[clang] [clang-tools-extra] [clang-tidy] Add new check `modernize-use-designated-initializers` (PR #80541)

[Danny Mösch via cfe-commits]

https://github.com/SimplyDanny updated 
https://github.com/llvm/llvm-project/pull/80541

From a6f7d8f72ab4af680dc17004e9bccefbe268b712 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Danny=20M=C3=B6sch?= <danny.moe...@icloud.com>
Date: Sat, 3 Feb 2024 13:13:50 +0100
Subject: [PATCH 01/23] Trigger on variable declarations

---
 .../clang-tidy/modernize/CMakeLists.txt       |  1 +
 .../modernize/ModernizeTidyModule.cpp         |  3 +
 .../UseDesignatedInitializersCheck.cpp        | 58 +++++++++++++++++++
 .../UseDesignatedInitializersCheck.h          | 33 +++++++++++
 clang-tools-extra/docs/ReleaseNotes.rst       |  5 ++
 .../docs/clang-tidy/checks/list.rst           |  1 +
 .../modernize/use-designated-initializers.rst |  6 ++
 .../modernize/use-designated-initializers.cpp | 32 ++++++++++
 8 files changed, 139 insertions(+)
 create mode 100644 
clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.cpp
 create mode 100644 
clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.h
 create mode 100644 
clang-tools-extra/docs/clang-tidy/checks/modernize/use-designated-initializers.rst
 create mode 100644 
clang-tools-extra/test/clang-tidy/checkers/modernize/use-designated-initializers.cpp

diff --git a/clang-tools-extra/clang-tidy/modernize/CMakeLists.txt 
b/clang-tools-extra/clang-tidy/modernize/CMakeLists.txt
index 28ca52f46943a8..6852db6c2ee311 100644
--- a/clang-tools-extra/clang-tidy/modernize/CMakeLists.txt
+++ b/clang-tools-extra/clang-tidy/modernize/CMakeLists.txt
@@ -31,6 +31,7 @@ add_clang_library(clangTidyModernizeModule
   UseBoolLiteralsCheck.cpp
   UseConstraintsCheck.cpp
   UseDefaultMemberInitCheck.cpp
+  UseDesignatedInitializersCheck.cpp
   UseEmplaceCheck.cpp
   UseEqualsDefaultCheck.cpp
   UseEqualsDeleteCheck.cpp
diff --git a/clang-tools-extra/clang-tidy/modernize/ModernizeTidyModule.cpp 
b/clang-tools-extra/clang-tidy/modernize/ModernizeTidyModule.cpp
index 654f4bd0c6ba47..e96cf274f58cfe 100644
--- a/clang-tools-extra/clang-tidy/modernize/ModernizeTidyModule.cpp
+++ b/clang-tools-extra/clang-tidy/modernize/ModernizeTidyModule.cpp
@@ -32,6 +32,7 @@
 #include "UseBoolLiteralsCheck.h"
 #include "UseConstraintsCheck.h"
 #include "UseDefaultMemberInitCheck.h"
+#include "UseDesignatedInitializersCheck.h"
 #include "UseEmplaceCheck.h"
 #include "UseEqualsDefaultCheck.h"
 #include "UseEqualsDeleteCheck.h"
@@ -68,6 +69,8 @@ class ModernizeModule : public ClangTidyModule {
     CheckFactories.registerCheck<MakeSharedCheck>("modernize-make-shared");
     CheckFactories.registerCheck<MakeUniqueCheck>("modernize-make-unique");
     CheckFactories.registerCheck<PassByValueCheck>("modernize-pass-by-value");
+    CheckFactories.registerCheck<UseDesignatedInitializersCheck>(
+        "modernize-use-designated-initializers");
     CheckFactories.registerCheck<UseStartsEndsWithCheck>(
         "modernize-use-starts-ends-with");
     CheckFactories.registerCheck<UseStdNumbersCheck>(
diff --git 
a/clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.cpp 
b/clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.cpp
new file mode 100644
index 00000000000000..06f0bb0dc06eac
--- /dev/null
+++ b/clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.cpp
@@ -0,0 +1,58 @@
+//===--- UseDesignatedInitializersCheck.cpp - clang-tidy 
------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM 
Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "UseDesignatedInitializersCheck.h"
+#include "clang/AST/Decl.h"
+#include "clang/AST/Expr.h"
+#include "clang/AST/Stmt.h"
+#include "clang/ASTMatchers/ASTMatchFinder.h"
+#include "clang/ASTMatchers/ASTMatchers.h"
+#include <algorithm>
+#include <iterator>
+#include <vector>
+
+using namespace clang::ast_matchers;
+
+namespace clang::tidy::modernize {
+
+static std::vector<Stmt *>
+getAllUndesignatedInits(const InitListExpr *SyntacticInitList) {
+  std::vector<Stmt *> Result;
+  std::copy_if(SyntacticInitList->begin(), SyntacticInitList->end(),
+               std::back_inserter(Result),
+               [](auto S) { return !isa<DesignatedInitExpr>(S); });
+  return Result;
+}
+
+void UseDesignatedInitializersCheck::registerMatchers(MatchFinder *Finder) {
+  Finder->addMatcher(varDecl(allOf(has(initListExpr().bind("init")),
+                                   hasType(recordDecl().bind("type")))),
+                     this);
+}
+
+void UseDesignatedInitializersCheck::check(
+    const MatchFinder::MatchResult &Result) {
+  const auto *InitList = Result.Nodes.getNodeAs<InitListExpr>("init");
+  const auto *Type = Result.Nodes.getNodeAs<CXXRecordDecl>("type");
+  if (!Type || !InitList || !Type->isAggregate())
+    return;
+  if (const auto *SyntacticInitList = InitList->getSyntacticForm()) {
+    const auto UndesignatedParts = getAllUndesignatedInits(SyntacticInitList);
+    if (UndesignatedParts.empty())
+      return;
+    if (UndesignatedParts.size() == SyntacticInitList->getNumInits()) {
+      diag(InitList->getLBraceLoc(), "use designated initializer list");
+      return;
+    }
+    for (const auto *InitExpr : UndesignatedParts) {
+      diag(InitExpr->getBeginLoc(), "use designated init expression");
+    }
+  }
+}
+
+} // namespace clang::tidy::modernize
diff --git 
a/clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.h 
b/clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.h
new file mode 100644
index 00000000000000..aeaa3f19deb7e8
--- /dev/null
+++ b/clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.h
@@ -0,0 +1,33 @@
+//===--- UseDesignatedInitializersCheck.h - clang-tidy ----------*- C++ 
-*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM 
Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef 
LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_MODERNIZE_USEDESIGNATEDINITIALIZERSCHECK_H
+#define 
LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_MODERNIZE_USEDESIGNATEDINITIALIZERSCHECK_H
+
+#include "../ClangTidyCheck.h"
+
+namespace clang::tidy::modernize {
+
+/// FIXME: Write a short description.
+///
+/// For the user-facing documentation see:
+/// 
http://clang.llvm.org/extra/clang-tidy/checks/modernize/use-designated-initializers.html
+class UseDesignatedInitializersCheck : public ClangTidyCheck {
+public:
+  UseDesignatedInitializersCheck(StringRef Name, ClangTidyContext *Context)
+      : ClangTidyCheck(Name, Context) {}
+  void registerMatchers(ast_matchers::MatchFinder *Finder) override;
+  void check(const ast_matchers::MatchFinder::MatchResult &Result) override;
+  std::optional<TraversalKind> getCheckTraversalKind() const override {
+    return TK_IgnoreUnlessSpelledInSource;
+  }
+};
+
+} // namespace clang::tidy::modernize
+
+#endif // 
LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_MODERNIZE_USEDESIGNATEDINITIALIZERSCHECK_H
diff --git a/clang-tools-extra/docs/ReleaseNotes.rst 
b/clang-tools-extra/docs/ReleaseNotes.rst
index 9e819ea34c3971..a9e4305e7ca5a6 100644
--- a/clang-tools-extra/docs/ReleaseNotes.rst
+++ b/clang-tools-extra/docs/ReleaseNotes.rst
@@ -100,6 +100,11 @@ Improvements to clang-tidy
 New checks
 ^^^^^^^^^^
 
+- New :doc:`modernize-use-designated-initializers
+  <clang-tidy/checks/modernize/use-designated-initializers>` check.
+
+  FIXME: add release notes.
+
 New check aliases
 ^^^^^^^^^^^^^^^^^
 
diff --git a/clang-tools-extra/docs/clang-tidy/checks/list.rst 
b/clang-tools-extra/docs/clang-tidy/checks/list.rst
index f40192ed9dea27..5d3b99e0996c24 100644
--- a/clang-tools-extra/docs/clang-tidy/checks/list.rst
+++ b/clang-tools-extra/docs/clang-tidy/checks/list.rst
@@ -287,6 +287,7 @@ Clang-Tidy Checks
    :doc:`modernize-use-bool-literals <modernize/use-bool-literals>`, "Yes"
    :doc:`modernize-use-constraints <modernize/use-constraints>`, "Yes"
    :doc:`modernize-use-default-member-init 
<modernize/use-default-member-init>`, "Yes"
+   :doc:`modernize-use-designated-initializers 
<modernize/use-designated-initializers>`, "Yes"
    :doc:`modernize-use-emplace <modernize/use-emplace>`, "Yes"
    :doc:`modernize-use-equals-default <modernize/use-equals-default>`, "Yes"
    :doc:`modernize-use-equals-delete <modernize/use-equals-delete>`, "Yes"
diff --git 
a/clang-tools-extra/docs/clang-tidy/checks/modernize/use-designated-initializers.rst
 
b/clang-tools-extra/docs/clang-tidy/checks/modernize/use-designated-initializers.rst
new file mode 100644
index 00000000000000..e0487f9b0e843d
--- /dev/null
+++ 
b/clang-tools-extra/docs/clang-tidy/checks/modernize/use-designated-initializers.rst
@@ -0,0 +1,6 @@
+.. title:: clang-tidy - modernize-use-designated-initializers
+
+modernize-use-designated-initializers
+=====================================
+
+FIXME: Describe what patterns does the check detect and why. Give examples.
diff --git 
a/clang-tools-extra/test/clang-tidy/checkers/modernize/use-designated-initializers.cpp
 
b/clang-tools-extra/test/clang-tidy/checkers/modernize/use-designated-initializers.cpp
new file mode 100644
index 00000000000000..c945454201ee13
--- /dev/null
+++ 
b/clang-tools-extra/test/clang-tidy/checkers/modernize/use-designated-initializers.cpp
@@ -0,0 +1,32 @@
+// RUN: %check_clang_tidy %s modernize-use-designated-initializers %t
+
+struct S1 {};
+
+S1 s11{};
+S1 s12 = {};
+S1 s13();
+S1 s14;
+
+struct S2 { int i, j; };
+
+S2 s21{.i=1, .j =2};
+
+S2 s22 = {1, 2};
+// CHECK-MESSAGES: :[[@LINE-1]]:10: warning: use designated initializer list 
[modernize-use-designated-initializers]
+
+S2 s23{1};
+// CHECK-MESSAGES: :[[@LINE-1]]:7: warning: use designated initializer list 
[modernize-use-designated-initializers]
+
+S2 s24{.i = 1};
+
+S2 s25 = {.i=1, 2};
+// CHECK-MESSAGES: :[[@LINE-1]]:17: warning: use designated init expression 
[modernize-use-designated-initializers]
+
+struct S3 {
+    S2 s2;
+    double d;
+};
+
+S3 s31 = {.s2 = 1, 2, 3.1};
+// CHECK-MESSAGES: :[[@LINE-1]]:20: warning: use designated init expression 
[modernize-use-designated-initializers]
+// CHECK-MESSAGES: :[[@LINE-2]]:23: warning: use designated init expression 
[modernize-use-designated-initializers]

