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# Find the prefix from the `*Config.cmake` file being generated.
#
# When generating an installed `*Config.cmake` file, we often want to be able
# to refer to the ancestor directory which contains all the installed files.
#
# We want to do this without baking in an absolute path when the config file is
# generated, in order to allow for a "relocatable" binary distribution that
# doesn't need to know what path it ends up being installed at when it is
# built.
#
# The solution that we know the relative path that the config file will be at
# within that prefix, like `"${prefix_var}/lib/cmake/${project}"`, so we count
# the number of components in that path to figure out how many parent dirs we
# need to traverse from the location of the config file to get to the prefix
# dir.
#
# out_var:
# variable to set the "return value" of the function, which is the code to
# include in the config file under construction.
#
# prefix_var:
# Name of the variable to define in the returned code (not directory for the
# faller!) that will contain the prefix path.
#
# path_to_leave:
# Path from the prefix to the config file, a relative path which we wish to
# go up and out from to find the prefix directory.
function(find_prefix_from_config out_var prefix_var path_to_leave)
set(config_code
"# Compute the installation prefix from this LLVMConfig.cmake file location."
"get_filename_component(${prefix_var} \"\${CMAKE_CURRENT_LIST_FILE}\" REALPATH)")
# Construct the proper number of get_filename_component(... PATH)
# calls to compute the installation prefix.
string(REGEX REPLACE "/" ";" _count "prefix/${path_to_leave}")
foreach(p ${_count})
list(APPEND config_code
"get_filename_component(${prefix_var} \"\${${prefix_var}}\" PATH)")
endforeach(p)
string(REPLACE ";" "\n" config_code "${config_code}")
set("${out_var}" "${config_code}" PARENT_SCOPE)
endfunction()
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