Export user-defined FORGIT variables for backwards compatibility

Before forgit became a standalone script, users defined their FORGIT
variables (e.g. FORGIT_FZF_DEFAULT_OPTS) in the shell environment before
sourcing the forgit shell plugin. This worked because the forgit code
was executed within the currently running shell.
With forgit being an executable script, these variables are only
available to forgit when being exported. This patch adds an automatism
for this so that users do not have to change their configuration.
A warning is issued in this case so that users get notified to update
their configuration.

conf.d/forgit.plugin.fish

@@ -1,7 +1,26 @@
 # MIT (c) Chris Apple
 
-set -g FORGIT_INSTALL_DIR (dirname (dirname (status -f)))
-set -g FORGIT "$FORGIT_INSTALL_DIR/conf.d/bin/git-forgit"
+set INSTALL_DIR (dirname (dirname (status -f)))
+set FORGIT "$INSTALL_DIR/conf.d/bin/git-forgit"
+
+function forgit::warn
+    printf "%b[Warn]%b %s\n" '\e[0;33m' '\e[0m' "$argv" >&2;
+end
+
+# backwards compatibility:
+# export all user-defined FORGIT variables to make them available in git-forgit
+set unexported_vars 0
+set | awk -F ' ' '{ print $1 }' | grep FORGIT_ | while read var
+    if ! set -x | grep -q "^$var "
+        if test $unexported_vars = 0
+            forgit::warn "Config options have to be exported in future versions of forgit."
+            forgit::warn "Please update your config accordingly:"
+        end
+        forgit::warn "  set -x $var \"$$var\""
+        set unexported_vars (math $unexported_vars + 1)
+        set -x $var $$var
+    end
+end
 
 function forgit::log -d "git commit viewer"
     "$FORGIT" log $argv

forgit.plugin.zsh

@@ -2,20 +2,37 @@
 # MIT (c) Wenxuan Zhang
 
 forgit::error() { printf "%b[Error]%b %s\n" '\e[0;31m' '\e[0m' "$@" >&2; return 1; }
+forgit::warn() { printf "%b[Warn]%b %s\n" '\e[0;33m' '\e[0m' "$@" >&2; }
 
 # determine installation path
 if [[ -n "$ZSH_VERSION" ]]; then
     # shellcheck disable=2277,2296,2299
     0="${ZERO:-${${0:#$ZSH_ARGZERO}:-${(%):-%N}}}"
     # shellcheck disable=2277,2296,2298
     0="${${(M)0:#/*}:-$PWD/$0}"
-    FORGIT_INSTALL_DIR="${0:h}"
+    INSTALL_DIR="${0:h}"
 elif [[ -n "$BASH_VERSION" ]]; then
-    FORGIT_INSTALL_DIR="$(dirname -- "${BASH_SOURCE[0]}")"
+    INSTALL_DIR="$(dirname -- "${BASH_SOURCE[0]}")"
 else
     forgit::error "Only zsh and bash are supported"
 fi
-export FORGIT="$FORGIT_INSTALL_DIR/bin/git-forgit"
+FORGIT="$INSTALL_DIR/bin/git-forgit"
+
+# backwards compatibility:
+# export all user-defined FORGIT variables to make them available in git-forgit
+unexported_vars=0
+set | awk -F '=' '{ print $1 }' | grep FORGIT_ | while read -r var; do
+    if ! export | grep -q "^$var="; then
+        if [[ $unexported_vars == 0 ]]; then
+            forgit::warn "Config options have to be exported in future versions of forgit."
+            forgit::warn "Please update your config accordingly:"
+        fi
+        forgit::warn "  export $var"
+        unexported_vars=$((unexported_vars + 1))
+        # shellcheck disable=SC2163
+        export "$var"
+    fi
+done
 
 # register shell functions
 forgit::log() {