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

[Danny Mösch via cfe-commits]

================
@@ -0,0 +1,127 @@
+//===--- 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/APValue.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 "clang/ASTMatchers/ASTMatchersMacros.h"
+#include "clang/Basic/Diagnostic.h"
+#include "clang/Lex/Lexer.h"
+#include "clang/Tooling/DesignatedInitializers.h"
+
+using namespace clang::ast_matchers;
+
+namespace clang::tidy::modernize {
+
+static const char *IgnoreSingleElementAggregatesName =
+    "IgnoreSingleElementAggregates";
+static const bool IgnoreSingleElementAggregatesDefault = true;
+
+static const char *RestrictToPODTypesName = "RestrictToPODTypes";
+static const bool RestrictToPODTypesDefault = false;
+
+UseDesignatedInitializersCheck::UseDesignatedInitializersCheck(
+    StringRef Name, ClangTidyContext *Context)
+    : 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 std::all_of(Node.begin(), Node.end(), [](auto *InitExpr) {
+    return isa<DesignatedInitExpr>(InitExpr);
+  });
+}
+
+AST_MATCHER(InitListExpr, hasSingleElement) { return Node.getNumInits() == 1; }
+
+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(RestrictToPODTypes ? isPOD() : isAggregate(),
+                                unless(hasBaseWithFields()),
+                                unless(has(fieldDecl(isAnonymousDecl()))))
+                      .bind("type")),
+          unless(IgnoreSingleElementAggregates ? hasSingleElement()
+                                               : unless(anything())),
+          unless(isFullyDesignated()))
+          .bind("init"),
+      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");
+  const auto *Type = Result.Nodes.getNodeAs<CXXRecordDecl>("type");
+  if (!Type || !InitList)
+    return;
+  if (const auto *SyntacticInitList = InitList->getSyntacticForm()) {
+    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 += "=";
----------------
SimplyDanny wrote:

I have no objections. However, this is the style that's also used by the inlay hints generated by Clangd which is the reason why I omitted the spaces. Does that change your opinion?

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