Feature: add empty state messages for checkout commands (#478)

Show informative messages when there is nothing to checkout:
  - checkout_file: "Nothing to checkout." when no modified files
  - checkout_tag: "Nothing to checkout: there are no tags."

bin/git-forgit

@@ -842,6 +842,7 @@ _forgit_checkout_file() {
     _forgit_inside_work_tree || return 1
     local files opts
     _forgit_contains_non_flags "$@" && { _forgit_git_checkout_file "$@"; return $?; }
+    [[ $(_forgit_list_files --modified | wc -l) -eq 0 ]] && echo 'Nothing to checkout.' && return 1
     opts="
         $FORGIT_FZF_DEFAULT_OPTS
         -m -0
@@ -958,8 +959,9 @@ _forgit_git_checkout_tag() {
 # git checkout-tag selector
 _forgit_checkout_tag() {
     _forgit_inside_work_tree || return 1
-    local opts
+    local opts tag
     [[ $# -ne 0 ]] && { _forgit_git_checkout_tag "$@"; return $?; }
+    [[ $(git tag -l | wc -l) -eq 0 ]] && echo 'Nothing to checkout: there are no tags.' && return 1
     opts="
         $FORGIT_FZF_DEFAULT_OPTS
         +s +m --tiebreak=index

tests/empty-state.test.sh

@@ -0,0 +1,29 @@
+#!/usr/bin/env bash
+
+function set_up_before_script() {
+    source bin/git-forgit
+
+    # Create a temporary git repository for testing
+    cd "$(bashunit::temp_dir)" || return 1
+    git init -q
+    git config user.email "test@example.com"
+    git config user.name "Test User"
+    # Create an initial commit so we have a valid repo
+    echo "initial" > README.md
+    git add README.md
+    git commit -q -m "Initial commit"
+}
+
+function test_checkout_file_shows_message_when_no_modified_files() {
+    output=$(_forgit_checkout_file 2>&1)
+    assert_general_error
+
+    assert_same "Nothing to checkout." "$output"
+}
+
+function test_checkout_tag_shows_message_when_no_tags() {
+    output=$(_forgit_checkout_tag 2>&1)
+    assert_general_error
+
+    assert_same "Nothing to checkout: there are no tags." "$output"
+}