CMake Ninja show link commands

CMake can show the compile commands that will be issued to compile targets by setting the CMAKE_EXPORT_COMPILE_COMMANDS variable to ON. This generates ${CMAKE_BINARY_DIR}/compile_commands.json file that contains the JSON compilation database for each source file. However, this does not include the link commands used to link the final executable or library.

There are a couple ways to make the build system emit the link commands without actually yet linking the target:

Ninja JSON compilation database method

To show the compile and link commands in JSON compilation database format using Ninja for a specific target including target dependencies use the compdb-targets Ninja tool.

cmake -B build -G Ninja

cmake --build build -- -t compdb-targets MyTarget > compile_and_link_commands.json
# equivalent to
ninja -C build -t compdb-targets MyTarget > compile_and_link_commands.json

GNU Make or Ninja dry-run method

The Ninja compdb-targets method above is preferred, since the drawbacks of this “dry-run” method include:

• have to clean-first to show all the dependecies, otherwise if some dependencies have been built already, they won’t be shown in the output.
• the output is not in JSON format, so it may be harder to parse.

The -n dryrun flag shows the compile and link commands without executing them.

cmake -B build

cmake --build build --target mytarg --verbose --clean-first -- -n