The document discusses clang-tidy, which is a tool for statically analyzing C++ code and finding typical programming errors. It has over 200 built-in rules for checking adherence to coding guidelines and best practices. The document provides examples of running clang-tidy on sample code and detecting issues. It also discusses how to develop custom rules by traversing the AST and registering matchers. Overall, the document serves as an introduction to using clang-tidy for code reviews and improving code quality.

1. Clang-tidy:
путешествие внутрь AST С++
Юрий Ефимочев

2. Обо мне
Solarwinds
Lead Developer
MSP Backup & Recovery

3. Что такое clang-tidy?
Инструмент для статического анализа кода и
поиска типичных ошибок программирования

4. Встроенные правила(~200)
● ClangAnalyzer
● Readability/Modernize/Performance
● CppCoreGuidelines
● LLVM/Google-style

5. Пример запуска
class TestClass
{
public:
TestClass() :
m_B(),
m_C()
{
}
private:
int m_A;
int m_B;
int m_C;
};

6. Пример запуска
$ clang-tidy -checks="cppcoreguidelines-*" ./test.cpp
1 warning generated.
./test.cpp:4:5: warning: constructor does not initialize these fields: m_A
[cppcoreguidelines-pro-type-member-init]
TestClass() :
^
m_A(),

7. Code review

8. Цели code review
● Соответствие реализации задаче
● Поиск ошибок и неоптимальностей реализации
● Соответствие guidelines и best practices

9. Clang-tidy и code review?
Платформа для построения собственных
инструментов статического анализа кода

10. Расширяемость
● Полный доступ к AST и препроцессору
● Модульная архитектура
● Инфраструктура для разработки и
тестирования

11. Что необходимо для использования?
● Код должен собираться clang
● Необходима compilation database

12. Алгоритм разработки правила
1. Подготовить пример
2. Посмотреть в AST
3. ???
4. Profit

13. Пример 1
#include <iostream>
class TestClass
{
public:
static int const Constant;
int m_public;
private:
int m_private;
};
struct TestStruct
{
int Field;
};
// style: class public field

14. Clang-check: визуализация AST
$ clang-check -ast-dump -ast-dump-filter="Test" ./test.cpp
Dumping TestClass:
CXXRecordDecl 0xaf665da8 <test.cpp:3:1, line:12:1> line:3:7 class TestClass definition
|-CXXRecordDecl 0xaf665ec0 <col:1, col:7> col:7 implicit class TestClass
|-AccessSpecDecl 0xaf665f50 <line:5:1, col:7> col:1 public
|-VarDecl 0xaf665f88 <line:6:5, col:22> col:22 Constant 'const int' static
|-FieldDecl 0xaf665ff8 <line:8:5, col:9> col:9 m_public 'int'
|-AccessSpecDecl 0xaf666040 <line:10:1, col:8> col:1 private
`-FieldDecl 0xaf666078 <line:11:5, col:9> col:9 m_private 'int'
Dumping TestStruct:
CXXRecordDecl 0xaf6660c0 <test.cpp:14:1, line:17:1> line:14:8 struct TestStruct definition
|-CXXRecordDecl 0xaf6661d0 <col:1, col:8> col:8 implicit struct TestStruct
`-FieldDecl 0xaf666270 <line:16:5, col:9> col:9 Field 'int'

15. AST Nodes
● Decl
● Stmt
● Type

16. AST Nodes
● Decl
CXXRecordDecl
CXXMethodDecl
VarDecl
● Stmt
● Type

17. AST Nodes
● Decl
● Stmt
ifStmt
CXXTryStmt
BinaryOperator
● Type

18. AST Nodes
● Decl
● Stmt
● Type
PointerType
ReferenceType
LValueReferenceType

19. Пример 1: AST
$ clang-check -ast-dump -ast-dump-filter="Test" ./test.cpp
Dumping TestClass:
CXXRecordDecl 0xaf665da8 <test.cpp:3:1, line:12:1> line:3:7 class TestClass definition
|-CXXRecordDecl 0xaf665ec0 <col:1, col:7> col:7 implicit class TestClass
|-AccessSpecDecl 0xaf665f50 <line:5:1, col:7> col:1 public
|-VarDecl 0xaf665f88 <line:6:5, col:22> col:22 Constant 'const int' static
|-FieldDecl 0xaf665ff8 <line:8:5, col:9> col:9 m_public 'int'
|-AccessSpecDecl 0xaf666040 <line:10:1, col:8> col:1 private
`-FieldDecl 0xaf666078 <line:11:5, col:9> col:9 m_private 'int'
Dumping TestStruct:
CXXRecordDecl 0xaf6660c0 <test.cpp:14:1, line:17:1> line:14:8 struct TestStruct definition
|-CXXRecordDecl 0xaf6661d0 <col:1, col:8> col:8 implicit struct TestStruct
`-FieldDecl 0xaf666270 <line:16:5, col:9> col:9 Field 'int'

