[Lldb-commits] [PATCH] D79219: [CMake] Simplify CMake handling for zlib

Pavel Labath via Phabricator via lldb-commits lldb-commits at lists.llvm.org
Tue May 12 00:30:16 PDT 2020

labath added inline comments.

Comment at: llvm/cmake/config-ix.cmake:514
+      "Use zlib for compression/decompression if available. Can be ON, OFF, or FORCE_ON"
JDevlieghere wrote:
> phosek wrote:
> > JDevlieghere wrote:
> > > If I understand correctly, after running the configuration phase with LLVM_ENABLE_ZLIB to FORCE_ON, the cached value will be overwritten by ON? 
> > Correct, we used `FORCE_ON` above when invoking `find_package` setting `REQUIRED` which makes the check fail if the library is missing. Recording this information is important for LLVM consumers because it'll be stored in `LLVMConfig.cmake` and AFAIU we don't want to propagate `FORCE_ON` there.
> I get that. My worry is that if for whatever reason the library disappears (system upgrade, package removal, ...) this will silently disable ZLIB support because now LLVM_ENABLE_ZLIB just equals on. This might sound far fetched, but happens all the time with "internal installs". This is why I prefer the ON/OFF/Auto approach because it doesn't update the cache variable, but would set the internal variable to either ON or OFF.
I agree with Jonas, though I don't think the actual values (FORCE_ON/ON vs. ON/Auto) really matter here. The important part is not overwriting the cache variables specified by the user, as that can create various problems with reconfigurations (like the zlib becoming unavailable example).



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