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Fix Qt and libcaesium detection in CMakeLists.txt - #392
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Lymphatus merged 4 commits intoOct 5, 2026
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This check assumes the only way CMake can find Qt is via an explicitly set CMAKE_PREFIX_PATH (as an env var or cache variable), which isn't true in general: a build system can locate Qt6Config.cmake through other legitimate channels (Qt6_DIR, CMAKE_MODULE_PATH, a default system prefix, or a package-manager-specific search path mechanism) without CMAKE_PREFIX_PATH ever being set. The following find_package(QT NAMES Qt6 Qt5 ... REQUIRED) call already fails loudly and clearly if Qt truly can't be found, making this earlier check both redundant and a source of false negatives.
ExternalProject_Add(libcaesium ...) and the matching add_dependencies() ran unconditionally, even though it's only meant to be a fallback for when find_library(LIBCAESIUM caesium) fails to find an existing system library. The install() rules further down are already correctly gated behind `if (NOT LIBCAESIUM)`. As written, every build attempts to git-clone and cargo-build libcaesium, which fails outright in network- or git-less build environments (e.g. sandboxed package builds) even when a system libcaesium is readily available.
The Linux target_link_libraries() call only linked the "caesium" library when LIBCAESIUM was NOT found (i.e. only in the cargo-built fallback case, relying on the earlier link_directories() pointing at the ExternalProject's cargo target dir). When a system libcaesium IS found via find_library(LIBCAESIUM caesium), it was never linked in at all, leading to undefined references to c_compress/c_compress_to_size at link time. Link against the full path returned by find_library() in that case.
MainWindow declares a QElapsedTimer member (compressionTimer) without including <QElapsedTimer>, relying on it being pulled in transitively by another Qt header. This is fragile and breaks with some Qt/stdlib header configurations, failing with "'QElapsedTimer' does not name a type".
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Found while packaging this project for nixpkgs, where the build must use a system-installed
libcaesiumwith no network/git access available during the build. See individual commits for details on each fix.