Skip to content

feat: add cast_ptr_sized_int lint#16262

Open
ab22593k wants to merge 1 commit intorust-lang:masterfrom
ab22593k:master
Open

feat: add cast_ptr_sized_int lint#16262
ab22593k wants to merge 1 commit intorust-lang:masterfrom
ab22593k:master

Conversation

@ab22593k
Copy link

@ab22593k ab22593k commented Dec 18, 2025 •
edited
Loading

Introduce a new restriction lint to identify casts between pointer-sized integer types (usize, isize) and fixed-size integer types.

Encourage the use of TryFrom or TryInto over direct as casts to make potential platform-specific truncation or zero-extension explicit and handled.

Also Provide machine-applicable suggestions to replace risky casts with fallible conversions while excluding constant contexts where such traits are not yet stable.

Closes: #9231

changelog: add cast_ptr_sized_int lint

@rustbot rustbot added needs-fcp S-waiting-on-review Status: Awaiting review from the assignee but also interested parties labels Dec 18, 2025
@rustbot
Copy link
Collaborator

rustbot commented Dec 18, 2025

r? @samueltardieu

rustbot has assigned @samueltardieu.
They will have a look at your PR within the next two weeks and either review your PR or reassign to another reviewer.

Use r? to explicitly pick a reviewer

@rustbot

This comment has been minimized.

Sign in to view
@github-actions
Copy link

github-actions bot commented Dec 18, 2025 •
edited
Loading

Lintcheck changes for 3a6e6b3

Lint Added Removed Changed
clippy::cast_ptr_sized_int 1382 0 0

This comment will be updated if you push new changes

samueltardieu
samueltardieu reviewed Dec 19, 2025
View reviewed changes
Copy link
Member

@samueltardieu samueltardieu left a comment •
edited by rustbot
Loading

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Aren't those cases already covered by the cast_lossless, cast_possible_truncation, cast_possible_wrap, and cast_sign_loss lints?

Moreover, the suggestion transforms integer types into options, which is not a directly applicable fix.

View changes since this review

@samueltardieu
Copy link
Member

samueltardieu commented Dec 19, 2025

@rustbot author

@rustbot rustbot removed the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties label Dec 19, 2025
@rustbot
Copy link
Collaborator

rustbot commented Dec 19, 2025

Reminder, once the PR becomes ready for a review, use @rustbot ready.

@rustbot rustbot added the S-waiting-on-author Status: This is awaiting some action from the author. (Use `@rustbot ready` to update this status) label Dec 19, 2025
@ab22593k
Copy link
Author

ab22593k commented Dec 19, 2025

This is exactly the gap the lint addresses: If you compile on 64-bit, usize as u64 looks safe. But the same code behaves differently on 32-bit. No existing lint catches this architecture-dependent behavior.

The suggestion is not directly applicable: should i remove the suggestion (just warn without providing a fix)?

@samueltardieu
Copy link
Member

samueltardieu commented Dec 19, 2025

The lint still triggers inconsistently. For example:

  • usize can also be a 16-bit integer on some tier 3 platforms such as MSP430
  • A cast from u8 or u16 to usize will always succeed and should not be warned about
  • A cast from usize to u64 or u128 will always succeed and should not be warned about

And indeed, no fix should be provided if it would be incorrect, but the help message may suggest using try_from() and let the user act on it.

@ab22593k ab22593k force-pushed the master branch 2 times, most recently from fa57af9 to fba9c01 Compare December 26, 2025 08:14
@rustbot

This comment has been minimized.

Sign in to view
@ab22593k
Copy link
Author

ab22593k commented Dec 26, 2025

@rustbot ready

@rustbot rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties and removed S-waiting-on-author Status: This is awaiting some action from the author. (Use `@rustbot ready` to update this status) labels Dec 26, 2025
samueltardieu
samueltardieu requested changes Jan 18, 2026
View reviewed changes
Copy link
Member

@samueltardieu samueltardieu left a comment •
edited by rustbot
Loading

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

If you add

#![deny(clippy::cast_lossless, clippy::cast_possible_truncation, clippy::cast_possible_wrap, clippy::cast_sign_loss)]

at the top of your test file, you'll see that most of the lines that your PR lints will already be linted.

I wonder if it would be more useful to extend existing lints with an additional configuration option to warn when pointer sized ints could cause issues even though they don't on the platform on which they are compiled.

Maybe the user could even specify the range of sizes it is interested in compiling for. For example, target_usize_supported_bounds = [32, 64] would let the user indicate that they are not interested in compiling for 16 bit platforms, and the lint should report an error if the current platform is outside this range.

What do you think?

View changes since this review

tests/ui/cast_ptr_sized_int.rs Outdated
@@ -0,0 +1,89 @@
//@no-rustfix
#![warn(clippy::cast_ptr_sized_int)]
#![allow(clippy::unnecessary_cast)]
Copy link
Member

@samueltardieu samueltardieu Jan 18, 2026

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Why is this needed?

Copy link
Author

@ab22593k ab22593k Feb 1, 2026

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Sorry; just keep #![warn(clippy::cast_ptr_sized_int)]

tests/ui/cast_ptr_sized_int.stderr Outdated
@@ -0,0 +1,229 @@
error: casting `usize` to `u8`: the behavior depends on the target pointer width
Copy link
Member

@samueltardieu samueltardieu Jan 18, 2026

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

The message is not great here: casting usize to u8 will always truncate.

Copy link
Author

@ab22593k ab22593k Feb 1, 2026

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Fixed

@rustbot rustbot added S-waiting-on-author Status: This is awaiting some action from the author. (Use `@rustbot ready` to update this status) and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties labels Jan 18, 2026
@ab22593k
feat(clippy_lints): add cast_ptr_sized_int lint
3a6e6b3 
Implement a new lint to detect casts between pointer-sized integers (`usize`, `isize`)
and fixed-size integers that exhibit architecture-dependent behavior.
@rustbot
Copy link
Collaborator

rustbot commented Feb 1, 2026

This PR was rebased onto a different master commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

@ab22593k
Copy link
Author

ab22593k commented Feb 1, 2026

I think the extend cast_possible_truncation with platform bounds configuration is more is compelling.

clippy.toml Configuration:
target_pointer_widths = [32, 64] # Platforms the user targets
Default: [16, 32, 64] # Warns for all platforms

With proposed Error message with target_pointer_widths = [32, 64] like:
casting u64 to usize may truncate the value on 32-bit platforms

Benefits: No duplication. User control. Leverages existing code

@rustbot rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties and removed S-waiting-on-author Status: This is awaiting some action from the author. (Use `@rustbot ready` to update this status) labels Feb 1, 2026
@ab22593k
Copy link
Author

ab22593k commented Feb 1, 2026

@rustbot ready

Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment

Reviewers

@samueltardieu samueltardieu Awaiting requested review from samueltardieu

Requested changes must be addressed to merge this pull request.

Assignees

@samueltardieu samueltardieu

Labels

needs-fcp S-waiting-on-review Status: Awaiting review from the assignee but also interested parties

Projects

None yet

Milestone

No milestone

Development

Successfully merging this pull request may close these issues.

Have a lint against usize-to-u64 casts (or, against *all* integer casts)

3 participants

@ab22593k @rustbot @samueltardieu