as_ptr_cast: move the unfixable case into a separate file (#15475)

allows creating `.fixed` for the main file

changelog: none

tests/ui/as_ptr_cast_mut.fixed

@@ -0,0 +1,38 @@
+#![allow(unused)]
+#![warn(clippy::as_ptr_cast_mut)]
+#![allow(clippy::wrong_self_convention, clippy::unnecessary_cast)]
+
+struct MutPtrWrapper(Vec<u8>);
+impl MutPtrWrapper {
+    fn as_ptr(&mut self) -> *const u8 {
+        self.0.as_mut_ptr() as *const u8
+    }
+}
+
+struct Covariant<T>(*const T);
+impl<T> Covariant<T> {
+    fn as_ptr(self) -> *const T {
+        self.0
+    }
+}
+
+fn main() {
+    let mut string = String::new();
+    let _ = string.as_mut_ptr();
+    //~^ as_ptr_cast_mut
+
+    let _ = string.as_ptr() as *const i8;
+    let _ = string.as_mut_ptr();
+    let _ = string.as_mut_ptr() as *mut u8;
+    let _ = string.as_mut_ptr() as *const u8;
+
+    let nn = std::ptr::NonNull::new(4 as *mut u8).unwrap();
+    let _ = nn.as_ptr() as *mut u8;
+
+    let mut wrap = MutPtrWrapper(Vec::new());
+    let _ = wrap.as_ptr() as *mut u8;
+
+    let mut local = 4;
+    let ref_with_write_perm = Covariant(std::ptr::addr_of_mut!(local) as *const _);
+    let _ = ref_with_write_perm.as_ptr() as *mut u8;
+}

tests/ui/as_ptr_cast_mut.rs

@@ -1,7 +1,6 @@
 #![allow(unused)]
 #![warn(clippy::as_ptr_cast_mut)]
 #![allow(clippy::wrong_self_convention, clippy::unnecessary_cast)]
-//@no-rustfix: incorrect suggestion
 
 struct MutPtrWrapper(Vec<u8>);
 impl MutPtrWrapper {
@@ -22,9 +21,6 @@ fn main() {
     let _ = string.as_ptr() as *mut u8;
     //~^ as_ptr_cast_mut
 
-    let _: *mut i8 = string.as_ptr() as *mut _;
-    //~^ as_ptr_cast_mut
-
     let _ = string.as_ptr() as *const i8;
     let _ = string.as_mut_ptr();
     let _ = string.as_mut_ptr() as *mut u8;

tests/ui/as_ptr_cast_mut.stderr

@@ -1,5 +1,5 @@
 error: casting the result of `as_ptr` to *mut u8
-  --> tests/ui/as_ptr_cast_mut.rs:22:13
+  --> tests/ui/as_ptr_cast_mut.rs:21:13
    |
 LL |     let _ = string.as_ptr() as *mut u8;
    |             ^^^^^^^^^^^^^^^^^^^^^^^^^^ help: replace with: `string.as_mut_ptr()`
@@ -7,11 +7,5 @@ LL |     let _ = string.as_ptr() as *mut u8;
    = note: `-D clippy::as-ptr-cast-mut` implied by `-D warnings`
    = help: to override `-D warnings` add `#[allow(clippy::as_ptr_cast_mut)]`
 
-error: casting the result of `as_ptr` to *mut i8
-  --> tests/ui/as_ptr_cast_mut.rs:25:22
-   |
-LL |     let _: *mut i8 = string.as_ptr() as *mut _;
-   |                      ^^^^^^^^^^^^^^^^^^^^^^^^^ help: replace with: `string.as_mut_ptr()`
-
-error: aborting due to 2 previous errors
+error: aborting due to 1 previous error
 

tests/ui/as_ptr_cast_mut_unfixable.rs

@@ -0,0 +1,16 @@
+//@no-rustfix
+#![allow(unused)]
+#![warn(clippy::as_ptr_cast_mut)]
+
+fn main() {
+    let mut string = String::new();
+
+    // the `*mut _` is actually necessary since it does two things at once:
+    // - changes the mutability (caught by the lint)
+    // - changes the type
+    //
+    // and so replacing this with `as_mut_ptr` removes the second thing,
+    // resulting in a type mismatch
+    let _: *mut i8 = string.as_ptr() as *mut _;
+    //~^ as_ptr_cast_mut
+}

tests/ui/as_ptr_cast_mut_unfixable.stderr

@@ -0,0 +1,11 @@
+error: casting the result of `as_ptr` to *mut i8
+  --> tests/ui/as_ptr_cast_mut_unfixable.rs:14:22
+   |
+LL |     let _: *mut i8 = string.as_ptr() as *mut _;
+   |                      ^^^^^^^^^^^^^^^^^^^^^^^^^ help: replace with: `string.as_mut_ptr()`
+   |
+   = note: `-D clippy::as-ptr-cast-mut` implied by `-D warnings`
+   = help: to override `-D warnings` add `#[allow(clippy::as_ptr_cast_mut)]`
+
+error: aborting due to 1 previous error
+