Rollup merge of rust-lang#107306 - compiler-errors:correct-sugg-for-c…

…losure-arg-needs-borrow, r=oli-obk

Correct suggestions for closure arguments that need a borrow

Fixes rust-lang#107301 by dealing with binders correctly
Fixes another issue where we were suggesting adding just `&` when we expected `&mut _` in a closure arg

compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs

@@ -3759,13 +3759,13 @@ fn hint_missing_borrow<'tcx>(
  err: &mut Diagnostic,
 ) {
  let found_args = match found.kind() {
- ty::FnPtr(f) => f.inputs().skip_binder().iter(),
+ ty::FnPtr(f) => infcx.replace_bound_vars_with_placeholders(*f).inputs().iter(),
  kind => {
  span_bug!(span, "found was converted to a FnPtr above but is now {:?}", kind)
  }
  };
  let expected_args = match expected.kind() {
- ty::FnPtr(f) => f.inputs().skip_binder().iter(),
+ ty::FnPtr(f) => infcx.replace_bound_vars_with_placeholders(*f).inputs().iter(),
  kind => {
  span_bug!(span, "expected was converted to a FnPtr above but is now {:?}", kind)
  }
@@ -3776,12 +3776,12 @@ fn hint_missing_borrow<'tcx>(
 
  let args = fn_decl.inputs.iter().map(|ty| ty);
 
- fn get_deref_type_and_refs(mut ty: Ty<'_>) -> (Ty<'_>, usize) {
- let mut refs = 0;
+ fn get_deref_type_and_refs(mut ty: Ty<'_>) -> (Ty<'_>, Vec<hir::Mutability>) {
+ let mut refs = vec![];
 
- while let ty::Ref(_, new_ty, _) = ty.kind() {
+ while let ty::Ref(_, new_ty, mutbl) = ty.kind() {
  ty = *new_ty;
- refs += 1;
+ refs.push(*mutbl);
  }
 
  (ty, refs)
@@ -3795,11 +3795,21 @@ fn hint_missing_borrow<'tcx>(
  let (expected_ty, expected_refs) = get_deref_type_and_refs(*expected_arg);
 
  if infcx.can_eq(param_env, found_ty, expected_ty).is_ok() {
- if found_refs < expected_refs {
- to_borrow.push((arg.span.shrink_to_lo(), "&".repeat(expected_refs - found_refs)));
- } else if found_refs > expected_refs {
+ // FIXME: This could handle more exotic cases like mutability mismatches too!
+ if found_refs.len() < expected_refs.len()
+ && found_refs[..] == expected_refs[expected_refs.len() - found_refs.len()..]
+ {
+ to_borrow.push((
+ arg.span.shrink_to_lo(),
+ expected_refs[..expected_refs.len() - found_refs.len()]
+ .iter()
+ .map(|mutbl| format!("&{}", mutbl.prefix_str()))
+ .collect::<Vec<_>>()
+ .join(""),
+ ));
+ } else if found_refs.len() > expected_refs.len() {
  let mut span = arg.span.shrink_to_lo();
- let mut left = found_refs - expected_refs;
+ let mut left = found_refs.len() - expected_refs.len();
  let mut ty = arg;
  while let hir::TyKind::Ref(_, mut_ty) = &ty.kind && left > 0 {
  span = span.with_hi(mut_ty.ty.span.lo());

tests/ui/suggestions/late-bound-in-borrow-closure-sugg.rs

@@ -0,0 +1,28 @@
+use std::cell::RefCell;
+use std::collections::HashMap;
+use std::rc::Rc;
+
+pub struct Trader<'a> {
+ closure: Box<dyn Fn(&mut Trader) + 'a>,
+}
+
+impl<'a> Trader<'a> {
+ pub fn new() -> Self {
+ Trader {
+ closure: Box::new(|_| {}),
+ }
+ }
+ pub fn set_closure(&mut self, function: impl Fn(&mut Trader) + 'a) {
+ //foo
+ }
+}
+
+fn main() {
+ let closure = |trader : Trader| {
+ println!("Woooosh!");
+ };
+
+ let mut trader = Trader::new();
+ trader.set_closure(closure);
+ //~^ ERROR type mismatch in closure arguments
+}

tests/ui/suggestions/late-bound-in-borrow-closure-sugg.stderr

@@ -0,0 +1,26 @@
+error[E0631]: type mismatch in closure arguments
+ --> $DIR/late-bound-in-borrow-closure-sugg.rs:26:24
+ |
+LL | let closure = |trader : Trader| {
+ | ----------------- found signature defined here
+...
+LL | trader.set_closure(closure);
+ | ----------- ^^^^^^^ expected due to this
+ | |
+ | required by a bound introduced by this call
+ |
+ = note: expected closure signature `for<'a, 'b> fn(&'a mut Trader<'b>) -> _`
+ found closure signature `for<'a> fn(Trader<'a>) -> _`
+note: required by a bound in `Trader::<'a>::set_closure`
+ --> $DIR/late-bound-in-borrow-closure-sugg.rs:15:50
+ |
+LL | pub fn set_closure(&mut self, function: impl Fn(&mut Trader) + 'a) {
+ | ^^^^^^^^^^^^^^^ required by this bound in `Trader::<'a>::set_closure`
+help: consider borrowing the argument
+ |
+LL | let closure = |trader : &mut Trader| {
+ | ++++
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0631`.