Since learning Eiffel in the 90's I keep looking forward for them to become mainstream, beyond the typical assert like statements.
So far we had annotations in Java (which required additional tooling and never took off), .NET (hidden behind enterprise license, thus hardly adopted), D (which suffers from adoption), Common Lisp (nice, but again adoption issues), Ada (again the language adoption), C++26 (if they actually land, and only as MVP)
Almost 40 years later, and still no good story for DbC.
So far we had annotations in Java (which required additional tooling and never took off), .NET (hidden behind enterprise license, thus hardly adopted), D (which suffers from adoption), Common Lisp (nice, but again adoption issues), Ada (again the language adoption), C++26 (if they actually land, and only as MVP)
Almost 40 years later, and still no good story for DbC.