Rename `replace_bound_vars_with_*` to `instantiate_binder_with_*`
Mentioning "binder" rather than "bound vars", imo, makes it clearer that we're doing something to the binder as a whole.
Also, "instantiate" is the verb that I'm always reaching for when I'm looking for these functions, and the name that we use in the new solver anyways.
r? types
small refactor to new projection code
extract `eq_term_and_make_canonical_response` into a helper function which also is another guarantee that the expected term does not influence candidate selection for projections.
also change `evaluate_all(vec![single_goal])` to use `evaluate_goal`.
the second commit now also adds a `debug_assert!` to `evaluate_goal`.
Remove `ControlFlow::{BREAK, CONTINUE}`
Libs-API decided to remove these in #102697.
Follow-up to #107023, which removed them from `compiler/`, but a couple new ones showed up since that was merged.
r? libs
Minor tweaks in the new solver
1. `InferCtxt::probe` is not needed in `compute_subtype_goal` and `compute_well_formed_goal`.
2. Add a handful of comments.
3. Add a micro-optimization in `consider_assumption` where we check the def-ids of the assumption and goal match before instantiating any binders.
r? ``@lcnr``
Libs-API decided to remove these in #102697.
Follow-up to #107023, which removed them from `compiler/`, but a couple new ones showed up since that was merged.
Compute generator saved locals on MIR
Generators are currently type-checked by introducing a `witness` type variable, which is unified with a `GeneratorWitness(captured types)` whose purpose is to ensure that the auto traits correctly migrate from the captured types to the `witness` type. This requires computing the captured types on HIR during type-checking, only to re-do it on MIR later.
This PR proposes to drop the HIR-based computation, and only keep the MIR one. This is done in 3 steps.
1. During type-checking, the `witness` type variable is never unified. This allows to stall all the obligations that depend on it until the end of type-checking. Then, the stalled obligations are marked as successful, and saved into the typeck results for later verification.
2. At type-checking writeback, `witness` is replaced by `GeneratorWitnessMIR(def_id, substs)`. From this point on, all trait selection involving `GeneratorWitnessMIR` will fetch the MIR-computed locals, similar to what opaque types do. There is no lifetime to be preserved here: we consider all the lifetimes appearing in this witness type to be higher-ranked.
3. After borrowck, the stashed obligations are verified against the actually computed types, in the `check_generator_obligations` query. If any obligation was wrongly marked as fulfilled in step 1, it should be reported here.
There are still many issues:
- ~I am not too happy having to filter out some locals from the checked bounds, I think this is MIR building that introduces raw pointers polluting the analysis;~ solved by a check specific to static variables.
- the diagnostics for captured types don't show where they are used/dropped;
- I do not attempt to support chalk.
cc `@eholk` `@jyn514` for the drop-tracking work
r? `@oli-obk` as you warned me of potential unsoundness
ICE in new solver if we see an inference variable
By construction, we do not expect to see any `ty::Infer(ty::TyVar(_))` inference types in the solver (we treat this as ambiguous, since we need to be able to structurally resolve the self type at least one layer to assemble candidates for it). Additionally, since we're doing no freshening, we also don't expect to see any fresh vars of any kind in the solver.
Let's make that an ICE so we can catch any mistakes.
When #107282 lands, we should also ICE there too if we see a non-int/float infer.
r? `@lcnr`
