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Rollup merge of rust-lang#107553 - edward-shen:edward-shen/suggest-null-ptr, r=WaffleLapkin
Suggest std::ptr::null if literal 0 is given to a raw pointer function argument Implementation feels a little sus (we're parsing the span for a `0`) but it seems to fall in line the string-expected-found-char condition right above this check, so I think it's fine. Feedback appreciated on help text? I think it's consistent but it does sound a little awkward maybe? Fixes rust-lang#107517
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‎compiler/rustc_hir_typeck/src/demand.rs

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Original file line numberDiff line numberDiff line change
@@ -60,6 +60,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
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|| self.suggest_clone_for_ref(err, expr, expr_ty, expected)
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|| self.suggest_into(err, expr, expr_ty, expected)
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|| self.suggest_floating_point_literal(err, expr, expected)
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|| self.suggest_null_ptr_for_literal_zero_given_to_ptr_arg(err, expr, expected)
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|| self.note_result_coercion(err, expr, expected, expr_ty);
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if !suggested {
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self.point_at_expr_source_of_inferred_type(err, expr, expr_ty, expected, expr.span);

‎compiler/rustc_hir_typeck/src/fn_ctxt/suggestions.rs

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@@ -13,6 +13,7 @@ use rustc_hir::{
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use rustc_hir_analysis::astconv::AstConv;
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use rustc_infer::traits::{self, StatementAsExpression};
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use rustc_middle::lint::in_external_macro;
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use rustc_middle::ty::print::with_no_trimmed_paths;
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use rustc_middle::ty::{
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self, suggest_constraining_type_params, Binder, DefIdTree, IsSuggestable, ToPredicate, Ty,
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TypeVisitable,
@@ -1244,6 +1245,49 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
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}
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}
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/// Suggest providing `std::ptr::null()` or `std::ptr::null_mut()` if they
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/// pass in a literal 0 to an raw pointer.
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#[instrument(skip(self, err))]
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pub(crate) fn suggest_null_ptr_for_literal_zero_given_to_ptr_arg(
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&self,
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err: &mut Diagnostic,
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expr: &hir::Expr<'_>,
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expected_ty: Ty<'tcx>,
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) -> bool {
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// Expected type needs to be a raw pointer.
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let ty::RawPtr(ty::TypeAndMut { mutbl, .. }) = expected_ty.kind() else {
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return false;
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};
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// Provided expression needs to be a literal `0`.
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let ExprKind::Lit(Spanned {
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node: rustc_ast::LitKind::Int(0, _),
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span,
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}) = expr.kind else {
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return false;
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};
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// We need to find a null pointer symbol to suggest
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let null_sym = match mutbl {
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hir::Mutability::Not => sym::ptr_null,
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hir::Mutability::Mut => sym::ptr_null_mut,
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};
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let Some(null_did) = self.tcx.get_diagnostic_item(null_sym) else {
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return false;
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};
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let null_path_str = with_no_trimmed_paths!(self.tcx.def_path_str(null_did));
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// We have satisfied all requirements to provide a suggestion. Emit it.
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err.span_suggestion(
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span,
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format!("if you meant to create a null pointer, use `{null_path_str}()`"),
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null_path_str + "()",
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Applicability::MachineApplicable,
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);
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true
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}
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pub(crate) fn suggest_associated_const(
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&self,
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err: &mut Diagnostic,

‎tests/ui/suggest-null-ptr.fixed

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@@ -0,0 +1,31 @@
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// run-rustfix
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// Suggest providing a std::ptr::null{,_mut}() to a function that takes in a raw
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// pointer if a literal 0 was provided by the user.
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extern "C" {
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fn foo(ptr: *const u8);
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fn foo_mut(ptr: *mut u8);
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fn usize(ptr: *const usize);
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fn usize_mut(ptr: *mut usize);
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}
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fn main() {
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unsafe {
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foo(std::ptr::null());
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//~^ mismatched types [E0308]
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//~| if you meant to create a null pointer, use `std::ptr::null()`
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foo_mut(std::ptr::null_mut());
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//~^ mismatched types [E0308]
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//~| if you meant to create a null pointer, use `std::ptr::null_mut()`
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usize(std::ptr::null());
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//~^ mismatched types [E0308]
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//~| if you meant to create a null pointer, use `std::ptr::null()`
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usize_mut(std::ptr::null_mut());
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//~^ mismatched types [E0308]
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//~| if you meant to create a null pointer, use `std::ptr::null_mut()`
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}
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}