From 17301b2e09157b6b571c744b0a28a740d8f51c26 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Danny=20M=C3=B6sch?= <danny.moe...@icloud.com>
Date: Sat, 3 Feb 2024 13:34:58 +0100
Subject: [PATCH 02/23] Support nested initializer lists

---
 .../modernize/UseDesignatedInitializersCheck.cpp     |  5 ++---
 .../modernize/use-designated-initializers.cpp        | 12 ++++++++++++
 2 files changed, 14 insertions(+), 3 deletions(-)

diff --git 
a/clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.cpp 
b/clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.cpp
index 06f0bb0dc06eac..e0400db473db25 100644
--- a/clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.cpp
+++ b/clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.cpp
@@ -30,9 +30,8 @@ getAllUndesignatedInits(const InitListExpr 
*SyntacticInitList) {
 }
 
 void UseDesignatedInitializersCheck::registerMatchers(MatchFinder *Finder) {
-  Finder->addMatcher(varDecl(allOf(has(initListExpr().bind("init")),
-                                   hasType(recordDecl().bind("type")))),
-                     this);
+  Finder->addMatcher(
+      initListExpr(hasType(recordDecl().bind("type"))).bind("init"), this);
 }
 
 void UseDesignatedInitializersCheck::check(
diff --git 
a/clang-tools-extra/test/clang-tidy/checkers/modernize/use-designated-initializers.cpp
 
b/clang-tools-extra/test/clang-tidy/checkers/modernize/use-designated-initializers.cpp
index c945454201ee13..a5eeb5553a9093 100644
--- 
a/clang-tools-extra/test/clang-tidy/checkers/modernize/use-designated-initializers.cpp
+++ 
b/clang-tools-extra/test/clang-tidy/checkers/modernize/use-designated-initializers.cpp
@@ -30,3 +30,15 @@ struct S3 {
 S3 s31 = {.s2 = 1, 2, 3.1};
 // CHECK-MESSAGES: :[[@LINE-1]]:20: warning: use designated init expression 
[modernize-use-designated-initializers]
 // CHECK-MESSAGES: :[[@LINE-2]]:23: warning: use designated init expression 
[modernize-use-designated-initializers]
+
+S3 s32 = {{.i = 1, 2}};
+// CHECK-MESSAGES: :[[@LINE-1]]:10: warning: use designated initializer list 
[modernize-use-designated-initializers]
+// CHECK-MESSAGES: :[[@LINE-2]]:20: warning: use designated init expression 
[modernize-use-designated-initializers]
+
+struct S4 {
+    double d;
+    private: static int i;
+};
+
+S4 s41 {2.2};
+// CHECK-MESSAGES: :[[@LINE-1]]:8: warning: use designated initializer list 
[modernize-use-designated-initializers]

From 301893ebc4366be0598a57fbe31d20dfac9ba200 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Danny=20M=C3=B6sch?= <danny.moe...@icloud.com>
Date: Sat, 3 Feb 2024 13:35:12 +0100
Subject: [PATCH 03/23] Rename

---
 .../modernize/UseDesignatedInitializersCheck.cpp      | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git 
a/clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.cpp 
b/clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.cpp
index e0400db473db25..7cf6dcb21ac1be 100644
--- a/clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.cpp
+++ b/clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.cpp
@@ -21,7 +21,7 @@ using namespace clang::ast_matchers;
 namespace clang::tidy::modernize {
 
 static std::vector<Stmt *>
-getAllUndesignatedInits(const InitListExpr *SyntacticInitList) {
+getUndesignatedComponents(const InitListExpr *SyntacticInitList) {
   std::vector<Stmt *> Result;
   std::copy_if(SyntacticInitList->begin(), SyntacticInitList->end(),
                std::back_inserter(Result),
@@ -41,14 +41,15 @@ void UseDesignatedInitializersCheck::check(
   if (!Type || !InitList || !Type->isAggregate())
     return;
   if (const auto *SyntacticInitList = InitList->getSyntacticForm()) {
-    const auto UndesignatedParts = getAllUndesignatedInits(SyntacticInitList);
-    if (UndesignatedParts.empty())
+    const auto UndesignatedComponents =
+        getUndesignatedComponents(SyntacticInitList);
+    if (UndesignatedComponents.empty())
       return;
-    if (UndesignatedParts.size() == SyntacticInitList->getNumInits()) {
+    if (UndesignatedComponents.size() == SyntacticInitList->getNumInits()) {
       diag(InitList->getLBraceLoc(), "use designated initializer list");
       return;
     }
-    for (const auto *InitExpr : UndesignatedParts) {
+    for (const auto *InitExpr : UndesignatedComponents) {
       diag(InitExpr->getBeginLoc(), "use designated init expression");
     }
   }

From b71c6fab7c24859df17d051eb0b8746aa089e574 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Danny=20M=C3=B6sch?= <danny.moe...@icloud.com>
Date: Sat, 3 Feb 2024 13:36:10 +0100
Subject: [PATCH 04/23] Enable for C++20 only

---
 .../clang-tidy/modernize/UseDesignatedInitializersCheck.h      | 3 +++
 .../checkers/modernize/use-designated-initializers.cpp         | 2 +-
 2 files changed, 4 insertions(+), 1 deletion(-)

diff --git 
a/clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.h 
b/clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.h
index aeaa3f19deb7e8..12a9850ada6a14 100644
--- a/clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.h
+++ b/clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.h
@@ -26,6 +26,9 @@ class UseDesignatedInitializersCheck : public ClangTidyCheck {
   std::optional<TraversalKind> getCheckTraversalKind() const override {
     return TK_IgnoreUnlessSpelledInSource;
   }
+  bool isLanguageVersionSupported(const LangOptions &LangOpts) const override {
+    return LangOpts.CPlusPlus20;
+  }
 };
 
 } // namespace clang::tidy::modernize
diff --git 
a/clang-tools-extra/test/clang-tidy/checkers/modernize/use-designated-initializers.cpp
 
b/clang-tools-extra/test/clang-tidy/checkers/modernize/use-designated-initializers.cpp
index a5eeb5553a9093..7e41943e884061 100644
--- 
a/clang-tools-extra/test/clang-tidy/checkers/modernize/use-designated-initializers.cpp
+++ 
b/clang-tools-extra/test/clang-tidy/checkers/modernize/use-designated-initializers.cpp
@@ -1,4 +1,4 @@
-// RUN: %check_clang_tidy %s modernize-use-designated-initializers %t
+// RUN: %check_clang_tidy -std=c++20 %s modernize-use-designated-initializers 
%t
 
 struct S1 {};
 

From 444b58996764e2585369a3c3112a42fa43365a4f Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Danny=20M=C3=B6sch?= <danny.moe...@icloud.com>
Date: Sat, 3 Feb 2024 13:56:08 +0100
Subject: [PATCH 05/23] Add option to ignore aggregates with single elements

---
 .../UseDesignatedInitializersCheck.cpp        | 19 +++++++++++++++++++
 .../UseDesignatedInitializersCheck.h          |  9 +++++++--
 .../modernize/use-designated-initializers.cpp |  5 ++++-
 3 files changed, 30 insertions(+), 3 deletions(-)

diff --git 
a/clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.cpp 
b/clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.cpp
index 7cf6dcb21ac1be..d269cef13e6aaa 100644
--- a/clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.cpp
+++ b/clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.cpp
@@ -20,6 +20,10 @@ using namespace clang::ast_matchers;
 
 namespace clang::tidy::modernize {
 
+static constexpr auto IgnoreSingleElementAggregatesName =
+    "IgnoreSingleElementAggregates";
+static constexpr auto IgnoreSingleElementAggregatesDefault = true;
+
 static std::vector<Stmt *>
 getUndesignatedComponents(const InitListExpr *SyntacticInitList) {
   std::vector<Stmt *> Result;
@@ -29,6 +33,13 @@ getUndesignatedComponents(const InitListExpr 
*SyntacticInitList) {
   return Result;
 }
 
+UseDesignatedInitializersCheck::UseDesignatedInitializersCheck(
+    StringRef Name, ClangTidyContext *Context)
+    : ClangTidyCheck(Name, Context),
+      IgnoreSingleElementAggregates(
+          Options.getLocalOrGlobal(IgnoreSingleElementAggregatesName,
+                                   IgnoreSingleElementAggregatesDefault)) {}
+
 void UseDesignatedInitializersCheck::registerMatchers(MatchFinder *Finder) {
   Finder->addMatcher(
       initListExpr(hasType(recordDecl().bind("type"))).bind("init"), this);
@@ -40,6 +51,8 @@ void UseDesignatedInitializersCheck::check(
   const auto *Type = Result.Nodes.getNodeAs<CXXRecordDecl>("type");
   if (!Type || !InitList || !Type->isAggregate())
     return;
+  if (IgnoreSingleElementAggregates && InitList->getNumInits() == 1)
+    return;
   if (const auto *SyntacticInitList = InitList->getSyntacticForm()) {
     const auto UndesignatedComponents =
         getUndesignatedComponents(SyntacticInitList);
@@ -55,4 +68,10 @@ void UseDesignatedInitializersCheck::check(
   }
 }
 
+void UseDesignatedInitializersCheck::storeOptions(
+    ClangTidyOptions::OptionMap &Opts) {
+  Options.store(Opts, IgnoreSingleElementAggregatesName,
+                IgnoreSingleElementAggregates);
+}
+
 } // namespace clang::tidy::modernize
diff --git 
a/clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.h 
b/clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.h
index 12a9850ada6a14..8a60fd7b31c5a4 100644
--- a/clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.h
+++ b/clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.h
@@ -19,16 +19,21 @@ namespace clang::tidy::modernize {
 /// 
http://clang.llvm.org/extra/clang-tidy/checks/modernize/use-designated-initializers.html
 class UseDesignatedInitializersCheck : public ClangTidyCheck {
 public:
-  UseDesignatedInitializersCheck(StringRef Name, ClangTidyContext *Context)
-      : ClangTidyCheck(Name, Context) {}
+  UseDesignatedInitializersCheck(StringRef Name, ClangTidyContext *Context);
   void registerMatchers(ast_matchers::MatchFinder *Finder) override;
   void check(const ast_matchers::MatchFinder::MatchResult &Result) override;
+
+private:
   std::optional<TraversalKind> getCheckTraversalKind() const override {
     return TK_IgnoreUnlessSpelledInSource;
   }
   bool isLanguageVersionSupported(const LangOptions &LangOpts) const override {
     return LangOpts.CPlusPlus20;
   }
+  void storeOptions(ClangTidyOptions::OptionMap &Opts) override;
+
+private:
+  bool IgnoreSingleElementAggregates;
 };
 
