Aaron Hill 48a48fd1b8 Improve opaque type higher-ranked region error message under NLL ... Currently, any higher-ranked region errors involving opaque types fall back to a generic "higher-ranked subtype error" message when run under NLL. This PR adds better error message handling for this case, giving us the same kinds of error messages that we currently get without NLL: ``` error: implementation of `MyTrait` is not general enough --> $DIR/opaque-hrtb.rs:12:13 | LL | fn foo() -> impl for<'a> MyTrait<&'a str> { | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ implementation of `MyTrait` is not general enough | = note: `impl MyTrait<&'2 str>` must implement `MyTrait<&'1 str>`, for any lifetime `'1`... = note: ...but it actually implements `MyTrait<&'2 str>`, for some specific lifetime `'2` error: aborting due to previous error ``` To accomplish this, several different refactoring needed to be made: * We now have a dedicated `InstantiateOpaqueType` struct which implements `TypeOp`. This is used to invoke `instantiate_opaque_types` during MIR type checking. * `TypeOp` is refactored to pass around a `MirBorrowckCtxt`, which is needed to report opaque type region errors. * We no longer assume that all `TypeOp`s correspond to canonicalized queries. This allows us to properly handle opaque type instantiation (which does not occur in a query) as a `TypeOp`. A new `ErrorInfo` associated type is used to determine what additional information is used during higher-ranked region error handling. * The body of `try_extract_error_from_fulfill_cx` has been moved out to a new function `try_extract_error_from_region_constraints`. This allows us to re-use the same error reporting code between canonicalized queries (which can extract region constraints directly from a fresh `InferCtxt`) and opaque type handling (which needs to take region constraints from the pre-existing `InferCtxt` that we use throughout MIR borrow checking).		2022-02-08 12:35:42 -05:00
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src	Improve opaque type higher-ranked region error message under NLL	2022-02-08 12:35:42 -05:00
Cargo.toml	Update itertools to deduplicate it	2022-01-14 12:33:54 +01:00