Auto merge of #61864 - lzutao:ptr-null, r=sfackler

Make use of `ptr::null(_mut)` instead of casting zero

There are few places that I don't replace the zero casting pointer with `ptr::null`
or `ptr::null_mut`:
```bash
% git grep -E '[ ([{]0 as \*'
src/libcore/ptr/mod.rs:216:pub const fn null<T>() -> *const T { 0 as *const T }
src/libcore/ptr/mod.rs:231:pub const fn null_mut<T>() -> *mut T { 0 as *mut T }
src/test/run-pass/consts/const-cast-ptr-int.rs:12:static a: TestStruct = TestStruct{x: 0 as *const u8};
src/test/ui/issues/issue-45730.rs:5:    let x: *const _ = 0 as *const _; //~ ERROR cannot cast
src/test/ui/issues/issue-45730.rs:8:    let x = 0 as *const i32 as *const _ as *mut _; //~ ERROR cannot cast
src/test/ui/issues/issue-45730.stderr:14:LL |     let x: *const _ = 0 as *const _;
src/test/ui/issues/issue-45730.stderr:24:LL |     let x = 0 as *const i32 as *const _ as *mut _;
src/test/ui/lint/lint-forbid-internal-unsafe.rs:15:    println!("{}", evil!(*(0 as *const u8)));
src/test/ui/order-dependent-cast-inference.rs:5:    let mut y = 0 as *const _;
src/test/ui/order-dependent-cast-inference.stderr:4:LL |     let mut y = 0 as *const _;
```

r? @sfackler

Author: bors

src/bootstrap/job.rs

@@ -32,6 +32,7 @@
 use std::env;
 use std::io;
 use std::mem;
+use std::ptr;
 use crate::Build;
 
 type HANDLE = *mut u8;
@@ -118,8 +119,8 @@ pub unsafe fn setup(build: &mut Build) {
     SetErrorMode(mode & !SEM_NOGPFAULTERRORBOX);
 
     // Create a new job object for us to use
-    let job = CreateJobObjectW(0 as *mut _, 0 as *const _);
-    assert!(job != 0 as *mut _, "{}", io::Error::last_os_error());
+    let job = CreateJobObjectW(ptr::null_mut(), ptr::null());
+    assert!(!job.is_null(), "{}", io::Error::last_os_error());
 
     // Indicate that when all handles to the job object are gone that all
     // process in the object should be killed. Note that this includes our
@@ -166,8 +167,8 @@ pub unsafe fn setup(build: &mut Build) {
     };
 
     let parent = OpenProcess(PROCESS_DUP_HANDLE, FALSE, pid.parse().unwrap());
-    assert!(parent != 0 as *mut _, "{}", io::Error::last_os_error());
-    let mut parent_handle = 0 as *mut _;
+    assert!(!parent.is_null(), "{}", io::Error::last_os_error());
+    let mut parent_handle = ptr::null_mut();
     let r = DuplicateHandle(GetCurrentProcess(), job,
                             parent, &mut parent_handle,
                             0, FALSE, DUPLICATE_SAME_ACCESS);

src/bootstrap/util.rs

@@ -209,7 +209,7 @@ pub fn symlink_dir(config: &Config, src: &Path, dest: &Path) -> io::Result<()> {
             let h = CreateFileW(path.as_ptr(),
                                 GENERIC_WRITE,
                                 FILE_SHARE_READ | FILE_SHARE_WRITE | FILE_SHARE_DELETE,
-                                0 as *mut _,
+                                ptr::null_mut(),
                                 OPEN_EXISTING,
                                 FILE_FLAG_OPEN_REPARSE_POINT | FILE_FLAG_BACKUP_SEMANTICS,
                                 ptr::null_mut());

src/libarena/lib.rs

@@ -114,8 +114,8 @@ impl<T> Default for TypedArena<T> {
         TypedArena {
             // We set both `ptr` and `end` to 0 so that the first call to
             // alloc() will trigger a grow().
-            ptr: Cell::new(0 as *mut T),
-            end: Cell::new(0 as *mut T),
+            ptr: Cell::new(ptr::null_mut()),
+            end: Cell::new(ptr::null_mut()),
             chunks: RefCell::new(vec![]),
             _own: PhantomData,
         }
@@ -370,8 +370,8 @@ impl Default for DroplessArena {
     #[inline]
     fn default() -> DroplessArena {
         DroplessArena {
-            ptr: Cell::new(0 as *mut u8),
-            end: Cell::new(0 as *mut u8),
+            ptr: Cell::new(ptr::null_mut()),
+            end: Cell::new(ptr::null_mut()),
             chunks: Default::default(),
         }
     }

