CMake: use GNUInstallDirs to define installation locations.

Same change as in Corrade, additionally reflected also inside
FindMagnum.cmake for reuse by depending projects. Besides moving closer
to the "standard" way of doing things, using this module allows me to
drop the custom logic around LIB_SUFFIX, as the /usr/lib vs /usr/lib64
etc. distinction is now handled by GNUInstallDirs along with any other
variants.

CMakeLists.txt

@@ -682,14 +682,23 @@ if(CORRADE_TARGET_EMSCRIPTEN AND NOT PROJECT_SOURCE_DIR STREQUAL CMAKE_SOURCE_DI
 endif()
 
 # Installation paths
-include(${CORRADE_LIB_SUFFIX_MODULE})
-set(MAGNUM_BINARY_INSTALL_DIR bin)
-set(MAGNUM_LIBRARY_INSTALL_DIR lib${LIB_SUFFIX})
-set(MAGNUM_DATA_INSTALL_DIR share/magnum)
-set(MAGNUM_CMAKE_MODULE_INSTALL_DIR share/cmake/Magnum)
-set(MAGNUM_INCLUDE_INSTALL_DIR include/Magnum)
-set(MAGNUM_EXTERNAL_INCLUDE_INSTALL_DIR include/MagnumExternal)
-set(MAGNUM_PLUGINS_INCLUDE_INSTALL_DIR include/MagnumPlugins)
+include(GNUInstallDirs)
+# On Android, if we're using CMake's builtin support and not the NDK  toolchain
+# (i.e., with CMAKE_ANDROID_ARCH_TRIPLE defined), point CMAKE_INSTALL_LIBDIR to
+# a subdirectory based on the target. If the subdirectory doesn't exist, don't
+# adjust anything -- in that case the  assumption is that it's being installed
+# in some other place that doesn't match the NDK layout.
+# TODO could GNUInstallDirs do this on their own? Ugh...
+if(CORRADE_TARGET_ANDROID AND CMAKE_ANDROID_ARCH_TRIPLE AND EXISTS "${CMAKE_INSTALL_PREFIX}/${CMAKE_INSTALL_LIBDIR}/${CMAKE_ANDROID_ARCH_TRIPLE}/${CMAKE_SYSTEM_VERSION}")
+    set(CMAKE_INSTALL_LIBDIR "${CMAKE_INSTALL_LIBDIR}/${CMAKE_ANDROID_ARCH_TRIPLE}/${CMAKE_SYSTEM_VERSION}")
+endif()
+set(MAGNUM_BINARY_INSTALL_DIR ${CMAKE_INSTALL_BINDIR})
+set(MAGNUM_LIBRARY_INSTALL_DIR ${CMAKE_INSTALL_LIBDIR})
+set(MAGNUM_DATA_INSTALL_DIR ${CMAKE_INSTALL_DATADIR}/magnum)
+set(MAGNUM_CMAKE_MODULE_INSTALL_DIR ${CMAKE_INSTALL_DATADIR}/cmake/Magnum)
+set(MAGNUM_INCLUDE_INSTALL_DIR ${CMAKE_INSTALL_INCLUDEDIR}/Magnum)
+set(MAGNUM_EXTERNAL_INCLUDE_INSTALL_DIR ${CMAKE_INSTALL_INCLUDEDIR}/MagnumExternal)
+set(MAGNUM_PLUGINS_INCLUDE_INSTALL_DIR ${CMAKE_INSTALL_INCLUDEDIR}/MagnumPlugins)
 if(MAGNUM_BUILD_DEPRECATED AND MAGNUM_INCLUDE_INSTALL_PREFIX AND NOT MAGNUM_INCLUDE_INSTALL_PREFIX STREQUAL ".")
     message(DEPRECATION "MAGNUM_INCLUDE_INSTALL_PREFIX is obsolete as its primary use was for old Android NDK versions. Please switch to the NDK r19+ layout instead of using this variable and recreate your build directory to get rid of this warning.")
     set(MAGNUM_DATA_INSTALL_DIR ${MAGNUM_INCLUDE_INSTALL_PREFIX}/${MAGNUM_DATA_INSTALL_DIR})

doc/building.dox

@@ -815,15 +815,15 @@ semi-automatically when using Magnum in depending projects, see @ref cmake for
 more information.
 
