code-in-cpp/compile-commands

Compilation Database Manipulation Utility

Compilation Database Manipulation Utility

This utility facilitates the use and modifications of compilation databases.
Modifying compilation databases can be useful especially when you don't have control over how a project is built.

Install

pip install compile-commands

Requirements

Requires at least python 3.4.

Usage

This tool has many possible uses, I'll go through some of them to showcase how it can be used.

In a project composed of subproject with their own build folder, you can use --merge and indicate the root --dir and it will merge them in the specified directory.
This is particularly useful for LSP servers that don't handle these projects well.

compile-commands --dir /path/to/project --merge

You can also indicate to the LSP server that you prefer using libc++ instead of libstdc++ even if your buildsystem doesn't use it.

compile-commands --file /path/to/project/compile-commands.json \
                 --add_flags='-stdlib=libc++'

--add_flags takes in a string so you can add multiple flags

compile-commands --file /path/to/project/compile-commands.json \
                 --add_flags='-stdlib=libc++ -O0'

You can combine --add_flags with --run to monitor warnings as example:

compile-commands --file /path/to/project/compile-commands.json \
                 --add_flags='-Wall -Wextra -pedantic -fsyntax' \
                 --run --threads=12

You can decide to treat only a subset of your project by using --filter-files or --remove-files.
--filter-files takes in a regular expression whereas --remove-files takes in a comma-separated list of absolute paths.

You can as example filter out .c files from the database:

compile-commands --file /path/to/project/compile-commands.json \
                 --filter-files='.*\.c$' \
                 --remove-files='path/to/file1,path/to/file2'

You can decide to treat only a subset of your project by using --include-files which takes in a comma-separated list of absolute paths, which means compile-commands file will just include files listed in this option, by using --path-prefix which means path prefix of remove files list and include file list

You can as example filter out .c files from the database:

compile-commands --file /path/to/project/compile-commands.json \
                 --include-files='path/to/file1,path/to/file2'

You can use the -o flag to specify the name of the output file in case you don't want to overwrite

compile-commands --file /path/to/project/compile-commands.json \
                 --filter-files='.*\.c$' \
                 --remove-files='path/to/file1,path/to/file2' \
                 -o 'my-db-without-c-files.json'

You can also filter out parts of the commands based on a regular expression using --filter.
This is particularly useful when you need to modify the -o from the command. A good example of that is using ClangBuildAnalyzer.

mkdir ftime
cd ftime
./compile-commands --file=/path/to/project/compile-commands.json \
                   --add_flags='-ftime-trace' \
                   --filter='-o .*\\.o' \
                   --run -j 12

# .json and .o files are created in-place!
ClangBuildAnalyzer --all . capture_file
ClangBuildAnalyzer --analyze capture_file

We add the clang's -ftime-trace as required by ClangBuildAnalyzer and remove every occurences of -o path/to/object/file.o and run each commands to produces the json tracings.
What if g++ was used during the creation of compilation database ? In this case we can use --clang and --gcc to switch between the two compilers and even change the path of the compiler with --compiler_path if let's say gcc is in /usr/bin and the clang we want to use is in /usr/bin/local.

./compile-commands.py --file=/path/to/project/compile-commands.json \
                      --clang --compiler_path='/usr/bin/local' \
                      --add_flags='-ftime-trace' \
                      --filter='-o .*\\.o' \
                      --run -j 12 

--filter also accepts a replacement through the --replacement flag, it accepts reference to groups within the regular expression as per re.sub()

--filter is also useful to remove flags that are not compatible with both compilers.