CMake: Simplify symlink creation and install translated man pages.

It helps that cmake_install.cmake doesn't parallelize installation
so symlinks can be created so that the target is always known to
exist (a requirement on Windows in some cases).

This bumps the minimum CMake version from 3.13 to 3.14 to use
file(CREATE_LINK ...). It could be made to work on 3.13 by
calling "cmake -E create_symlink" but it's uglier code and
slower in "make install". 3.14 should be a reasonable version
to require nowadays, especially since the Autotools build
is still the primary build system for most OSes.

CMakeLists.txt

@@ -42,7 +42,7 @@
 #############################################################################
 
 # NOTE: Translation support is disabled with CMake older than 3.20.
-cmake_minimum_required(VERSION 3.13...3.27 FATAL_ERROR)
+cmake_minimum_required(VERSION 3.14...3.27 FATAL_ERROR)
 
 include(CMakePushCheckState)
 include(CheckIncludeFile)
@@ -1256,6 +1256,73 @@ if(NOT MSVC)
 endif()
 
 
+#############################################################################
+# Helper functions for installing files
+#############################################################################
+
+# For each non-empty element in the list LINK_NAMES, creates symbolic links
+# ${LINK_NAME}${LINK_SUFFIX} -> ${TARGET_NAME} in the directory ${DIR}.
+# The target file should exist because on Cygwin and MSYS2 symlink creation
+# can fail under certain conditions if the target doesn't exist.
+function(my_install_symlinks COMPONENT DIR TARGET_NAME LINK_SUFFIX LINK_NAMES)
+    install(CODE "set(D \"\$ENV{DESTDIR}\${CMAKE_INSTALL_PREFIX}/${DIR}\")
+                 foreach(L ${LINK_NAMES})
+                     file(CREATE_LINK \"${TARGET_NAME}\"
+                                      \"\${D}/\${L}${LINK_SUFFIX}\"
+                                      SYMBOLIC)
+                 endforeach()"
+            COMPONENT "${COMPONENT}")
+endfunction()
+
+# Installs a man page file of a given language ("" for the untranslated file)
+# and optionally its alternative names as symlinks. This is a helper function
+# for my_install_man() below.
+function(my_install_man_lang COMPONENT SRC_FILE MAN_LANG LINK_NAMES)
+    # Get the man page section from the filename suffix.
+    string(REGEX REPLACE "^.*\.([^/.]+)$" "\\1" MAN_SECTION "${SRC_FILE}")
+
+    # A few man pages might be missing from translations.
+    # Don't attempt to install them or create the related symlinks.
+    if(NOT MAN_LANG STREQUAL "" AND NOT EXISTS "${SRC_FILE}")
+        return()
+    endif()
+
+    # Installing the file must be done before creating the symlinks
+    # due to Cygwin and MSYS2.
+    install(FILES "${SRC_FILE}"
+            DESTINATION "${CMAKE_INSTALL_MANDIR}/${MAN_LANG}/man${MAN_SECTION}"
+            COMPONENT "${COMPONENT}")
+
+    # Get the basename of the file to be used as the symlink target.
+    get_filename_component(BASENAME "${SRC_FILE}" NAME)
+
+    # LINK_NAMES don't contain the man page filename suffix (like ".1")
+    # so it needs to be told to my_install_symlinks.
+    my_install_symlinks("${COMPONENT}"
+                        "${CMAKE_INSTALL_MANDIR}/${MAN_LANG}/man${MAN_SECTION}"
+                        "${BASENAME}" ".${MAN_SECTION}" "${LINK_NAMES}")
+endfunction()
+
+# Installs a man page file and optionally its alternative names as symlinks.
+# Does the same for translations if ENABLE_NLS.
+function(my_install_man COMPONENT SRC_FILE LINK_NAMES)
+    my_install_man_lang("${COMPONENT}" "${SRC_FILE}" "" "${LINK_NAMES}")
+
+    if(ENABLE_NLS)
+        # Find the translated versions of this man page.
+        get_filename_component(BASENAME "${SRC_FILE}" NAME)
+        file(GLOB MAN_FILES "po4a/man/*/${BASENAME}")
+
+        foreach(F ${MAN_FILES})
+            get_filename_component(MAN_LANG "${F}" DIRECTORY)
+            get_filename_component(MAN_LANG "${MAN_LANG}" NAME)
+            my_install_man_lang("${COMPONENT}" "${F}" "${MAN_LANG}"
+                                "${LINK_NAMES}")
+        endforeach()
+    endif()
+endfunction()
+
+
 #############################################################################
 # libgnu (getopt_long)
 #############################################################################
@@ -1364,9 +1431,7 @@ if(HAVE_DECODERS AND (NOT MSVC OR MSVC_VERSION GREATER_EQUAL 1900))
                     COMPONENT xzdec)
 
