Find source directory from build directory in cmake

Question

I want to create a bash helper script to diff a generated file against its source. The directory structure of the output matches the source, so I should be able to find the name of the source file if I had this data:

• The name of the generated file (This will be passed to the script)
• CMAKE_PROJECT_SOURCE_DIR (I need to find this out)

My plan to get this is:

• go up the directory tree searching for a CMakeCache.txt file.
• When/if found, run CMake somehow to print out the path to the source

How do I do that? Preferably without having to configure/generate(as that introduces a bit of delay). Should I instead grep a specific file in the build folder? Which one?

Answer 1

Another way of doing is is to let CMake load the cache and print the desired variable.

Create a little CMake script print-source-dir.cmake

load_cache("${BUILD_DIR}" READ_WITH_PREFIX cache_ CMAKE_HOME_DIRECTORY)
message("${cache_CMAKE_HOME_DIRECTORY}")

and run it like this

$ cmake -DBUILD_DIR=/home/wuff/projects/whatever/build -P print-source-dir.cmake 
/home/wuff/projects/whatever

Answer 2

You can grep for home directory in CMakeCache.txt:

grep ^CMAKE_HOME_DIRECTORY CMakeCache.txt | cut -d = -f2-

My cmake version:

$ cmake --version
cmake version 3.28.1

Answer 3

Once you have located the CMakeCache.txt you can grep for the project source dir in it in the following way:

cat CMakeCache.txt | grep -E '.*_SOURCE_DIR:STATIC=.*' | grep -E -o '/.*'

This outputs the value of the _SOURCE_DIR variable.