Spec# was a Microsoft Research project that added automated verification to C# through the addition of method contracts, class invariants and loop invariants. This was all integrated into the Visual Studio IDE to make for a very different user experience from normal verification: they wanted verification to be integrated into the development flow. This paper gives a retrospective on the project with a particular focus on efforts to get the techniques adopted.
Spec# was an ambitious project with many different parts:
Frontend: Visual Studio integration so that verification errors show up as “squigglies” under the offending code.
Language: it was a superset of C# which brought advantages of a large codebase and userbase to try things on but tracking a large language as it evolves is hard and the language brings several problems of its own.
(HAVOC was a spinoff that applied some Spec# ideas to low-level C code.)
Platform: their work built on Microsoft’s .NET framework which gave them even more potential impact but also meant that Spec# code could be linked against programs written in other languages that did not have contracts. This lead to the development of a language-neutral contract library, see also logozzo:vmcai:2011.
Contracts that could be used for dynamic checking or static verification. An early goal was to integrate with established programming practice so a subset of their contract language can be checked dynamically.
(Although different, this reminds me of Executable ACSL.)
One of the most frequent things stated in function contracts is whether a pointer can be null or not. So, by default, object references in Spec# are non-null and you have to explicitly request a nullable type. They strongly urge language designers to follow this model.
Compiler integration: instead of extending the parser for C#, they verify the MSIL bytecode. This requires them to reverse engineer some of the transformations that the compiler made and they would have benefited from having the compiler provide extra information to make this easier.
I have probably missed out a lot of important stuff – read the paper!
Papers related to Specification and verification: The Spec# experience
- The Boogie verification debugger [legoues:sefm:2011]