Add require function to support plugin dep

In order to support dependency between plugins a function called
`require` has been added.

init.fish

@@ -41,20 +41,20 @@ source $OMF_CONFIG/before.init.fish ^/dev/null
 set -l user_function_path $fish_function_path[1]
 set fish_function_path[1] $OMF_PATH/lib
 
-set -l theme {$OMF_PATH,$OMF_CONFIG}/themes/(cat $OMF_CONFIG/theme)
+# Autoload util functions
+autoload $OMF_PATH/lib $OMF_PATH/lib/git
 
-for path in $OMF_PATH/lib $OMF_PATH/lib/git {$OMF_PATH,$OMF_CONFIG}/pkg/* $theme
-  contains -- (basename $path) $OMF_IGNORE; and continue
+for path in {$OMF_PATH,$OMF_CONFIG}/pkg/*
+  set -l name (basename $path)
 
-  autoload $path $path/completions
-
-  if source $path/init.fish ^/dev/null
-  else
-    source $path/(basename $path).fish ^/dev/null;
-    #and echo "Plugin '"(basename $path)"' has a deprecated structure. Run `omf update`."
-  end; and emit init_(basename $path) $path
+  contains -- $name $OMF_IGNORE; and continue
+  require $name
 end
 
+# Autoload theme
+autoload {$OMF_PATH,$OMF_CONFIG}/themes/(cat $OMF_CONFIG/theme)
+
+# Autoload custom functions
 autoload $OMF_CONFIG/functions
 autoload $user_function_path
 

lib/autoload.fish

@@ -1,15 +1,20 @@
 # SYNOPSIS
-#   autoload <path [path...]>
+#   autoload <path>...
 #
 # OVERVIEW
 #   Autoload a function or completion path. Add the specified list of
 #   directories to $fish_function_path. Any `completions` directories
 #   are correctly added to the $fish_complete_path.
+#
+#   Returns 0 if one of the paths exist.
+#   Returns != 0 if all paths are missing.
 
 function autoload -d "autoload a function or completion path"
   for path in $argv
+    set -l dest fish_function_path
+
     if test -d "$path"
-      set -l dest fish_function_path
+      set path_exist
 
       if test (basename "$path") = completions
         set dest fish_complete_path
@@ -18,4 +23,6 @@ function autoload -d "autoload a function or completion path"
       contains "$path" $$dest; or set $dest "$path" $$dest
     end
   end
+
+  set -q path_exist
 end

lib/available.fish

@@ -2,8 +2,8 @@
 #   available [name]
 #
 # OVERVIEW
-#   Check if a program is available.
+#   Check if a function or program is available.
 
-function available -a program -d "check if a program is available."
-  type "$program" ^/dev/null >&2
+function available -a name -d "Check if a function or program is available."
+  type "$name" ^/dev/null >&2
 end

lib/require.fish

@@ -0,0 +1,26 @@
+# SYNOPSIS
+#   require [name]
+#
+# OVERVIEW
+#   Require a plugin:
+#     - Autoload its functions and completions.
+#     - Source its initialization file.
+#     - Emit its initialization event.
+#
+#   If the required plugin has already been loaded, does nothing.
+
+function require -a name
+  # Skip if plugin has already been loaded.
+  contains -- $OMF_PATH/pkg/$name $fish_function_path;
+    or contains -- $OMF_CONFIG/pkg/$name $fish_function_path;
+    and return 0
+
+  for path in {$OMF_PATH,$OMF_CONFIG}/pkg/$name
+    if autoload $path $path/completions
+
+      source $path/init.fish ^/dev/null;
+        or source $path/$name.fish ^/dev/null;
+        and emit init_$name $path
+    end
+  end
+end