diff --git a/compiler/rustc_hir_typeck/src/method/suggest.rs b/compiler/rustc_hir_typeck/src/method/suggest.rs
index a199f57aad9..754866c85c4 100644
--- a/compiler/rustc_hir_typeck/src/method/suggest.rs
+++ b/compiler/rustc_hir_typeck/src/method/suggest.rs
@@ -529,16 +529,44 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
Applicability::MachineApplicable,
);
}
- if let ty::RawPtr(_, _) = &rcvr_ty.kind() {
- err.note(
- "try using `<*const T>::as_ref()` to get a reference to the \
- type behind the pointer: https://doc.rust-lang.org/std/\
- primitive.pointer.html#method.as_ref",
- );
- err.note(
- "using `<*const T>::as_ref()` on a pointer which is unaligned or points \
- to invalid or uninitialized memory is undefined behavior",
+
+ // on pointers, check if the method would exist on a reference
+ if let SelfSource::MethodCall(rcvr_expr) = source
+ && let ty::RawPtr(ty, ptr_mutbl) = *rcvr_ty.kind()
+ && let Ok(pick) = self.lookup_probe_for_diagnostic(
+ item_name,
+ Ty::new_ref(tcx, ty::Region::new_error_misc(tcx), ty, ptr_mutbl),
+ self.tcx.hir().expect_expr(self.tcx.parent_hir_id(rcvr_expr.hir_id)),
+ ProbeScope::TraitsInScope,
+ None,
+ )
+ && let ty::Ref(_, _, sugg_mutbl) = *pick.self_ty.kind()
+ && (sugg_mutbl.is_not() || ptr_mutbl.is_mut())
+ {
+ let (method, method_anchor) = match sugg_mutbl {
+ Mutability::Not => {
+ let method_anchor = match ptr_mutbl {
+ Mutability::Not => "as_ref",
+ Mutability::Mut => "as_ref-1",
+ };
+ ("as_ref", method_anchor)
+ }
+ Mutability::Mut => ("as_mut", "as_mut"),
+ };
+ err.span_note(
+ tcx.def_span(pick.item.def_id),
+ format!("the method `{item_name}` exists on the type `{ty}`", ty = pick.self_ty),
);
+ let mut_str = ptr_mutbl.ptr_str();
+ err.note(format!(
+ "you might want to use the unsafe method `<*{mut_str} T>::{method}` to get \
+ an optional reference to the value behind the pointer"
+ ));
+ err.note(format!(
+ "read the documentation for `<*{mut_str} T>::{method}` and ensure you satisfy its \
+ safety preconditions before calling it to avoid undefined behavior: \
+ https://doc.rust-lang.org/std/primitive.pointer.html#method.{method_anchor}"
+ ));
}
let mut ty_span = match rcvr_ty.kind() {
diff --git a/tests/ui/methods/suggest-convert-ptr-to-ref.rs b/tests/ui/methods/suggest-convert-ptr-to-ref.rs
index 79f6c91d9ac..ccce3c65470 100644
--- a/tests/ui/methods/suggest-convert-ptr-to-ref.rs
+++ b/tests/ui/methods/suggest-convert-ptr-to-ref.rs
@@ -1,5 +1,17 @@
fn main() {
- let x = 8u8;
+ let mut x = 8u8;
let z: *const u8 = &x;
- println!("{}", z.to_string()); //~ ERROR E0599
+ // issue #21596
+ println!("{}", z.to_string()); //~ ERROR E0599
+
+ let t: *mut u8 = &mut x;
+ println!("{}", t.to_string()); //~ ERROR E0599
+ t.make_ascii_lowercase(); //~ ERROR E0599
+
+ // suggest `as_mut` simply because the name is similar
+ let _ = t.as_mut_ref(); //~ ERROR E0599
+ let _ = t.as_ref_mut(); //~ ERROR E0599
+
+ // no ptr-to-ref suggestion
+ z.make_ascii_lowercase(); //~ ERROR E0599
}
diff --git a/tests/ui/methods/suggest-convert-ptr-to-ref.stderr b/tests/ui/methods/suggest-convert-ptr-to-ref.stderr
index 8a7fca5f436..69b20d57be8 100644
--- a/tests/ui/methods/suggest-convert-ptr-to-ref.stderr
+++ b/tests/ui/methods/suggest-convert-ptr-to-ref.stderr
@@ -1,15 +1,70 @@
error[E0599]: `*const u8` doesn't implement `std::fmt::Display`
- --> $DIR/issue-21596.rs:4:22
+ --> $DIR/suggest-convert-ptr-to-ref.rs:5:22
|
LL | println!("{}", z.to_string());
