Add spec for `completion` strategy

spec/strategies/completion_spec.rb

@@ -0,0 +1,30 @@
+describe 'the `completion` suggestion strategy' do
+  let(:options) { ['ZSH_AUTOSUGGEST_STRATEGY=completion'] }
+  let(:before_sourcing) do
+    -> do
+      session.
+        run_command('autoload compinit && compinit').
+        run_command('_foo() { compadd bar }').
+        run_command('compdef _foo baz')
+    end
+  end
+
+  it 'suggests the first completion result' do
+    session.send_string('baz ')
+    wait_for { session.content }.to eq('baz bar')
+  end
+
+  context 'when async mode is enabled' do
+    before do
+      skip 'Async mode not supported below v5.0.8' if session.zsh_version < Gem::Version.new('5.0.8')
+    end
+
+    let(:options) { ['ZSH_AUTOSUGGEST_USE_ASYNC=true', 'ZSH_AUTOSUGGEST_STRATEGY=completion'] }
+
+    it 'suggests the first completion result' do
+      session.send_string('baz ')
+      wait_for { session.content }.to eq('baz bar')
+    end
+  end
+end
+

spec/strategies/match_prev_cmd_spec.rb

@@ -1,6 +1,6 @@
 require 'strategies/special_characters_helper'
 
-describe 'the match_prev_cmd strategy' do
+describe 'the `match_prev_cmd` strategy' do
   let(:options) { ['ZSH_AUTOSUGGEST_STRATEGY=match_prev_cmd'] }
 
   it 'suggests the last matching history entry after the previous command' do

src/strategies/completion.zsh

@@ -9,7 +9,10 @@
 _zsh_autosuggest_capture_setup() {
 	zmodload zsh/zutil # For `zparseopts`
 
-	autoload compinit && compinit
+	# Ensure completions have been initialized
+	if ! whence compdef >/dev/null; then
+		autoload -Uz compinit && compinit
+	fi
 
 	# There is a bug in zpty module (fixed in zsh/master) by which a
 	# zpty that exits will kill all zpty processes that were forked

zsh-autosuggestions.zsh

@@ -506,7 +506,10 @@ zle -N autosuggest-toggle _zsh_autosuggest_widget_toggle
 _zsh_autosuggest_capture_setup() {
 	zmodload zsh/zutil # For `zparseopts`
 
-	autoload compinit && compinit
+	# Ensure completions have been initialized
+	if ! whence compdef >/dev/null; then
+		autoload -Uz compinit && compinit
+	fi
 
 	# There is a bug in zpty module (fixed in zsh/master) by which a
 	# zpty that exits will kill all zpty processes that were forked