 } // namespace clang::tidy::modernize
diff --git 
a/clang-tools-extra/test/clang-tidy/checkers/modernize/use-designated-initializers.cpp
 
b/clang-tools-extra/test/clang-tidy/checkers/modernize/use-designated-initializers.cpp
index 7e41943e884061..350ee03d581ae8 100644
--- 
a/clang-tools-extra/test/clang-tidy/checkers/modernize/use-designated-initializers.cpp
+++ 
b/clang-tools-extra/test/clang-tidy/checkers/modernize/use-designated-initializers.cpp
@@ -1,4 +1,7 @@
 // RUN: %check_clang_tidy -std=c++20 %s modernize-use-designated-initializers 
%t
+// RUN: %check_clang_tidy -check-suffixes=,SINGLE-ELEMENT -std=c++20 %s 
modernize-use-designated-initializers %t \
+// RUN:     -- -config="{CheckOptions: [{key: 
modernize-use-designated-initializers.IgnoreSingleElementAggregates, value: 
false}]}" \
+// RUN:     --
 
 struct S1 {};
 
@@ -41,4 +44,4 @@ struct S4 {
 };
 
 S4 s41 {2.2};
-// CHECK-MESSAGES: :[[@LINE-1]]:8: warning: use designated initializer list 
[modernize-use-designated-initializers]
+// CHECK-MESSAGES-SINGLE-ELEMENT: :[[@LINE-1]]:8: warning: use designated 
initializer list [modernize-use-designated-initializers]

From 69bad8a270b266271cb274d04794312054aca90d Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Danny=20M=C3=B6sch?= <danny.moe...@icloud.com>
Date: Sat, 3 Feb 2024 14:06:17 +0100
Subject: [PATCH 06/23] Test class

---
 .../checkers/modernize/use-designated-initializers.cpp         | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git 
a/clang-tools-extra/test/clang-tidy/checkers/modernize/use-designated-initializers.cpp
 
b/clang-tools-extra/test/clang-tidy/checkers/modernize/use-designated-initializers.cpp
index 350ee03d581ae8..d932e2d5e4863b 100644
--- 
a/clang-tools-extra/test/clang-tidy/checkers/modernize/use-designated-initializers.cpp
+++ 
b/clang-tools-extra/test/clang-tidy/checkers/modernize/use-designated-initializers.cpp
@@ -25,7 +25,8 @@ S2 s24{.i = 1};
 S2 s25 = {.i=1, 2};
 // CHECK-MESSAGES: :[[@LINE-1]]:17: warning: use designated init expression 
[modernize-use-designated-initializers]
 
-struct S3 {
+class S3 {
+  public:
     S2 s2;
     double d;
 };

From 06091a0112d994c3618243dd13ca2d1581c352dd Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Danny=20M=C3=B6sch?= <danny.moe...@icloud.com>
Date: Sat, 3 Feb 2024 14:22:56 +0100
Subject: [PATCH 07/23] Add documentation and release notes

---
 .../UseDesignatedInitializersCheck.h          |  3 +-
 clang-tools-extra/docs/ReleaseNotes.rst       |  3 +-
 .../modernize/use-designated-initializers.rst | 40 ++++++++++++++++++-
 3 files changed, 43 insertions(+), 3 deletions(-)

diff --git 
a/clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.h 
b/clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.h
index 8a60fd7b31c5a4..34290aba06fab1 100644
--- a/clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.h
+++ b/clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.h
@@ -13,7 +13,8 @@
 
 namespace clang::tidy::modernize {
 
-/// FIXME: Write a short description.
+/// Triggers on initializer lists for aggregate type that could be
+/// written as designated initializers instead.
 ///
 /// For the user-facing documentation see:
 /// 
http://clang.llvm.org/extra/clang-tidy/checks/modernize/use-designated-initializers.html
diff --git a/clang-tools-extra/docs/ReleaseNotes.rst 
b/clang-tools-extra/docs/ReleaseNotes.rst
index a9e4305e7ca5a6..ce86f2ea455ff3 100644
--- a/clang-tools-extra/docs/ReleaseNotes.rst
+++ b/clang-tools-extra/docs/ReleaseNotes.rst
@@ -103,7 +103,8 @@ New checks
 - New :doc:`modernize-use-designated-initializers
   <clang-tidy/checks/modernize/use-designated-initializers>` check.
 
-  FIXME: add release notes.
+  Triggers on initializer lists for aggregate type that could be
+  written as designated initializers instead.
 
 New check aliases
 ^^^^^^^^^^^^^^^^^
diff --git 
a/clang-tools-extra/docs/clang-tidy/checks/modernize/use-designated-initializers.rst
 
b/clang-tools-extra/docs/clang-tidy/checks/modernize/use-designated-initializers.rst
index e0487f9b0e843d..1e182218dbd8eb 100644
--- 
a/clang-tools-extra/docs/clang-tidy/checks/modernize/use-designated-initializers.rst
+++ 
b/clang-tools-extra/docs/clang-tidy/checks/modernize/use-designated-initializers.rst
@@ -3,4 +3,42 @@
 modernize-use-designated-initializers
 =====================================
 
-FIXME: Describe what patterns does the check detect and why. Give examples.
+Triggers on initializer lists for aggregate type that could be written as
+designated initializers instead.
+
+With plain initializer lists, it is very easy to introduce bugs when adding
+new fields in the middle of a struct or class type. The same confusion might
+arise when changing the order of fields.
+
+C++ 20 supports the designated initializer syntax for aggregate types.
+By applying it, we can always be sure that aggregates are constructed 
correctly,
+because the every variable being initialized is referenced by name.
+
+Example:
+
+.. code-block::
+
+    struct S { int i, j; };
+
+is an aggregate type that should be initialized as
+
+.. code-block::
+
+    S s{.i = 1, .j = 2};
+
+instead of
+
+.. code-block::
+
+    S s{1, 2};
+
+which could easily become an issue when ``i`` and ``j`` are swapped in the
+declaration of ``S``.
+
+Options
+-------
+
+.. options:: IgnoreSingleElementAggregates
+
+    The value `false` specifies that even initializers for aggregate types
+    with only a single element should be checked. The default value is `true`.

From 0654d19199210985bf7d4435598aeb66604fd76f Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Danny=20M=C3=B6sch?= <danny.moe...@icloud.com>
Date: Sat, 3 Feb 2024 14:31:30 +0100
Subject: [PATCH 08/23] Fix typo

---
 .../clang-tidy/checks/modernize/use-designated-initializers.rst | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git 
a/clang-tools-extra/docs/clang-tidy/checks/modernize/use-designated-initializers.rst
 
b/clang-tools-extra/docs/clang-tidy/checks/modernize/use-designated-initializers.rst
index 1e182218dbd8eb..27474921a53d5e 100644
--- 
a/clang-tools-extra/docs/clang-tidy/checks/modernize/use-designated-initializers.rst
+++ 
b/clang-tools-extra/docs/clang-tidy/checks/modernize/use-designated-initializers.rst
@@ -38,7 +38,7 @@ declaration of ``S``.
 Options
 -------
 
-.. options:: IgnoreSingleElementAggregates
+.. option:: IgnoreSingleElementAggregates
 
     The value `false` specifies that even initializers for aggregate types
     with only a single element should be checked. The default value is `true`.

From 42a09ddd287e9c84d05e7b495d0856cc1241e265 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Danny=20M=C3=B6sch?= <danny.moe...@icloud.com>
Date: Sat, 3 Feb 2024 17:24:32 +0100
Subject: [PATCH 09/23] Specify explicit type

---
 .../clang-tidy/modernize/UseDesignatedInitializersCheck.cpp     | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git 
a/clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.cpp 
b/clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.cpp
index d269cef13e6aaa..d836a2b81741f2 100644
--- a/clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.cpp
+++ b/clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.cpp
@@ -20,7 +20,7 @@ using namespace clang::ast_matchers;
 
 namespace clang::tidy::modernize {
 
-static constexpr auto IgnoreSingleElementAggregatesName =
+static constexpr const char *IgnoreSingleElementAggregatesName =
     "IgnoreSingleElementAggregates";
 static constexpr auto IgnoreSingleElementAggregatesDefault = true;
 

From 5f786a9e90df81e363d7cc50c00db4177db35661 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Danny=20M=C3=B6sch?= <danny.moe...@icloud.com>
Date: Sat, 3 Feb 2024 17:24:44 +0100
Subject: [PATCH 10/23] Get only local option

---
 .../clang-tidy/modernize/UseDesignatedInitializersCheck.cpp   | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git 
a/clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.cpp 
b/clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.cpp
index d836a2b81741f2..c2e9b68f9be271 100644
--- a/clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.cpp
+++ b/clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.cpp
@@ -37,8 +37,8 @@ 
UseDesignatedInitializersCheck::UseDesignatedInitializersCheck(
     StringRef Name, ClangTidyContext *Context)
     : ClangTidyCheck(Name, Context),
       IgnoreSingleElementAggregates(
-          Options.getLocalOrGlobal(IgnoreSingleElementAggregatesName,
-                                   IgnoreSingleElementAggregatesDefault)) {}
+          Options.get(IgnoreSingleElementAggregatesName,
+                      IgnoreSingleElementAggregatesDefault)) {}
 
 void UseDesignatedInitializersCheck::registerMatchers(MatchFinder *Finder) {
   Finder->addMatcher(

From 954f1900ca1617c26684e24aba72e29331eea5c7 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Danny=20M=C3=B6sch?= <danny.moe...@icloud.com>
Date: Sat, 3 Feb 2024 17:25:03 +0100
Subject: [PATCH 11/23] Improve check description

---
 .../clang-tidy/modernize/UseDesignatedInitializersCheck.h       | 2 +-
 clang-tools-extra/docs/ReleaseNotes.rst                         | 2 +-
 .../clang-tidy/checks/modernize/use-designated-initializers.rst | 2 +-
 3 files changed, 3 insertions(+), 3 deletions(-)

diff --git 
a/clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.h 
b/clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.h
index 34290aba06fab1..de06250b0d3d06 100644
--- a/clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.h
+++ b/clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.h
@@ -13,7 +13,7 @@
 
 namespace clang::tidy::modernize {
 
-/// Triggers on initializer lists for aggregate type that could be
+/// Finds initializer lists for aggregate type that could be
 /// written as designated initializers instead.
 ///
 /// For the user-facing documentation see:
diff --git a/clang-tools-extra/docs/ReleaseNotes.rst 
b/clang-tools-extra/docs/ReleaseNotes.rst
index ce86f2ea455ff3..190b1b83252ea8 100644
--- a/clang-tools-extra/docs/ReleaseNotes.rst
+++ b/clang-tools-extra/docs/ReleaseNotes.rst
@@ -103,7 +103,7 @@ New checks
 - New :doc:`modernize-use-designated-initializers
   <clang-tidy/checks/modernize/use-designated-initializers>` check.
 
-  Triggers on initializer lists for aggregate type that could be
+  Finds initializer lists for aggregate type that could be
   written as designated initializers instead.
 
 New check aliases
diff --git 
a/clang-tools-extra/docs/clang-tidy/checks/modernize/use-designated-initializers.rst
 
b/clang-tools-extra/docs/clang-tidy/checks/modernize/use-designated-initializers.rst
index 27474921a53d5e..0f313eec2b1990 100644
--- 
a/clang-tools-extra/docs/clang-tidy/checks/modernize/use-designated-initializers.rst
+++ 
b/clang-tools-extra/docs/clang-tidy/checks/modernize/use-designated-initializers.rst
@@ -3,7 +3,7 @@
 modernize-use-designated-initializers
 =====================================
 
-Triggers on initializer lists for aggregate type that could be written as
+Finds initializer lists for aggregate type that could be written as
 designated initializers instead.
 
