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Lint to disallow using as for pointer casts in favor of .cast() #5890

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retep998 opened this issue Aug 11, 2020 · 4 comments · Fixed by #6542
Closed

Lint to disallow using as for pointer casts in favor of .cast() #5890

retep998 opened this issue Aug 11, 2020 · 4 comments · Fixed by #6542
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A-lint Area: New lints E-medium Call for participation: Medium difficulty level problem and requires some initial experience. L-suggestion Lint: Improving, adding or fixing lint suggestions

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@retep998
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retep998 commented Aug 11, 2020 •
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What it does

Any raw pointer cast from *const T to *const U or *mut T to *mut U that uses as should be caught by this lint. Instead you should use .cast().

Should probably be a pedantic lint.

Drawbacks

None.

Example

foo as *const c_void

Could be written as:

foo.cast()
@retep998 retep998 added the A-lint Area: New lints label Aug 11, 2020
@matthiaskrgr
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There's a lint that seems to lint on as in general: https://rust-lang.github.io/rust-clippy/master/index.html#as_conversions

@retep998
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Yes, and there are also lints for specific types of as casts. There is no lint for specifically pointer casts while still allowing other kinds of as casts.

@ErichDonGubler
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This would seem to affect the transmutes_expressible_as_ptr_casts lint -- that link suggests using as, e.g., p as *const [u16];.

@flip1995 flip1995 added L-suggestion Lint: Improving, adding or fixing lint suggestions E-medium Call for participation: Medium difficulty level problem and requires some initial experience. labels Aug 16, 2020
@rail-rain
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It seems to me this lint has already suggested twice (#4065 and #4708 (comment)). Maybe 4065 can be closed since 5890 has a bit more details.

@flip1995 flip1995 mentioned this issue Aug 29, 2020
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@rail-rain rail-rain mentioned this issue Jan 3, 2021
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@bors bors closed this as completed in a6b72d3 Jan 5, 2021
@rail-rain rail-rain mentioned this issue Jan 19, 2021
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bors added a commit that referenced this issue Jan 19, 2021
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Auto merge of #6608 - rail-rain:note_on_as_conversions, r=phansch
e21270b 
Add a note to `as_conversions`

I have seen a couple of examples where there are some misunderstandings of `as_conversions` ([1](#5890 (comment)), [2](#6116 (comment)) and [3](#6428)). This PR adds the note that explains its purpose and relationship with other `as` related casts. Open question: should I list every related lints for discoverbility, or just suggest how to find these? I chose the former because there's no way to list only and all `as` related lints (e.g. on All the Clippt Lints, 'cast' includes some noises, but `cast_` excludes some) even though I cannot guarantee the list will be updated to include future changes.

---

changelog: Add a note to the document of `as_conversions`
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A-lint Area: New lints E-medium Call for participation: Medium difficulty level problem and requires some initial experience. L-suggestion Lint: Improving, adding or fixing lint suggestions
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Add a new lint ptr_as_ptr rail-rain/rust-clippy
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@matthiaskrgr @ErichDonGubler @retep998 @flip1995 @rail-rain