# find\_package in config mode doesn't seem to be appropriately ignoring CMAKE\_IGNORE\_PREFIX\_PATH

**URL:** <https://discourse.cmake.org/t/find-package-in-config-mode-doesnt-seem-to-be-appropriately-ignoring-cmake-ignore-prefix-path/11727>\
**Category:** Code\
**Created:** [September 19, 2024, 6:08pm UTC](https://discourse.cmake.org/t/find-package-in-config-mode-doesnt-seem-to-be-appropriately-ignoring-cmake-ignore-prefix-path/11727 "2024-09-19T18:08:57Z")\
**Posts on this page:** 1\
**Page:** 1

<div class="post-metadata">

**Author:** ![jcm](https://discourse.cmake.org/letter_avatar_proxy/v4/letter/j/58f4c7/32.png) [@jcm](https://discourse.cmake.org/u/jcm)\
**Post date:** [September 19, 2024, 6:08pm UTC](https://discourse.cmake.org/t/find-package-in-config-mode-doesnt-seem-to-be-appropriately-ignoring-cmake-ignore-prefix-path/11727/1 "2024-09-19T18:08:57Z")

</div>

Bit confused about the behavior of CMAKE\_IGNORE\_PREFIX\_PATH. I’m on macOS and trying to exclude homebrew for a particular package (or in general). I’ve added an ignore prefix like so:

```auto
list(APPEND CMAKE_IGNORE_PREFIX_PATH "/opt/homebrew" "/usr/local/lib")

```

Running --debug-find for this package with and without this exclusion reveals some oddities.

Without the ignore:

```auto
  find_package considered the following locations for MbedTLS's Config
  module:

    /Users/me/code/cmaketest/obs-studio/build_macos/CMakeFiles/pkgRedirects/MbedTLSConfig.cmake
    /Users/me/code/cmaketest/obs-studio/build_macos/CMakeFiles/pkgRedirects/mbedtls-config.cmake
    /Users/me/code/cmaketest/obs-studio/.deps/obs-deps-2024-09-05-universal/MbedTLSConfig.cmake
    /Users/me/code/cmaketest/obs-studio/.deps/obs-deps-2024-09-05-universal/mbedtls-config.cmake
    /Users/me/code/cmaketest/obs-studio/.deps/obs-deps-qt6-2024-09-05-universal/MbedTLSConfig.cmake
    /Users/me/code/cmaketest/obs-studio/.deps/obs-deps-qt6-2024-09-05-universal/mbedtls-config.cmake
    /opt/homebrew/MbedTLSConfig.cmake
    /opt/homebrew/mbedtls-config.cmake
    /opt/homebrew/lib/cmake/MbedTLS/MbedTLSConfig.cmake
    /opt/homebrew/lib/cmake/MbedTLS/mbedtls-config.cmake
    /MbedTLSConfig.cmake
    /mbedtls-config.cmake
    /usr/local/opt/game-porting-toolkit/MbedTLSConfig.cmake
    /usr/local/opt/game-porting-toolkit/mbedtls-config.cmake
    /usr/local/MbedTLSConfig.cmake
    /usr/local/mbedtls-config.cmake
    /usr/local/lib/cmake/MbedTLS/MbedTLSConfig.cmake
    /usr/local/lib/cmake/MbedTLS/mbedtls-config.cmake
    /System/Cryptexes/App/usr/MbedTLSConfig.cmake
    /System/Cryptexes/App/usr/mbedtls-config.cmake
    /usr/MbedTLSConfig.cmake
    /usr/mbedtls-config.cmake
    /opt/X11/MbedTLSConfig.cmake