‎tests/ui/suggest-null-ptr.rs

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@@ -0,0 +1,31 @@
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// run-rustfix
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// Suggest providing a std::ptr::null{,_mut}() to a function that takes in a raw
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// pointer if a literal 0 was provided by the user.
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extern "C" {
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fn foo(ptr: *const u8);
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fn foo_mut(ptr: *mut u8);
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fn usize(ptr: *const usize);
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fn usize_mut(ptr: *mut usize);
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}
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fn main() {
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unsafe {
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foo(0);
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//~^ mismatched types [E0308]
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//~| if you meant to create a null pointer, use `std::ptr::null()`
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foo_mut(0);
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//~^ mismatched types [E0308]
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//~| if you meant to create a null pointer, use `std::ptr::null_mut()`
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usize(0);
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//~^ mismatched types [E0308]
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//~| if you meant to create a null pointer, use `std::ptr::null()`
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usize_mut(0);
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//~^ mismatched types [E0308]
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//~| if you meant to create a null pointer, use `std::ptr::null_mut()`
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}
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}

‎tests/ui/suggest-null-ptr.stderr

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error[E0308]: mismatched types
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--> $DIR/suggest-null-ptr.rs:18:13
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|
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LL | foo(0);
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| --- ^ expected `*const u8`, found `usize`
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| |
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| arguments to this function are incorrect
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|
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= note: expected raw pointer `*const u8`
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found type `usize`
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note: function defined here
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--> $DIR/suggest-null-ptr.rs:7:8
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|
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LL | fn foo(ptr: *const u8);
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| ^^^
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help: if you meant to create a null pointer, use `std::ptr::null()`
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|
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LL | foo(std::ptr::null());
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| ~~~~~~~~~~~~~~~~
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error[E0308]: mismatched types
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--> $DIR/suggest-null-ptr.rs:21:17
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|
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LL | foo_mut(0);
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| ------- ^ expected `*mut u8`, found `usize`
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| |
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| arguments to this function are incorrect
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|
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= note: expected raw pointer `*mut u8`
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found type `usize`
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note: function defined here
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--> $DIR/suggest-null-ptr.rs:9:8
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|
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LL | fn foo_mut(ptr: *mut u8);
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| ^^^^^^^
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help: if you meant to create a null pointer, use `std::ptr::null_mut()`
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|
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LL | foo_mut(std::ptr::null_mut());
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| ~~~~~~~~~~~~~~~~~~~~
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error[E0308]: mismatched types
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--> $DIR/suggest-null-ptr.rs:24:15
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|
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LL | usize(0);
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| ----- ^ expected `*const usize`, found `usize`
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| |
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| arguments to this function are incorrect
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|
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= note: expected raw pointer `*const usize`
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found type `usize`
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note: function defined here
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--> $DIR/suggest-null-ptr.rs:11:8
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|
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LL | fn usize(ptr: *const usize);
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| ^^^^^
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help: if you meant to create a null pointer, use `std::ptr::null()`
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|
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LL | usize(std::ptr::null());
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| ~~~~~~~~~~~~~~~~
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error[E0308]: mismatched types
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--> $DIR/suggest-null-ptr.rs:27:19
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|
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LL | usize_mut(0);
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| --------- ^ expected `*mut usize`, found `usize`
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| |
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| arguments to this function are incorrect
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|
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= note: expected raw pointer `*mut usize`
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found type `usize`
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note: function defined here
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--> $DIR/suggest-null-ptr.rs:13:8
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|
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LL | fn usize_mut(ptr: *mut usize);
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| ^^^^^^^^^
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help: if you meant to create a null pointer, use `std::ptr::null_mut()`
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|
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LL | usize_mut(std::ptr::null_mut());
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| ~~~~~~~~~~~~~~~~~~~~
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error: aborting due to 4 previous errors
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For more information about this error, try `rustc --explain E0308`.

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