[clang-tidy] Add readability-redundant-casting check (#70595)

PiotrZSL · web-flow · commit 1ad1f981a622 · 2024-01-20T10:11:05.000+01:00
Detects explicit type casting operations that involve the same source and destination types, and subsequently recommend their removal. Covers a range of explicit casting operations. Its primary objective is to enhance code readability and maintainability by eliminating unnecessary type casting. Closes #67534
diff --git a/clang-tools-extra/clang-tidy/readability/CMakeLists.txt b/clang-tools-extra/clang-tidy/readability/CMakeLists.txt
@@ -35,6 +35,7 @@ add_clang_library(clangTidyReadabilityModule
   QualifiedAutoCheck.cpp
   ReadabilityTidyModule.cpp
   RedundantAccessSpecifiersCheck.cpp
+  RedundantCastingCheck.cpp
   RedundantControlFlowCheck.cpp
   RedundantDeclarationCheck.cpp
   RedundantFunctionPtrDereferenceCheck.cpp
diff --git a/clang-tools-extra/clang-tidy/readability/ReadabilityTidyModule.cpp b/clang-tools-extra/clang-tidy/readability/ReadabilityTidyModule.cpp
@@ -38,6 +38,7 @@
 #include "OperatorsRepresentationCheck.h"
 #include "QualifiedAutoCheck.h"
 #include "RedundantAccessSpecifiersCheck.h"
+#include "RedundantCastingCheck.h"
 #include "RedundantControlFlowCheck.h"
 #include "RedundantDeclarationCheck.h"
 #include "RedundantFunctionPtrDereferenceCheck.h"
@@ -117,6 +118,8 @@ class ReadabilityModule : public ClangTidyModule {
         "readability-qualified-auto");
     CheckFactories.registerCheck<RedundantAccessSpecifiersCheck>(
         "readability-redundant-access-specifiers");
+    CheckFactories.registerCheck<RedundantCastingCheck>(
+        "readability-redundant-casting");
     CheckFactories.registerCheck<RedundantFunctionPtrDereferenceCheck>(
         "readability-redundant-function-ptr-dereference");
     CheckFactories.registerCheck<RedundantMemberInitCheck>(
diff --git a/clang-tools-extra/clang-tidy/readability/RedundantCastingCheck.cpp b/clang-tools-extra/clang-tidy/readability/RedundantCastingCheck.cpp
@@ -0,0 +1,252 @@
+//===--- RedundantCastingCheck.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 "RedundantCastingCheck.h"
+#include "../utils/FixItHintUtils.h"
+#include "clang/AST/ASTContext.h"
+#include "clang/ASTMatchers/ASTMatchFinder.h"
+#include "clang/Lex/Lexer.h"
+
+using namespace clang::ast_matchers;
+
+namespace clang::tidy::readability {
+
+static bool areTypesEqual(QualType S, QualType D) {
+  if (S == D)
+    return true;
+
+  const auto *TS = S->getAs<TypedefType>();
+  const auto *TD = D->getAs<TypedefType>();
+  if (TS != TD)
+    return false;
+
+  QualType PtrS = S->getPointeeType();
+  QualType PtrD = D->getPointeeType();
+
+  if (!PtrS.isNull() && !PtrD.isNull())
+    return areTypesEqual(PtrS, PtrD);
+
+  const DeducedType *DT = S->getContainedDeducedType();
+  if (DT && DT->isDeduced())
+    return D == DT->getDeducedType();
+
+  return false;
+}
+
+static bool areTypesEqual(QualType TypeS, QualType TypeD,
+                          bool IgnoreTypeAliases) {
+  const QualType CTypeS = TypeS.getCanonicalType();
+  const QualType CTypeD = TypeD.getCanonicalType();
+  if (CTypeS != CTypeD)
+    return false;
+
+  return IgnoreTypeAliases || areTypesEqual(TypeS.getLocalUnqualifiedType(),
+                                            TypeD.getLocalUnqualifiedType());
+}
+
+static bool areBinaryOperatorOperandsTypesEqualToOperatorResultType(
+    const Expr *E, bool IgnoreTypeAliases) {
+  if (!E)
+    return true;
+  const Expr *WithoutImplicitAndParen = E->IgnoreParenImpCasts();
+  if (!WithoutImplicitAndParen)
+    return true;
+  if (const auto *B = dyn_cast<BinaryOperator>(WithoutImplicitAndParen)) {
+    const QualType Type = WithoutImplicitAndParen->getType();
+    if (Type.isNull())
+      return true;
+