 With plain initializer lists, it is very easy to introduce bugs when adding

From 8aa4243081f2fb8fbe07dede6304d88841a07ac7 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Danny=20M=C3=B6sch?= <danny.moe...@icloud.com>
Date: Sat, 3 Feb 2024 18:25:29 +0100
Subject: [PATCH 12/23] Move logic into matcher

---
 .../UseDesignatedInitializersCheck.cpp        | 21 +++++++++++++------
 1 file changed, 15 insertions(+), 6 deletions(-)

diff --git 
a/clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.cpp 
b/clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.cpp
index c2e9b68f9be271..a139a369be7746 100644
--- a/clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.cpp
+++ b/clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.cpp
@@ -12,6 +12,7 @@
 #include "clang/AST/Stmt.h"
 #include "clang/ASTMatchers/ASTMatchFinder.h"
 #include "clang/ASTMatchers/ASTMatchers.h"
+#include "clang/ASTMatchers/ASTMatchersMacros.h"
 #include <algorithm>
 #include <iterator>
 #include <vector>
@@ -40,24 +41,32 @@ 
UseDesignatedInitializersCheck::UseDesignatedInitializersCheck(
           Options.get(IgnoreSingleElementAggregatesName,
                       IgnoreSingleElementAggregatesDefault)) {}
 
+AST_MATCHER(CXXRecordDecl, isAggregate) { return Node.isAggregate(); }
+
+AST_MATCHER(InitListExpr, isFullyDesignated) {
+  return getUndesignatedComponents(&Node).empty();
+}
+
+AST_MATCHER(InitListExpr, hasSingleElement) { return Node.getNumInits() == 1; }
 void UseDesignatedInitializersCheck::registerMatchers(MatchFinder *Finder) {
   Finder->addMatcher(
-      initListExpr(hasType(recordDecl().bind("type"))).bind("init"), this);
+      initListExpr(hasType(cxxRecordDecl(isAggregate()).bind("type")),
+                   unless(IgnoreSingleElementAggregates ? hasSingleElement()
+                                                        : unless(anything())),
+                   unless(isFullyDesignated()))
+          .bind("init"),
+      this);
 }
 
 void UseDesignatedInitializersCheck::check(
     const MatchFinder::MatchResult &Result) {
   const auto *InitList = Result.Nodes.getNodeAs<InitListExpr>("init");
   const auto *Type = Result.Nodes.getNodeAs<CXXRecordDecl>("type");
-  if (!Type || !InitList || !Type->isAggregate())
-    return;
-  if (IgnoreSingleElementAggregates && InitList->getNumInits() == 1)
+  if (!Type || !InitList)
     return;
   if (const auto *SyntacticInitList = InitList->getSyntacticForm()) {
     const auto UndesignatedComponents =
         getUndesignatedComponents(SyntacticInitList);
-    if (UndesignatedComponents.empty())
-      return;
     if (UndesignatedComponents.size() == SyntacticInitList->getNumInits()) {
       diag(InitList->getLBraceLoc(), "use designated initializer list");
       return;

From 19e4a21c66b12a97d3e81ca0218123ee464c83b1 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Danny=20M=C3=B6sch?= <danny.moe...@icloud.com>
Date: Sat, 3 Feb 2024 18:40:45 +0100
Subject: [PATCH 13/23] Add template test

---
 .../modernize/use-designated-initializers.cpp         | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git 
a/clang-tools-extra/test/clang-tidy/checkers/modernize/use-designated-initializers.cpp
 
b/clang-tools-extra/test/clang-tidy/checkers/modernize/use-designated-initializers.cpp
index d932e2d5e4863b..b6f0c3758163d6 100644
--- 
a/clang-tools-extra/test/clang-tidy/checkers/modernize/use-designated-initializers.cpp
+++ 
b/clang-tools-extra/test/clang-tidy/checkers/modernize/use-designated-initializers.cpp
@@ -46,3 +46,14 @@ struct S4 {
 
 S4 s41 {2.2};
 // CHECK-MESSAGES-SINGLE-ELEMENT: :[[@LINE-1]]:8: warning: use designated 
initializer list [modernize-use-designated-initializers]
+
+S4 s42 = {{}};
+// CHECK-MESSAGES-SINGLE-ELEMENT: :[[@LINE-1]]:10: warning: use designated 
initializer list [modernize-use-designated-initializers]
+
+template<typename S> S template1() { return {10, 11}; }
+
+S2 s26 = template1<S2>();
+
+template<typename S> S template2() { return {}; }
+
+S2 s27 = template2<S2>();

From da85a16c15678f784c0e293d564424bde6eae1d7 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Danny=20M=C3=B6sch?= <danny.moe...@icloud.com>
Date: Sat, 3 Feb 2024 19:00:42 +0100
Subject: [PATCH 14/23] fixup! Specify explicit type

---
 .../clang-tidy/modernize/UseDesignatedInitializersCheck.cpp     | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git 
a/clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.cpp 
b/clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.cpp
index a139a369be7746..072d6e33c3fde4 100644
--- a/clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.cpp
+++ b/clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.cpp
@@ -23,7 +23,7 @@ namespace clang::tidy::modernize {
 
 static constexpr const char *IgnoreSingleElementAggregatesName =
     "IgnoreSingleElementAggregates";
-static constexpr auto IgnoreSingleElementAggregatesDefault = true;
+static constexpr bool IgnoreSingleElementAggregatesDefault = true;
 
 static std::vector<Stmt *>
 getUndesignatedComponents(const InitListExpr *SyntacticInitList) {

From 89e544bfec911568056dd93e8c443d208407385c Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Danny=20M=C3=B6sch?= <danny.moe...@icloud.com>
Date: Sun, 4 Feb 2024 11:50:12 +0100
Subject: [PATCH 15/23] Ignore types inheriting fields

---
 .../modernize/UseDesignatedInitializersCheck.cpp  | 15 +++++++++++----
 .../modernize/use-designated-initializers.cpp     |  4 ++++
 2 files changed, 15 insertions(+), 4 deletions(-)

diff --git 
a/clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.cpp 
b/clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.cpp
index 072d6e33c3fde4..58b277b6ff626e 100644
--- a/clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.cpp
+++ b/clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.cpp
@@ -48,12 +48,19 @@ AST_MATCHER(InitListExpr, isFullyDesignated) {
 }
 
 AST_MATCHER(InitListExpr, hasSingleElement) { return Node.getNumInits() == 1; }
+
+AST_MATCHER_FUNCTION(::internal::Matcher<CXXRecordDecl>, hasBaseWithFields) {
+  return hasAnyBase(hasType(cxxRecordDecl(has(fieldDecl()))));
+}
+
 void UseDesignatedInitializersCheck::registerMatchers(MatchFinder *Finder) {
   Finder->addMatcher(
-      initListExpr(hasType(cxxRecordDecl(isAggregate()).bind("type")),
-                   unless(IgnoreSingleElementAggregates ? hasSingleElement()
-                                                        : unless(anything())),
-                   unless(isFullyDesignated()))
+      initListExpr(
+          hasType(cxxRecordDecl(isAggregate(), unless(hasBaseWithFields()))
+                      .bind("type")),
+          unless(IgnoreSingleElementAggregates ? hasSingleElement()
+                                               : unless(anything())),
+          unless(isFullyDesignated()))
           .bind("init"),
       this);
 }
diff --git 
a/clang-tools-extra/test/clang-tidy/checkers/modernize/use-designated-initializers.cpp
 
b/clang-tools-extra/test/clang-tidy/checkers/modernize/use-designated-initializers.cpp
index b6f0c3758163d6..0a4a098a7737be 100644
--- 
a/clang-tools-extra/test/clang-tidy/checkers/modernize/use-designated-initializers.cpp
+++ 
b/clang-tools-extra/test/clang-tidy/checkers/modernize/use-designated-initializers.cpp
@@ -57,3 +57,7 @@ S2 s26 = template1<S2>();
 template<typename S> S template2() { return {}; }
 
 S2 s27 = template2<S2>();
+
+struct S5: S2 { int x, y; };
+
+S5 s51 {1, 2, .x = 3, .y = 4};

From a8dddd6a7b8e3429b1ed1aa6c9409de2af04bd84 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Danny=20M=C3=B6sch?= <danny.moe...@icloud.com>
Date: Sun, 4 Feb 2024 13:21:26 +0100
Subject: [PATCH 16/23] Ignore types with anonymous fields

---
 .../UseDesignatedInitializersCheck.cpp        | 13 +++++++++++-
 .../modernize/use-designated-initializers.cpp | 20 +++++++++++++++++++
 2 files changed, 32 insertions(+), 1 deletion(-)

diff --git 
a/clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.cpp 
b/clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.cpp
index 58b277b6ff626e..d2c5d02128819b 100644
--- a/clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.cpp
+++ b/clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.cpp
@@ -7,6 +7,7 @@
 
//===----------------------------------------------------------------------===//
 
 #include "UseDesignatedInitializersCheck.h"
+#include "clang/AST/APValue.h"
 #include "clang/AST/Decl.h"
 #include "clang/AST/Expr.h"
 #include "clang/AST/Stmt.h"
@@ -14,6 +15,7 @@
 #include "clang/ASTMatchers/ASTMatchers.h"
 #include "clang/ASTMatchers/ASTMatchersMacros.h"
 #include <algorithm>
+#include <iostream>
 #include <iterator>
 #include <vector>
 
@@ -53,10 +55,19 @@ AST_MATCHER_FUNCTION(::internal::Matcher<CXXRecordDecl>, 
hasBaseWithFields) {
   return hasAnyBase(hasType(cxxRecordDecl(has(fieldDecl()))));
 }
 
+AST_MATCHER(FieldDecl, isAnonymousDecl) {
+  if (const auto *Record =
+          Node.getType().getCanonicalType()->getAsRecordDecl()) {
+    return Record->isAnonymousStructOrUnion() || !Record->getIdentifier();
+  }
+  return false;
+}
+
 void UseDesignatedInitializersCheck::registerMatchers(MatchFinder *Finder) {
   Finder->addMatcher(
       initListExpr(
-          hasType(cxxRecordDecl(isAggregate(), unless(hasBaseWithFields()))
+          hasType(cxxRecordDecl(isAggregate(), unless(hasBaseWithFields()),
+                                unless(has(fieldDecl(isAnonymousDecl()))))
                       .bind("type")),
           unless(IgnoreSingleElementAggregates ? hasSingleElement()
                                                : unless(anything())),
diff --git 
a/clang-tools-extra/test/clang-tidy/checkers/modernize/use-designated-initializers.cpp
 
b/clang-tools-extra/test/clang-tidy/checkers/modernize/use-designated-initializers.cpp
index 0a4a098a7737be..46859435c588e4 100644
--- 
a/clang-tools-extra/test/clang-tidy/checkers/modernize/use-designated-initializers.cpp
+++ 
b/clang-tools-extra/test/clang-tidy/checkers/modernize/use-designated-initializers.cpp
@@ -61,3 +61,23 @@ S2 s27 = template2<S2>();
 struct S5: S2 { int x, y; };
 
