Allow skipping completion suggestions when buffer matches a pattern

Set ZSH_AUTOSUGGEST_COMPLETION_IGNORE to a glob pattern to have the
completion suggestion strategy never make suggestions when the buffer
matches the pattern.

This can be helpful when some completion routines you have are
particularly expensive and you want to prevent them from running
automatically on every keystroke.

See GitHub issue #463.

spec/strategies/completion_spec.rb

@@ -5,7 +5,9 @@ describe 'the `completion` suggestion strategy' do
       session.
         run_command('autoload compinit && compinit').
         run_command('_foo() { compadd bar; compadd bat }').
-        run_command('compdef _foo baz')
+        run_command('_num() { compadd two; compadd three }').
+        run_command('compdef _foo baz').
+        run_command('compdef _num one')
     end
   end
 
@@ -37,6 +39,21 @@ describe 'the `completion` suggestion strategy' do
     end
   end
 
+  context 'when ZSH_AUTOSUGGEST_COMPLETION_IGNORE is set to a pattern' do
+    let(:options) { ['ZSH_AUTOSUGGEST_STRATEGY=completion', 'ZSH_AUTOSUGGEST_COMPLETION_IGNORE="one *"'] }
+
+    it 'makes suggestions when the buffer does not match the pattern' do
+      session.send_string('baz ')
+      wait_for { session.content }.to eq('baz bar')
+    end
+
+    it 'does not make suggestions when the buffer matches the pattern' do
+      session.send_string('one t')
+      sleep 1
+      expect(session.content).to eq('one t')
+    end
+  end
+
   context 'when async mode is enabled' do
     let(:options) { ['ZSH_AUTOSUGGEST_USE_ASYNC=true', 'ZSH_AUTOSUGGEST_STRATEGY=completion'] }