[clang-tidy] readability check for const params in declarations

Summary: Adds a clang-tidy warning for top-level consts in function declarations.

Reviewers: hokein, sbenza, alexfh

Subscribers: cfe-commits

Patch by Matt Kulukundis!

Differential Revision: http://reviews.llvm.org/D18408


git-svn-id: https://llvm.org/svn/llvm-project/clang-tools-extra/trunk@264856 91177308-0d34-0410-b5e6-96231b3b80d8

clang-tidy/readability/AvoidConstParamsInDecls.cpp

@@ -0,0 +1,71 @@
+//===--- AvoidConstParamsInDecls.cpp - clang-tidy--------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "AvoidConstParamsInDecls.h"
+#include "clang/ASTMatchers/ASTMatchFinder.h"
+#include "clang/ASTMatchers/ASTMatchers.h"
+#include "clang/Lex/Lexer.h"
+
+using namespace clang::ast_matchers;
+
+namespace clang {
+namespace tidy {
+namespace readability {
+namespace {
+
+SourceRange getTypeRange(const ParmVarDecl &Param) {
+  if (Param.getIdentifier() != nullptr)
+    return SourceRange(Param.getLocStart(),
+                       Param.getLocEnd().getLocWithOffset(-1));
+  return Param.getSourceRange();
+}
+
+} // namespace
+
+
+void AvoidConstParamsInDecls::registerMatchers(MatchFinder *Finder) {
+  const auto ConstParamDecl =
+      parmVarDecl(hasType(qualType(isConstQualified()))).bind("param");
+  Finder->addMatcher(functionDecl(unless(isDefinition()),
+                                  has(typeLoc(forEach(ConstParamDecl))))
+                         .bind("func"),
+                     this);
+}
+
+void AvoidConstParamsInDecls::check(const MatchFinder::MatchResult &Result) {
+  const auto *Func = Result.Nodes.getNodeAs<FunctionDecl>("func");
+  const auto *Param = Result.Nodes.getNodeAs<ParmVarDecl>("param");
+
+  QualType Type = Param->getType();
+  if (!Type.isLocalConstQualified())
+    return;
+
+  Type.removeLocalConst();
+
+  auto Diag = diag(Param->getLocStart(),
+                   "parameter %0 is const-qualified in the function "
+                   "declaration; const-qualification of parameters only has an "
+                   "effect in function definitions");
+  if (Param->getName().empty()) {
+    for (unsigned int i = 0; i < Func->getNumParams(); ++i) {
+      if (Param == Func->getParamDecl(i)) {
+        Diag << (i + 1);
+        break;
+      }
+    }
+  } else {
+    Diag << Param;
+  }
+  Diag << FixItHint::CreateReplacement(getTypeRange(*Param),
+                                       Type.getAsString());
+}
+
+} // namespace readability
+} // namespace tidy
+} // namespace clang

clang-tidy/readability/AvoidConstParamsInDecls.h

@@ -0,0 +1,33 @@
+//===--- AvoidConstParamsInDecls.h - clang-tidy----------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_READABILITY_AVOID_CONST_PARAMS_IN_DECLS_H
+#define LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_READABILITY_AVOID_CONST_PARAMS_IN_DECLS_H
+
+#include "../ClangTidy.h"
+
+namespace clang {
+namespace tidy {
+namespace readability {
+
+// Detect function declarations that have const value parameters and discourage
+// them.
+class AvoidConstParamsInDecls : public ClangTidyCheck {
+public:
+  using ClangTidyCheck::ClangTidyCheck;
+
+  void registerMatchers(ast_matchers::MatchFinder *Finder) override;
+  void check(const ast_matchers::MatchFinder::MatchResult &Result) override;
+};
+
+} // namespace readability
+} // namespace tidy
+} // namespace clang
+
+#endif // LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_READABILITY_AVOID_CONST_PARAMS_IN_DECLS_H

clang-tidy/readability/CMakeLists.txt

@@ -1,6 +1,7 @@
 set(LLVM_LINK_COMPONENTS support)
 
 add_clang_library(clangTidyReadabilityModule
+  AvoidConstParamsInDecls.cpp
   BracesAroundStatementsCheck.cpp
   ContainerSizeEmptyCheck.cpp
   ElseAfterReturnCheck.cpp

clang-tidy/readability/ReadabilityTidyModule.cpp

@@ -10,6 +10,7 @@
 #include "../ClangTidy.h"
 #include "../ClangTidyModule.h"
 #include "../ClangTidyModuleRegistry.h"
+#include "AvoidConstParamsInDecls.h"
 #include "BracesAroundStatementsCheck.h"
 #include "ContainerSizeEmptyCheck.h"
 #include "ElseAfterReturnCheck.h"
@@ -32,6 +33,8 @@ namespace readability {
 class ReadabilityModule : public ClangTidyModule {
 public:
   void addCheckFactories(ClangTidyCheckFactories &CheckFactories) override {
+    CheckFactories.registerCheck<AvoidConstParamsInDecls>(
+        "readability-avoid-const-params-in-decls");
     CheckFactories.registerCheck<BracesAroundStatementsCheck>(
         "readability-braces-around-statements");
     CheckFactories.registerCheck<ContainerSizeEmptyCheck>(