 S5 s51 {1, 2, .x = 3, .y = 4};
+
+struct S6 {
+    int i;
+    struct { int j; } s;
+};
+
+S6 s61 {1, 2};
+
+struct S7 {
+    union {
+        int k;
+        double d;
+    } u;
+};
+
+S7 s71 {1};
+
+struct S8: S7 { int i; };
+
+S8 s81{1, 2};

From 79d13e3353d7598c37e5556a5748d19bcbd0bba7 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Danny=20M=C3=B6sch?= <danny.moe...@icloud.com>
Date: Sun, 4 Feb 2024 13:29:52 +0100
Subject: [PATCH 17/23] Remove restriction to C++ 20

---
 .../clang-tidy/modernize/UseDesignatedInitializersCheck.h   | 3 ---
 .../checks/modernize/use-designated-initializers.rst        | 6 +++++-
 .../checkers/modernize/use-designated-initializers.cpp      | 4 ++--
 3 files changed, 7 insertions(+), 6 deletions(-)

diff --git 
a/clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.h 
b/clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.h
index de06250b0d3d06..54dca26c6d735a 100644
--- a/clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.h
+++ b/clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.h
@@ -28,9 +28,6 @@ class UseDesignatedInitializersCheck : public ClangTidyCheck {
   std::optional<TraversalKind> getCheckTraversalKind() const override {
     return TK_IgnoreUnlessSpelledInSource;
   }
-  bool isLanguageVersionSupported(const LangOptions &LangOpts) const override {
-    return LangOpts.CPlusPlus20;
-  }
   void storeOptions(ClangTidyOptions::OptionMap &Opts) override;
 
 private:
diff --git 
a/clang-tools-extra/docs/clang-tidy/checks/modernize/use-designated-initializers.rst
 
b/clang-tools-extra/docs/clang-tidy/checks/modernize/use-designated-initializers.rst
index 0f313eec2b1990..105daf2c50ef2e 100644
--- 
a/clang-tools-extra/docs/clang-tidy/checks/modernize/use-designated-initializers.rst
+++ 
b/clang-tools-extra/docs/clang-tidy/checks/modernize/use-designated-initializers.rst
@@ -12,7 +12,11 @@ arise when changing the order of fields.
 
 C++ 20 supports the designated initializer syntax for aggregate types.
 By applying it, we can always be sure that aggregates are constructed 
correctly,
-because the every variable being initialized is referenced by name.
+because every variable being initialized is referenced by name.
+
+Even when compiling in a language version older than C++ 20, depending on you 
compiler,
+designated initializers are potentially supported. Therefore, the check is not 
restricted
+to C++ 20 and older.
 
 Example:
 
diff --git 
a/clang-tools-extra/test/clang-tidy/checkers/modernize/use-designated-initializers.cpp
 
b/clang-tools-extra/test/clang-tidy/checkers/modernize/use-designated-initializers.cpp
index 46859435c588e4..9780bf7f0080d0 100644
--- 
a/clang-tools-extra/test/clang-tidy/checkers/modernize/use-designated-initializers.cpp
+++ 
b/clang-tools-extra/test/clang-tidy/checkers/modernize/use-designated-initializers.cpp
@@ -1,5 +1,5 @@
-// RUN: %check_clang_tidy -std=c++20 %s modernize-use-designated-initializers 
%t
-// RUN: %check_clang_tidy -check-suffixes=,SINGLE-ELEMENT -std=c++20 %s 
modernize-use-designated-initializers %t \
+// RUN: %check_clang_tidy -std=c++17 %s modernize-use-designated-initializers 
%t
+// RUN: %check_clang_tidy -check-suffixes=,SINGLE-ELEMENT -std=c++17 %s 
modernize-use-designated-initializers %t \
 // RUN:     -- -config="{CheckOptions: [{key: 
modernize-use-designated-initializers.IgnoreSingleElementAggregates, value: 
false}]}" \
 // RUN:     --
 

From 77627dfb26cad62d653e608d9f89ba7628dc56e9 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Danny=20M=C3=B6sch?= <danny.moe...@icloud.com>
Date: Sun, 4 Feb 2024 13:37:09 +0100
Subject: [PATCH 18/23] fixup! Ignore types with anonymous fields

---
 .../clang-tidy/modernize/UseDesignatedInitializersCheck.cpp      | 1 -
 1 file changed, 1 deletion(-)

diff --git 
a/clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.cpp 
b/clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.cpp
index d2c5d02128819b..2a9a80ef8cd9cd 100644
--- a/clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.cpp
+++ b/clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.cpp
@@ -15,7 +15,6 @@
 #include "clang/ASTMatchers/ASTMatchers.h"
 #include "clang/ASTMatchers/ASTMatchersMacros.h"
 #include <algorithm>
-#include <iostream>
 #include <iterator>
 #include <vector>
 

From 6772e617c3d22823a58c52f4112767eee12d5ae4 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Danny=20M=C3=B6sch?= <danny.moe...@icloud.com>
Date: Sun, 4 Feb 2024 13:38:42 +0100
Subject: [PATCH 19/23] fixup! Specify explicit type

---
 .../clang-tidy/modernize/UseDesignatedInitializersCheck.cpp   | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git 
a/clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.cpp 
b/clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.cpp
index 2a9a80ef8cd9cd..84fb59e5a76397 100644
--- a/clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.cpp
+++ b/clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.cpp
@@ -22,9 +22,9 @@ using namespace clang::ast_matchers;
 
 namespace clang::tidy::modernize {
 
-static constexpr const char *IgnoreSingleElementAggregatesName =
+static const char *IgnoreSingleElementAggregatesName =
     "IgnoreSingleElementAggregates";
-static constexpr bool IgnoreSingleElementAggregatesDefault = true;
+static const bool IgnoreSingleElementAggregatesDefault = true;
 
 static std::vector<Stmt *>
 getUndesignatedComponents(const InitListExpr *SyntacticInitList) {

From aab52394d58a3002ef44acfc81af100cce7e013b Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Danny=20M=C3=B6sch?= <danny.moe...@icloud.com>
Date: Sun, 4 Feb 2024 14:05:31 +0100
Subject: [PATCH 20/23] Add option to restrict check to POD types

---
 .../UseDesignatedInitializersCheck.cpp         | 18 +++++++++++++-----
 .../modernize/UseDesignatedInitializersCheck.h |  1 +
 .../modernize/use-designated-initializers.rst  |  6 ++++++
 .../modernize/use-designated-initializers.cpp  | 18 ++++++++++++++++++
 4 files changed, 38 insertions(+), 5 deletions(-)

diff --git 
a/clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.cpp 
b/clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.cpp
index 84fb59e5a76397..b1b44289111c7a 100644
--- a/clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.cpp
+++ b/clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.cpp
@@ -26,6 +26,9 @@ static const char *IgnoreSingleElementAggregatesName =
     "IgnoreSingleElementAggregates";
 static const bool IgnoreSingleElementAggregatesDefault = true;
 
+static const char *RestrictToPODTypesName = "RestrictToPODTypes";
+static const bool RestrictToPODTypesDefault = false;
+
 static std::vector<Stmt *>
 getUndesignatedComponents(const InitListExpr *SyntacticInitList) {
   std::vector<Stmt *> Result;
@@ -37,13 +40,16 @@ getUndesignatedComponents(const InitListExpr 
*SyntacticInitList) {
 
 UseDesignatedInitializersCheck::UseDesignatedInitializersCheck(
     StringRef Name, ClangTidyContext *Context)
-    : ClangTidyCheck(Name, Context),
-      IgnoreSingleElementAggregates(
-          Options.get(IgnoreSingleElementAggregatesName,
-                      IgnoreSingleElementAggregatesDefault)) {}
+    : ClangTidyCheck(Name, Context), IgnoreSingleElementAggregates(Options.get(
+                                         IgnoreSingleElementAggregatesName,
+                                         
IgnoreSingleElementAggregatesDefault)),
+      RestrictToPODTypes(
+          Options.get(RestrictToPODTypesName, RestrictToPODTypesDefault)) {}
 
 AST_MATCHER(CXXRecordDecl, isAggregate) { return Node.isAggregate(); }
 
+AST_MATCHER(CXXRecordDecl, isPOD) { return Node.isPOD(); }
+
 AST_MATCHER(InitListExpr, isFullyDesignated) {
   return getUndesignatedComponents(&Node).empty();
 }
@@ -65,7 +71,8 @@ AST_MATCHER(FieldDecl, isAnonymousDecl) {
 void UseDesignatedInitializersCheck::registerMatchers(MatchFinder *Finder) {
   Finder->addMatcher(
       initListExpr(
-          hasType(cxxRecordDecl(isAggregate(), unless(hasBaseWithFields()),
+          hasType(cxxRecordDecl(RestrictToPODTypes ? isPOD() : isAggregate(),
+                                unless(hasBaseWithFields()),
                                 unless(has(fieldDecl(isAnonymousDecl()))))
                       .bind("type")),
           unless(IgnoreSingleElementAggregates ? hasSingleElement()
@@ -98,6 +105,7 @@ void UseDesignatedInitializersCheck::storeOptions(
     ClangTidyOptions::OptionMap &Opts) {
   Options.store(Opts, IgnoreSingleElementAggregatesName,
                 IgnoreSingleElementAggregates);
+  Options.store(Opts, RestrictToPODTypesName, RestrictToPODTypes);
 }
 
 } // namespace clang::tidy::modernize
diff --git 
a/clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.h 
b/clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.h
index 54dca26c6d735a..9aa216d30ef6b6 100644
--- a/clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.h
+++ b/clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.h
@@ -32,6 +32,7 @@ class UseDesignatedInitializersCheck : public ClangTidyCheck {
 
 private:
   bool IgnoreSingleElementAggregates;
+  bool RestrictToPODTypes;
 };
 
 } // namespace clang::tidy::modernize
diff --git 
a/clang-tools-extra/docs/clang-tidy/checks/modernize/use-designated-initializers.rst
 
b/clang-tools-extra/docs/clang-tidy/checks/modernize/use-designated-initializers.rst
index 105daf2c50ef2e..a306e784c33562 100644
--- 
a/clang-tools-extra/docs/clang-tidy/checks/modernize/use-designated-initializers.rst
+++ 
b/clang-tools-extra/docs/clang-tidy/checks/modernize/use-designated-initializers.rst
@@ -46,3 +46,9 @@ Options
 
     The value `false` specifies that even initializers for aggregate types
     with only a single element should be checked. The default value is `true`.
+
+.. option:: RestrictToPODTypes
+
+    The value `true` specifies that only Plain Old Data (POD) types shall be
+    checked. This makes the check applicable to even older C++ standards.
+    The default value is `false`.
diff --git 
a/clang-tools-extra/test/clang-tidy/checkers/modernize/use-designated-initializers.cpp
 
b/clang-tools-extra/test/clang-tidy/checkers/modernize/use-designated-initializers.cpp
index 9780bf7f0080d0..e0b722ec091671 100644
--- 
a/clang-tools-extra/test/clang-tidy/checkers/modernize/use-designated-initializers.cpp
+++ 
b/clang-tools-extra/test/clang-tidy/checkers/modernize/use-designated-initializers.cpp
@@ -2,6 +2,9 @@
 // RUN: %check_clang_tidy -check-suffixes=,SINGLE-ELEMENT -std=c++17 %s 
modernize-use-designated-initializers %t \
 // RUN:     -- -config="{CheckOptions: [{key: 
modernize-use-designated-initializers.IgnoreSingleElementAggregates, value: 
false}]}" \
 // RUN:     --
+// RUN: %check_clang_tidy -check-suffixes=POD -std=c++17 %s 
modernize-use-designated-initializers %t \
+// RUN:     -- -config="{CheckOptions: [{key: 
modernize-use-designated-initializers.RestrictToPODTypes, value: true}]}" \
+// RUN:     --
 
 struct S1 {};
 