    /opt/X11/mbedtls-config.cmake
    /Library/Apple/usr/MbedTLSConfig.cmake
    /Library/Apple/usr/mbedtls-config.cmake
    /usr/local/share/dotnet/MbedTLSConfig.cmake
    /usr/local/share/dotnet/mbedtls-config.cmake
    /Library/Frameworks/Mono.framework/Versions/Current/Commands/MbedTLSConfig.cmake
    /Library/Frameworks/Mono.framework/Versions/Current/Commands/mbedtls-config.cmake
    /Users/me/.cargo/MbedTLSConfig.cmake
    /Users/me/.cargo/mbedtls-config.cmake
    /Applications/Xcode-beta.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX15.0.sdk/usr/MbedTLSConfig.cmake
    /Applications/Xcode-beta.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX15.0.sdk/usr/mbedtls-config.cmake
    /opt/homebrew/Cellar/cmake/3.30.2/MbedTLSConfig.cmake
    /opt/homebrew/Cellar/cmake/3.30.2/mbedtls-config.cmake
    /opt/MbedTLSConfig.cmake
    /opt/mbedtls-config.cmake
    /opt/local/MbedTLSConfig.cmake
    /opt/local/mbedtls-config.cmake
    /Applications/Xcode-beta.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX15.0.sdk/System/Library/Frameworks/MbedTLSConfig.cmake
    /Applications/Xcode-beta.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX15.0.sdk/System/Library/Frameworks/mbedtls-config.cmake
    /Applications/Xcode-beta.app/Contents/Developer/Platforms/MacOSX.platform/Developer/Library/Frameworks/MbedTLSConfig.cmake
    /Applications/Xcode-beta.app/Contents/Developer/Platforms/MacOSX.platform/Developer/Library/Frameworks/mbedtls-config.cmake
    /Applications/Xcode-beta.app/Contents/Developer/Library/Frameworks/MbedTLSConfig.cmake
    /Applications/Xcode-beta.app/Contents/Developer/Library/Frameworks/mbedtls-config.cmake
    /Library/Frameworks/MbedTLSConfig.cmake
    /Library/Frameworks/mbedtls-config.cmake
    /System/Library/Frameworks/MbedTLSConfig.cmake
    /System/Library/Frameworks/mbedtls-config.cmake
    /Users/me/Applications/MbedTLSConfig.cmake
    /Users/me/Applications/mbedtls-config.cmake
    /Applications/MbedTLSConfig.cmake
    /Applications/mbedtls-config.cmake
    /Applications/Xcode-beta.app/Contents/Applications/MbedTLSConfig.cmake
    /Applications/Xcode-beta.app/Contents/Applications/mbedtls-config.cmake
    /Applications/Xcode-beta.app/Contents/Developer/Applications/MbedTLSConfig.cmake
    /Applications/Xcode-beta.app/Contents/Developer/Applications/mbedtls-config.cmake

  The file was not found.

  find_package considered the following paths for FindMbedTLS.cmake:

    /Users/me/code/cmaketest/obs-studio/cmake/common/FindMbedTLS.cmake
    /opt/homebrew/Cellar/cmake/3.30.2/share/cmake/Modules/FindMbedTLS.cmake

  The file was found at

    /Users/me/code/cmaketest/obs-studio/cmake/finders/FindMbedTLS.cmake

