rust-rust-lang-rust-update-comment

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Before…lines 1–10 unchanged (10 lines)
  for &my_bool in &[true, false] {
      let mask = -(my_bool as TwoPtrs); // false -> 0, true -> -1 aka !0
      // This is branchless code to select one or the other pointer.
      // However, it drops provenance when transmuting to TwoPtrs, so this is UB.
      let val = unsafe {
          transmute::<_, &str>(
              //~^ ERROR: constructing invalid value: encountered a dangling reference
              !mask & transmute::<_, TwoPtrs>("false !")
                  | mask & transmute::<_, TwoPtrs>("true !"),
          )
      };
      println!("{}", val);
  }
24}
25

After…lines 1–10 unchanged (10 lines)
  for &my_bool in &[true, false] {
      let mask = -(my_bool as TwoPtrs); // false -> 0, true -> -1 aka !0
      // This is branchless code to select one or the other pointer.
      // However, it drops provenance when transmuting to TwoPtrs, so this is UB.
      let val = unsafe {
          transmute::<_, &str>(
              //~^ ERROR: encountered a dangling reference
              !mask & transmute::<_, TwoPtrs>("false !")
                  | mask & transmute::<_, TwoPtrs>("true !"),
          )
      };
      println!("{}", val);
  }
24}
25

Before…lines 1–10 unchanged (10 lines)
  for &my_bool in &[true, false] {
      let mask = -(my_bool as TwoPtrs); // false -> 0, true -> -1 aka !0
      // This is branchless code to select one or the other pointer.
      // However, it drops provenance when transmuting to TwoPtrs, so this is UB.
      let val = unsafe {
          transmute::<_, &str>(
              //~^ ERROR: constructing invalid value: encountered a dangling reference
              !mask & transmute::<_, TwoPtrs>("false !")
                  | mask & transmute::<_, TwoPtrs>("true !"),
          )
      };
      println!("{}", val);
  }
24}
25

After…lines 1–10 unchanged (10 lines)
  for &my_bool in &[true, false] {
      let mask = -(my_bool as TwoPtrs); // false -> 0, true -> -1 aka !0
      // This is branchless code to select one or the other pointer.
      // However, it drops provenance when transmuting to TwoPtrs, so this is UB.
      let val = unsafe {
          transmute::<_, &str>(
              //~^ ERROR: encountered a dangling reference
              !mask & transmute::<_, TwoPtrs>("false !")
                  | mask & transmute::<_, TwoPtrs>("true !"),
          )
      };
      println!("{}", val);
  }
24}
25

Before…lines 1–10 unchanged (10 lines)
  for &my_bool in &[true, false] {
      let mask = -(my_bool as TwoPtrs); // false -> 0, true -> -1 aka !0
      // This is branchless code to select one or the other pointer.
      // However, it drops provenance when transmuting to TwoPtrs, so this is UB.
      let val = unsafe {
          transmute::<_, &str>(
              //~^ ERROR: constructing invalid value: encountered a dangling reference
              !mask & transmute::<_, TwoPtrs>("false !")
                  | mask & transmute::<_, TwoPtrs>("true !"),
          )
      };
      println!("{}", val);
  }
24}
25

After…lines 1–10 unchanged (10 lines)
  for &my_bool in &[true, false] {
      let mask = -(my_bool as TwoPtrs); // false -> 0, true -> -1 aka !0
      // This is branchless code to select one or the other pointer.
      // However, it drops provenance when transmuting to TwoPtrs, so this is UB.
      let val = unsafe {
          transmute::<_, &str>(
              //~^ ERROR: encountered a dangling reference
              !mask & transmute::<_, TwoPtrs>("false !")
                  | mask & transmute::<_, TwoPtrs>("true !"),
          )
      };
      println!("{}", val);
  }
24}
25

Before

source_file

inner_attribute_item

# "#"

! "!"

