GNUInstallDirs: Add macro to expose internal logic publicly

Help/release/dev/GNUInstallDirs-function.rst

@@ -0,0 +1,5 @@
+GNUInstallDirs-function
+-----------------------
+
+* The :module:`GNUInstallDirs` module gained a new
+  :command:`GNUInstallDirs_get_absolute_install_dir` command.

Modules/GNUInstallDirs.cmake

@@ -99,6 +99,23 @@
 #   `Filesystem Hierarchy Standard`_.
 #
 # .. _`Filesystem Hierarchy Standard`: https://refspecs.linuxfoundation.org/FHS_3.0/fhs/index.html
+#
+# Macros
+# ^^^^^^
+#
+# .. command:: GNUInstallDirs_get_absolute_install_dir
+#
+#   ::
+#
+#     GNUInstallDirs_get_absolute_install_dir(absvar var)
+#
+#   Set the given variable ``absvar`` to the absolute path contained
+#   within the variable ``var``.  This is to allow the computation of an
+#   absolute path, accounting for all the special cases documented
+#   above.  While this macro is used to compute the various
+#   ``CMAKE_INSTALL_FULL_<dir>`` variables, it is exposed publicly to
+#   allow users who create additional path variables to also compute
+#   absolute paths where necessary, using the same logic.
 
 #=============================================================================
 # Copyright 2015 Alex Turbov <[email protected]>
@@ -300,55 +317,59 @@ mark_as_advanced(
   CMAKE_INSTALL_DOCDIR
   )
 
-# Result directories
-#
-foreach(dir
-    BINDIR
-    SBINDIR
-    LIBEXECDIR
-    SYSCONFDIR
-    SHAREDSTATEDIR
-    LOCALSTATEDIR
-    LIBDIR
-    INCLUDEDIR
-    OLDINCLUDEDIR
-    DATAROOTDIR
-    DATADIR
-    INFODIR
-    LOCALEDIR
-    MANDIR
-    DOCDIR
-    )
-  if(NOT IS_ABSOLUTE "${CMAKE_INSTALL_${dir}}")
+macro(GNUInstallDirs_get_absolute_install_dir absvar var)
+  if(NOT IS_ABSOLUTE "${${var}}")
     # Handle special cases:
     # - CMAKE_INSTALL_PREFIX == /
     # - CMAKE_INSTALL_PREFIX == /usr
     # - CMAKE_INSTALL_PREFIX == /opt/...
     if("${CMAKE_INSTALL_PREFIX}" STREQUAL "/")
       if("${dir}" STREQUAL "SYSCONFDIR" OR "${dir}" STREQUAL "LOCALSTATEDIR")
-        set(CMAKE_INSTALL_FULL_${dir} "/${CMAKE_INSTALL_${dir}}")
+        set(${absvar} "/${${var}}")
       else()
-        if (NOT "${CMAKE_INSTALL_${dir}}" MATCHES "^usr/")
-          set(CMAKE_INSTALL_${dir} "usr/${CMAKE_INSTALL_${dir}}")
+        if (NOT "${${var}}" MATCHES "^usr/")
+          set(${var} "usr/${${var}}")
         endif()
-        set(CMAKE_INSTALL_FULL_${dir} "/${CMAKE_INSTALL_${dir}}")
+        set(${absvar} "/${${var}}")
       endif()
     elseif("${CMAKE_INSTALL_PREFIX}" MATCHES "^/usr/?$")
       if("${dir}" STREQUAL "SYSCONFDIR" OR "${dir}" STREQUAL "LOCALSTATEDIR")
-        set(CMAKE_INSTALL_FULL_${dir} "/${CMAKE_INSTALL_${dir}}")
+        set(${absvar} "/${${var}}")
       else()
-        set(CMAKE_INSTALL_FULL_${dir} "${CMAKE_INSTALL_PREFIX}/${CMAKE_INSTALL_${dir}}")
+        set(${absvar} "${CMAKE_INSTALL_PREFIX}/${${var}}")
       endif()
     elseif("${CMAKE_INSTALL_PREFIX}" MATCHES "^/opt/.*")
       if("${dir}" STREQUAL "SYSCONFDIR" OR "${dir}" STREQUAL "LOCALSTATEDIR")
-        set(CMAKE_INSTALL_FULL_${dir} "/${CMAKE_INSTALL_${dir}}${CMAKE_INSTALL_PREFIX}")
+        set(${absvar} "/${${var}}${CMAKE_INSTALL_PREFIX}")
       else()
-        set(CMAKE_INSTALL_FULL_${dir} "${CMAKE_INSTALL_PREFIX}/${CMAKE_INSTALL_${dir}}")
+        set(${absvar} "${CMAKE_INSTALL_PREFIX}/${${var}}")
       endif()
     else()
-      set(CMAKE_INSTALL_FULL_${dir} "${CMAKE_INSTALL_PREFIX}/${CMAKE_INSTALL_${dir}}")
+      set(${absvar} "${CMAKE_INSTALL_PREFIX}/${${var}}")
     endif()
   else()
-    set(CMAKE_INSTALL_FULL_${dir} "${CMAKE_INSTALL_${dir}}")
+    set(${absvar} "${${var}}")
   endif()
+endmacro()
+
+# Result directories
+#
+foreach(dir
+    BINDIR
+    SBINDIR
+    LIBEXECDIR
+    SYSCONFDIR
+    SHAREDSTATEDIR
+    LOCALSTATEDIR
+    LIBDIR
+    INCLUDEDIR
+    OLDINCLUDEDIR
+    DATAROOTDIR
+    DATADIR
+    INFODIR
+    LOCALEDIR
+    MANDIR
+    DOCDIR
+    )
+  GNUInstallDirs_get_absolute_install_dir(CMAKE_INSTALL_FULL_${dir} CMAKE_INSTALL_${dir})
 endforeach()