     if(UNIX)
-        install(FILES src/xzdec/xzdec.1
+        my_install_man(xzdec src/xzdec/xzdec.1 "")
-                DESTINATION "${CMAKE_INSTALL_MANDIR}/man1"
-                COMPONENT xzdec)
     endif()
 endif()
 
@@ -1553,15 +1618,28 @@ if(NOT MSVC OR MSVC_VERSION GREATER_EQUAL 1900)
         endforeach()
     endif()
 
+    # This command must be before the symlink creation to keep things working
+    # on Cygwin and MSYS2 in all cases.
+    #
+    #   - Cygwin can encode symlinks in multiple ways. This can be
+    #     controlled via the environment variable "CYGWIN". If it contains
+    #     "winsymlinks:nativestrict" then symlink creation will fail if
+    #     the link target doesn't exist. This mode isn't the default though.
+    #     See: https://cygwin.com/faq.html#faq.api.symlinks
+    #
+    #   - MSYS2 supports the same winsymlinks option in the environment
+    #     variable "MSYS" (not "MSYS2). The default in MSYS2 is to make
+    #     a copy of the file instead of any kind of symlink. Thus the link
+    #     target must exist or the creation of the "symlink" (copy) will fail.
+    #
+    # Our installation order must be such that when a symbolic link is created
+    # its target must already exists. There is no race condition for parallel
+    # builds because the generated cmake_install.cmake executes serially.
     install(TARGETS xz
             RUNTIME DESTINATION "${CMAKE_INSTALL_BINDIR}"
                     COMPONENT xz)
 
     if(UNIX)
-        install(FILES src/xz/xz.1
-                DESTINATION "${CMAKE_INSTALL_MANDIR}/man1"
-                COMPONENT xz)
-
         option(CREATE_XZ_SYMLINKS "Create unxz and xzcat symlinks" ON)
         option(CREATE_LZMA_SYMLINKS "Create lzma, unlzma, and lzcat symlinks"
                ON)
@@ -1575,96 +1653,19 @@ if(NOT MSVC OR MSVC_VERSION GREATER_EQUAL 1900)
             list(APPEND XZ_LINKS "lzma" "unlzma" "lzcat")
         endif()
 