| ^^^^^^^^^ `*const u8` cannot be formatted with the default formatter
|
- = note: try using `<*const T>::as_ref()` to get a reference to the type behind the pointer: https://doc.rust-lang.org/std/primitive.pointer.html#method.as_ref
- = note: using `<*const T>::as_ref()` on a pointer which is unaligned or points to invalid or uninitialized memory is undefined behavior
+note: the method `to_string` exists on the type `&u8`
+ --> $SRC_DIR/alloc/src/string.rs:LL:COL
+ = note: you might want to use the unsafe method `<*const T>::as_ref` to get an optional reference to the value behind the pointer
+ = note: read the documentation for `<*const T>::as_ref` and ensure you satisfy its safety preconditions before calling it to avoid undefined behavior: https://doc.rust-lang.org/std/primitive.pointer.html#method.as_ref
= note: the following trait bounds were not satisfied:
`*const u8: std::fmt::Display`
which is required by `*const u8: ToString`
-error: aborting due to 1 previous error
+error[E0599]: `*mut u8` doesn't implement `std::fmt::Display`
+ --> $DIR/suggest-convert-ptr-to-ref.rs:8:22
+ |
+LL | println!("{}", t.to_string());
+ | ^^^^^^^^^ `*mut u8` cannot be formatted with the default formatter
+ |
+note: the method `to_string` exists on the type `&&mut u8`
+ --> $SRC_DIR/alloc/src/string.rs:LL:COL
+ = note: you might want to use the unsafe method `<*mut T>::as_ref` to get an optional reference to the value behind the pointer
+ = note: read the documentation for `<*mut T>::as_ref` and ensure you satisfy its safety preconditions before calling it to avoid undefined behavior: https://doc.rust-lang.org/std/primitive.pointer.html#method.as_ref-1
+ = note: the following trait bounds were not satisfied:
+ `*mut u8: std::fmt::Display`
+ which is required by `*mut u8: ToString`
+
+error[E0599]: no method named `make_ascii_lowercase` found for raw pointer `*mut u8` in the current scope
+ --> $DIR/suggest-convert-ptr-to-ref.rs:9:7
+ |
+LL | t.make_ascii_lowercase();
+ | ^^^^^^^^^^^^^^^^^^^^ method not found in `*mut u8`
+ |
+note: the method `make_ascii_lowercase` exists on the type `&mut u8`
+ --> $SRC_DIR/core/src/num/mod.rs:LL:COL
+ = note: you might want to use the unsafe method `<*mut T>::as_mut` to get an optional reference to the value behind the pointer
+ = note: read the documentation for `<*mut T>::as_mut` and ensure you satisfy its safety preconditions before calling it to avoid undefined behavior: https://doc.rust-lang.org/std/primitive.pointer.html#method.as_mut
+
+error[E0599]: no method named `as_mut_ref` found for raw pointer `*mut u8` in the current scope
+ --> $DIR/suggest-convert-ptr-to-ref.rs:12:15
+ |
+LL | let _ = t.as_mut_ref();
+ | ^^^^^^^^^^
+ |
+help: there is a method `as_mut` with a similar name
+ |
+LL | let _ = t.as_mut();
+ | ~~~~~~
+
+error[E0599]: no method named `as_ref_mut` found for raw pointer `*mut u8` in the current scope
+ --> $DIR/suggest-convert-ptr-to-ref.rs:13:15
+ |
+LL | let _ = t.as_ref_mut();
+ | ^^^^^^^^^^
+ |
+help: there is a method `as_mut` with a similar name
+ |
+LL | let _ = t.as_mut();
+ | ~~~~~~
+
+error[E0599]: no method named `make_ascii_lowercase` found for raw pointer `*const u8` in the current scope
+ --> $DIR/suggest-convert-ptr-to-ref.rs:16:7
+ |
+LL | z.make_ascii_lowercase();
+ | ^^^^^^^^^^^^^^^^^^^^ method not found in `*const u8`
+
+error: aborting due to 6 previous errors
For more information about this error, try `rustc --explain E0599`.