Updated expect messages for `CString` struct and method documentation by asder8215 · Pull Request #159853 · rust-lang/rust

asder8215 · 2026-07-24T17:01:22Z

Completes a task with #159751. Updates the expect messages in library/alloc/src/ffi/c_str.rs.

rustbot · 2026-07-24T17:01:29Z

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fee1-dead · 2026-07-24T18:06:33Z

 /// // We are certain that our string doesn't have 0 bytes in the middle,
 /// // so we can .expect()
-/// let c_to_print = CString::new("Hello, world!").expect("CString::new failed");
+/// let c_to_print = CString::new("Hello, world!").expect("the provided string should not have a nul byte");


Thinking a bit on these messages that are more documentation facing (so more effort to consider what's the best), "the provided string" language seems to vaguely suggesting a variable, when we're actually using a constant. Perhaps it would be more clear to say like:

"we provided a string without NUL bytes, so CString::new should not fail" "we provided bytes that are invalid UTF-8, so `into_string` should fail" // (we can also use `expect_err` instead of `.ok().expect`) "we provided bytes that has one NUL byte exactly at the end, so CString::from_vec_with_nul should not fail"

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rustbot · 2026-07-24T18:07:27Z

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

asder8215 · 2026-07-24T22:49:52Z

Since this was reviewed earlier by @fee1-dead, I'll assign them as the reviewer. I hope that isn't an issue.

r? @fee1-dead

fee1-dead · 2026-07-25T02:05:46Z

nice! I don't de jure have the perms to approve something in libcore, but given that this is only a user facing change for docs, should be pretty uncontroversial:

@bors r+ rollup

rust-bors · 2026-07-25T02:05:48Z

📌 Commit a32fa44 has been approved by fee1-dead

It is now in the queue for this repository.

Updated expect messages for `CString` struct and method documentation Completes a task with rust-lang#159751. Updates the expect messages in `library/alloc/src/ffi/c_str.rs`.

Rollup of 20 pull requests Successful merges: - #138618 (Support using const pointers in asm `const` operand) - #157962 (Lower paths to functions in const args as ConstKind::Error) - #158404 (trait_solver: normalize next-gen region constraints) - #158709 (rustdoc: warn on improperly interleaved HTML/MD) - #159720 (document #[global_allocator] constraints) - #159732 (optimization: don't look for diagnostic/canonical items without rustc_attrs enabled) - #159738 (implement `CovariantUnsafeCell`) - #159740 (reuse regular exported_non_generic_symbols logic in Miri) - #159780 (check `extern "custom"` function pointers) - #159786 (rustdoc-js: ignore editor temp files in test folder discovery) - #159819 (std::sync::poison: disable auto_cfg on PoisonError::new) - #155388 (stepping into where-clauses during normalization may be productive) - #155914 (when bailing on ambiguity, don't force other results to ambig) - #159439 (Fix(lib/fs/win): Fall back on Win32 delete for `Dir::remove_file`) - #159676 (Update wasm-component-ld to 0.5.27) - #159730 (allow accessing the contents of UnsafeCell without going through get) - #159809 (Avoid `#[target_features]`) - #159826 (Remove redundant `#[rustc_paren_sugar]` feature gate) - #159853 (Updated expect messages for `CString` struct and method documentation) - #159877 (Revert "Export `derive` at `core::derive` and `std::derive`")

Updated expect messages for `CString` struct and method documentation Completes a task with rust-lang#159751. Updates the expect messages in `library/alloc/src/ffi/c_str.rs`.