-        # With Windows Cygwin and MSYS2 the symlinking is complicated. Both
+        # On Cygwin, don't add the .exe suffix to the symlinks.
-        # of these environments set the UNIX variable so they will try to
-        # make the symlinks. The ability for Cygwin and MSYS2 to make
-        # broken symlinks is determined by the CYGWIN and MSYS2 environment
-        # variables, respectively. Broken symlinks are needed for the man
-        # page symlinks and for determining if the xz and lzma symlinks need
-        # to depend on the xz target or not. If broken symlinks cannot be
-        # made then the xz binary must be created before the symlinks.
-        set(ALLOW_BROKEN_SYMLINKS ON)
-
-        if(CMAKE_SYSTEM_NAME STREQUAL "CYGWIN")
-            # The Cygwin env variable can be set to four possible values:
-            #
-            # 1. "lnk". Create symlinks as Windows shortcuts.
-            #
-            # 2. "native". Create symlinks as native Windows symlinks
-            #    if supported by the system. Fallback to "lnk" if native
-            #    symlinks are not supported.
-            #
-            # 3. "nativestrict". Create symlinks as native Windows symlinks
-            #    if supported by the system. If the target of the symlink
-            #    does not exist or the creation of the symlink fails for any
-            #    reason, do not create the symlink.
-            #
-            # 4. "sys". Create symlinks as plain files with a special
-            #    system attribute containing the path to the symlink target.
-            #
-            # So, the only case we care about for broken symlinks is
-            # "nativestrict" since all other values mean that broken
-            # symlinks are allowed. If the env variable is not set the
-            # default is "native". If the env variable is set but not
-            # assigned one of the four values, then the default is the same
-            # as option 1 "lnk".
-            string(FIND "$ENV{CYGWIN}" "winsymlinks:nativestrict" SYMLINK_POS)
-            if(SYMLINK_POS GREATER -1)
-                set(ALLOW_BROKEN_SYMLINKS OFF)
-            endif()
-        elseif(CMAKE_SYSTEM_NAME STREQUAL "MSYS")
-            # The MSYS env variable behaves similar to the CYGWIN but has a
-            # different default behavior. If winsymlinks is set but not
-            # assigned one of the four supported values, the default is to
-            # *copy* the target to the symlink destination. This will fail
-            # if the target does not exist so broken symlinks cannot be
-            # allowed.
-            string(FIND "$ENV{MSYS}" "winsymlinks" SYMLINK_POS)
-            if(SYMLINK_POS GREATER -1)
-                string(FIND "$ENV{MSYS}" "winsymlinks:nativestrict"
-                        SYMLINK_POS)
-                if(SYMLINK_POS GREATER -1)
-                    set(ALLOW_BROKEN_SYMLINKS OFF)
-                endif()
-            else()
-                set(ALLOW_BROKEN_SYMLINKS OFF)
-            endif()
-        endif()
-
-        # Create symlinks in the build directory and then install them.
         #
-        # The symlinks do not likely need any special extension since
+        # FIXME? Does this make sense on MSYS & MSYS2 where "ln -s"
-        # even on Windows the symlink can still be executed without
+        # by default makes copies? Inside MSYS & MSYS2 it is possible
-        # the .exe extension.
+        # to execute files without the .exe suffix but not outside
-        foreach(LINK IN LISTS XZ_LINKS)
+        # (like in Command Prompt). Omitting the suffix matches
-            add_custom_target("create_${LINK}" ALL
+        # what configure.ac has done for many years though.
-                "${CMAKE_COMMAND}" -E create_symlink
+        my_install_symlinks(xz "${CMAKE_INSTALL_BINDIR}"
-                    "$<TARGET_FILE_NAME:xz>" "${LINK}"
+                            "xz${CMAKE_EXECUTABLE_SUFFIX}" "" "${XZ_LINKS}")
-                BYPRODUCTS "${LINK}"
-                VERBATIM)
-            install(FILES "${CMAKE_CURRENT_BINARY_DIR}/${LINK}"
-                    DESTINATION "${CMAKE_INSTALL_BINDIR}"
-                    COMPONENT xz)
 
-            # Only create the man page symlinks if the symlinks can be
+        # Install the man pages and (optionally) their symlinks
-            # created broken. The symlinks will not be valid until install
+        # and translations.
-            # so they cannot be created on these system environments.
+        my_install_man(xz src/xz/xz.1 "${XZ_LINKS}")
-            if(ALLOW_BROKEN_SYMLINKS)
-                add_custom_target("create_${LINK}.1" ALL
-                    "${CMAKE_COMMAND}" -E create_symlink "xz.1" "${LINK}.1"
-                    BYPRODUCTS "${LINK}.1"
-                    VERBATIM)
-                install(FILES "${CMAKE_CURRENT_BINARY_DIR}/${LINK}.1"
-                        DESTINATION "${CMAKE_INSTALL_MANDIR}/man1"
-                        COMPONENT xz)
-            else()
-                # Add the xz target as dependency when broken symlinks
-                # cannot be made. This ensures parallel builds do not fail
-                # since it will enforce the order of creating xz first, then
-                # the symlinks.
-                add_dependencies("create_${LINK}" xz)
-            endif()
-        endforeach()
     endif()
 endif()