20. AST Matchers
● Node Matchers
cxxRecordDecl, cxxMethodDecl, namespaceDecl, ifStmt, ...
● Narrowing Matchers
isConstant, isFinal, hasName, matchesName, unless, ...
● Traversal Matchers
hasDescendant, hasParent, hasBody, ...
cxxMethodDecl(matchesName(“Get.*”), hasParent(cxxRecordDecl(isStruct()))

21. Пример 1
clang-query> match fieldDecl()
Match #1:
/home/yury/Projects/test.cpp:8:5: note: "root" binds here
int m_public;
^~~~~~~~~~~~
Match #2:
/home/yury/Projects/test.cpp:11:5: note: "root" binds here
int m_private;
^~~~~~~~~~~~~
Match #3:
/home/yury/Projects/test.cpp:16:5: note: "root" binds here
int Field;
^~~~~~~~~
3 matches.

22. Пример 1
clang-query> match fieldDecl(isPublic())
Match #1:
/home/yury/Projects/test.cpp:8:5: note: "root" binds here
int m_public;
^~~~~~~~~~~~
Match #2:
/home/yury/Projects/test.cpp:16:5: note: "root" binds here
int Field;
^~~~~~~~~
2 matches.

23. Пример 1
clang-query> match fieldDecl(isPublic(), hasParent(cxxRecordDecl(isClass())))
Match #1:
/home/yury/Projects/test.cpp:8:5: note: "root" binds here
int m_public;
^~~~~~~~~~~~
1 match.

24. Добавление правила
$ ./add_new_check.py misc field-visibility
Updating ./misc/CMakeLists.txt...
Creating ./misc/FieldVisibilityCheck.h...
Creating ./misc/FieldVisibilityCheck.cpp...
Updating ./misc/MiscTidyModule.cpp...
Creating ../test/clang-tidy/misc-field-visibility.cpp...
Creating ../docs/clang-tidy/checks/misc-field-visibility.rst...
Updating ../docs/clang-tidy/checks/list.rst...
Done. Now it's your turn!

25. Пример 1: шаблон реализации
class FieldVisibilityCheck : public ClangTidyCheck
{
public:
FieldVisibilityCheck(StringRef name, ClangTidyContext* context) :
ClangTidyCheck(name, context)
{
}
private:
void registerMatchers(ast_matchers::MatchFinder* finder) override
{
}
void check(ast_matchers::MatchFinder::MatchResult const& result) override
{
}
};

26. Пример 1: реализация
class FieldVisibilityCheck : public ClangTidyCheck
{
public:
FieldVisibilityCheck(StringRef name, ClangTidyContext* context) :
ClangTidyCheck(name, context)
{
}
private:
void registerMatchers(ast_matchers::MatchFinder* finder) override
{
finder->addMatcher(fieldDecl(isPublic(), hasParent(cxxRecordDecl(isClass()))).bind("field"), this);
}
void check(ast_matchers::MatchFinder::MatchResult const& result) override
{
FieldDecl const& field = *result.Nodes.getNodeAs<FieldDecl const>("field");
diag(field.getLocStart(), "Class field should be private");
}
};

27. Пример 1: результат
$ clang-tidy -checks="misc-field-visibility-check" ./test.cpp
1 warning generated.
./test.cpp:8:5: warning: Class field should be private [misc-field-visibility-check]
int m_public;
^

28. Пример 2
int Function(int a)
{
// ...
a = something;
// ...
return a;
}
// style: mutable parameter

29. Пример 2
struct Test
{
virtual int VirtualMethod(int a) = 0;
int Method(int a, int const b, int& c, int* d)
{
a = b;
return a;
}
};

