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CMake/Tests/RunCMake/CMP0019/CMP0019-code.cmake

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Add policy CMP0019 to skip include/link variable re-expansion Historically CMake has always expanded ${} variable references in the values given to include_directories(), link_directories(), and link_libraries(). This has been unnecessary since general ${} evaluation syntax was added to the language a LONG time ago, but has remained for compatibility with VERY early CMake versions. For a long time the re-expansion was a lightweight operation because it was only processed once at the directory level and the fast-path of cmMakefile::ExpandVariablesInString was usually taken because values did not have any '$' in them. Then commit d899eb71 (Call ExpandVariablesInString for each target's INCLUDE_DIRECTORIES, 2012-02-22) made the operation a bit heavier because the expansion is now needed on a per-target basis. In the future we will support generator expressions in INCLUDE_DIRECTORIES with $<> syntax, so the fast-path in cmMakefile::ExpandVariablesInString will no longer be taken and re-expansion will be very expensive. Add policy CMP0019 to skip the re-expansion altogether in NEW behavior. In OLD behavior perform the expansion but improve the fast-path heuristic to match ${} but not $<>. If the policy is not set then warn if expansion actually does anything. We expect this to be encountered very rarely in practice.
2012-12-06 18:59:18 +04:00
set(VAR_INCLUDE "VAL_INCLUDE")
set(VAR_LINK_DIRS "VAL_LINK_DIRS")
set(VAR_LINK_LIBS "VAL_LINK_LIBS")
add_custom_target(some_target)
include_directories("/usr/include/\${VAR_INCLUDE}" /usr/include/normal)
link_directories("/usr/lib/\${VAR_LINK_DIRS}" /usr/lib/normal)
link_libraries("\${VAR_LINK_LIBS}" normal)
add_custom_target(other_target)
set_property(TARGET other_target PROPERTY INCLUDE_DIRECTORIES "")