[clang-tools-extra] Adding an initial version of the "Initialized Class Members" checker. (PR #65189)

[Piotr Zegar via cfe-commits]

================
@@ -0,0 +1,105 @@
+//===--- CppInitClassMembersCheck.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 <string>
+
+#include "CppInitClassMembersCheck.h"
+#include "clang/AST/ASTContext.h"
+#include "clang/AST/Decl.h"
+#include "clang/AST/Type.h"
+#include "clang/ASTMatchers/ASTMatchFinder.h"
+#include "clang/ASTMatchers/ASTMatchers.h"
+#include "clang/ASTMatchers/ASTMatchersMacros.h"
+#include "clang/Basic/Diagnostic.h"
+#include "clang/Basic/LLVM.h"
+#include "llvm/ADT/STLExtras.h"
+#include "llvm/Support/raw_ostream.h"
+
+using namespace clang::ast_matchers;
+
+namespace clang::tidy::google {
+
+namespace {
+
+// Matches records that have a default constructor.
+AST_MATCHER(CXXRecordDecl, hasDefaultConstructor) {
+  return Node.hasDefaultConstructor();
+}
+
+// Returns the names of `Fields` in a comma separated string.
+std::string
+toCommaSeparatedString(const SmallVector<const FieldDecl *, 16> &Fields) {
+  std::string Buffer;
+  llvm::raw_string_ostream OS(Buffer);
+  llvm::interleave(
+      Fields, OS, [&OS](const FieldDecl *Decl) { OS << Decl->getName(); },
+      ", ");
+  return Buffer;
+}
+
+// Returns `true` for field types that should be reported (if additional
+// conditions are also met). For example, returns `true` for `int` because an
+// uninitialized `int` field can contain uninitialized values.
+bool shouldReportThisFieldType(QualType Ty) {
+  if (Ty.isNull())
+    return false;
+
+  // FIXME: For now, this checker focuses on several allowlisted types. We will
+  // expand coverage in future.
+  return Ty->isIntegerType() || Ty->isBooleanType();
+}
+
+} // anonymous namespace
+
+void CppInitClassMembersCheck::checkMissingMemberInitializer(
+    ASTContext &Context, const CXXRecordDecl &ClassDecl,
+    const CXXConstructorDecl *Ctor) {
+  SmallVector<const FieldDecl *, 16> FieldsToReport;
+
+  for (const FieldDecl *F : ClassDecl.fields()) {
+    if (shouldReportThisFieldType(F->getType()) && !F->hasInClassInitializer())
+      FieldsToReport.push_back(F);
+  }
+
+  if (FieldsToReport.empty())
+    return;
+
+  DiagnosticBuilder Diag =
+      diag(Ctor ? Ctor->getBeginLoc() : ClassDecl.getLocation(),
+           "%select{these fields should be initialized|constructor should "
+           "initialize these fields}0: %1")
+      << (Ctor != nullptr) << toCommaSeparatedString(FieldsToReport);
+
+  // FIXME: generate fixes.
+}
+
+void CppInitClassMembersCheck::registerMatchers(MatchFinder *Finder) {
+  Finder->addMatcher(cxxConstructorDecl(isDefinition(), isDefaultConstructor(),
+                                        unless(isUserProvided()))
+                         .bind("ctor"),
+                     this);
+
+  Finder->addMatcher(cxxRecordDecl(isDefinition(), hasDefaultConstructor(),
----------------
PiotrZSL wrote:

hasDefaultConstructor and  unless(has(cxxConstructorDecl())) may opose them self, be more specific, like has user specific constructor....

https://github.com/llvm/llvm-project/pull/65189