30. Пример 2: AST
Dumping Test:
CXXRecordDecl 0x46b1b20 <test.cpp:1:1, line:9:1> line:1:8 struct Test definition
|-CXXRecordDecl 0x46b1c30 <col:1, col:8> col:8 implicit struct Test
|-CXXMethodDecl 0x46b1d90 <line:3:5, col:32> col:9 VirtualMethod 'int (int)'
| `-ParmVarDecl 0x46b1cd0 <col:23, col:27> col:27 a 'int'
`-CXXMethodDecl 0x46b2140 <line:4:5, line:8:5> line:4:9 Method 'int (int, const int, int &, int *)'
|-ParmVarDecl 0x46b1e50 <col:16, col:20> col:20 used a 'int'
|-ParmVarDecl 0x46b1ec0 <col:23, col:33> col:33 used b 'const int'
|-ParmVarDecl 0x46b1f60 <col:36, col:41> col:41 c 'int &'
|-ParmVarDecl 0x46b2000 <col:44, col:49> col:49 d 'int *'
`-CompoundStmt 0x46b2320 <line:5:5, line:8:5>
|-BinaryOperator 0x46b22a0 <line:6:9, col:13> 'int' lvalue '='
| |-DeclRefExpr 0x46b2238 <col:9> 'int' lvalue ParmVar 0x46b1e50 'a' 'int'
| `-ImplicitCastExpr 0x46b2288 <col:13> 'int' <LValueToRValue>
| `-DeclRefExpr 0x46b2260 <col:13> 'const int' lvalue ParmVar 0x46b1ec0 'b' 'const int'
`-ReturnStmt 0x46b2308 <line:7:9, col:16>
`-ImplicitCastExpr 0x46b22f0 <col:16> 'int' <LValueToRValue>
`-DeclRefExpr 0x46b22c8 <col:16> 'int' lvalue ParmVar 0x46b1e50 'a' 'int'

31. Пример 2: реализация
void ImmutableParamsCheck::registerMatchers(MatchFinder* finder)
{
finder->addMatcher(
parmVarDecl(
hasAncestor(functionDecl(hasBody(stmt()))),
unless(anyOf(
hasType(isConstQualified()),
hasType(referenceType()),
hasType(pointerType())))).bind("parameter"), this);
}
void ImmutableParamsCheck::check(MatchFinder::MatchResult const& result)
{
ParmVarDecl const& parameter = *result.Nodes.getNodeAs<ParmVarDecl const>("parameter");
SourceLocation const location = parameter.getSourceRange().getEnd();
diag(location, "Consider making constant") <<
FixItHint::CreateInsertion(location, "const ");
}

32. Пример 2: результат
$ clang-tidy -checks="misc-immutable-parameters-check" -fix ./test.cpp
2 warnings generated.
./test.cpp:4:20: warning: Consider making constant [iaso-immutable-params]
int Method(int a, int const b, int& c, int* d)
^
const
./test.cpp:4:20: note: FIX-IT applied suggested code changes
int Method(int a, int const b, int& c, int* d)
^
clang-tidy applied 1 of 1 suggested fixes.

33. Пример 2: результат
struct Test
{
virtual int VirtualMethod(int a) = 0;
int Method(int a, int const b, int& c, int* d)
{
a = b;
return a;
}
};

34. Пример 2: результат
struct Test
{
virtual int VirtualMethod(int a) = 0;
int Method(int const a, int const b, int& c, int* d)
{
a = b;
return a;
}
};

35. Пример 3
// cxxRecordDecl(unless(matchesName("::[A-Z][a-zA-Z0-9]*$")))
class TestClass
{
public:
// cxxMethodDecl(unless(matchesName("::[A-Z][a-zA-Z0-9]*$")))
// parmVarDecl(unless(matchesName("::[a-z][a-zA-Z0-9]*$")))
void Method(int arg);
private:
// fieldDecl(unless(matchesName("::m_[a-z][a-zA-Z0-9]*$")),
// hasParent(cxxRecordDecl(isClass())))
int m_field;
};
struct TestStruct
{
// fieldDecl(unless(matchesName("::[A-Z][a-zA-Z0-9]*$")),
// hasParent(cxxRecordDecl(isStruct())))
int Field;
};

36. Пример 3
// varDecl(hasLocalStorage(), unless(matchesName("::[a-z][a-zA-Z0-9]*$")))
int localVariable;
// varDecl(hasGlobalStorage(),
// unless(anyOf(matchesName("::s_[a-z][a-zA-Z0-9]*$"), hasType(isConstQualified()))))
static int s_staticVariable;
// varDecl(hasGlobalStorage(),
// unless(anyOf(matchesName("::[A-Z][a-zA-Z0-9]*$"), unless(hasType(isConstQualified())))))
static int const Constant = 42;

37. Пример 4
Можно ли бросать исключение из
деструктора?