+    const QualType NonReferenceType = Type.getNonReferenceType();
+    const QualType LHSType = B->getLHS()->IgnoreImplicit()->getType();
+    if (LHSType.isNull() || !areTypesEqual(LHSType.getNonReferenceType(),
+                                           NonReferenceType, IgnoreTypeAliases))
+      return false;
+    const QualType RHSType = B->getRHS()->IgnoreImplicit()->getType();
+    if (RHSType.isNull() || !areTypesEqual(RHSType.getNonReferenceType(),
+                                           NonReferenceType, IgnoreTypeAliases))
+      return false;
+  }
+  return true;
+}
+
+static const Decl *getSourceExprDecl(const Expr *SourceExpr) {
+  const Expr *CleanSourceExpr = SourceExpr->IgnoreParenImpCasts();
+  if (const auto *E = dyn_cast<DeclRefExpr>(CleanSourceExpr)) {
+    return E->getDecl();
+  }
+
+  if (const auto *E = dyn_cast<CallExpr>(CleanSourceExpr)) {
+    return E->getCalleeDecl();
+  }
+
+  if (const auto *E = dyn_cast<MemberExpr>(CleanSourceExpr)) {
+    return E->getMemberDecl();
+  }
+  return nullptr;
+}
+
+RedundantCastingCheck::RedundantCastingCheck(StringRef Name,
+                                             ClangTidyContext *Context)
+    : ClangTidyCheck(Name, Context),
+      IgnoreMacros(Options.getLocalOrGlobal("IgnoreMacros", true)),
+      IgnoreTypeAliases(Options.getLocalOrGlobal("IgnoreTypeAliases", false)) {}
+
+void RedundantCastingCheck::storeOptions(ClangTidyOptions::OptionMap &Opts) {
+  Options.store(Opts, "IgnoreMacros", IgnoreMacros);
+  Options.store(Opts, "IgnoreTypeAliases", IgnoreTypeAliases);
+}
+
+void RedundantCastingCheck::registerMatchers(MatchFinder *Finder) {
+  auto SimpleType = qualType(hasCanonicalType(
+      qualType(anyOf(builtinType(), references(builtinType()),
+                     references(pointsTo(qualType())), pointsTo(qualType())))));
+
+  auto BitfieldMemberExpr = memberExpr(member(fieldDecl(isBitField())));
+
+  Finder->addMatcher(
+      explicitCastExpr(
+          unless(hasCastKind(CK_ConstructorConversion)),
+          unless(hasCastKind(CK_UserDefinedConversion)),
+          unless(cxxFunctionalCastExpr(hasDestinationType(unless(SimpleType)))),
+
+          hasDestinationType(qualType().bind("dstType")),
+          hasSourceExpression(anyOf(
+              expr(unless(initListExpr()), unless(BitfieldMemberExpr),
+                   hasType(qualType().bind("srcType")))
+                  .bind("source"),
+              initListExpr(unless(hasInit(1, expr())),
+                           hasInit(0, expr(unless(BitfieldMemberExpr),
+                                           hasType(qualType().bind("srcType")))
+                                          .bind("source"))))))
+          .bind("cast"),
+      this);
+}
+
+void RedundantCastingCheck::check(const MatchFinder::MatchResult &Result) {
+  const auto *SourceExpr = Result.Nodes.getNodeAs<Expr>("source");
+  auto TypeD = *Result.Nodes.getNodeAs<QualType>("dstType");
+
+  if (SourceExpr->getValueKind() == VK_LValue &&
+      TypeD.getCanonicalType()->isRValueReferenceType())
+    return;
+
+  const auto TypeS =
+      Result.Nodes.getNodeAs<QualType>("srcType")->getNonReferenceType();
+  TypeD = TypeD.getNonReferenceType();
+
+  if (!areTypesEqual(TypeS, TypeD, IgnoreTypeAliases))
+    return;
+
+  if (!areBinaryOperatorOperandsTypesEqualToOperatorResultType(
+          SourceExpr, IgnoreTypeAliases))
+    return;
+
+  const auto *CastExpr = Result.Nodes.getNodeAs<ExplicitCastExpr>("cast");
+  if (IgnoreMacros &&
+      (CastExpr->getBeginLoc().isMacroID() ||
+       CastExpr->getEndLoc().isMacroID() || CastExpr->getExprLoc().isMacroID()))
+    return;
+
+  {
+    auto Diag = diag(CastExpr->getExprLoc(),
+                     "redundant explicit casting to the same type %0 as the "
+                     "sub-expression, remove this casting");