[ "["

attribute

identifier "allow"

token_tree

( "("

identifier "integer_to_ptr_transmutes"

) ")"

] "]"

use_declaration

use "use"

scoped_identifier

identifier "std"

:: "::"

identifier "mem"

:: "::"

identifier "transmute"

; ";"

attribute_item

# "#"

[ "["

attribute

identifier "cfg"

token_tree

( "("

identifier "target_pointer_width"

= "="

string_literal

" "\""

string_content "32"

" "\""

) ")"

] "]"

type_item

type "type"

type_identifier "TwoPtrs"

= "="

primitive_type "i64"

; ";"

attribute_item

# "#"

[ "["

attribute

identifier "cfg"

token_tree

( "("

identifier "target_pointer_width"

= "="

string_literal

" "\""

string_content "64"

" "\""

) ")"

] "]"

type_item

type "type"

type_identifier "TwoPtrs"

= "="

primitive_type "i128"

; ";"

function_item

fn "fn"

identifier "main"

parameters

( "("

) ")"

block

{ "{"

expression_statement

for_expression

for "for"

reference_pattern

& "&"

identifier "my_bool"

in "in"

reference_expression

& "&"

array_expression

[ "["

boolean_literal

true "true"

, ","

boolean_literal

false "false"

] "]"

block

{ "{"

let_declaration

let "let"

identifier "mask"

= "="

unary_expression

- "-"

parenthesized_expression

( "("

type_cast_expression

identifier "my_bool"

as "as"

type_identifier "TwoPtrs"

) ")"

; ";"

line_comment

// "//"

line_comment

// "//"

line_comment

// "//"

let_declaration

let "let"

identifier "val"

= "="

unsafe_block

unsafe "unsafe"

block

{ "{"

call_expression

generic_function

identifier "transmute"

:: "::"

type_arguments

< "<"

type_identifier "_"

, ","

reference_type

& "&"

primitive_type "str"

> ">"

arguments

( "("

line_comment

// "//"

binary_expression (+44 nodes collapsed)

, ","

) ")"

} "}"

; ";"

expression_statement

macro_invocation

identifier "println"

! "!"

token_tree

( "("

string_literal

" "\""

string_content "{}"

" "\""

, ","

identifier "val"

) ")"

; ";"

} "}"

After

source_file

inner_attribute_item

# "#"

! "!"

[ "["

attribute

identifier "allow"

token_tree

( "("

identifier "integer_to_ptr_transmutes"

) ")"

] "]"

use_declaration

use "use"

scoped_identifier

identifier "std"

:: "::"

identifier "mem"

:: "::"

identifier "transmute"

; ";"

attribute_item

# "#"

[ "["

attribute

identifier "cfg"

token_tree

( "("

identifier "target_pointer_width"

= "="

string_literal

" "\""

string_content "32"

" "\""

) ")"

] "]"

type_item

type "type"

type_identifier "TwoPtrs"

= "="

primitive_type "i64"

; ";"

attribute_item

# "#"

[ "["

attribute

identifier "cfg"

token_tree

( "("

identifier "target_pointer_width"

= "="

string_literal

" "\""

string_content "64"

" "\""

) ")"

] "]"

type_item

type "type"

type_identifier "TwoPtrs"

= "="

primitive_type "i128"

; ";"

function_item

fn "fn"

identifier "main"

parameters

( "("

) ")"

block

{ "{"

expression_statement

for_expression

for "for"

reference_pattern

& "&"

identifier "my_bool"

in "in"

reference_expression

& "&"

array_expression

[ "["

boolean_literal

true "true"

, ","

boolean_literal

false "false"

] "]"

block

{ "{"

let_declaration

let "let"

identifier "mask"

= "="

unary_expression

- "-"

parenthesized_expression

( "("

type_cast_expression

identifier "my_bool"

as "as"

type_identifier "TwoPtrs"

) ")"

; ";"

line_comment

// "//"

line_comment

// "//"

line_comment

// "//"

let_declaration

let "let"

identifier "val"

= "="

unsafe_block

unsafe "unsafe"

block

{ "{"

call_expression

generic_function

identifier "transmute"

:: "::"

type_arguments

< "<"

type_identifier "_"

, ","

reference_type

& "&"

primitive_type "str"

> ">"

arguments

( "("

line_comment

// "//"

binary_expression (+44 nodes collapsed)

, ","

) ")"

} "}"

; ";"

expression_statement

macro_invocation

identifier "println"

! "!"

token_tree

( "("

string_literal

" "\""

string_content "{}"

" "\""

, ","

identifier "val"

) ")"

; ";"

} "}"