ESC'17

The goal of this exercise is to learn how to use clang-tidy to verify that your code satisfies certain rules. The checks are applied statically, i.e. without running the code.

Consider again hello.cc, in its formatted version.

[studentNM@esc-XY ~]$ cd esc17/hands-on/basic
[studentNM@esc-XY basic]$ cat hello.cc
#include <iostream>
int main(int argc, char* argv[]) {
  std::cout << "Hello, ";
  if (argc > 1)
    std::cout << argv[1];
...

Note how the statements in the if and else branches are not included in a block, i.e. they are not surrounded by braces, which is something that we want to have.

[studentNM@esc-XY basic]$ clang-tidy -checks=readability-braces-around-statements hello.cc
Error while trying to load a compilation database:
...
/export/students-home/student40/esc17/hands-on/basic/hello.cc:4:16: warning: statement should be inside braces [readability-braces-around-statements]
  if (argc > 1)
               ^
                {
...

Let’s ignore for a moment the compilation database error. Let’s ask clang-tidy to also add the braces (-fix) and, since we have already a .clang-format, to also reformat the resulting code (-format-style=file).

[studentNM@esc-XY basic]$ clang-tidy -checks=readability-braces-around-statements -fix -format-style=file hello.cc
...
[studentNM@esc-XY basic]$ cat hello.cc
#include <iostream>
int main(int argc, char*argv[]){std::cout<<"Hello, ";
  if (argc > 1) {
    std::cout << argv[1];
  } else {
    std::cout << "world";
  }
  std::cout << "!\n";
}

The result is not always perfect. Better rerun clang-format manuall

[studentNM@esc-XY basic]$ clang-format -i hello.cc
[studentNM@esc-XY basic]$ cat hello.cc
#include <iostream>
int main(int argc, char* argv[]) {
  std::cout << "Hello, ";
  if (argc > 1) {
    std::cout << argv[1];
  } else {
    std::cout << "world";
  }
  std::cout << "!\n";
}

Tens of checks are available. To list the enabled checks:

[studentNM@esc-XY basic]$ clang-tidy -list-checks

To list all the available checks:

[studentNM@esc-XY basic]$ clang-tidy -checks=* -list-checks

To dump a configuration file including all the checks but the mpi ones:

[studentNM@esc-XY basic]$ clang-tidy -checks=*,-mpi* -dump-config

Coming back to the “compilation database”, the easiest way to create one is through cmake. The compilation database is a file called compile_commands.json.

[studentNM@esc-XY basic]$ mkdir build && cd build
[studentNM@esc-XY build]$ cmake -DCMAKE_EXPORT_COMPILE_COMMANDS=1 ..
[studentNM@esc-XY build]$ cd ..
[studentNM@esc-XY basic]$ git checkout -- hello.cc
[studentNM@esc-XY basic]$ clang-tidy -checks=readability-braces-around-statements -p build hello.c

Static analysis