@@ -16,14 +19,17 @@ S2 s21{.i=1, .j =2};
 
 S2 s22 = {1, 2};
 // CHECK-MESSAGES: :[[@LINE-1]]:10: warning: use designated initializer list 
[modernize-use-designated-initializers]
+// CHECK-MESSAGES-POD: :[[@LINE-2]]:10: warning: use designated initializer 
list [modernize-use-designated-initializers]
 
 S2 s23{1};
 // CHECK-MESSAGES: :[[@LINE-1]]:7: warning: use designated initializer list 
[modernize-use-designated-initializers]
+// CHECK-MESSAGES-POD: :[[@LINE-2]]:7: warning: use designated initializer 
list [modernize-use-designated-initializers]
 
 S2 s24{.i = 1};
 
 S2 s25 = {.i=1, 2};
 // CHECK-MESSAGES: :[[@LINE-1]]:17: warning: use designated init expression 
[modernize-use-designated-initializers]
+// CHECK-MESSAGES-POD: :[[@LINE-2]]:17: warning: use designated init 
expression [modernize-use-designated-initializers]
 
 class S3 {
   public:
@@ -34,10 +40,14 @@ class S3 {
 S3 s31 = {.s2 = 1, 2, 3.1};
 // CHECK-MESSAGES: :[[@LINE-1]]:20: warning: use designated init expression 
[modernize-use-designated-initializers]
 // CHECK-MESSAGES: :[[@LINE-2]]:23: warning: use designated init expression 
[modernize-use-designated-initializers]
+// CHECK-MESSAGES-POD: :[[@LINE-3]]:20: warning: use designated init 
expression [modernize-use-designated-initializers]
+// CHECK-MESSAGES-POD: :[[@LINE-4]]:23: warning: use designated init 
expression [modernize-use-designated-initializers]
 
 S3 s32 = {{.i = 1, 2}};
 // CHECK-MESSAGES: :[[@LINE-1]]:10: warning: use designated initializer list 
[modernize-use-designated-initializers]
 // CHECK-MESSAGES: :[[@LINE-2]]:20: warning: use designated init expression 
[modernize-use-designated-initializers]
+// CHECK-MESSAGES-POD: :[[@LINE-3]]:10: warning: use designated initializer 
list [modernize-use-designated-initializers]
+// CHECK-MESSAGES-POD: :[[@LINE-4]]:20: warning: use designated init 
expression [modernize-use-designated-initializers]
 
 struct S4 {
     double d;
@@ -81,3 +91,11 @@ S7 s71 {1};
 struct S8: S7 { int i; };
 
 S8 s81{1, 2};
+
+struct S9 {
+    int i, j;
+    S9 &operator=(S9);
+};
+
+S9 s91{1, 2};
+// CHECK-MESSAGES: :[[@LINE-1]]:7: warning: use designated initializer list 
[modernize-use-designated-initializers]

From f44987dc4a23dbc657c75a5b02df014a17ad74af Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Danny=20M=C3=B6sch?= <danny.moe...@icloud.com>
Date: Sun, 11 Feb 2024 11:52:29 +0100
Subject: [PATCH 21/23] Add fix-its

---
 .../modernize/UseDesignatedInitializersCheck.cpp  | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git 
a/clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.cpp 
b/clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.cpp
index b1b44289111c7a..081286081b4cbf 100644
--- a/clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.cpp
+++ b/clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.cpp
@@ -95,8 +95,19 @@ void UseDesignatedInitializersCheck::check(
       diag(InitList->getLBraceLoc(), "use designated initializer list");
       return;
     }
-    for (const auto *InitExpr : UndesignatedComponents) {
-      diag(InitExpr->getBeginLoc(), "use designated init expression");
+    const auto FieldIterator = Type->fields().begin();
+    for (const auto *InitExpr : *SyntacticInitList) {
+      const auto Field = std::next(FieldIterator);
+      if (std::find(UndesignatedComponents.begin(),
+                    UndesignatedComponents.end(),
+                    InitExpr) == UndesignatedComponents.end())
+        continue;
+      if (const auto *FieldID = Field->getIdentifier()) {
+        const auto FieldName = FieldID->getName();
+        diag(InitExpr->getBeginLoc(), "use designated init expression")
+            << FixItHint::CreateInsertion(InitExpr->getBeginLoc(),
+                                          "." + FieldName.str() + "=");
+      }
     }
   }
 }

From fc072d8c005662bf0eacd30b5002617c6759dbc9 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Danny=20M=C3=B6sch?= <danny.moe...@icloud.com>
Date: Sun, 11 Feb 2024 14:36:19 +0100
Subject: [PATCH 22/23] Move computation of designated initializers to common
 place

---
 clang-tools-extra/clangd/InlayHints.cpp       | 167 +--------------
 .../clang/Tooling/DesignatedInitializers.h    |  43 ++++
 clang/lib/Tooling/CMakeLists.txt              |   1 +
 clang/lib/Tooling/DesignatedInitializers.cpp  | 195 ++++++++++++++++++
 4 files changed, 241 insertions(+), 165 deletions(-)
 create mode 100644 clang/include/clang/Tooling/DesignatedInitializers.h
 create mode 100644 clang/lib/Tooling/DesignatedInitializers.cpp

diff --git a/clang-tools-extra/clangd/InlayHints.cpp 
b/clang-tools-extra/clangd/InlayHints.cpp
index 671a9c30ffa959..09f5dba5697b10 100644
--- a/clang-tools-extra/clangd/InlayHints.cpp
+++ b/clang-tools-extra/clangd/InlayHints.cpp
@@ -23,8 +23,8 @@
 #include "clang/Basic/Builtins.h"
 #include "clang/Basic/OperatorKinds.h"
 #include "clang/Basic/SourceManager.h"
+#include "clang/Tooling/DesignatedInitializers.h"
 #include "llvm/ADT/DenseSet.h"
-#include "llvm/ADT/ScopeExit.h"
 #include "llvm/ADT/StringExtras.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/ADT/Twine.h"
@@ -42,169 +42,6 @@ namespace {
 // For now, inlay hints are always anchored at the left or right of their 
range.
 enum class HintSide { Left, Right };
 
-// Helper class to iterate over the designator names of an aggregate type.
-//
-// For an array type, yields [0], [1], [2]...
-// For aggregate classes, yields null for each base, then .field1, .field2, ...
-class AggregateDesignatorNames {
-public:
-  AggregateDesignatorNames(QualType T) {
-    if (!T.isNull()) {
-      T = T.getCanonicalType();
-      if (T->isArrayType()) {
-        IsArray = true;
-        Valid = true;
-        return;
-      }
-      if (const RecordDecl *RD = T->getAsRecordDecl()) {
-        Valid = true;
-        FieldsIt = RD->field_begin();
-        FieldsEnd = RD->field_end();
-        if (const auto *CRD = llvm::dyn_cast<CXXRecordDecl>(RD)) {
-          BasesIt = CRD->bases_begin();
-          BasesEnd = CRD->bases_end();
-          Valid = CRD->isAggregate();
-        }
-        OneField = Valid && BasesIt == BasesEnd && FieldsIt != FieldsEnd &&
-                   std::next(FieldsIt) == FieldsEnd;
-      }
-    }
-  }
-  // Returns false if the type was not an aggregate.
-  operator bool() { return Valid; }
-  // Advance to the next element in the aggregate.
-  void next() {
-    if (IsArray)
-      ++Index;
-    else if (BasesIt != BasesEnd)
-      ++BasesIt;
-    else if (FieldsIt != FieldsEnd)
-      ++FieldsIt;
-  }
-  // Print the designator to Out.
-  // Returns false if we could not produce a designator for this element.
-  bool append(std::string &Out, bool ForSubobject) {
-    if (IsArray) {
-      Out.push_back('[');
-      Out.append(std::to_string(Index));
-      Out.push_back(']');
-      return true;
-    }
-    if (BasesIt != BasesEnd)
-      return false; // Bases can't be designated. Should we make one up?
-    if (FieldsIt != FieldsEnd) {
-      llvm::StringRef FieldName;
-      if (const IdentifierInfo *II = FieldsIt->getIdentifier())
-        FieldName = II->getName();
-
-      // For certain objects, their subobjects may be named directly.
-      if (ForSubobject &&
-          (FieldsIt->isAnonymousStructOrUnion() ||
-           // std::array<int,3> x = {1,2,3}. Designators not strictly valid!
-           (OneField && isReservedName(FieldName))))
-        return true;
-
-      if (!FieldName.empty() && !isReservedName(FieldName)) {
-        Out.push_back('.');
-        Out.append(FieldName.begin(), FieldName.end());
-        return true;
-      }
-      return false;
-    }
-    return false;
-  }
-
-private:
-  bool Valid = false;
-  bool IsArray = false;
-  bool OneField = false; // e.g. std::array { T __elements[N]; }
-  unsigned Index = 0;
-  CXXRecordDecl::base_class_const_iterator BasesIt;
-  CXXRecordDecl::base_class_const_iterator BasesEnd;
-  RecordDecl::field_iterator FieldsIt;
-  RecordDecl::field_iterator FieldsEnd;
-};
-
-// Collect designator labels describing the elements of an init list.
-//
-// This function contributes the designators of some (sub)object, which is
-// represented by the semantic InitListExpr Sem.
-// This includes any nested subobjects, but *only* if they are part of the same
-// original syntactic init list (due to brace elision).
-// In other words, it may descend into subobjects but not written init-lists.
-//
-// For example: struct Outer { Inner a,b; }; struct Inner { int x, y; }
-//              Outer o{{1, 2}, 3};
-// This function will be called with Sem = { {1, 2}, {3, ImplicitValue} }
-// It should generate designators '.a:' and '.b.x:'.
-// '.a:' is produced directly without recursing into the written sublist.
-// (The written sublist will have a separate collectDesignators() call later).
-// Recursion with Prefix='.b' and Sem = {3, ImplicitValue} produces '.b.x:'.
-void collectDesignators(const InitListExpr *Sem,
-                        llvm::DenseMap<SourceLocation, std::string> &Out,
-                        const llvm::DenseSet<SourceLocation> &NestedBraces,
-                        std::string &Prefix) {
-  if (!Sem || Sem->isTransparent())
-    return;
-  assert(Sem->isSemanticForm());
-
-  // The elements of the semantic form all correspond to direct subobjects of
-  // the aggregate type. `Fields` iterates over these subobject names.
-  AggregateDesignatorNames Fields(Sem->getType());
-  if (!Fields)
-    return;
-  for (const Expr *Init : Sem->inits()) {
-    auto Next = llvm::make_scope_exit([&, Size(Prefix.size())] {
-      Fields.next();       // Always advance to the next subobject name.
-      Prefix.resize(Size); // Erase any designator we appended.
-    });
-    // Skip for a broken initializer or if it is a "hole" in a subobject that
-    // was not explicitly initialized.
-    if (!Init || llvm::isa<ImplicitValueInitExpr>(Init))
-      continue;
-
-    const auto *BraceElidedSubobject = llvm::dyn_cast<InitListExpr>(Init);
-    if (BraceElidedSubobject &&
-        NestedBraces.contains(BraceElidedSubobject->getLBraceLoc()))
-      BraceElidedSubobject = nullptr; // there were braces!
-
-    if (!Fields.append(Prefix, BraceElidedSubobject != nullptr))
-      continue; // no designator available for this subobject
-    if (BraceElidedSubobject) {
-      // If the braces were elided, this aggregate subobject is initialized
-      // inline in the same syntactic list.
-      // Descend into the semantic list describing the subobject.
-      // (NestedBraces are still correct, they're from the same syntactic 
list).
-      collectDesignators(BraceElidedSubobject, Out, NestedBraces, Prefix);
-      continue;
-    }
-    Out.try_emplace(Init->getBeginLoc(), Prefix);
-  }
-}
-
-// Get designators describing the elements of a (syntactic) init list.
-// This does not produce designators for any explicitly-written nested lists.
-llvm::DenseMap<SourceLocation, std::string>
-getDesignators(const InitListExpr *Syn) {
-  assert(Syn->isSyntacticForm());
-
-  // collectDesignators needs to know which InitListExprs in the semantic tree
-  // were actually written, but InitListExpr::isExplicit() lies.
-  // Instead, record where braces of sub-init-lists occur in the syntactic 
form.
-  llvm::DenseSet<SourceLocation> NestedBraces;
-  for (const Expr *Init : Syn->inits())
-    if (auto *Nested = llvm::dyn_cast<InitListExpr>(Init))
-      NestedBraces.insert(Nested->getLBraceLoc());
-
-  // Traverse the semantic form to find the designators.
-  // We use their SourceLocation to correlate with the syntactic form later.
-  llvm::DenseMap<SourceLocation, std::string> Designators;
-  std::string EmptyPrefix;
-  collectDesignators(Syn->isSemanticForm() ? Syn : Syn->getSemanticForm(),
-                     Designators, NestedBraces, EmptyPrefix);
-  return Designators;
-}
-
 void stripLeadingUnderscores(StringRef &Name) { Name = Name.ltrim('_'); }
 
