
// file locations for references (as it aligns the behavior of clangd's
>From 52a924d3bff04c64a06252662b16bc1b51c1582e Mon Sep 17 00:00:00 2001
From: Timon Ulrich <timon.ulrich at advantest.com>
Date: Wed, 26 Nov 2025 23:48:15 +0100
Subject: [PATCH 4/8] clangd: rename new visitor to better reflect task
---
clang-tools-extra/clangd/index/SymbolCollector.cpp | 11 ++++++-----
1 file changed, 6 insertions(+), 5 deletions(-)
diff --git a/clang-tools-extra/clangd/index/SymbolCollector.cpp b/clang-tools-extra/clangd/index/SymbolCollector.cpp
index aed74ddac1f46..f08e753eadda5 100644
--- a/clang-tools-extra/clangd/index/SymbolCollector.cpp
+++ b/clang-tools-extra/clangd/index/SymbolCollector.cpp
@@ -577,9 +577,10 @@ SymbolCollector::getRefContainer(const Decl *Enclosing,
return Enclosing;
}
-class ForwardVisitor : public RecursiveASTVisitor<ForwardVisitor> {
+class ForwardingToConstructorVisitor
+ : public RecursiveASTVisitor<ForwardingToConstructorVisitor> {
public:
- ForwardVisitor() {}
+ ForwardingToConstructorVisitor() {}
bool VisitCXXConstructExpr(CXXConstructExpr *E) {
if (auto *Callee = E->getConstructor()) {
@@ -673,14 +674,14 @@ bool SymbolCollector::handleDeclOccurrence(
if (auto *FD = llvm::dyn_cast<clang::FunctionDecl>(D)) {
if (auto *FT = FD->getDescribedFunctionTemplate();
FT && isLikelyForwardingFunction(FT)) {
- ForwardVisitor FS{};
+ ForwardingToConstructorVisitor Visitor{};
for (auto *Specialized : FT->specializations()) {
- FS.TraverseStmt(Specialized->getBody());
+ Visitor.TraverseStmt(Specialized->getBody());
}
auto FileLoc = SM.getFileLoc(Loc);
auto FID = SM.getFileID(FileLoc);
if (Opts.RefsInHeaders || FID == SM.getMainFileID()) {
- for (auto *Constructor : FS.Constructors) {
+ for (auto *Constructor : Visitor.Constructors) {
addRef(getSymbolIDCached(Constructor),
SymbolRef{FileLoc, FID, Roles, index::getSymbolInfo(ND).Kind,
getRefContainer(ASTNode.Parent, Opts),
>From 8a534aa88ee1d33158c3efe37139056bf4fba0b7 Mon Sep 17 00:00:00 2001
From: Timon Ulrich <timon.ulrich at advantest.com>
Date: Thu, 27 Nov 2025 00:03:10 +0100
Subject: [PATCH 5/8] clangd: moving new ref collection to correct location
---
.../clangd/index/SymbolCollector.cpp | 41 ++++++++++---------
1 file changed, 21 insertions(+), 20 deletions(-)
diff --git a/clang-tools-extra/clangd/index/SymbolCollector.cpp b/clang-tools-extra/clangd/index/SymbolCollector.cpp
index f08e753eadda5..11afd16e5f99d 100644
--- a/clang-tools-extra/clangd/index/SymbolCollector.cpp
+++ b/clang-tools-extra/clangd/index/SymbolCollector.cpp
@@ -671,26 +671,6 @@ bool SymbolCollector::handleDeclOccurrence(
// occurrence inside the base-specifier.
processRelations(*ND, ID, Relations);
- if (auto *FD = llvm::dyn_cast<clang::FunctionDecl>(D)) {
- if (auto *FT = FD->getDescribedFunctionTemplate();
- FT && isLikelyForwardingFunction(FT)) {
- ForwardingToConstructorVisitor Visitor{};
- for (auto *Specialized : FT->specializations()) {
- Visitor.TraverseStmt(Specialized->getBody());
- }
- auto FileLoc = SM.getFileLoc(Loc);
- auto FID = SM.getFileID(FileLoc);
- if (Opts.RefsInHeaders || FID == SM.getMainFileID()) {
- for (auto *Constructor : Visitor.Constructors) {
- addRef(getSymbolIDCached(Constructor),
- SymbolRef{FileLoc, FID, Roles, index::getSymbolInfo(ND).Kind,
- getRefContainer(ASTNode.Parent, Opts),
- isSpelled(FileLoc, *ND)});
- }
- }
- }
- }
-
bool CollectRef = static_cast<bool>(Opts.RefFilter & toRefKind(Roles));
// Unlike other fields, e.g. Symbols (which use spelling locations), we use
// file locations for references (as it aligns the behavior of clangd's
@@ -706,6 +686,27 @@ bool SymbolCollector::handleDeclOccurrence(
addRef(ID, SymbolRef{FileLoc, FID, Roles, index::getSymbolInfo(ND).Kind,
getRefContainer(ASTNode.Parent, Opts),
isSpelled(FileLoc, *ND)});
+ // Also collect indirect constructor calls like `make_unique`
+ if (auto *FD = llvm::dyn_cast<clang::FunctionDecl>(D)) {
+ if (auto *FT = FD->getDescribedFunctionTemplate();
+ FT && isLikelyForwardingFunction(FT)) {
+ ForwardingToConstructorVisitor Visitor{};
+ for (auto *Specialized : FT->specializations()) {
+ Visitor.TraverseStmt(Specialized->getBody());
+ }
+ auto FileLoc = SM.getFileLoc(Loc);
+ auto FID = SM.getFileID(FileLoc);
+ if (Opts.RefsInHeaders || FID == SM.getMainFileID()) {
+ for (auto *Constructor : Visitor.Constructors) {
+ addRef(getSymbolIDCached(Constructor),
+ SymbolRef{FileLoc, FID, Roles,
+ index::getSymbolInfo(ND).Kind,
+ getRefContainer(ASTNode.Parent, Opts),
+ isSpelled(FileLoc, *ND)});
+ }
+ }
+ }
+ }
}
}
// Don't continue indexing if this is a mere reference.