Rollup of 23 pull requests Successful merges: - #159720 (document #[global_allocator] constraints) - #159732 (optimization: don't look for diagnostic/canonical items without rustc_attrs enabled) - #159738 (implement `CovariantUnsafeCell`) - #159740 (reuse regular exported_non_generic_symbols logic in Miri) - #159780 (check `extern "custom"` function pointers) - #159786 (rustdoc-js: ignore editor temp files in test folder discovery) - #159819 (std::sync::poison: disable auto_cfg on PoisonError::new) - #155388 (stepping into where-clauses during normalization may be productive) - #155914 (when bailing on ambiguity, don't force other results to ambig) - #159204 (Add support to caller_location to rustc_public) - #159411 ([rustdoc] Correctly handle output options with --show-coverage) - #159439 (Fix(lib/fs/win): Fall back on Win32 delete for `Dir::remove_file`) - #159676 (Update wasm-component-ld to 0.5.27) - #159730 (allow accessing the contents of UnsafeCell without going through get) - #159809 (Avoid `#[target_features]`) - #159810 (Add tuple never coercion collection regression test) - #159826 (Remove redundant `#[rustc_paren_sugar]` feature gate) - #159853 (Updated expect messages for `CString` struct and method documentation) - #159877 (Revert "Export `derive` at `core::derive` and `std::derive`") - #159878 (bootstrap: Remove obsolete option `build.compiletest-use-stage0-libtest`) - #159882 (Update expect messages in library/alloc/boxed.rs and library/alloc/string.rs to follow the style guide) - #159891 (Split multiline derives into std/rustc macros) - #159895 (rustc-dev-guide subtree update)

Updated expect messages for `CString` struct and method documentation Completes a task with rust-lang#159751. Updates the expect messages in `library/alloc/src/ffi/c_str.rs`.

Rollup of 23 pull requests Successful merges: - #159673 (bootstrap: forward -fdebug-prefix-map when using cc) - #159720 (document #[global_allocator] constraints) - #159732 (optimization: don't look for diagnostic/canonical items without rustc_attrs enabled) - #159738 (implement `CovariantUnsafeCell`) - #159740 (reuse regular exported_non_generic_symbols logic in Miri) - #159780 (check `extern "custom"` function pointers) - #159786 (rustdoc-js: ignore editor temp files in test folder discovery) - #159819 (std::sync::poison: disable auto_cfg on PoisonError::new) - #155388 (stepping into where-clauses during normalization may be productive) - #155914 (when bailing on ambiguity, don't force other results to ambig) - #159204 (Add support to caller_location to rustc_public) - #159411 ([rustdoc] Correctly handle output options with --show-coverage) - #159439 (Fix(lib/fs/win): Fall back on Win32 delete for `Dir::remove_file`) - #159676 (Update wasm-component-ld to 0.5.27) - #159730 (allow accessing the contents of UnsafeCell without going through get) - #159809 (Avoid `#[target_features]`) - #159810 (Add tuple never coercion collection regression test) - #159826 (Remove redundant `#[rustc_paren_sugar]` feature gate) - #159853 (Updated expect messages for `CString` struct and method documentation) - #159878 (bootstrap: Remove obsolete option `build.compiletest-use-stage0-libtest`) - #159882 (Update expect messages in library/alloc/boxed.rs and library/alloc/string.rs to follow the style guide) - #159891 (Split multiline derives into std/rustc macros) - #159895 (rustc-dev-guide subtree update)

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-libs Relevant to the library team, which will review and decide on the PR/issue. labels Jul 24, 2026

rustbot assigned Mark-Simulacrum Jul 24, 2026

fee1-dead requested changes Jul 24, 2026

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rustbot added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Jul 24, 2026

Updated expect messages for CString struct and method documentation

a32fa44

asder8215 force-pushed the cstr_expect branch from 1da327f to a32fa44 Compare July 24, 2026 22:47

rustbot assigned fee1-dead and unassigned Mark-Simulacrum Jul 24, 2026

asder8215 requested a review from fee1-dead July 24, 2026 22:50

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 (such as code changes or more information) from the author. labels Jul 24, 2026

rust-bors Bot added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Jul 25, 2026

jhpratt mentioned this pull request Jul 25, 2026

Rollup of 19 pull requests #159879

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jhpratt mentioned this pull request Jul 25, 2026

Rollup of 20 pull requests #159888

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GuillaumeGomez mentioned this pull request Jul 25, 2026

Rollup of 23 pull requests #159903

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GuillaumeGomez mentioned this pull request Jul 25, 2026

Rollup of 23 pull requests #159905

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Updated expect messages for `CString` struct and method documentation#159853

Updated expect messages for `CString` struct and method documentation#159853
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