38. Пример 4
class Test
{
public:
~Test()
{
throw Exception();
}
};
// c++11: terminate

39. Пример 4
class Test
{
public:
~Test() noexcept(true)
{
throw Exception();
}
};
// c++11: terminate

40. Пример 4
class Test
{
public:
~Test() noexcept(false)
{
throw Exception();
}
};

41. Пример 4
class Test
{
public:
~Test() noexcept(false)
{
throw Exception();
}
};
int main()
{
std::unique_ptr<Test> test(new Test());
test.reset();
}
// c++11: terminate

42. Пример 4
class Parent
{
public:
~Parent() noexcept(false);
};
class Child : public Parent
{
public:
~Child()
{
}
};
int main()
{
std::unique_ptr<Child> test(new Child());
test.reset();
}
// c++11: terminate

43. Пример 4
class Parent
{
public:
~Parent() noexcept(false);
};
class Child : public Parent
{
public:
~Child() noexcept(true)
{
}
};
int main()
{
std::unique_ptr<Child> test(new Child());
test.reset();
}
// c++11: terminate

44. Пример 4
● Не бросать исключения из деструкторов
● Обозначить бросающие деструкторы
‘noexcept(false)’
● Не использовать ‘noexcept(true)’ для
деструкторов

45. Пример 4: реализация
void ExplicitThrowSpecificationCheck::registerMatchers(MatchFinder* finder)
{
finder->addMatcher(cxxDestructorDecl().bind("destructor"), this);
}
void ExplicitThrowSpecificationCheck::check(MatchFinder::MatchResult const& result)
{
FunctionDecl const& declaration = *result.Nodes.getNodeAs<FunctionDecl>("destructor");
FunctionProtoType const& prototype = *declaration.getType()->getAs<FunctionProtoType>();
bool const destructorCanThrow = prototype.getNoexceptSpec(*result.Context) == FunctionProtoType::NR_Throw;
bool const isSpecificationExplicit = declaration.getExceptionSpecSourceRange().isValid();
if (destructorCanThrow && !isSpecificationExplicit)
{
diag(declaration.getSourceRange().getEnd(), "This destructor should be marked with 'noexcept(false)'");
}
if (!destructorCanThrow && isSpecificationExplicit)
{
diag(declaration.getSourceRange().getEnd(), "Do not mark destructor with 'noexcept(true)'");
}
}

46. Пример 4: результат
class Parent
{
public:
~Parent() noexcept(false);
};
class Child : public Parent
{
public:
~Child() noexcept(true)
{
}
};
// do not use ‘noexept(true)’

47. Пример 4: результат
class Parent
{
public:
~Parent() noexcept(false);
};
class Child : public Parent
{
public:
~Child()
{
}
};
// can throw, mark with ‘noexcept(false)’

48. Пример 4: результат
class Parent
{
public:
~Parent() noexcept(false);
};
class Child : public Parent
{
public:
~Child() noexcept(false)
{
}
};

49. Пример 4
void Function();
struct Object
{
Object();
bool operator<(Object const& right) const;
};
struct Test
{
Test()
{
Object a, b;
if (a < b)
{
Function();
}
int* p = new int(42);
}
};

50. Пример 4: реализация
void ThrowFromDestructorCheck::registerMatchers(MatchFinder* finder)
{
finder->addMatcher(expr(hasAncestor(cxxDestructorDecl().bind("destructor"))).bind("expression"), this);
}
void ThrowFromDestructorCheck::check(MatchFinder::MatchResult const& result)
{
FunctionDecl const& declaration = *result.Nodes.getNodeAs<FunctionDecl>("destructor");
FunctionProtoType const& prototype = *declaration.getType()->getAs<FunctionProtoType>();
bool const destructorCanThrow = prototype.getNoexceptSpec(*result.Context) == FunctionProtoType::NR_Throw;
if (destructorCanThrow)
{
return;
}
Expr const& expression = *result.Nodes.getNodeAs<Expr>("expression");
bool const expressionCanThrow = m_compiler->getSema().canThrow(&expression) != CT_Cannot;
if (expressionCanThrow)
{
diag(expression.getExprLoc(), "Expression can throw exception");
}
}

51. Пример 4: результат
void Function();
struct Object
{
Object();
bool operator<(Object const& right) const;
};
struct Test
{
Test()
{
Object a, b;
if (a < b)
{
Function();
}
int* p = new int(42);
}
};
// can throw: constructor
// can throw: operator <
// can throw: Function call
// can throw: operator new

52. Пример 4: результат
void Function() noexcept(true);
struct Object
{
Object() noexcept(true);
bool operator<(Object const& right) const noexcept(true);
};
struct Test
{
Test()
{
Object a, b;
if (a < b)
{
Function();
}
}
};

53. Clang-tidy: итоги

54. Clang-tidy: итоги
● Простая реализация сложных проверок
● Автоматизация рутинных проверок
● Отличный способ лучше узнать C++

55. Полезные ссылки
http://clang.llvm.org/extra/clang-tidy
http://clang.llvm.org/docs/LibASTMatchersReference.html
http://clang.llvm.org/docs/IntroductionToTheClangAST.html

56. ?
efimyury@gmail.com
yury.efimochev@solarwinds.com