Add negative lookahead to avoid matching incorrect commands

lib/gitlab/quick_actions/substitution_definition.rb

@@ -10,14 +10,14 @@ module Gitlab
       end
 
       def match(content)
-        content.match %r{^/#{all_names.join('|')} ?(.*)$}
+        content.match %r{^/#{all_names.join('|')}(?![\S]) ?(.*)$}
       end
 
       def perform_substitution(context, content)
         return unless content
 
         all_names.each do |a_name|
-          content = content.gsub(%r{/#{a_name} ?(.*)$}i, execute_block(action_block, context, '\1'))
+          content = content.gsub(%r{/#{a_name}(?![\S]) ?(.*)$}i, execute_block(action_block, context, '\1'))
         end
 
         content

spec/lib/gitlab/quick_actions/substitution_definition_spec.rb

@@ -19,11 +19,29 @@ EOF
       expect(subject.perform_substitution(self, nil)).to be_nil
     end
 
-    it 'performs the substitution by default' do
-      expect(subject.perform_substitution(self, content)).to eq <<EOF
+    context 'when content contains command name' do
+      it 'performs the substitution by default' do
+        expect(subject.perform_substitution(self, content)).to eq <<EOF
 Hello! Let's do this!
 I like this stuff foo
 EOF
+      end
+    end
+
+    context 'when content contains command name in word' do
+      let(:content) do
+        <<EOF
+Hello! Let's do this!
+`/sub_names` I like this stuff
+EOF
+      end
+
+      it 'does not perform the substitution' do
+        expect(subject.perform_substitution(self, content)).to eq <<EOF
+Hello! Let's do this!
+`/sub_names` I like this stuff
+EOF
+      end
     end
   end
 
@@ -41,5 +59,9 @@ EOF
     it 'is nil if content does not have the command' do
       expect(subject.match('blah')).to be_falsey
     end
+
+    it 'is nil if content contains the command as prefix' do
+      expect(subject.match('/sub_namex')).to be_falsey
+    end
   end
 end