Use set -p and set -a for setting fish paths

assets/default/fish/init.fish

@@ -1,7 +1,11 @@
-set -gx fish_function_path "$fish_synced_dir/functions" $fish_function_path
-set -gx fish_complete_path "$fish_synced_dir/completions" $fish_complete_path
+if not contains -- "$fish_synced_dir/functions" $fish_function_path
+    set -p fish_function_path "$fish_synced_dir/functions"
+end
+if not contains -- "$fish_synced_dir/completions" $fish_complete_path
+    set -p fish_complete_path "$fish_synced_dir/completions"
+end
 
-function source_synced --description "Sources file from synced dir as well as optional local file"
+function _source_synced --description "Sources file from synced dir as well as optional local file"
     # Sources a config file and corresponding local config file if it exists
     set -l shared_config "$fish_synced_dir/$argv[1].fish"
     set -l local_config "$fish_synced_dir/$argv[1].local.fish"
@@ -14,7 +18,7 @@ function source_synced --description "Sources file from synced dir as well as op
 end
 
 if status --is-interactive
-    source_synced 'init/alias'
+    _source_synced 'init/alias'
 end
-source_synced 'init/paths'
-source_synced 'init/env'
+_source_synced 'init/paths'
+_source_synced 'init/env'

assets/default/fish/init/paths.fish

@@ -1,5 +1,19 @@
-set det_os "unknown"
+function _maybe_set --description "Either appends or prepends to a variable if the file or directory exists and isn't already present"
+    # Replicate some of the `set` args
+    argparse 'a/append' 'p/prepend' 'x/export' 'g/global' -- $argv
+    if [ (count $argv) -ne 2 ]
+        echo "_maybe_set Requires exactly two arguments"
+        return 1
+    end
+    set -l var_name "$argv[1]"
+    set -l existing_val (eval 'echo $'(echo $var_name))
+    set -l new_value "$argv[2]"
+    if not contains -- "$new_value" "$existing_val" ;and test -e "$new_value"
+        set $_flag_append $_flag_prepend $_flag_export $_flag_global $var_name $new_value
+    end
+end
 
+set det_os "unknown"
 switch (uname)
     case "Darwin"
         set det_os "mac"
@@ -10,21 +24,18 @@ switch (uname)
 end
 
 # opt directory
-if [ -d /opt/local ]
-    set -gx PATH /opt/local/bin /opt/local/sbin $PATH
-end
-
-if [ $det_os = "linux" ]
-    set android_sdk $HOME/workspace/adt-bundle-linux/sdk
-else if [ $det_os = "mac" ]
-    set android_sdk $HOME/workspace/android-sdk-macosx
+_maybe_set -p PATH /opt/local/sbin
+_maybe_set -p PATH /opt/local/bin
 
+# Set python paths
+if [ $det_os = "mac" ]
     # Fix Python path on OSX to avoid considering System extras over newer versions
     # Local
-    set -gx PATH $HOME/Library/Python/3.7/bin $HOME/Library/Python/2.7/bin $PATH
+    _maybe_set -p PATH "$HOME/Library/Python/2.7/bin"
+    _maybe_set -p PATH "$HOME/Library/Python/3.7/bin"
     # set -gx PYTHONPATH $HOME/Library/Python/2.7/lib/python/site-packages:$PYTHONPATH
     # Macports
-    set -gx PATH $PATH /opt/local/Library/Frameworks/Python.framework/Versions/Current/bin
+    _maybe_set -a PATH /opt/local/Library/Frameworks/Python.framework/Versions/Current/bin
     # set -gx PYTHONPATH /opt/local/Library/Frameworks/Python.framework/Versions/Current/lib $PYTHONPATH
     # set -gx PYTHONPATH /opt/local/Library/Frameworks/Python.framework/Versions/Current/lib/python2.7/site-packages /Library/Python/2.7/site-packages $PYTHONPATH
 end
@@ -36,41 +47,33 @@ if type -q npm
         # It's more robust to use the subshell, but far slower
         set npm_path (npm bin -g 2> /dev/null)
     end
-    if [ -d "$npm_path" ]
-        set -gx PATH $PATH $npm_path
-    end
+    _maybe_set -a PATH "$npm_path"
 end
 
-# Add rust path
-if [ -d "$HOME/.cargo/bin" ]
-    set -gx PATH $HOME/.cargo/bin $PATH
-end
+# Add rust cargo path
+_maybe_set -p PATH "$HOME/.cargo/bin"
 
 # Golang paths
 set -gx GOPATH $HOME/workspace/go_path
-if [ -d "$GOPATH" ]
-    set -gx PATH $GOPATH/bin $PATH
-end
+_maybe_set -p PATH "$GOPATH/bin"
 
 # Android paths
-if [ -d "$android_sdk" ]
-    set -gx ANDROID_HOME $android_sdk
-    set -gx PATH $PATH $android_sdk/platform-tools $android_sdk/tools
+if [ $det_os = "linux" ]
+    set -gx ANDROID_HOME "$HOME/workspace/adt-bundle-linux/sdk"
+else if [ $det_os = "mac" ]
+    set -gx ANDROID_HOME "$HOME/workspace/android-sdk-macosx"
 end
+_maybe_set -a PATH "$ANDROID_PATH/platform-tools"
+_maybe_set -a PATH "$ANDROID_PATH/tools"
 
 # Ruby paths
 if type -q rbenv ; and status --is-interactive
-    set -gx PATH $PATH $HOME/.rbenv/shims
+    _maybe_set -a PATH "$HOME/.rbenv/shims"
 else if [ -d "$HOME/.rvm" ]
-    set -gx PATH $PATH $HOME/.rvm/bin
+    _maybe_set -a PATH "$HOME/.rvm/bin"
     source "$HOME/.rvm/scripts/extras/rvm.fish"
 end
 
-# Home paths
-if [ -d "$HOME/.local/bin" ]
-    set -gx PATH $HOME/.local/bin $PATH
-end
-
-if [ -d "$HOME/bin" ]
-    set -gx PATH $HOME/bin $PATH
-end
+# Home paths to take final precedent
+_maybe_set -p PATH "$HOME/.local/bin"
+_maybe_set -p PATH "$HOME/bin"