The line number of the current file being processed.
This is the line number of the file currently being processed by cmake.
If CMake is currently processing deferred calls scheduled by the cmake_language(DEFER) command, this variable evaluates to DEFERRED instead of a specific line number.
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Licensed under the BSD 3-clause License.
https://cmake.org/cmake/help/v3.19/variable/CMAKE_CURRENT_LIST_LINE.html