feat(CLI): add `omz changelog` command

lib/cli.zsh

@@ -22,10 +22,11 @@ function omz {
 function _omz {
   local -a cmds subcmds
   cmds=(
+    'changelog:Print the changelog'
     'help:Usage information'
-        'plugin:Commands for Oh My Zsh plugins management'
-        'pr:Commands for Oh My Zsh Pull Requests management'
-        'theme:Commands for Oh My Zsh themes management'
+    'plugin:Manage plugins'
+    'pr:Manage Oh My Zsh Pull Requests'
+    'theme:Manage themes'
     'update:Update Oh My Zsh'
   )
 
@@ -33,6 +34,9 @@ function _omz {
     _describe 'command' cmds
   elif (( CURRENT == 3 )); then
     case "$words[2]" in
+      changelog) local -a refs
+        refs=("${(@f)$(command git for-each-ref --format="%(refname:short):%(subject)" refs/heads refs/tags)}")
+        _describe 'command' refs ;;
       plugin) subcmds=('list:List plugins')
         _describe 'command' subcmds ;;
       pr) subcmds=('test:Test a Pull Request' 'clean:Delete all Pull Request branches')
@@ -52,21 +56,7 @@ function _omz {
 
 compdef _omz omz
 
-
-function _omz::help {
-    cat <<EOF
-Usage: omz <command> [options]
-
-Available commands:
-
-    help                Print this help message
-    plugin <command>    Manage plugins
-    pr <command>        Manage Oh My Zsh Pull Requests
-    theme <command>     Manage themes
-    update              Update Oh My Zsh
-
-EOF
-}
+## Utility functions
 
 function _omz::confirm {
   # If question supplied, ask it before reading the answer
@@ -111,6 +101,41 @@ function _omz::log {
   esac >&2
 }
 
+## User-facing commands
+
+function _omz::help {
+  cat <<EOF
+Usage: omz <command> [options]
+
+Available commands:
+
+  help                Print this help message
+  changelog           Print the changelog
+  plugin <command>    Manage plugins
+  pr     <command>    Manage Oh My Zsh Pull Requests
+  theme  <command>    Manage themes
+  update              Update Oh My Zsh
+
+EOF
+}
+
+function _omz::changelog {
+  local version=${1:-HEAD} format=${3:-"--text"}
+
+  if ! command git -C "$ZSH" show-ref --verify refs/heads/$version &>/dev/null && \
+    ! command git -C "$ZSH" show-ref --verify refs/tags/$version &>/dev/null && \
+    ! command git -C "$ZSH" rev-parse --verify "${version}^{commit}" &>/dev/null; then
+    cat <<EOF
+Usage: omz changelog [version]
+
+NOTE: <version> must be a valid branch, tag or commit.
+EOF
+    return 1
+  fi
+
+  "$ZSH/tools/changelog.sh" "$version" "${2:-}" "$format"
+}
+
 function _omz::plugin {
   (( $# > 0 && $+functions[_omz::plugin::$1] )) || {
     cat <<EOF