Rollup merge of #148348 - hkBst:dangling-ptr-lint-1, r=Urgau

dangling ptr lint cleanup

This cleans up the dangling_pointers_from_locals lint.

Author: matthiaskrgr

compiler/rustc_lint/messages.ftl

@@ -193,11 +193,11 @@ lint_confusable_identifier_pair = found both `{$existing_sym}` and `{$sym}` as i
     .current_use = this identifier can be confused with `{$existing_sym}`
     .other_use = other identifier used here
 
-lint_dangling_pointers_from_locals = a dangling pointer will be produced because the local variable `{$local_var_name}` will be dropped
-    .ret_ty = return type of the {$fn_kind} is `{$ret_ty}`
-    .local_var = `{$local_var_name}` is part the {$fn_kind} and will be dropped at the end of the {$fn_kind}
+lint_dangling_pointers_from_locals = {$fn_kind} returns a dangling pointer to dropped local variable `{$local_var_name}`
+    .ret_ty = return type is `{$ret_ty}`
+    .local_var = local variable `{$local_var_name}` is dropped at the end of the {$fn_kind}
     .created_at = dangling pointer created here
-    .note = pointers do not have a lifetime; after returning, the `{$local_var_ty}` will be deallocated at the end of the {$fn_kind} because nothing is referencing it as far as the type system is concerned
+    .note = a dangling pointer is safe, but dereferencing one is undefined behavior
 
 lint_dangling_pointers_from_temporaries = a dangling pointer will be produced because the temporary `{$ty}` will be dropped
     .label_ptr = this pointer will immediately be invalid

tests/ui/lint/dangling-pointers-from-locals.rs

@@ -8,54 +8,54 @@ const X: u8 = 5;
 fn simple() -> *const u8 {
     let x = 0;
     &x
-    //~^ WARN a dangling pointer will be produced
+    //~^ WARN dangling pointer
 }
 
 fn bindings() -> *const u8 {
     let x = 0;
     let x = &x;
     x
-    //~^ WARN a dangling pointer will be produced
+    //~^ WARN dangling pointer
 }
 
 fn bindings_with_return() -> *const u8 {
     let x = 42;
     let y = &x;
     return y;
-    //~^ WARN a dangling pointer will be produced
+    //~^ WARN dangling pointer
 }
 
 fn with_simple_cast() -> *const u8 {
     let x = 0u8;
     &x as *const u8
-    //~^ WARN a dangling pointer will be produced
+    //~^ WARN dangling pointer
 }
 
 fn bindings_and_casts() -> *const u8 {
     let x = 0u8;
     let x = &x as *const u8;
     x as *const u8
-    //~^ WARN a dangling pointer will be produced
+    //~^ WARN dangling pointer
 }
 
 fn return_with_complex_cast() -> *mut u8 {
     let mut x = 0u8;
     return &mut x as *mut u8 as *const u8 as *mut u8;
-    //~^ WARN a dangling pointer will be produced
+    //~^ WARN dangling pointer
 }
 
 fn with_block() -> *const u8 {
     let x = 0;
     &{ x }
-    //~^ WARN a dangling pointer will be produced
+    //~^ WARN dangling pointer
 }
 
 fn with_many_blocks() -> *const u8 {
     let x = 0;
     {
         {
             &{
-                //~^ WARN a dangling pointer will be produced
+                //~^ WARN dangling pointer
                 { x }
             }
         }
@@ -65,41 +65,41 @@ fn with_many_blocks() -> *const u8 {
 fn simple_return() -> *const u8 {
     let x = 0;
     return &x;
-    //~^ WARN a dangling pointer will be produced
+    //~^ WARN dangling pointer
 }
 
 fn return_mut() -> *mut u8 {
     let mut x = 0;
     return &mut x;
-    //~^ WARN a dangling pointer will be produced
+    //~^ WARN dangling pointer
 }
 
 fn const_and_flow() -> *const u8 {
     if false {
         let x = 8;
         return &x;
-        //~^ WARN a dangling pointer will be produced
+        //~^ WARN dangling pointer
     }
     &X // not dangling
 }
 
 fn vector<T: Default>() -> *const Vec<T> {
     let x = vec![T::default()];
     &x
-    //~^ WARN a dangling pointer will be produced
+    //~^ WARN dangling pointer
 }
 
 fn local_adt() -> *const Adt {
     let x = Adt(5);
     return &x;
-    //~^ WARN a dangling pointer will be produced
+    //~^ WARN dangling pointer
 }
 
 fn closure() -> *const u8 {
     let _x = || -> *const u8 {
         let x = 8;
         return &x;
-        //~^ WARN a dangling pointer will be produced
+        //~^ WARN dangling pointer
     };
     &X // not dangling
 }
@@ -111,27 +111,27 @@ fn fn_ptr() -> *const fn() -> u8 {
 
     let x = ret_u8 as fn() -> u8;
     &x
-    //~^ WARN a dangling pointer will be produced
+    //~^ WARN dangling pointer
 }
 
 fn as_arg(a: Adt) -> *const Adt {
     &a
-    //~^ WARN a dangling pointer will be produced
+    //~^ WARN dangling pointer
 }
 
 fn fn_ptr_as_arg(a: fn() -> u8) -> *const fn() -> u8 {
     &a
-    //~^ WARN a dangling pointer will be produced
+    //~^ WARN dangling pointer
 }
 
 fn ptr_as_arg(a: *const Adt) -> *const *const Adt {
     &a
-    //~^ WARN a dangling pointer will be produced
+    //~^ WARN dangling pointer
 }
 
 fn adt_as_arg(a: &Adt) -> *const &Adt {
     &a
-    //~^ WARN a dangling pointer will be produced
+    //~^ WARN dangling pointer
 }
 
 fn unit() -> *const () {