readability-redundant-preprocessor

Finds potentially redundant preprocessor directives. At the moment the following cases are detected:

• #ifdef .. #endif pairs which are nested inside an outer pair with the same condition. For example:

#ifdef FOO
#ifdef FOO // inner ifdef is considered redundant
void f();
#endif
#endif

• Same for #ifndef .. #endif pairs. For example:

#ifndef FOO
#ifndef FOO // inner ifndef is considered redundant
void f();
#endif
#endif

• #ifndef inside an #ifdef with the same condition:

#ifdef FOO
#ifndef FOO // inner ifndef is considered redundant
void f();
#endif
#endif

• #ifdef inside an #ifndef with the same condition:

#ifndef FOO
#ifdef FOO // inner ifdef is considered redundant
void f();
#endif
#endif

• #if .. #endif pairs which are nested inside an outer pair with the same condition. For example:

#define FOO 4
#if FOO == 4
#if FOO == 4 // inner if is considered redundant
void f();
#endif
#endif