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diff --git a/src/tools/clippy/src/docs/ptr_as_ptr.txt b/src/tools/clippy/src/docs/ptr_as_ptr.txt
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index 000000000..8fb35c4aa
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+++ b/src/tools/clippy/src/docs/ptr_as_ptr.txt
@@ -0,0 +1,22 @@
+### What it does
+Checks for `as` casts between raw pointers without changing its mutability,
+namely `*const T` to `*const U` and `*mut T` to `*mut U`.
+
+### Why is this bad?
+Though `as` casts between raw pointers is not terrible, `pointer::cast` is safer because
+it cannot accidentally change the pointer's mutability nor cast the pointer to other types like `usize`.
+
+### Example
+```
+let ptr: *const u32 = &42_u32;
+let mut_ptr: *mut u32 = &mut 42_u32;
+let _ = ptr as *const i32;
+let _ = mut_ptr as *mut i32;
+```
+Use instead:
+```
+let ptr: *const u32 = &42_u32;
+let mut_ptr: *mut u32 = &mut 42_u32;
+let _ = ptr.cast::<i32>();
+let _ = mut_ptr.cast::<i32>();
+```
+\ No newline at end of file