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Rollup merge of rust-lang#94375 - WaffleLapkin:copy-suggestion, r=est…
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…ebank

Adt copy suggestions

Previously we've only suggested adding `Copy` bounds when the type being moved/copied is a type parameter (generic). With this PR we also suggest adding bounds when a type
- Can be copy
- All predicates that need to be satisfied for that are based on type params

i.e. we will suggest `T: Copy` for `Option<T>`, but won't suggest anything for `Option<String>`.

An example:
```rust
fn duplicate<T>(t: Option<T>) -> (Option<T>, Option<T>) {
    (t, t)
}
```
New error (current compiler doesn't provide `help`:):
```text
error[E0382]: use of moved value: `t`
 --> t.rs:2:9
  |
1 | fn duplicate<T>(t: Option<T>) -> (Option<T>, Option<T>) {
  |                 - move occurs because `t` has type `Option<T>`, which does not implement the `Copy` trait
2 |     (t, t)
  |      -  ^ value used here after move
  |      |
  |      value moved here
  |
help: consider restricting type parameter `T`
  |
1 | fn duplicate<T: Copy>(t: Option<T>) -> (Option<T>, Option<T>) {
  |               ++++++
```

Fixes rust-lang#93623
r? `````@estebank`````
`````@rustbot````` label +A-diagnostics +A-suggestion-diagnostics +C-enhancement

----

I'm not at all sure if this is the right implementation for this kind of suggestion, but it seems to work :')
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matthiaskrgr authored Mar 2, 2022
2 parents fa50d58 + f0a16b8 commit 4a6506a
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Showing 8 changed files with 608 additions and 164 deletions.
63 changes: 62 additions & 1 deletion compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs
Original file line number Diff line number Diff line change
Expand Up @@ -5,16 +5,21 @@ use rustc_errors::{Applicability, Diagnostic, DiagnosticBuilder, ErrorReported};
use rustc_hir as hir;
use rustc_hir::def_id::DefId;
use rustc_hir::{AsyncGeneratorKind, GeneratorKind};
use rustc_infer::infer::TyCtxtInferExt;
use rustc_infer::traits::ObligationCause;
use rustc_middle::mir::{
self, AggregateKind, BindingForm, BorrowKind, ClearCrossCrate, ConstraintCategory,
FakeReadCause, LocalDecl, LocalInfo, LocalKind, Location, Operand, Place, PlaceRef,
ProjectionElem, Rvalue, Statement, StatementKind, Terminator, TerminatorKind, VarBindingForm,
};
use rustc_middle::ty::{self, suggest_constraining_type_param, Ty};
use rustc_middle::ty::{
self, suggest_constraining_type_param, suggest_constraining_type_params, PredicateKind, Ty,
};
use rustc_mir_dataflow::move_paths::{InitKind, MoveOutIndex, MovePathIndex};
use rustc_span::symbol::sym;
use rustc_span::{BytePos, MultiSpan, Span, DUMMY_SP};
use rustc_trait_selection::infer::InferCtxtExt;
use rustc_trait_selection::traits::TraitEngineExt as _;

use crate::borrow_set::TwoPhaseActivation;
use crate::borrowck_errors;
Expand Down Expand Up @@ -423,7 +428,63 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
None,
);
}
} else {
// Try to find predicates on *generic params* that would allow copying `ty`

let tcx = self.infcx.tcx;
let generics = tcx.generics_of(self.mir_def_id());
if let Some(hir_generics) = tcx
.typeck_root_def_id(self.mir_def_id().to_def_id())
.as_local()
.and_then(|def_id| tcx.hir().get_generics(def_id))
{
let predicates: Result<Vec<_>, _> = tcx.infer_ctxt().enter(|infcx| {
let mut fulfill_cx =
<dyn rustc_infer::traits::TraitEngine<'_>>::new(infcx.tcx);

let copy_did = infcx.tcx.lang_items().copy_trait().unwrap();
let cause = ObligationCause::new(
span,
self.mir_hir_id(),
rustc_infer::traits::ObligationCauseCode::MiscObligation,
);
fulfill_cx.register_bound(&infcx, self.param_env, ty, copy_did, cause);
let errors = fulfill_cx.select_where_possible(&infcx);

// Only emit suggestion if all required predicates are on generic
errors
.into_iter()
.map(|err| match err.obligation.predicate.kind().skip_binder() {
PredicateKind::Trait(predicate) => {
match predicate.self_ty().kind() {
ty::Param(param_ty) => Ok((
generics.type_param(param_ty, tcx),
predicate
.trait_ref
.print_only_trait_path()
.to_string(),
)),
_ => Err(()),
}
}
_ => Err(()),
})
.collect()
});

if let Ok(predicates) = predicates {
suggest_constraining_type_params(
tcx,
hir_generics,
&mut err,
predicates.iter().map(|(param, constraint)| {
(param.name.as_str(), &**constraint, None)
}),
);
}
}
}

let span = if let Some(local) = place.as_local() {
let decl = &self.body.local_decls[local];
Some(decl.source_info.span)
Expand Down
1 change: 1 addition & 0 deletions compiler/rustc_middle/src/lib.rs
Original file line number Diff line number Diff line change
Expand Up @@ -56,6 +56,7 @@
#![feature(nonzero_ops)]
#![feature(unwrap_infallible)]
#![feature(decl_macro)]
#![feature(drain_filter)]
#![recursion_limit = "512"]
#![allow(rustc::potential_query_instability)]

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