docs/clang-tidy/checks/list.rst

@@ -90,8 +90,9 @@ Clang-Tidy Checks
    performance-faster-string-find
    performance-for-range-copy
    performance-implicit-cast-in-loop
-   performance-unnecessary-value-param
    performance-unnecessary-copy-initialization
+   performance-unnecessary-value-param
+   readability-avoid-const-params-in-decls
    readability-braces-around-statements
    readability-container-size-empty
    readability-else-after-return

docs/clang-tidy/checks/readability-avoid-const-params-in-decls.rst

@@ -0,0 +1,17 @@
+.. title:: clang-tidy - readability-avoid-const-params-in-decls
+
+readability-avoid-const-params-in-decls
+=======================================
+
+Checks whether a function declaration has parameters that are top level const.
+
+`const` values in declarations do not affect the signature of a function, so
+they should not be put there.  For example:
+
+Examples:
+
+.. code:: c++
+
+  void f(const string);   // Bad: const is top level.
+  void f(const string&);  // Good: const is not top level.
+

test/clang-tidy/readability-avoid-const-params-in-decls.cpp

@@ -0,0 +1,78 @@
+// RUN: %check_clang_tidy %s readability-avoid-const-params-in-decls %t
+
+using alias_type = bool;
+using alias_const_type = const bool;
+
+
+void F1(const int i);
+// CHECK-MESSAGES: :[[@LINE-1]]:9: warning: parameter 'i' is const-qualified in the function declaration; const-qualification of parameters only has an effect in function definitions [readability-avoid-const-params-in-decls]
+// CHECK-FIXES: void F1(int i);
+
+void F2(const int *const i);
+// CHECK-MESSAGES: :[[@LINE-1]]:9: warning: parameter 'i' is const-qualified
+// CHECK-FIXES: void F2(const int * i);
+
+void F3(int const i);
+// CHECK-MESSAGES: :[[@LINE-1]]:9: warning: parameter 'i' is const-qualified
+// CHECK-FIXES: void F3(int i);
+
+void F4(alias_type const i);
+// CHECK-MESSAGES: :[[@LINE-1]]:9: warning: parameter 'i' is const-qualified
+// CHECK-FIXES: void F4(alias_type i);
+
+void F5(const int);
+// CHECK-MESSAGES: :[[@LINE-1]]:9: warning: parameter 1 is const-qualified
+// CHECK-FIXES: void F5(int);
+
+void F6(const int *const);
+// CHECK-MESSAGES: :[[@LINE-1]]:9: warning: parameter 1 is const-qualified
+// BUG(b/27584482): void F6(const int *);  should be produced
+
+void F7(int, const int);
+// CHECK-MESSAGES: :[[@LINE-1]]:14: warning: parameter 2 is const-qualified
+// CHECK-FIXES: void F7(int, int);
+
+void F8(const int, const int);
+// CHECK-MESSAGES: :[[@LINE-1]]:9: warning: parameter 1 is const-qualified
+// CHECK-MESSAGES: :[[@LINE-2]]:20: warning: parameter 2 is const-qualified
+// CHECK-FIXES: void F8(int, int);
+
+void F9(const int long_name);
+// CHECK-MESSAGES: :[[@LINE-1]]:9: warning: parameter 'long_name'
+// CHECK-FIXES: void F9(int long_name);
+
+void F10(const int *const *const long_name);
+// CHECK-MESSAGES: :[[@LINE-1]]:10: warning: parameter 'long_name'
+// CHECK-FIXES: void F10(const int *const * long_name);
+
+
+struct Foo {
+  Foo(const int i);
+  // CHECK-MESSAGES: :[[@LINE-1]]:7: warning: parameter 'i'
+  // CHECK-FIXES: Foo(int i);
+
+  void operator()(const int i);
+  // CHECK-MESSAGES: :[[@LINE-1]]:19: warning: parameter 'i'
+  // CHECK-FIXES: void operator()(int i);
+};
+
+// Do not match on definitions
+void NF1(const int i) {}
+void NF2(const int *const i) {}
+void NF3(int const i) {}
+void NF4(alias_type const i) {}
+void NF5(const int) {}
+void NF6(const int *const) {}
+void NF7(int, const int) {}
+void NF8(const int, const int) {}
+
+// Do not match on other stuff
+void NF(const alias_type& i);
+void NF(const int &i);
+void NF(const int *i);
+void NF(alias_const_type i);
+void NF(const alias_type&);
+void NF(const int&);
+void NF(const int*);
+void NF(const int* const*);
+void NF(alias_const_type);