+    Diag << TypeD;
+
+    const SourceManager &SM = *Result.SourceManager;
+    const SourceLocation SourceExprBegin =
+        SM.getExpansionLoc(SourceExpr->getBeginLoc());
+    const SourceLocation SourceExprEnd =
+        SM.getExpansionLoc(SourceExpr->getEndLoc());
+
+    if (SourceExprBegin != CastExpr->getBeginLoc())
+      Diag << FixItHint::CreateRemoval(SourceRange(
+          CastExpr->getBeginLoc(), SourceExprBegin.getLocWithOffset(-1)));
+
+    const SourceLocation NextToken = Lexer::getLocForEndOfToken(
+        SourceExprEnd, 0U, SM, Result.Context->getLangOpts());
+
+    if (SourceExprEnd != CastExpr->getEndLoc()) {
+      Diag << FixItHint::CreateRemoval(
+          SourceRange(NextToken, CastExpr->getEndLoc()));
+    }
+
+    if (utils::fixit::areParensNeededForStatement(*SourceExpr)) {
+      Diag << FixItHint::CreateInsertion(SourceExprBegin, "(")
+           << FixItHint::CreateInsertion(NextToken, ")");
+    }
+  }
+
+  const auto *SourceExprDecl = getSourceExprDecl(SourceExpr);
+  if (!SourceExprDecl)
+    return;
+
+  if (const auto *D = dyn_cast<CXXConstructorDecl>(SourceExprDecl)) {
+    diag(D->getLocation(),
+         "source type originates from the invocation of this constructor",
+         DiagnosticIDs::Note);
+    return;
+  }
+
+  if (const auto *D = dyn_cast<FunctionDecl>(SourceExprDecl)) {
+    diag(D->getLocation(),
+         "source type originates from the invocation of this "
+         "%select{function|method}0",
+         DiagnosticIDs::Note)
+        << isa<CXXMethodDecl>(D) << D->getReturnTypeSourceRange();
+    return;
+  }
+
+  if (const auto *D = dyn_cast<FieldDecl>(SourceExprDecl)) {
+    diag(D->getLocation(),
+         "source type originates from referencing this member",
+         DiagnosticIDs::Note)
+        << SourceRange(D->getTypeSpecStartLoc(), D->getTypeSpecEndLoc());
+    return;
+  }
+
+  if (const auto *D = dyn_cast<ParmVarDecl>(SourceExprDecl)) {
+    diag(D->getLocation(),
+         "source type originates from referencing this parameter",
+         DiagnosticIDs::Note)
+        << SourceRange(D->getTypeSpecStartLoc(), D->getTypeSpecEndLoc());
+    return;
+  }
+
+  if (const auto *D = dyn_cast<VarDecl>(SourceExprDecl)) {
+    diag(D->getLocation(),
+         "source type originates from referencing this variable",
+         DiagnosticIDs::Note)
+        << SourceRange(D->getTypeSpecStartLoc(), D->getTypeSpecEndLoc());
+    return;
+  }
+
+  if (const auto *D = dyn_cast<EnumConstantDecl>(SourceExprDecl)) {
+    diag(D->getLocation(),
+         "source type originates from referencing this enum constant",
+         DiagnosticIDs::Note);
+    return;
+  }
+
+  if (const auto *D = dyn_cast<BindingDecl>(SourceExprDecl)) {
+    diag(D->getLocation(),
+         "source type originates from referencing this bound variable",
+         DiagnosticIDs::Note);
+    return;
+  }
+
+  if (const auto *D = dyn_cast<NonTypeTemplateParmDecl>(SourceExprDecl)) {
+    diag(D->getLocation(),
+         "source type originates from referencing this non-type template "
+         "parameter",
+         DiagnosticIDs::Note);
+    return;
+  }
+}
+
+} // namespace clang::tidy::readability
diff --git a/clang-tools-extra/clang-tidy/readability/RedundantCastingCheck.h b/clang-tools-extra/clang-tidy/readability/RedundantCastingCheck.h
@@ -0,0 +1,38 @@
+//===--- RedundantCastingCheck.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_REDUNDANTCASTINGCHECK_H
+#define LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_READABILITY_REDUNDANTCASTINGCHECK_H
+
+#include "../ClangTidyCheck.h"
+
+namespace clang::tidy::readability {
+
+/// Detects explicit type casting operations that involve the same source and
+/// destination types, and subsequently recommend their removal.