 // getDeclForType() returns the decl responsible for Type's spelling.
@@ -854,7 +691,7 @@ class InlayHintVisitor : public 
RecursiveASTVisitor<InlayHintVisitor> {
     if (Syn->isIdiomaticZeroInitializer(AST.getLangOpts()))
       return true;
     llvm::DenseMap<SourceLocation, std::string> Designators =
-        getDesignators(Syn);
+        clang::tooling::getDesignators(Syn);
     for (const Expr *Init : Syn->inits()) {
       if (llvm::isa<DesignatedInitExpr>(Init))
         continue;
diff --git a/clang/include/clang/Tooling/DesignatedInitializers.h 
b/clang/include/clang/Tooling/DesignatedInitializers.h
new file mode 100644
index 00000000000000..e978dfe639f0c0
--- /dev/null
+++ b/clang/include/clang/Tooling/DesignatedInitializers.h
@@ -0,0 +1,43 @@
+//===--- DesignatedInitializers.h -------------------------------*- C++ 
-*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM 
Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+///
+/// \file
+/// This file provides utilities for designated initializers.
+///
+//===----------------------------------------------------------------------===//
+
+#include "clang/AST/Expr.h"
+#include "clang/Basic/SourceLocation.h"
+#include "llvm/ADT/DenseMap.h"
+
+namespace clang::tooling {
+
+/// Get designators describing the elements of a (syntactic) init list.
+///
+/// Given for example the type
+///
+///     struct S { int i, j; };
+///
+/// and the definition
+///
+///     S s{1, 2};
+///
+/// calling `getDesignators` for the initializer list expression `{1, 2}`
+/// would produce the map `{loc(1): ".i", loc(2): ".j"}`.
+///
+/// It does not produce designators for any explicitly-written nested lists,
+/// e.g. `{1, .j=2}` would only return `{loc(1): ".i"}`.
+///
+/// It also considers structs with fields of record types like
+/// `struct T { S s; };`. In this case, there would be designators of the
+/// form
+/// `.s.i` and `.s.j` in the returned map.
+llvm::DenseMap<clang::SourceLocation, std::string>
+getDesignators(const clang::InitListExpr *Syn);
+
+} // namespace clang::tooling
diff --git a/clang/lib/Tooling/CMakeLists.txt b/clang/lib/Tooling/CMakeLists.txt
index aff39e4de13c0b..8b0853d9150bb3 100644
--- a/clang/lib/Tooling/CMakeLists.txt
+++ b/clang/lib/Tooling/CMakeLists.txt
@@ -106,6 +106,7 @@ add_clang_library(clangTooling
   ArgumentsAdjusters.cpp
   CommonOptionsParser.cpp
   CompilationDatabase.cpp
+  DesignatedInitializers.cpp
   Execution.cpp
   ExpandResponseFilesCompilationDatabase.cpp
   FileMatchTrie.cpp
diff --git a/clang/lib/Tooling/DesignatedInitializers.cpp 
b/clang/lib/Tooling/DesignatedInitializers.cpp
new file mode 100644
index 00000000000000..8671625bd19ea3
--- /dev/null
+++ b/clang/lib/Tooling/DesignatedInitializers.cpp
@@ -0,0 +1,195 @@
+//===--- DesignatedInitializers.cpp 
---------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM 
Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+///
+/// \file
+/// This file provides utilities for designated initializers.
+///
+//===----------------------------------------------------------------------===//
+
+#include "clang/Tooling/DesignatedInitializers.h"
+#include "clang/AST/DeclCXX.h"
+#include "llvm/ADT/DenseSet.h"
+#include "llvm/ADT/ScopeExit.h"
+
+namespace clang::tooling {
+
+namespace {
+
+/// Returns true if Name is reserved, like _Foo or __Vector_base.
+static inline bool isReservedName(llvm::StringRef Name) {
+  // This doesn't catch all cases, but the most common.
+  return Name.size() >= 2 && Name[0] == '_' &&
+         (isUppercase(Name[1]) || Name[1] == '_');
+}
+
+// Helper class to iterate over the designator names of an aggregate type.
+//
+// For an array type, yields [0], [1], [2]...
+// For aggregate classes, yields null for each base, then .field1, .field2,
+// ...
+class AggregateDesignatorNames {
+public:
+  AggregateDesignatorNames(QualType T) {
+    if (!T.isNull()) {
+      T = T.getCanonicalType();
+      if (T->isArrayType()) {
+        IsArray = true;
+        Valid = true;
+        return;
+      }
+      if (const RecordDecl *RD = T->getAsRecordDecl()) {
+        Valid = true;
+        FieldsIt = RD->field_begin();
+        FieldsEnd = RD->field_end();
+        if (const auto *CRD = llvm::dyn_cast<CXXRecordDecl>(RD)) {
+          BasesIt = CRD->bases_begin();
+          BasesEnd = CRD->bases_end();
+          Valid = CRD->isAggregate();
+        }
+        OneField = Valid && BasesIt == BasesEnd && FieldsIt != FieldsEnd &&
+                   std::next(FieldsIt) == FieldsEnd;
+      }
+    }
+  }
+  // Returns false if the type was not an aggregate.
+  operator bool() { return Valid; }
+  // Advance to the next element in the aggregate.
+  void next() {
+    if (IsArray)
+      ++Index;
+    else if (BasesIt != BasesEnd)
+      ++BasesIt;
+    else if (FieldsIt != FieldsEnd)
+      ++FieldsIt;
+  }
+  // Print the designator to Out.
+  // Returns false if we could not produce a designator for this element.
+  bool append(std::string &Out, bool ForSubobject) {
+    if (IsArray) {
+      Out.push_back('[');
+      Out.append(std::to_string(Index));
+      Out.push_back(']');
+      return true;
+    }
+    if (BasesIt != BasesEnd)
+      return false; // Bases can't be designated. Should we make one up?
+    if (FieldsIt != FieldsEnd) {
+      llvm::StringRef FieldName;
+      if (const IdentifierInfo *II = FieldsIt->getIdentifier())
+        FieldName = II->getName();
+
+      // For certain objects, their subobjects may be named directly.
+      if (ForSubobject &&
+          (FieldsIt->isAnonymousStructOrUnion() ||
+           // std::array<int,3> x = {1,2,3}. Designators not strictly valid!
+           (OneField && isReservedName(FieldName))))
+        return true;
+
+      if (!FieldName.empty() && !isReservedName(FieldName)) {
+        Out.push_back('.');
+        Out.append(FieldName.begin(), FieldName.end());
+        return true;
+      }
+      return false;
+    }
+    return false;
+  }
+
+private:
+  bool Valid = false;
+  bool IsArray = false;
+  bool OneField = false; // e.g. std::array { T __elements[N]; }
+  unsigned Index = 0;
+  CXXRecordDecl::base_class_const_iterator BasesIt;
+  CXXRecordDecl::base_class_const_iterator BasesEnd;
+  RecordDecl::field_iterator FieldsIt;
+  RecordDecl::field_iterator FieldsEnd;
+};
+
+// Collect designator labels describing the elements of an init list.
+//
+// This function contributes the designators of some (sub)object, which is
+// represented by the semantic InitListExpr Sem.
+// This includes any nested subobjects, but *only* if they are part of the
+// same original syntactic init list (due to brace elision). In other words,
+// it may descend into subobjects but not written init-lists.
+//
+// For example: struct Outer { Inner a,b; }; struct Inner { int x, y; }
+//              Outer o{{1, 2}, 3};
+// This function will be called with Sem = { {1, 2}, {3, ImplicitValue} }
+// It should generate designators '.a:' and '.b.x:'.
+// '.a:' is produced directly without recursing into the written sublist.
+// (The written sublist will have a separate collectDesignators() call later).
+// Recursion with Prefix='.b' and Sem = {3, ImplicitValue} produces '.b.x:'.
+void collectDesignators(const InitListExpr *Sem,
+                        llvm::DenseMap<SourceLocation, std::string> &Out,
+                        const llvm::DenseSet<SourceLocation> &NestedBraces,
+                        std::string &Prefix) {
+  if (!Sem || Sem->isTransparent())
+    return;
+  assert(Sem->isSemanticForm());
+
+  // The elements of the semantic form all correspond to direct subobjects of
+  // the aggregate type. `Fields` iterates over these subobject names.
+  AggregateDesignatorNames Fields(Sem->getType());
+  if (!Fields)
+    return;
+  for (const Expr *Init : Sem->inits()) {
+    auto Next = llvm::make_scope_exit([&, Size(Prefix.size())] {
+      Fields.next();       // Always advance to the next subobject name.
+      Prefix.resize(Size); // Erase any designator we appended.
+    });
+    // Skip for a broken initializer or if it is a "hole" in a subobject that
+    // was not explicitly initialized.
+    if (!Init || llvm::isa<ImplicitValueInitExpr>(Init))
+      continue;
+
+    const auto *BraceElidedSubobject = llvm::dyn_cast<InitListExpr>(Init);
+    if (BraceElidedSubobject &&
+        NestedBraces.contains(BraceElidedSubobject->getLBraceLoc()))
+      BraceElidedSubobject = nullptr; // there were braces!
+
+    if (!Fields.append(Prefix, BraceElidedSubobject != nullptr))
+      continue; // no designator available for this subobject
+    if (BraceElidedSubobject) {
+      // If the braces were elided, this aggregate subobject is initialized
+      // inline in the same syntactic list.
+      // Descend into the semantic list describing the subobject.
+      // (NestedBraces are still correct, they're from the same syntactic
+      // list).
+      collectDesignators(BraceElidedSubobject, Out, NestedBraces, Prefix);
+      continue;
+    }
+    Out.try_emplace(Init->getBeginLoc(), Prefix);
+  }
+}
+
+} // namespace
+
+llvm::DenseMap<SourceLocation, std::string>
+getDesignators(const InitListExpr *Syn) {
+  assert(Syn->isSyntacticForm());
+
+  // collectDesignators needs to know which InitListExprs in the semantic tree
+  // were actually written, but InitListExpr::isExplicit() lies.
+  // Instead, record where braces of sub-init-lists occur in the syntactic 
form.
+  llvm::DenseSet<SourceLocation> NestedBraces;
+  for (const Expr *Init : Syn->inits())
+    if (auto *Nested = llvm::dyn_cast<InitListExpr>(Init))
+      NestedBraces.insert(Nested->getLBraceLoc());
+
+  // Traverse the semantic form to find the designators.
+  // We use their SourceLocation to correlate with the syntactic form later.
+  llvm::DenseMap<SourceLocation, std::string> Designators;
+  std::string EmptyPrefix;
+  collectDesignators(Syn->isSemanticForm() ? Syn : Syn->getSemanticForm(),
+                     Designators, NestedBraces, EmptyPrefix);
+  return Designators;
+}
+
+} // namespace clang::tooling