src/libpanic_unwind/dummy.rs

@@ -7,7 +7,7 @@ use core::any::Any;
 use core::intrinsics;
 
 pub fn payload() -> *mut u8 {
-    0 as *mut u8
+    core::ptr::null_mut()
 }
 
 pub unsafe fn cleanup(_ptr: *mut u8) -> Box<dyn Any + Send> {

src/libpanic_unwind/seh.rs

@@ -104,7 +104,7 @@ mod imp {
     pub const NAME2: [u8; 7] = [b'.', b'P', b'A', b'X', 0, 0, 0];
 
     macro_rules! ptr {
-        (0) => (0 as *mut u8);
+        (0) => (core::ptr::null_mut());
         ($e:expr) => ($e as *mut u8);
     }
 }
@@ -223,13 +223,13 @@ extern "C" {
 #[cfg_attr(not(test), lang = "msvc_try_filter")]
 static mut TYPE_DESCRIPTOR1: _TypeDescriptor = _TypeDescriptor {
     pVFTable: unsafe { &TYPE_INFO_VTABLE } as *const _ as *const _,
-    spare: 0 as *mut _,
+    spare: core::ptr::null_mut(),
     name: imp::NAME1,
 };
 
 static mut TYPE_DESCRIPTOR2: _TypeDescriptor = _TypeDescriptor {
     pVFTable: unsafe { &TYPE_INFO_VTABLE } as *const _ as *const _,
-    spare: 0 as *mut _,
+    spare: core::ptr::null_mut(),
     name: imp::NAME2,
 };
 

src/librustc_errors/lock.rs

@@ -64,7 +64,7 @@ pub fn acquire_global_lock(name: &str) -> Box<dyn Any> {
         //
         // This will silently create one if it doesn't already exist, or it'll
         // open up a handle to one if it already exists.
-        let mutex = CreateMutexA(0 as *mut _, 0, cname.as_ptr() as *const u8);
+        let mutex = CreateMutexA(std::ptr::null_mut(), 0, cname.as_ptr() as *const u8);
         if mutex.is_null() {
             panic!("failed to create global mutex named `{}`: {}",
                    name,

src/librustc_metadata/dynamic_lib.rs

@@ -115,7 +115,7 @@ mod dl {
     {
         use std::sync::{Mutex, Once};
         static INIT: Once = Once::new();
-        static mut LOCK: *mut Mutex<()> = 0 as *mut _;
+        static mut LOCK: *mut Mutex<()> = ptr::null_mut();
         unsafe {
             INIT.call_once(|| {
                 LOCK = Box::into_raw(Box::new(Mutex::new(())));

src/librustc_typeck/error_codes.rs

@@ -3904,7 +3904,7 @@ x as Vec<u8>; // error: non-primitive cast: `u8` as `std::vec::Vec<u8>`
 
 // Another example
 
-let v = 0 as *const u8; // So here, `v` is a `*const u8`.
+let v = core::ptr::null::<u8>(); // So here, `v` is a `*const u8`.
 v as &u8; // error: non-primitive cast: `*const u8` as `&u8`
 ```
 
@@ -3914,7 +3914,7 @@ Only primitive types can be cast into each other. Examples:
 let x = 0u8;
 x as u32; // ok!
 
-let v = 0 as *const u8;
+let v = core::ptr::null::<u8>();
 v as *const i8; // ok!
 ```
 
@@ -3954,7 +3954,7 @@ A cast between a thin and a fat pointer was attempted.
 Erroneous code example:
 
 ```compile_fail,E0607
-let v = 0 as *const u8;
+let v = core::ptr::null::<u8>();
 v as *const [u8];
 ```
 

src/libstd/sys/wasi/args.rs

@@ -32,7 +32,7 @@ fn maybe_args() -> io::Result<Args> {
         let (mut argc, mut argv_buf_size) = (0, 0);
         cvt_wasi(libc::__wasi_args_sizes_get(&mut argc, &mut argv_buf_size))?;
 
-        let mut argc = vec![0 as *mut libc::c_char; argc];
+        let mut argc = vec![core::ptr::null_mut::<libc::c_char>(); argc];
         let mut argv_buf = vec![0; argv_buf_size];
         cvt_wasi(libc::__wasi_args_get(argc.as_mut_ptr(), argv_buf.as_mut_ptr()))?;
 

src/libstd/sys/wasm/thread_local_atomics.rs

@@ -11,7 +11,7 @@ struct ThreadControlBlock {
 impl ThreadControlBlock {
     fn new() -> ThreadControlBlock {
         ThreadControlBlock {
-            keys: [0 as *mut u8; MAX_KEYS],
+            keys: [core::ptr::null_mut(); MAX_KEYS],
         }
     }