type certainty: clear `DefId` when an expression's type changes to non-adt Fixes rust-lang#12585 The root cause of the ICE in the linked issue was in the expression `one.x`, in the array literal. The type of `one` is the `One` struct: an adt with a DefId, so its certainty is `Certain(def_id_of_one)`. However, the field access `.x` can then change the type (to `i32` here) and that should update that `DefId` accordingly. It does do that correctly when `one.x` would be another adt with a DefId: https://github.com/rust-lang/rust-clippy/blob/97ba291d5aa026353ad93e48cf00e06f08c73830/clippy_utils/src/ty/type_certainty/mod.rs#L90-L91 but when it *isn't* an adt and there is no def id (which is the case in the linked issue: `one.x` is an i32), it keeps the `DefId` of `One`, even though that's the wrong type (which would then lead to a contradiction later when joining `Certainty`s): https://github.com/rust-lang/rust-clippy/blob/97ba291d5aa026353ad93e48cf00e06f08c73830/clippy_utils/src/ty/type_certainty/mod.rs#L92-L93 In particular, in the linked issue, `from_array([one.x, two.x])` would try to join the `Certainty` of the two array elements, which *should* have been `[Certain(None), Certain(None)]`, because `i32`s have no `DefId`, but instead it was `[Certain(One), Certain(Two)]`, because the DefId wasn't cleared from when it was visiting `one` and `two`. This is the "contradiction" that could be seen in the ICE message ... so this changes it to clear the `DefId` when it isn't an adt. cc `@smoelius` you implemented this initially in rust-lang#11135, does this change make sense to you? changelog: none

src/librustc/middle/typeck/infer/test.rs needs salvaging #12585

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