Load vendor configuration directories outside prefix

Vendor configuration provided by third party packages is sourced first
from $EXTRA_VENDOR_PATH/vendor_* and $PREFIX/share/fish/vendor_*
instead of only the latter.  The default for $EXTRA_VENDOR_PATH is
/usr/local/share/fish:/usr/share/fish, which enables fish to source
third party configuration from packages installed there, even if fish is
installed with a different prefix. The directories in $EXTRA_VENDOR_PATH
will not be created by (installing) fish.

In particular, with this change
/usr/bin/fish also uses /usr/local/share/fish/vendor_completions.d, and
/usr/local/bin/fish also uses /usr/share/fish/vendor_completions.d

Fixes fish-shell#5029

CHANGELOG.md

@@ -146,6 +146,7 @@
 - The `INTERNAL_WCWIDTH` build option has been removed, as fish now always uses an internal `wcwidth` function. It has a number of configuration options that make it more suitable for general use (#5777).
 - mandoc can now be used to format the output from `--help` if `nroff` is not installed, reducing the number of external dependencies on systems with `mandoc` installed (#5489).
 - Some bugs preventing building on Solaris-derived systems such as Illumos were fixed (#5458, #5461, #5611).
+- Vendored configuration like completions and functions are sourced first from `{/usr/local,/usr}/share/fish/vendor_{completions,conf,functions}.d` and second from `$PREFIX/share/fish/vendor_{completions,conf,functions}.d` . Previously, only the latter was used. The former paths can be customized using the CMake variable `EXTRA_VENDOR_PATH`; set it to an empty string to restore the old behavior (#5029).
 
 ---
 

cmake/Install.cmake

@@ -16,6 +16,10 @@ SET(mandir ${CMAKE_INSTALL_MANDIR})
 
 SET(rel_datadir ${CMAKE_INSTALL_DATADIR})
 SET(datadir ${CMAKE_INSTALL_FULL_DATADIR})
+SET(EXTRA_VENDOR_PATH "/usr/local/share/fish:/usr/share/fish" CACHE PATH
+"Additional prefix to look for third-party completions, configuration and \
+functions. This directory is usually not managed by a package manager, \
+this is to support locally installed software.")
 
 SET(docdir ${CMAKE_INSTALL_DOCDIR})
 
@@ -30,7 +34,7 @@ SET(extra_completionsdir
 
 SET(extra_functionsdir
     ${datadir}/fish/vendor_functions.d
-    CACHE STRING "Path for extra completions")
+    CACHE STRING "Path for extra functions")
 
 SET(extra_confdir
     ${datadir}/fish/vendor_conf.d

share/__fish_build_paths.fish.in

@@ -3,6 +3,4 @@
 # the local "vendor" completions, functions and configuration conf.
 # It is sourced by share/config.fish, if it exists.
 
-set __extra_completionsdir @extra_completionsdir@
-set __extra_functionsdir @extra_functionsdir@
-set __extra_confdir @extra_confdir@
+set __EXTRA_VENDOR_PATH @EXTRA_VENDOR_PATH@

share/config.fish

@@ -47,26 +47,29 @@ end
 # __fish_data_dir, __fish_sysconf_dir, __fish_help_dir, __fish_bin_dir
 # are expected to have been set up by read_init from fish.cpp
 
+set -l __EXTRA_VENDOR_PATH
 # Grab extra directories (as specified by the build process, usually for
 # third-party packages to ship completions &c.
-set -l __extra_completionsdir
-set -l __extra_functionsdir
-set -l __extra_confdir
 if test -f $__fish_data_dir/__fish_build_paths.fish
     source $__fish_data_dir/__fish_build_paths.fish
 end
 
 # Set up function and completion paths. Make sure that the fish
 # default functions/completions are included in the respective path.
 
+set -l vendor_data_dirs $__EXTRA_VENDOR_PATH
+if not contains -- $__fish_data_dir $vendor_data_dirs # Ensure that $PREFIX/share/fish/vendor_* is included.
+    set -a vendor_data_dirs $__fish_data_dir
+end
+
 if not set -q fish_function_path
-    set fish_function_path $__fish_config_dir/functions $__fish_sysconf_dir/functions $__extra_functionsdir $__fish_data_dir/functions
+    set fish_function_path $__fish_config_dir/functions $__fish_sysconf_dir/functions $vendor_data_dirs/vendor_functions.d $__fish_data_dir/functions
 else if not contains -- $__fish_data_dir/functions $fish_function_path
     set -a fish_function_path $__fish_data_dir/functions
 end
 
 if not set -q fish_complete_path
-    set fish_complete_path $__fish_config_dir/completions $__fish_sysconf_dir/completions $__extra_completionsdir $__fish_data_dir/completions $__fish_user_data_dir/generated_completions
+    set fish_complete_path $__fish_config_dir/completions $__fish_sysconf_dir/completions $vendor_data_dirs/vendor_completions.d $__fish_data_dir/completions $__fish_user_data_dir/generated_completions
 else if not contains -- $__fish_data_dir/completions $fish_complete_path
     set -a fish_complete_path $__fish_data_dir/completions
 end
@@ -249,7 +252,7 @@ end
 # As last part of initialization, source the conf directories.
 # Implement precedence (User > Admin > Extra (e.g. vendors) > Fish) by basically doing "basename".
 set -l sourcelist
-for file in $__fish_config_dir/conf.d/*.fish $__fish_sysconf_dir/conf.d/*.fish $__extra_confdir/*.fish
+for file in $__fish_config_dir/conf.d/*.fish $__fish_sysconf_dir/conf.d/*.fish $vendor_data_dirs/vendor_conf.d/*.fish
     set -l basename (string replace -r '^.*/' '' -- $file)
     contains -- $basename $sourcelist
     and continue