+///
+/// For the user-facing documentation see:
+/// http://clang.llvm.org/extra/clang-tidy/checks/readability/redundant-casting.html
+class RedundantCastingCheck : public ClangTidyCheck {
+public:
+  RedundantCastingCheck(StringRef Name, ClangTidyContext *Context);
+  void registerMatchers(ast_matchers::MatchFinder *Finder) override;
+  void check(const ast_matchers::MatchFinder::MatchResult &Result) override;
+  void storeOptions(ClangTidyOptions::OptionMap &Opts) override;
+  std::optional<TraversalKind> getCheckTraversalKind() const override {
+    return TK_IgnoreUnlessSpelledInSource;
+  }
+
+private:
+  const bool IgnoreMacros;
+  const bool IgnoreTypeAliases;
+};
+
+} // namespace clang::tidy::readability
+
+#endif // LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_READABILITY_REDUNDANTCASTINGCHECK_H
diff --git a/clang-tools-extra/clang-tidy/utils/FixItHintUtils.h b/clang-tools-extra/clang-tidy/utils/FixItHintUtils.h
@@ -51,6 +51,7 @@ std::string formatDereference(const Expr &ExprNode, const ASTContext &Context);
 // \brief Checks whatever a expression require extra () to be always used in
 // safe way in any other expression.
 bool areParensNeededForStatement(const Stmt &Node);
+
 } // namespace clang::tidy::utils::fixit
 
 #endif // LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_UTILS_FIXITHINTUTILS_H
diff --git a/clang-tools-extra/docs/ReleaseNotes.rst b/clang-tools-extra/docs/ReleaseNotes.rst
@@ -235,6 +235,12 @@ New checks
   Finds return statements with ``void`` values used within functions with
   ``void`` result types.
 
+- New :doc:`readability-redundant-casting
+  <clang-tidy/checks/readability/redundant-casting>` check.
+
+  Detects explicit type casting operations that involve the same source and
+  destination types, and subsequently recommend their removal.
+
 - New :doc:`readability-reference-to-constructed-temporary
   <clang-tidy/checks/readability/reference-to-constructed-temporary>` check.
 
diff --git a/clang-tools-extra/docs/clang-tidy/checks/list.rst b/clang-tools-extra/docs/clang-tidy/checks/list.rst
@@ -365,6 +365,7 @@ Clang-Tidy Checks
    :doc:`readability-operators-representation <readability/operators-representation>`, "Yes"
    :doc:`readability-qualified-auto <readability/qualified-auto>`, "Yes"
    :doc:`readability-redundant-access-specifiers <readability/redundant-access-specifiers>`, "Yes"
+   :doc:`readability-redundant-casting <readability/redundant-casting>`, "Yes"
    :doc:`readability-redundant-control-flow <readability/redundant-control-flow>`, "Yes"
    :doc:`readability-redundant-declaration <readability/redundant-declaration>`, "Yes"
    :doc:`readability-redundant-function-ptr-dereference <readability/redundant-function-ptr-dereference>`, "Yes"
diff --git a/clang-tools-extra/docs/clang-tidy/checks/readability/redundant-casting.rst b/clang-tools-extra/docs/clang-tidy/checks/readability/redundant-casting.rst
@@ -0,0 +1,37 @@
+.. title:: clang-tidy - readability-redundant-casting
+
+readability-redundant-casting
+=============================
+
+Detects explicit type casting operations that involve the same source and
+destination types, and subsequently recommend their removal. Covers a range of
+explicit casting operations, including ``static_cast``, ``const_cast``, C-style
+casts, and ``reinterpret_cast``. Its primary objective is to enhance code
+readability and maintainability by eliminating unnecessary type casting.
+
+.. code-block:: c++
+
+  int value = 42;
+  int result = static_cast<int>(value);
+
+In this example, the ``static_cast<int>(value)`` is redundant, as it performs
+a cast from an ``int`` to another ``int``.
+
+Casting operations involving constructor conversions, user-defined conversions,
+functional casts, type-dependent casts, casts between distinct type aliases that
+refer to the same underlying type, as well as bitfield-related casts and casts
+directly from lvalue to rvalue, are all disregarded by the check.
+
+Options
+-------
+
+.. option:: IgnoreMacros
+
+   If set to `true`, the check will not give warnings inside macros. Default
+   is `true`.
+
+.. option:: IgnoreTypeAliases
+
+   When set to `false`, the check will consider type aliases, and when set to
+   `true`, it will resolve all type aliases and operate on the underlying
+   types. Default is `false`.
diff --git a/clang-tools-extra/test/clang-tidy/checkers/readability/redundant-casting.cpp b/clang-tools-extra/test/clang-tidy/checkers/readability/redundant-casting.cpp
