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cmake: doesn't fail if zlib support is requested but the zlib library can't be found #6173

reddwarf69 opened this issue Nov 4, 2020 · 5 comments


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Running cmake -DCURL_ZLIB:BOOL=ON succeeds even if find_package(ZLIB) fails.

In general the checks are inconsistent. With find_package(Brotli QUIET) ( immediately followed by find_package(Zstd REQUIRED) (

On autotools you have --with-zlib/--without-zlib and autodetection. If --with-zlib is used the configure script fails if the zlib library can't be found.

@bagder bagder added the cmake label Nov 4, 2020
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snikulov commented Nov 5, 2020

@bagder should we completely mimic autotools? As I see it was the initial intention (12 years or so 600460f) not to fail if CURL_ZLIB=ON, but zlib is not found.
Should we re-work CMakeLists.txt now to match autotools?

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bagder commented Nov 5, 2020

I don't think we need to "blindly" follow and mimic autotools in cmake (as it certainly has its flaws and peculiarities as well), but the things that are done "right" and that we like we certainly could.

I think when a user asks for enabling a feature, like zlib, we should fail if that can't be done - using any build system. If the user doesn't ask for it, then detecting it automatically and using it or not based on that seems reasonable. Right?

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I'm with @bagder . CMake build should probably behave "the CMake way" mimicking autotools where it makes sense.
But in any case in autodetection mode we should be able to decide what to do if dependency is not found (like skip it) but if the user asks for a particular option and it cannot be delivered, that's a hard error.

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snikulov commented Nov 6, 2020

@jzakrzewski I'm also not arguing. Then we should re-write all CMake build to new rules.

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bagder commented Nov 6, 2020

It's good enough if we keep fixing things, one by one. Just like we always have!

@bagder bagder closed this as completed in 529423a Nov 18, 2020
bagder pushed a commit that referenced this issue Nov 19, 2020
By differentiating between ON and AUTO it can make a missing zlib
library a hard error when CURL_ZLIB=ON is used.

Reviewed-by: Jakub Zakrzewski
Closes #6221
Fixes #6173
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