Uplift `temporary-cstring-as-ptr` lint from `clippy` into rustc #75671

nathanwhit · 2020-08-18T16:14:50Z

The general consensus seems to be that this lint covers a common enough mistake to warrant inclusion in rustc.
The diagnostic message might need some tweaking, as I'm not sure the use of second-person perspective matches the rest of rustc, but I'd like to hear others' thoughts on that.

(cc #53224).

r? @oli-obk

Mark-Simulacrum · 2020-08-18T16:23:05Z

@bors try @rust-timer queue

rust-timer · 2020-08-18T16:23:06Z

Awaiting bors try build completion

bors · 2020-08-18T16:23:19Z

⌛ Trying commit f7da096488c6fd9d4be7c480affa26d9f7b80a02 with merge ca7ac508d257828878fb0e7cade1ad46381056f8...

oli-obk · 2020-08-18T16:39:12Z

Sgtm, modulo CI passing, perf being clean and we'll need an MCP so the entire compiler team is informed about this. Can you open an MCP? It just needs a sentence or two and maybe an example on what is now being linted.

src/librustc_lint/methods.rs

estebank · 2020-08-18T17:40:41Z

src/librustc_lint/methods.rs

We'll need a crater run to check the fallout from this (but it should still be deny by default unless we break some foundational crate, IMO).

dependencies get their lints capped anyway, so it will only break building that crate directly.

I feel that it shouldn't be deny by default as long as it considers func(CString::new("...").unwrap().as_ptr()); to be erroneous (since in typical situations this would be a false positive).

+1 for making this Warn, and not Deny (though I don't know if we have other similar deny-by-default lints).

I think we also should add a regression test for func(CString::new("...").unwrap().as_ptr());. I wouldn't personally call it as a false-positive though: it's not UB, but still sufficiently obscure style worth linting against.

I agree on the Warn by default, since the lint covers cases that aren't incorrect. That's reflected in the PR now.

src/librustc_lint/methods.rs

nathanwhit · 2020-08-18T18:19:04Z

Sgtm, modulo CI passing, perf being clean and we'll need an MCP so the entire compiler team is informed about this. Can you open an MCP? It just needs a sentence or two and maybe an example on what is now being linted.

Sure thing! Filed rust-lang/compiler-team#346.

src/test/ui/lint/lint-temporary-cstring-as-ptr.stderr

src/librustc_lint/methods.rs

library/std/src/ffi/c_str.rs

bors · 2020-08-23T04:25:40Z

☔ The latest upstream changes (presumably #73084) made this pull request unmergeable. Please resolve the merge conflicts.

jyn514 · 2020-09-01T14:26:56Z

I think rust-lang/rust-clippy#5838 should be fixed before making this deny-by-default. Warn-by-default is fine if fixing the false positive is too difficult and we want to get this in soon.

matklad · 2020-09-01T14:32:55Z

I feel moderately strongly that rust-lang/rust-clippy#5838 is not a false positive.

it is false-positive for "this code is UB", as it is not UB. But it absolutely is a true positive for "this code is confusing, because you need to be a language lawyer to understand why it is not UB".

jyn514 · 2020-09-01T14:37:37Z

it is false-positive for "this code is UB", as it is not UB. But it absolutely is a true positive for "this code is confusing, because you need to be a language lawyer to understand why it is not UB".

Then it should say that. Instead it currently says

= note: that pointer will be invalid outside this expression

Which is not true. It will be invalid outside the statement, which encompasses both the .as_ptr() and the function call.

jyn514 · 2020-09-01T14:40:04Z

Also I think it would be nice for it to link to https://doc.rust-lang.org/reference/destructors.html, but I won't block on that.

jyn514

I think this should add a test case for rust-lang/rust-clippy#5838. If the behavior there is intentional, then it should be tested; it shouldn't slip in by accident. If it's not intentional, the lint should be fixed.

src/librustc_lint/methods.rs

jyn514 · 2020-10-27T16:35:24Z

 Command failed. Attempt 5/5:
    Updating crates.io index
warning: spurious network error (2 tries remaining): error inflating zlib stream; class=Zlib (5)
warning: spurious network error (1 tries remaining): error inflating zlib stream; class=Zlib (5)
error: failed to get `cc` as a dependency of package `bootstrap v0.0.0 (D:\a\rust\rust\src\bootstrap)`

Caused by:
  failed to fetch `https://github.com/rust-lang/crates.io-index`

Caused by:
  error inflating zlib stream; class=Zlib (5)
failed to run: D:\a\rust\rust\build\i686-pc-windows-gnu\stage0\bin\cargo.exe build --manifest-path D:\a\rust\rust\src/bootstrap/Cargo.toml --locked

@bors retry

bors · 2020-10-27T22:59:18Z

⌛ Testing commit 572cd35 with merge 90e6d0d...

bors · 2020-10-28T01:39:58Z

☀️ Test successful - checks-actions
Approved by: oli-obk
Pushing 90e6d0d to master...

flip1995 · 2020-10-29T12:51:02Z

Uh, can we have a policy that the Clippy team is pinged for major changes to Clippy in rustc, such as uplifting lints. Even though the lint was removed, it wasn't deprecated properly (which is a lengthy process by design). Luckily @ebroto caught that in the rustup. But with a ping to the Clippy team we can avoid pull requests, like this "emergency sync": #78505

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Uplift temporary-cstring-as-ptr lint from clippy into rustc rust-lang/compiler-team#346

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jonas-schievink mentioned this pull request Oct 27, 2020

Rollup of 9 pull requests #78451

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bors added the merged-by-bors This PR was explicitly merged by bors. label Oct 28, 2020

bors merged commit 90e6d0d into rust-lang:master Oct 28, 2020

rustbot added this to the 1.49.0 milestone Oct 28, 2020

This was referenced Oct 28, 2020

Implement RFC 2945: "C-unwind" ABI #76570

Merged

Always print lints from plugins, if they're available #77671

Merged

Add lint for panic!("{}") #78088

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ebroto mentioned this pull request Oct 28, 2020

Update Clippy - temporary_cstring_as_ptr deprecation #78505

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jyn514 mentioned this pull request Nov 3, 2020

dangling_pointers_from_temporaries lint is imprecise (false positives and false negatives) #78691

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thomcc mentioned this pull request Dec 3, 2020

Uplift the invalid_atomic_ordering lint from clippy to rustc #79654

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jyn514 mentioned this pull request Apr 9, 2021

Uplift the invalid_atomic_ordering lint from clippy to rustc #84039

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oli-obk mentioned this pull request May 10, 2022

lint against unexpectedly late drop for temporaries in match scrutinee expressions #93883

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matthiaskrgr mentioned this pull request Apr 13, 2024

ICE: unsized arguments must not be 'extern' types #123887

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Uplift temporary-cstring-as-ptr lint from clippy into rustc #75671

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Uplift `temporary-cstring-as-ptr` lint from `clippy` into rustc #75671

Uplift `temporary-cstring-as-ptr` lint from `clippy` into rustc #75671