linking Qt6::BundledZLIB breaks with Emscripten and Conan (Qt6 + cpr/libcurl + Zlib)

[qwendt]

I am working on a project where I want to build a Qt6 + WebAssembly (Emscripten) application and link it together with a custom library that uses cpr/libcurl (installed via Conan).

my Setup

• Host: Linux (gcc 13, CMake 3.31, Conan 2.4, CLion 2025.1)

• Target: WebAssembly (Emscripten 3.1.56, wasm_singlethread)

• Dependencies via Conan: cpr, libcurl, nlohmann_json, spdlog, zlib

• GUI layer: Qt6.8.3 (prebuilt wasm_singlethread package from the Qt installer)

The issue

When configuring my project with CMake, Qt’s CMake files insist on looking for Qt6::BundledZLIB. Since my prebuilt Qt6/WASM installation doesn’t ship Qt6BundledZLIBConfig.cmake, I get:

Can't find Qt6::BundledZLIB.

Actually I don’t want to use Qt’s internal Zlib at all. Both cpr/libcurl and Qt’s network module should be able to use the system Zlib provided by Emscripten (-sUSE_ZLIB=1, or Conan’s ZLIB::ZLIB target).

Linking it directly in my own executable/library causes conflicts: I’d end up with two Zlib implementations in the link (Qt’s bundled one and Emscripten’s system one).

I also set the CMake options:

-DCMAKE_DISABLE_FIND_PACKAGE_Qt6BundledZLIB=ON
-DQT_FEATURE_system_zlib=ON
-DQT_NO_ZLIB=OFF

Did not help at all.

Is there a recommended way to configure a prebuilt Qt WASM package so that it doesn’t try to pull in Qt6::BundledZLIB, but uses the system Zlib instead?

Thank you