>From 484ba5620270ad3bb3dd14ae07997a7cf8c057aa Mon Sep 17 00:00:00 2001
From: Timon Ulrich <timon.ulrich at advantest.com>
Date: Thu, 27 Nov 2025 00:13:39 +0100
Subject: [PATCH 6/8] clangd: test include formatting
---
clang-tools-extra/clangd/unittests/XRefsTests.cpp | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/clang-tools-extra/clangd/unittests/XRefsTests.cpp b/clang-tools-extra/clangd/unittests/XRefsTests.cpp
index 51e29f5f1af43..d3b6faa5fa25f 100644
--- a/clang-tools-extra/clangd/unittests/XRefsTests.cpp
+++ b/clang-tools-extra/clangd/unittests/XRefsTests.cpp
@@ -5,8 +5,8 @@
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
-#include "Annotations.h"
#include "AST.h"
+#include "Annotations.h"
#include "ParsedAST.h"
#include "Protocol.h"
#include "SourceCode.h"
>From 8c6928c3893abc2d023bc40fa4ca0c6616a9498a Mon Sep 17 00:00:00 2001
From: Timon Ulrich <timon.ulrich at advantest.com>
Date: Thu, 27 Nov 2025 00:39:32 +0100
Subject: [PATCH 7/8] clangd: removed redundant code
---
.../clangd/index/SymbolCollector.cpp | 15 +++++----------
1 file changed, 5 insertions(+), 10 deletions(-)
diff --git a/clang-tools-extra/clangd/index/SymbolCollector.cpp b/clang-tools-extra/clangd/index/SymbolCollector.cpp
index 11afd16e5f99d..54e4333870978 100644
--- a/clang-tools-extra/clangd/index/SymbolCollector.cpp
+++ b/clang-tools-extra/clangd/index/SymbolCollector.cpp
@@ -694,16 +694,11 @@ bool SymbolCollector::handleDeclOccurrence(
for (auto *Specialized : FT->specializations()) {
Visitor.TraverseStmt(Specialized->getBody());
}
- auto FileLoc = SM.getFileLoc(Loc);
- auto FID = SM.getFileID(FileLoc);
- if (Opts.RefsInHeaders || FID == SM.getMainFileID()) {
- for (auto *Constructor : Visitor.Constructors) {
- addRef(getSymbolIDCached(Constructor),
- SymbolRef{FileLoc, FID, Roles,
- index::getSymbolInfo(ND).Kind,
- getRefContainer(ASTNode.Parent, Opts),
- isSpelled(FileLoc, *ND)});
- }
+ for (auto *Constructor : Visitor.Constructors) {
+ addRef(getSymbolIDCached(Constructor),
+ SymbolRef{FileLoc, FID, Roles, index::getSymbolInfo(ND).Kind,
+ getRefContainer(ASTNode.Parent, Opts),
+ isSpelled(FileLoc, *ND)});
}
}
}
>From 7f4693cba8616a6870ad78bb7a85f595fc4f953c Mon Sep 17 00:00:00 2001
From: Timon Ulrich <timon.ulrich at advantest.com>
Date: Fri, 28 Nov 2025 19:31:58 +0100
Subject: [PATCH 8/8] clangd: draft commit, trying different direction
idea is to directly at the instantiation index the template for
constructor calls. For some reason the function declaration never is an
instantiation though.
---
.../clangd/index/SymbolCollector.cpp | 23 ++++++++++---------
1 file changed, 12 insertions(+), 11 deletions(-)
diff --git a/clang-tools-extra/clangd/index/SymbolCollector.cpp b/clang-tools-extra/clangd/index/SymbolCollector.cpp
index 54e4333870978..2b5f4541d6fa7 100644
--- a/clang-tools-extra/clangd/index/SymbolCollector.cpp
+++ b/clang-tools-extra/clangd/index/SymbolCollector.cpp
@@ -688,17 +688,18 @@ bool SymbolCollector::handleDeclOccurrence(
isSpelled(FileLoc, *ND)});
// Also collect indirect constructor calls like `make_unique`
if (auto *FD = llvm::dyn_cast<clang::FunctionDecl>(D)) {
- if (auto *FT = FD->getDescribedFunctionTemplate();
- FT && isLikelyForwardingFunction(FT)) {
- ForwardingToConstructorVisitor Visitor{};
- for (auto *Specialized : FT->specializations()) {
- Visitor.TraverseStmt(Specialized->getBody());
- }
- for (auto *Constructor : Visitor.Constructors) {
- addRef(getSymbolIDCached(Constructor),
- SymbolRef{FileLoc, FID, Roles, index::getSymbolInfo(ND).Kind,
- getRefContainer(ASTNode.Parent, Opts),
- isSpelled(FileLoc, *ND)});
+ if (FD->isTemplateInstantiation()) {
+ if (auto *PT = FD->getPrimaryTemplate();
+ PT && isLikelyForwardingFunction(PT)) {
+ ForwardingToConstructorVisitor Visitor{};
+ Visitor.TraverseStmt(FD->getBody());
+ for (auto *Constructor : Visitor.Constructors) {
+ addRef(getSymbolIDCached(Constructor),
+ SymbolRef{FileLoc, FID, Roles,
+ index::getSymbolInfo(ND).Kind,
+ getRefContainer(ASTNode.Parent, Opts),
+ isSpelled(FileLoc, *ND)});
+ }
}
}
}
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