From 68de71cb9ca3f30565f66d10ccc70bdd923d355f Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Danny=20M=C3=B6sch?= <danny.moe...@icloud.com>
Date: Sun, 11 Feb 2024 14:37:45 +0100
Subject: [PATCH 23/23] Fully implement fix-its reusing designated initializer
 computation from Clangd

---
 .../UseDesignatedInitializersCheck.cpp        | 67 ++++++++++---------
 .../modernize/use-designated-initializers.cpp |  8 +++
 2 files changed, 44 insertions(+), 31 deletions(-)

diff --git 
a/clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.cpp 
b/clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.cpp
index 081286081b4cbf..9e90df711df66a 100644
--- a/clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.cpp
+++ b/clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.cpp
@@ -14,9 +14,9 @@
 #include "clang/ASTMatchers/ASTMatchFinder.h"
 #include "clang/ASTMatchers/ASTMatchers.h"
 #include "clang/ASTMatchers/ASTMatchersMacros.h"
-#include <algorithm>
-#include <iterator>
-#include <vector>
+#include "clang/Basic/Diagnostic.h"
+#include "clang/Lex/Lexer.h"
+#include "clang/Tooling/DesignatedInitializers.h"
 
 using namespace clang::ast_matchers;
 
@@ -29,15 +29,6 @@ static const bool IgnoreSingleElementAggregatesDefault = 
true;
 static const char *RestrictToPODTypesName = "RestrictToPODTypes";
 static const bool RestrictToPODTypesDefault = false;
 
-static std::vector<Stmt *>
-getUndesignatedComponents(const InitListExpr *SyntacticInitList) {
-  std::vector<Stmt *> Result;
-  std::copy_if(SyntacticInitList->begin(), SyntacticInitList->end(),
-               std::back_inserter(Result),
-               [](auto S) { return !isa<DesignatedInitExpr>(S); });
-  return Result;
-}
-
 UseDesignatedInitializersCheck::UseDesignatedInitializersCheck(
     StringRef Name, ClangTidyContext *Context)
     : ClangTidyCheck(Name, Context), IgnoreSingleElementAggregates(Options.get(
@@ -51,7 +42,9 @@ AST_MATCHER(CXXRecordDecl, isAggregate) { return 
Node.isAggregate(); }
 AST_MATCHER(CXXRecordDecl, isPOD) { return Node.isPOD(); }
 
 AST_MATCHER(InitListExpr, isFullyDesignated) {
-  return getUndesignatedComponents(&Node).empty();
+  return std::all_of(Node.begin(), Node.end(), [](auto *InitExpr) {
+    return isa<DesignatedInitExpr>(InitExpr);
+  });
 }
 
 AST_MATCHER(InitListExpr, hasSingleElement) { return Node.getNumInits() == 1; }
@@ -82,6 +75,12 @@ void 
UseDesignatedInitializersCheck::registerMatchers(MatchFinder *Finder) {
       this);
 }
 
+static bool isFullyUndesignated(const InitListExpr *SyntacticInitList) {
+  return std::all_of(
+      SyntacticInitList->begin(), SyntacticInitList->end(),
+      [](auto *InitExpr) { return !isa<DesignatedInitExpr>(InitExpr); });
+}
+
 void UseDesignatedInitializersCheck::check(
     const MatchFinder::MatchResult &Result) {
   const auto *InitList = Result.Nodes.getNodeAs<InitListExpr>("init");
@@ -89,24 +88,30 @@ void UseDesignatedInitializersCheck::check(
   if (!Type || !InitList)
     return;
   if (const auto *SyntacticInitList = InitList->getSyntacticForm()) {
-    const auto UndesignatedComponents =
-        getUndesignatedComponents(SyntacticInitList);
-    if (UndesignatedComponents.size() == SyntacticInitList->getNumInits()) {
-      diag(InitList->getLBraceLoc(), "use designated initializer list");
-      return;
-    }
-    const auto FieldIterator = Type->fields().begin();
-    for (const auto *InitExpr : *SyntacticInitList) {
-      const auto Field = std::next(FieldIterator);
-      if (std::find(UndesignatedComponents.begin(),
-                    UndesignatedComponents.end(),
-                    InitExpr) == UndesignatedComponents.end())
-        continue;
-      if (const auto *FieldID = Field->getIdentifier()) {
-        const auto FieldName = FieldID->getName();
-        diag(InitExpr->getBeginLoc(), "use designated init expression")
-            << FixItHint::CreateInsertion(InitExpr->getBeginLoc(),
-                                          "." + FieldName.str() + "=");
+    const llvm::DenseMap<clang::SourceLocation, std::string> Designators =
+        clang::tooling::getDesignators(SyntacticInitList);
+    if (isFullyUndesignated(SyntacticInitList)) {
+      std::string NewList = "{";
+      for (const Stmt *InitExpr : *SyntacticInitList) {
+        if (InitExpr != *SyntacticInitList->begin())
+          NewList += ", ";
+        NewList += Designators.at(InitExpr->getBeginLoc());
+        NewList += "=";
+        NewList += Lexer::getSourceText(
+            CharSourceRange::getTokenRange(InitExpr->getSourceRange()),
+            *Result.SourceManager, getLangOpts());
+      }
+      NewList += "}";
+      diag(InitList->getLBraceLoc(), "use designated initializer list")
+          << FixItHint::CreateReplacement(InitList->getSourceRange(), NewList);
+    } else {
+      for (const auto *InitExpr : *SyntacticInitList) {
+        if (!isa<DesignatedInitExpr>(InitExpr)) {
+          diag(InitExpr->getBeginLoc(), "use designated init expression")
+              << FixItHint::CreateInsertion(
+                     InitExpr->getBeginLoc(),
+                     Designators.at(InitExpr->getBeginLoc()) + "=");
+        }
       }
     }
   }
diff --git 
a/clang-tools-extra/test/clang-tidy/checkers/modernize/use-designated-initializers.cpp
 
b/clang-tools-extra/test/clang-tidy/checkers/modernize/use-designated-initializers.cpp
index e0b722ec091671..7d8c2ee63b4aef 100644
--- 
a/clang-tools-extra/test/clang-tidy/checkers/modernize/use-designated-initializers.cpp
+++ 
b/clang-tools-extra/test/clang-tidy/checkers/modernize/use-designated-initializers.cpp
@@ -20,16 +20,19 @@ S2 s21{.i=1, .j =2};
 S2 s22 = {1, 2};
 // CHECK-MESSAGES: :[[@LINE-1]]:10: warning: use designated initializer list 
[modernize-use-designated-initializers]
 // CHECK-MESSAGES-POD: :[[@LINE-2]]:10: warning: use designated initializer 
list [modernize-use-designated-initializers]
+// CHECK-FIXES: S2 s22 = {.i=1, .j=2};
 
 S2 s23{1};
 // CHECK-MESSAGES: :[[@LINE-1]]:7: warning: use designated initializer list 
[modernize-use-designated-initializers]
 // CHECK-MESSAGES-POD: :[[@LINE-2]]:7: warning: use designated initializer 
list [modernize-use-designated-initializers]
+// CHECK-FIXES: S2 s23{.i=1};
 
 S2 s24{.i = 1};
 
 S2 s25 = {.i=1, 2};
 // CHECK-MESSAGES: :[[@LINE-1]]:17: warning: use designated init expression 
[modernize-use-designated-initializers]
 // CHECK-MESSAGES-POD: :[[@LINE-2]]:17: warning: use designated init 
expression [modernize-use-designated-initializers]
+// CHECK-FIXES: S2 s25 = {.i=1, .j=2};
 
 class S3 {
   public:
@@ -42,12 +45,14 @@ S3 s31 = {.s2 = 1, 2, 3.1};
 // CHECK-MESSAGES: :[[@LINE-2]]:23: warning: use designated init expression 
[modernize-use-designated-initializers]
 // CHECK-MESSAGES-POD: :[[@LINE-3]]:20: warning: use designated init 
expression [modernize-use-designated-initializers]
 // CHECK-MESSAGES-POD: :[[@LINE-4]]:23: warning: use designated init 
expression [modernize-use-designated-initializers]
+// CHECK-FIXES: S3 s31 = {.s2 = 1, .s2.j=2, .d=3.1};
 
 S3 s32 = {{.i = 1, 2}};
 // CHECK-MESSAGES: :[[@LINE-1]]:10: warning: use designated initializer list 
[modernize-use-designated-initializers]
 // CHECK-MESSAGES: :[[@LINE-2]]:20: warning: use designated init expression 
[modernize-use-designated-initializers]
 // CHECK-MESSAGES-POD: :[[@LINE-3]]:10: warning: use designated initializer 
list [modernize-use-designated-initializers]
 // CHECK-MESSAGES-POD: :[[@LINE-4]]:20: warning: use designated init 
expression [modernize-use-designated-initializers]
+// CHECK-FIXES: S3 s32 = {.s2={.i = 1, 2}};
 
 struct S4 {
     double d;
@@ -56,9 +61,11 @@ struct S4 {
 
 S4 s41 {2.2};
 // CHECK-MESSAGES-SINGLE-ELEMENT: :[[@LINE-1]]:8: warning: use designated 
initializer list [modernize-use-designated-initializers]
+// CHECK-FIXES-SINGLE-ELEMENT: S4 s41 {.d=2.2};
 
 S4 s42 = {{}};
 // CHECK-MESSAGES-SINGLE-ELEMENT: :[[@LINE-1]]:10: warning: use designated 
initializer list [modernize-use-designated-initializers]
+// CHECK-FIXES-SINGLE-ELEMENT: S4 s42 = {.d={}};
 
 template<typename S> S template1() { return {10, 11}; }
 
@@ -99,3 +106,4 @@ struct S9 {
 
 S9 s91{1, 2};
 // CHECK-MESSAGES: :[[@LINE-1]]:7: warning: use designated initializer list 
[modernize-use-designated-initializers]
+// CHECK-FIXES: S9 s91{.i=1, .j=2};

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