fix: prefer (*p).clone to p.clone if the p is a raw pointer

compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs

@@ -1288,14 +1288,16 @@ impl<'tcx> MirBorrowckCtxt<'_, '_, '_, 'tcx> {
  return false;
  }
  // Try to find predicates on *generic params* that would allow copying `ty`
- let suggestion =
+ let mut suggestion =
  if let Some(symbol) = tcx.hir().maybe_get_struct_pattern_shorthand_field(expr) {
  format!(": {symbol}.clone()")
  } else {
  ".clone()".to_owned()
  };
  let mut sugg = Vec::with_capacity(2);
  let mut inner_expr = expr;
+ let mut is_raw_ptr = false;
+ let typeck_result = self.infcx.tcx.typeck(self.mir_def_id());
  // Remove uses of `&` and `*` when suggesting `.clone()`.
  while let hir::ExprKind::AddrOf(.., inner) | hir::ExprKind::Unary(hir::UnOp::Deref, inner) =
  &inner_expr.kind
@@ -1306,14 +1308,32 @@ impl<'tcx> MirBorrowckCtxt<'_, '_, '_, 'tcx> {
  return false;
  }
  inner_expr = inner;
+ if let Some(inner_type) = typeck_result.node_type_opt(inner.hir_id) {
+ if matches!(inner_type.kind(), ty::RawPtr(..)) {
+ is_raw_ptr = true;
+ break;
+ }
+ }
  }
- if inner_expr.span.lo() != expr.span.lo() {
+ // Cloning the raw pointer doesn't make sense in some cases and would cause a type mismatch error. (see #126863)
+ if inner_expr.span.lo() != expr.span.lo() && !is_raw_ptr {
+ // Remove "(*" or "(&"
  sugg.push((expr.span.with_hi(inner_expr.span.lo()), String::new()));
  }
+ // Check whether `expr` is surrounded by parentheses or not.
  let span = if inner_expr.span.hi() != expr.span.hi() {
  // Account for `(*x)` to suggest `x.clone()`.
- expr.span.with_lo(inner_expr.span.hi())
+ if is_raw_ptr {
+ expr.span.shrink_to_hi()
+ } else {
+ // Remove the close parenthesis ")"
+ expr.span.with_lo(inner_expr.span.hi())
+ }
  } else {
+ if is_raw_ptr {
+ sugg.push((expr.span.shrink_to_lo(), "(".to_string()));
+ suggestion = ").clone()".to_string();
+ }
  expr.span.shrink_to_hi()
  };
  sugg.push((span, suggestion));

compiler/rustc_borrowck/src/diagnostics/move_errors.rs

@@ -639,12 +639,27 @@ impl<'tcx> MirBorrowckCtxt<'_, '_, '_, 'tcx> {
  fn add_borrow_suggestions(&self, err: &mut Diag<'_>, span: Span) {
  match self.infcx.tcx.sess.source_map().span_to_snippet(span) {
  Ok(snippet) if snippet.starts_with('*') => {
- err.span_suggestion_verbose(
- span.with_hi(span.lo() + BytePos(1)),
- "consider removing the dereference here",
- String::new(),
- Applicability::MaybeIncorrect,
- );
+ let sp = span.with_lo(span.lo() + BytePos(1));
+ let inner = self.find_expr(sp);
+ let mut is_raw_ptr = false;
+ if let Some(inner) = inner {
+ let typck_result = self.infcx.tcx.typeck(self.mir_def_id());
+ if let Some(inner_type) = typck_result.node_type_opt(inner.hir_id) {
+ if matches!(inner_type.kind(), ty::RawPtr(..)) {
+ is_raw_ptr = true;
+ }
+ }
+ }
+ // If the `inner` is a raw pointer, do not suggest removing the "*", see #126863
+ // FIXME: need to check whether the assigned object can be a raw pointer, see `tests/ui/borrowck/issue-20801.rs`.
+ if !is_raw_ptr {
+ err.span_suggestion_verbose(
+ span.with_hi(span.lo() + BytePos(1)),
+ "consider removing the dereference here",
+ String::new(),
+ Applicability::MaybeIncorrect,
+ );
+ }
  }
  _ => {
  err.span_suggestion_verbose(

tests/ui/borrowck/borrowck-move-from-unsafe-ptr.stderr

@@ -4,16 +4,10 @@ error[E0507]: cannot move out of `*x` which is behind a raw pointer
 LL | let y = *x;
  | ^^ move occurs because `*x` has type `Box<isize>`, which does not implement the `Copy` trait
  |
-help: consider removing the dereference here
- |
-LL - let y = *x;
-LL + let y = x;
- |
 help: consider cloning the value if the performance cost is acceptable
  |
-LL - let y = *x;
-LL + let y = x.clone();
- |
+LL | let y = (*x).clone();
+ | + +++++++++
 
 error: aborting due to 1 previous error
 

tests/ui/borrowck/issue-20801.stderr

@@ -67,11 +67,6 @@ LL | struct T(u8);
 ...
 LL | let c = unsafe { *mut_ptr() };
  | ---------- you could clone this value
-help: consider removing the dereference here
- |
-LL - let c = unsafe { *mut_ptr() };
-LL + let c = unsafe { mut_ptr() };
- |
 
 error[E0507]: cannot move out of a raw pointer
  --> $DIR/issue-20801.rs:36:22
@@ -87,11 +82,6 @@ LL | struct T(u8);
 ...
 LL | let d = unsafe { *const_ptr() };
  | ------------ you could clone this value
-help: consider removing the dereference here
- |
-LL - let d = unsafe { *const_ptr() };
-LL + let d = unsafe { const_ptr() };
- |
 
 error: aborting due to 4 previous errors; 1 warning emitted
 

tests/ui/borrowck/move-from-union-field-issue-66500.stderr

@@ -30,9 +30,8 @@ LL | *u.c
  |
 help: consider cloning the value if the performance cost is acceptable
  |
-LL - *u.c
-LL + u.c.clone()
- |
+LL | (*u.c).clone()
+ | + +++++++++
 
 error[E0507]: cannot move out of `*u.d` which is behind a raw pointer
  --> $DIR/move-from-union-field-issue-66500.rs:24:5
@@ -42,9 +41,8 @@ LL | *u.d
  |
 help: consider cloning the value if the performance cost is acceptable
  |
-LL - *u.d
-LL + u.d.clone()
- |
+LL | (*u.d).clone()
+ | + +++++++++
 
 error: aborting due to 4 previous errors