 Particular platforms have additional requirements when it comes to location of
-installed files. The following variables are supported:
-
--   `LIB_SUFFIX` --- Setting this variable to `64` can be used to tell CMake to
-    install to `lib64/` instead of `lib/`. In most cases this variable is
-    autodetected, so you don't need to set it yourself. On
-    @ref CORRADE_TARGET_ANDROID "Android", if `CMAKE_INSTALL_PREFIX` points to
-    the NDK sysroot, it gets automatically set to
-    `/${CMAKE_ANDROID_ARCH_TRIPLE}/${CMAKE_SYSTEM_VERSION}` to put the binaries
-    to correct location for given architecture and API level version.
+installed files. The following special cases are recognized:
+
+-   On @ref CORRADE_TARGET_ANDROID "Android", if `CMAKE_INSTALL_PREFIX` points
+    to the NDK sysroot, `CMAKE_INSTALL_LIBDIR` gets adjusted to point to a
+    `${CMAKE_ANDROID_ARCH_TRIPLE}/${CMAKE_SYSTEM_VERSION}` subdir to put the
+    binaries to correct location for given architecture and API level version.
+
+The following variables are supported:
+
 -   `MAGNUM_DEPLOY_PREFIX` --- Used on @ref CORRADE_TARGET_EMSCRIPTEN "Emscripten"
     to override location where web demos and utilities (such as @ref magnum-gl-info)
     are installed, so you can have libraries installed to a system location and
@@ -1202,12 +1202,13 @@ manually loading all depending shared libraries using JNI would be too
 inconvenient. The engine is built for OpenGL ES 2.0 by default, switch to 3.0
 by disabling `MAGNUM_TARGET_GLES2`.
 
-If you set `CMAKE_INSTALL_PREFIX` to `/usr` subdirectory of the particular
-Android platform sysroot (as shown below), Magnum's buildsystem will also pick
-a `LIB_SUFFIX` corresponding to a particular ABI and version, which in turn
-makes the package automatically discoverable when compiling depending projects,
-both with vanilla CMake and with Gradle. Another option is to explicitly set
-`CMAKE_PREFIX_PATH` to the install location in depending projects.
+If you set `CMAKE_INSTALL_PREFIX` to the `/usr` subdirectory of the particular
+Android platform sysroot (as shown below), Magnum's buildsystem will also
+adjust `CMAKE_INSTALL_LIBDIR` to a subdirectory corresponding to a particular
+ABI and version, which in turn makes the package automatically discoverable
+when compiling depending projects, both with vanilla CMake and with Gradle.
+Another option is to explicitly set `CMAKE_PREFIX_PATH` to the install location
+in depending projects.
 
 <b></b>
 

doc/changelog.dox

@@ -1167,11 +1167,12 @@ See also:
     subproject. See the @ref Platform-Sdl2Application-usage "Platform::Sdl2Application docs"
     for more information. See also [mosra/magnum#496](https://github.com/mosra/magnum/issues/496).
 -   With CMake 3.20 and newer it's possible to compile for Android NDK r19+
-    without explicitly supplying various system paths. Additionally, when `CMAKE_INSTALL_PREFIX` points to Android NDK sysroot, the `LIB_SUFFIX`
-    gets autodetected to a correct triplet + API level version subdirectory,
-    making the installed project discoverable by both vanilla CMake and Gradle.
-    On CMake 3.16 to 3.19 it's required to set two extra variables for the
-    same effect. See @ref building-cross-android, @ref platforms-android and
+    without explicitly supplying various system paths. Additionally, when
+    `CMAKE_INSTALL_PREFIX` points to Android NDK sysroot, `CMAKE_INSTALL_LIBDIR`
+    gets adjusted to a correct triplet + API level version subdirectory, making
+    the installed project discoverable by both vanilla CMake and Gradle. On
+    CMake 3.16 to 3.19 it's required to set two extra variables for the same
+    effect. See @ref building-cross-android, @ref platforms-android and
     [mosra/magnum#310](https://github.com/mosra/magnum/issues/310) for more
     information.
 -   Suppressing a CMake policy-related warning if the global `CMAKE_AUTOMOC` is
@@ -1270,6 +1271,9 @@ See also:
 -   Undefining the `near` and `far` macros on Windows in a more robust way
     (see [mosra/magnum#689](https://github.com/mosra/magnum/issues/689) and
     [mosra/magnum#690](https://github.com/mosra/magnum/pull/690))
+-   The buildsystem now uses CMake's `GNUInstallDirs` module for a standardized
+    way to specify installation location of binaries, libraries, include files
+    and other data (see [mosra/magnum#696](https://github.com/mosra/magnum/issues/696))
 
