[clang-tidy]Add new check readability-avoid-nested-conditional-operator (#78022)

Finds nested conditional operator.
Nested conditional operators lead code hard to understand, so they
should be splited as several statement and stored in temporary varibale.

4 files changed, 89 insertions, 0 deletions

diff --git a/clang-tools-extra/clang-tidy/readability/AvoidNestedConditionalOperatorCheck.cpp b/clang-tools-extra/clang-tidy/readability/AvoidNestedConditionalOperatorCheck.cpp
new file mode 100644
index 0000000..2ea03c9
--- /dev/null
+++ b/clang-tools-extra/clang-tidy/readability/AvoidNestedConditionalOperatorCheck.cpp
@@ -0,0 +1,52 @@
+//===--- AvoidNestedConditionalOperatorCheck.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 "AvoidNestedConditionalOperatorCheck.h"
+#include "clang/ASTMatchers/ASTMatchFinder.h"
+#include "clang/ASTMatchers/ASTMatchers.h"
+#include "clang/Basic/DiagnosticIDs.h"
+
+using namespace clang::ast_matchers;
+
+namespace clang::tidy::readability {
+
+void AvoidNestedConditionalOperatorCheck::registerMatchers(
+    MatchFinder *Finder) {
+  Finder->addMatcher(
+      conditionalOperator(
+          anyOf(
+              hasCondition(ignoringParenCasts(
+                  conditionalOperator().bind("nested-conditional-operator"))),
+              hasTrueExpression(ignoringParenCasts(
+                  conditionalOperator().bind("nested-conditional-operator"))),
+              hasFalseExpression(ignoringParenCasts(
+                  conditionalOperator().bind("nested-conditional-operator")))))
+          .bind("conditional-operator"),
+      this);
+}
+
+void AvoidNestedConditionalOperatorCheck::check(
+    const MatchFinder::MatchResult &Result) {
+  const auto *CO =
+      Result.Nodes.getNodeAs<ConditionalOperator>("conditional-operator");
+  const auto *NCO = Result.Nodes.getNodeAs<ConditionalOperator>(
+      "nested-conditional-operator");
+  assert(CO);
+  assert(NCO);
+
+  if (CO->getBeginLoc().isMacroID() || NCO->getBeginLoc().isMacroID())
+    return;
+
+  diag(NCO->getBeginLoc(),
+       "conditional operator is used as sub-expression of parent conditional "
+       "operator, refrain from using nested conditional operators");
+  diag(CO->getBeginLoc(), "parent conditional operator here",
+       DiagnosticIDs::Note);
+}
+
+} // namespace clang::tidy::readability
diff --git a/clang-tools-extra/clang-tidy/readability/AvoidNestedConditionalOperatorCheck.h b/clang-tools-extra/clang-tidy/readability/AvoidNestedConditionalOperatorCheck.h
new file mode 100644
index 0000000..9010156
--- /dev/null
+++ b/clang-tools-extra/clang-tidy/readability/AvoidNestedConditionalOperatorCheck.h
@@ -0,0 +1,33 @@
+//===--- AvoidNestedConditionalOperatorCheck.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_READABILITY_AVOID_NESTED_CONDITIONAL_OPERATOR_CHECK_H
+#define LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_READABILITY_AVOID_NESTED_CONDITIONAL_OPERATOR_CHECK_H
+
+#include "../ClangTidyCheck.h"
+
+namespace clang::tidy::readability {
+
+/// Identifies instances of nested conditional operators in the code.
+///
+/// For the user-facing documentation see:
+/// http://clang.llvm.org/extra/clang-tidy/checks/readability/avoid-nested-conditional-operator.html
+class AvoidNestedConditionalOperatorCheck : public ClangTidyCheck {
+public:
+  AvoidNestedConditionalOperatorCheck(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::readability
+
+#endif // LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_READABILITY_AVOID_NESTED_CONDITIONAL_OPERATOR_CHECK_H
diff --git a/clang-tools-extra/clang-tidy/readability/CMakeLists.txt b/clang-tools-extra/clang-tidy/readability/CMakeLists.txt
index 408c822b..fa571d5 100644
--- a/clang-tools-extra/clang-tidy/readability/CMakeLists.txt
+++ b/clang-tools-extra/clang-tidy/readability/CMakeLists.txt
@@ -5,6 +5,7 @@ set(LLVM_LINK_COMPONENTS
 
 add_clang_library(clangTidyReadabilityModule
   AvoidConstParamsInDecls.cpp
+  AvoidNestedConditionalOperatorCheck.cpp
   AvoidReturnWithVoidValueCheck.cpp
   AvoidUnconditionalPreprocessorIfCheck.cpp
   BracesAroundStatementsCheck.cpp
diff --git a/clang-tools-extra/clang-tidy/readability/ReadabilityTidyModule.cpp b/clang-tools-extra/clang-tidy/readability/ReadabilityTidyModule.cpp
index 0b0aad7c..f769752 100644
--- a/clang-tools-extra/clang-tidy/readability/ReadabilityTidyModule.cpp
+++ b/clang-tools-extra/clang-tidy/readability/ReadabilityTidyModule.cpp
@@ -10,6 +10,7 @@
 #include "../ClangTidyModule.h"
 #include "../ClangTidyModuleRegistry.h"
 #include "AvoidConstParamsInDecls.h"
+#include "AvoidNestedConditionalOperatorCheck.h"
 #include "AvoidReturnWithVoidValueCheck.h"
 #include "AvoidUnconditionalPreprocessorIfCheck.h"
 #include "BracesAroundStatementsCheck.h"
@@ -64,6 +65,8 @@ public:
   void addCheckFactories(ClangTidyCheckFactories &CheckFactories) override {
     CheckFactories.registerCheck<AvoidConstParamsInDecls>(
         "readability-avoid-const-params-in-decls");
+    CheckFactories.registerCheck<AvoidNestedConditionalOperatorCheck>(
+        "readability-avoid-nested-conditional-operator");
     CheckFactories.registerCheck<AvoidReturnWithVoidValueCheck>(
         "readability-avoid-return-with-void-value");
     CheckFactories.registerCheck<AvoidUnconditionalPreprocessorIfCheck>(