```

With the ignore:

```auto
  find_package considered the following locations for MbedTLS's Config
  module:

    /Users/me/code/cmaketest/obs-studio/build_macos/CMakeFiles/pkgRedirects/MbedTLSConfig.cmake
    /Users/me/code/cmaketest/obs-studio/build_macos/CMakeFiles/pkgRedirects/mbedtls-config.cmake
    /Users/me/code/cmaketest/obs-studio/.deps/obs-deps-2024-09-05-universal/MbedTLSConfig.cmake
    /Users/me/code/cmaketest/obs-studio/.deps/obs-deps-2024-09-05-universal/mbedtls-config.cmake
    /Users/me/code/cmaketest/obs-studio/.deps/obs-deps-qt6-2024-09-05-universal/MbedTLSConfig.cmake
    /Users/me/code/cmaketest/obs-studio/.deps/obs-deps-qt6-2024-09-05-universal/mbedtls-config.cmake
    /MbedTLSConfig.cmake
    /mbedtls-config.cmake
    /usr/local/opt/game-porting-toolkit/MbedTLSConfig.cmake
    /usr/local/opt/game-porting-toolkit/mbedtls-config.cmake
    /usr/local/MbedTLSConfig.cmake
    /usr/local/mbedtls-config.cmake
    /usr/local/lib/cmake/MbedTLS/MbedTLSConfig.cmake
    /usr/local/lib/cmake/MbedTLS/mbedtls-config.cmake
    /System/Cryptexes/App/usr/MbedTLSConfig.cmake
    /System/Cryptexes/App/usr/mbedtls-config.cmake
    /usr/MbedTLSConfig.cmake
    /usr/mbedtls-config.cmake
    /opt/X11/MbedTLSConfig.cmake
    /opt/X11/mbedtls-config.cmake
    /Library/Apple/usr/MbedTLSConfig.cmake
    /Library/Apple/usr/mbedtls-config.cmake
    /usr/local/share/dotnet/MbedTLSConfig.cmake
    /usr/local/share/dotnet/mbedtls-config.cmake
    /Library/Frameworks/Mono.framework/Versions/Current/Commands/MbedTLSConfig.cmake
    /Library/Frameworks/Mono.framework/Versions/Current/Commands/mbedtls-config.cmake
    /Users/me/.cargo/MbedTLSConfig.cmake
    /Users/me/.cargo/mbedtls-config.cmake
    /Applications/Xcode-beta.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX15.0.sdk/usr/MbedTLSConfig.cmake
    /Applications/Xcode-beta.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX15.0.sdk/usr/mbedtls-config.cmake
    /opt/homebrew/Cellar/cmake/3.30.2/MbedTLSConfig.cmake
    /opt/homebrew/Cellar/cmake/3.30.2/mbedtls-config.cmake
    /opt/MbedTLSConfig.cmake
    /opt/mbedtls-config.cmake
    /opt/local/MbedTLSConfig.cmake
    /opt/local/mbedtls-config.cmake
    /Applications/Xcode-beta.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX15.0.sdk/System/Library/Frameworks/MbedTLSConfig.cmake
    /Applications/Xcode-beta.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX15.0.sdk/System/Library/Frameworks/mbedtls-config.cmake
    /Applications/Xcode-beta.app/Contents/Developer/Platforms/MacOSX.platform/Developer/Library/Frameworks/MbedTLSConfig.cmake
    /Applications/Xcode-beta.app/Contents/Developer/Platforms/MacOSX.platform/Developer/Library/Frameworks/mbedtls-config.cmake
    /Applications/Xcode-beta.app/Contents/Developer/Library/Frameworks/MbedTLSConfig.cmake
    /Applications/Xcode-beta.app/Contents/Developer/Library/Frameworks/mbedtls-config.cmake
    /Library/Frameworks/MbedTLSConfig.cmake
    /Library/Frameworks/mbedtls-config.cmake
    /System/Library/Frameworks/MbedTLSConfig.cmake
    /System/Library/Frameworks/mbedtls-config.cmake
    /Users/me/Applications/MbedTLSConfig.cmake
    /Users/me/Applications/mbedtls-config.cmake
    /Applications/MbedTLSConfig.cmake
    /Applications/mbedtls-config.cmake
    /Applications/Xcode-beta.app/Contents/Applications/MbedTLSConfig.cmake
    /Applications/Xcode-beta.app/Contents/Applications/mbedtls-config.cmake
    /Applications/Xcode-beta.app/Contents/Developer/Applications/MbedTLSConfig.cmake
    /Applications/Xcode-beta.app/Contents/Developer/Applications/mbedtls-config.cmake

  The file was not found.

  find_package considered the following paths for FindMbedTLS.cmake:

    /Users/me/code/cmaketest/obs-studio/cmake/common/FindMbedTLS.cmake
    /opt/homebrew/Cellar/cmake/3.30.2/share/cmake/Modules/FindMbedTLS.cmake

  The file was found at

    /Users/me/code/cmaketest/obs-studio/cmake/finders/FindMbedTLS.cmake

```

CMAKE\_IGNORE\_PREFIX\_PATH seems to be having some sort of effect, but many homebrew paths are still included, just shuffled around a bit.

Digging into the code a bit, I’m seeing some oddities. For example, FindConfig is called [here](https://gitlab.kitware.com/cmake/cmake/-/blob/master/Source/cmFindPackageCommand.cxx?ref_type=heads#L1475) for find\_package in config mode, but the subsequent call to ComputePrefixes [here](https://gitlab.kitware.com/cmake/cmake/-/blob/master/Source/cmFindPackageCommand.cxx?ref_type=heads#L1982) passes IgnorePaths::No, which seems to indicate that it’s not actually paying any attention at all to ignored prefixes.

Furthermore the actual call to FindConfigFile [here](https://gitlab.kitware.com/cmake/cmake/-/blob/master/Source/cmFindPackageCommand.cxx?ref_type=heads#L2455) is checking against IgnoredPaths explicitly, but not IgnoredPrefixPaths.

So overall in this call tree within find\_package, I’m a bit confused about where and how the ignored prefixes are actually supposed to be applied. I mean, clearly they are not fully being applied, which seems like a bug itself, but overall I’m just trying to understand why and how this is happening and what the intended behavior here is.