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

8 files changed, 10 insertions, 10 deletions

diff --git a/src/test/run-pass/cast.rs b/src/test/run-pass/cast.rs
index 37add8446f4..c7977f461df 100644
--- a/src/test/run-pass/cast.rs
+++ b/src/test/run-pass/cast.rs
@@ -15,5 +15,5 @@ pub fn main() {
     // Test that `_` is correctly inferred.
     let x = &"hello";
     let mut y = x as *const _;
-    y = 0 as *const _;
+    y = core::ptr::null_mut();
 }
diff --git a/src/test/run-pass/cleanup-shortcircuit.rs b/src/test/run-pass/cleanup-shortcircuit.rs
index 118fa0083ab..6e67a276d4f 100644
--- a/src/test/run-pass/cleanup-shortcircuit.rs
+++ b/src/test/run-pass/cleanup-shortcircuit.rs
@@ -16,6 +16,6 @@ pub fn main() {
 
     if args.len() >= 2 && args[1] == "signal" {
         // Raise a segfault.
-        unsafe { *(0 as *mut isize) = 0; }
+        unsafe { *std::ptr::null_mut::<isize>() = 0; }
     }
 }
diff --git a/src/test/run-pass/consts/const-block.rs b/src/test/run-pass/consts/const-block.rs
index 012523a61ef..7172a34c8cf 100644
--- a/src/test/run-pass/consts/const-block.rs
+++ b/src/test/run-pass/consts/const-block.rs
@@ -21,7 +21,7 @@ static BLOCK_EXPLICIT_UNIT: () = { () };
 static BLOCK_IMPLICIT_UNIT: () = { };
 static BLOCK_FLOAT: f64 = { 1.0 };
 static BLOCK_ENUM: Option<usize> = { Some(100) };
-static BLOCK_STRUCT: Foo = { Foo { a: 12, b: 0 as *const () } };
+static BLOCK_STRUCT: Foo = { Foo { a: 12, b: std::ptr::null::<()>() } };
 static BLOCK_UNSAFE: usize = unsafe { 1000 };
 
 static BLOCK_FN_INFERRED: fn(usize) -> usize = { foo };
@@ -36,7 +36,7 @@ pub fn main() {
     assert_eq!(BLOCK_IMPLICIT_UNIT, ());
     assert_eq!(BLOCK_FLOAT, 1.0_f64);
     assert_eq!(BLOCK_STRUCT.a, 12);
-    assert_eq!(BLOCK_STRUCT.b, 0 as *const ());
+    assert_eq!(BLOCK_STRUCT.b, std::ptr::null::<()>());
     assert_eq!(BLOCK_ENUM, Some(100));
     assert_eq!(BLOCK_UNSAFE, 1000);
     assert_eq!(BLOCK_FN_INFERRED(300), 300);
diff --git a/src/test/run-pass/issues/issue-13259-windows-tcb-trash.rs b/src/test/run-pass/issues/issue-13259-windows-tcb-trash.rs
index d79d34de571..740e7780de6 100644
--- a/src/test/run-pass/issues/issue-13259-windows-tcb-trash.rs
+++ b/src/test/run-pass/issues/issue-13259-windows-tcb-trash.rs
@@ -23,8 +23,8 @@ mod imp {
     pub fn test() {
         let mut buf: [u16; 50] = [0; 50];
         let ret = unsafe {
-            FormatMessageW(0x1000, 0 as *mut _, 1, 0x400,
-                           buf.as_mut_ptr(), buf.len() as u32, 0 as *const _)
+            FormatMessageW(0x1000, core::ptr::null_mut(), 1, 0x400,
+                           buf.as_mut_ptr(), buf.len() as u32, core::ptr::null())
         };
         // On some 32-bit Windowses (Win7-8 at least) this will panic with segmented
         // stacks taking control of pvArbitrary
diff --git a/src/test/run-pass/issues/issue-19001.rs b/src/test/run-pass/issues/issue-19001.rs
index 85f7a84ac29..76c380c2fc9 100644
--- a/src/test/run-pass/issues/issue-19001.rs
+++ b/src/test/run-pass/issues/issue-19001.rs
@@ -7,5 +7,5 @@ struct Loopy {
 }
 
 fn main() {
-    let _t = Loopy { ptr: 0 as *mut _ };
+    let _t = Loopy { ptr: core::ptr::null_mut() };
 }
diff --git a/src/test/run-pass/issues/issue-39367.rs b/src/test/run-pass/issues/issue-39367.rs
index 2e2b480e066..8314be3d14c 100644
--- a/src/test/run-pass/issues/issue-39367.rs
+++ b/src/test/run-pass/issues/issue-39367.rs
@@ -15,7 +15,7 @@ fn arena() -> &'static ArenaSet<Vec<u8>> {
         fn require_sync<T: Sync>(_: &T) { }
         unsafe fn __stability() -> &'static ArenaSet<Vec<u8>> {
             use std::mem::transmute;
-            static mut DATA: *const ArenaSet<Vec<u8>> = 0 as *const ArenaSet<Vec<u8>>;
+            static mut DATA: *const ArenaSet<Vec<u8>> = std::ptr::null_mut();
 
             static mut ONCE: Once = Once::new();
             ONCE.call_once(|| {
diff --git a/src/test/run-pass/issues/issue-46069.rs b/src/test/run-pass/issues/issue-46069.rs
index fba2a2ebe3b..1d4f789828d 100644
--- a/src/test/run-pass/issues/issue-46069.rs
+++ b/src/test/run-pass/issues/issue-46069.rs
@@ -17,7 +17,7 @@ fn copy_ex() {
 }
 
 fn main() {
-    let _f = 0 as *mut <Fuse<Cloned<Iter<u8>>> as Iterator>::Item;
+    let _f: *mut <Fuse<Cloned<Iter<u8>>> as Iterator>::Item = std::ptr::null_mut();
 
     copy_ex();
 }
diff --git a/src/test/run-pass/structs-enums/enum-null-pointer-opt.rs b/src/test/run-pass/structs-enums/enum-null-pointer-opt.rs
index f871c218558..32fdbf620a9 100644
--- a/src/test/run-pass/structs-enums/enum-null-pointer-opt.rs
+++ b/src/test/run-pass/structs-enums/enum-null-pointer-opt.rs
@@ -38,7 +38,7 @@ fn main() {
 
     // The optimization can't apply to raw pointers or unions with a ZST field.
     assert!(size_of::<Option<*const isize>>() != size_of::<*const isize>());
-    assert!(Some(0 as *const isize).is_some()); // Can't collapse None to null
+    assert!(Some(std::ptr::null::<isize>()).is_some()); // Can't collapse None to null
     assert_ne!(size_of::<fn(isize)>(), size_of::<Option<MaybeUninitUnion<fn(isize)>>>());
     assert_ne!(size_of::<&str>(), size_of::<Option<MaybeUninitUnion<&str>>>());
     assert_ne!(size_of::<NonNull<isize>>(), size_of::<Option<MaybeUninitUnion<NonNull<isize>>>>());