 @subsection changelog-latest-bugfixes Bug fixes
 

modules/FindMagnum.cmake

@@ -1340,13 +1340,22 @@ endif()
 set(MAGNUM_DEPLOY_PREFIX "."
     CACHE STRING "Prefix where to put final application executables")
 
-include(${CORRADE_LIB_SUFFIX_MODULE})
-set(MAGNUM_BINARY_INSTALL_DIR bin)
-set(MAGNUM_LIBRARY_INSTALL_DIR lib${LIB_SUFFIX})
-set(MAGNUM_DATA_INSTALL_DIR share/magnum)
-set(MAGNUM_INCLUDE_INSTALL_DIR include/Magnum)
-set(MAGNUM_EXTERNAL_INCLUDE_INSTALL_DIR include/MagnumExternal)
-set(MAGNUM_PLUGINS_INCLUDE_INSTALL_DIR include/MagnumPlugins)
+include(GNUInstallDirs)
+# On Android, if we're using CMake's builtin support and not the NDK  toolchain
+# (i.e., with CMAKE_ANDROID_ARCH_TRIPLE defined), point CMAKE_INSTALL_LIBDIR to
+# a subdirectory based on the target. If the subdirectory doesn't exist, don't
+# adjust anything -- in that case the  assumption is that it's being installed
+# in some other place that doesn't match the NDK layout.
+# TODO could GNUInstallDirs do this on their own? Ugh...
+if(CORRADE_TARGET_ANDROID AND CMAKE_ANDROID_ARCH_TRIPLE AND EXISTS "${CMAKE_INSTALL_PREFIX}/${CMAKE_INSTALL_LIBDIR}/${CMAKE_ANDROID_ARCH_TRIPLE}/${CMAKE_SYSTEM_VERSION}")
+    set(CMAKE_INSTALL_LIBDIR "${CMAKE_INSTALL_LIBDIR}/${CMAKE_ANDROID_ARCH_TRIPLE}/${CMAKE_SYSTEM_VERSION}")
+endif()
+set(MAGNUM_BINARY_INSTALL_DIR ${CMAKE_INSTALL_BINDIR})
+set(MAGNUM_LIBRARY_INSTALL_DIR ${CMAKE_INSTALL_LIBDIR})
+set(MAGNUM_DATA_INSTALL_DIR ${CMAKE_INSTALL_DATADIR}/magnum)
+set(MAGNUM_INCLUDE_INSTALL_DIR ${CMAKE_INSTALL_INCLUDEDIR}/Magnum)
+set(MAGNUM_EXTERNAL_INCLUDE_INSTALL_DIR ${CMAKE_INSTALL_INCLUDEDIR}/MagnumExternal)
+set(MAGNUM_PLUGINS_INCLUDE_INSTALL_DIR ${CMAKE_INSTALL_INCLUDEDIR}/MagnumPlugins)
 if(MAGNUM_BUILD_DEPRECATED AND MAGNUM_INCLUDE_INSTALL_PREFIX AND NOT MAGNUM_INCLUDE_INSTALL_PREFIX STREQUAL ".")
     message(DEPRECATION "MAGNUM_INCLUDE_INSTALL_PREFIX is obsolete as its primary use was for old Android NDK versions. Please switch to the NDK r19+ layout instead of using this variable and recreate your build directory to get rid of this warning.")
     set(MAGNUM_DATA_INSTALL_DIR ${MAGNUM_INCLUDE_INSTALL_PREFIX}/${MAGNUM_DATA_INSTALL_DIR})