Closure inference (again)

[xldenis]

Adds support for inferring the specifications of closures through Coma's novel extspec mechanism.

Using this, you can exclude a contract for your closure and Creusot will instead infer its contract as roughly the WP and SP for the pre and post conditions respectively. I've updated some of our iterator tests to use this feature.

[jhjourdan]

I don't understand all the details, but I find quite suspicious that there is no special case here when postcond_kind is FnMut.

More generally, I would have expected to only generate the term when closure_kind is equal to postcond_kind, and rely on the various compatibility laws to let the provers deduce the other cases.

[xldenis]

That's because what matters here is mainly the underlying type of the closure:

• If it's FnOnce it cannot have an FnMut
• If its Fn then its FnMut instance ignores the result (since it must be equal to the initial parameter), this fact being provided by the compatibility law.

[jhjourdan]

this fact being provided by the compatibility law.

Well, then, why not relying fully on the compatibility law for the whole post-condition?

[arnaudgolfouse]

I tried using the branch, and ran into a crash. Here is a minimal example:

pub fn foo() {
    let my_closure = |x: Option<i32>| match x {
        Some(y) => y,
        None => unreachable!("unwrapped None"),
    };
}

This crashes with error: internal compiler error: compiler/rustc_middle/src/ty/mod.rs:1607:13: item_name: no name for DefPath { data: [DisambiguatedDefPathData { data: ValueNs("foo"), disambiguator: 0 }, DisambiguatedDefPathData { data: Closure, disambiguator: 0 }], krate: crate0 }. It seems some code is trying to fetch the name of the type of the closure from rustc (but it does not exists).

[xldenis]

Does that crash happen on master?

[arnaudgolfouse]

Yes, it does 😕

[arnaudgolfouse]

I tried using the branch, and ran into a crash. Here is a minimal example:

pub fn foo() {
    let my_closure = |x: Option<i32>| match x {
        Some(y) => y,
        None => unreachable!("unwrapped None"),
    };
}

This crashes with error: internal compiler error: compiler/rustc_middle/src/ty/mod.rs:1607:13: item_name: no name for DefPath { data: [DisambiguatedDefPathData { data: ValueNs("foo"), disambiguator: 0 }, DisambiguatedDefPathData { data: Closure, disambiguator: 0 }], krate: crate0 }. It seems some code is trying to fetch the name of the type of the closure from rustc (but it does not exists).

I opened #1312 to track this.