Remove unneeded .as_bytes()

[samueltardieu]

&str already implements AsRef<[u8]>

changelog: none

[rustbot]

r? @llogiq

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[smoelius]

Dylint has an unnecessary_conversion_for_trait lint that suggests this and other similar, possible improvements (see below). I would be willing to donate it to Clippy. Would Clippy want it?

I understand that the lint would need to undergo the standard review process, that this would likely require changes, and that the review would not take place until the feature freeze has ended.

Warnings generated at commit 0450db3

$ find . -name Cargo.toml | xargs -n 1 cargo dylint --git https://github.com/trailofbits/dylint --pattern examples/supplementary/unnecessary_conversion_for_trait -- --manifes
t-path 2>&1 | grep -v 'no edition set' | grep -A 5 '^warning:'
warning: the receiver implements the required traits
   --> lintcheck/src/main.rs:177:55
    |
177 |             .env("CARGO_TARGET_DIR", shared_target_dir.as_os_str())
    |                                                       ^^^^^^^^^^^^ help: remove this
    |
--
warning: `lintcheck` (bin "lintcheck") generated 1 warning (run `cargo fix --bin "lintcheck"` to apply 1 suggestion)
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.05s
Building workspace metadata entry `unnecessary_conversion_for_trait`
    Finished `release` profile [optimized] target(s) in 0.08s
Checking with toolchain `nightly-2025-05-14-x86_64-unknown-linux-gnu`
warning: the receiver implements the required traits
   --> clippy_dev/src/fmt.rs:255:25
    |
255 |         fs::write(path, new_text.as_bytes())?;
    |                         ^^^^^^^^^^^^^^^^^^^ help: use: `&new_text`
    |
--
warning: the receiver implements the required traits
   --> clippy_dev/src/fmt.rs:352:19
    |
352 |         .args(args.iter())
    |                   ^^^^^^^ help: remove this

warning: the receiver implements the required traits
   --> clippy_dev/src/fmt.rs:387:67
    |
387 |     let output = Command::new(program).current_dir(&dir).args(args.iter()).output()?;
    |                                                                   ^^^^^^^ help: remove this

warning: the receiver implements the required traits
  --> clippy_dev/src/new_lint.rs:98:32
   |
98 |         write_file(&lint_path, lint_contents.as_bytes())?;
   |                                ^^^^^^^^^^^^^^^^^^^^^^^^ help: use: `&lint_contents`

warning: the receiver implements the required traits
   --> clippy_dev/src/new_lint.rs:436:16
    |
436 |     write_file(lint_file_path.as_path(), lint_file_contents)?;
    |                ^^^^^^^^^^^^^^^^^^^^^^^^ help: use: `&lint_file_path`

warning: `clippy_dev` (lib) generated 5 warnings (run `cargo fix --lib -p clippy_dev` to apply 5 suggestions)
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.03s
Building workspace metadata entry `unnecessary_conversion_for_trait`
    Finished `release` profile [optimized] target(s) in 0.08s
Checking with toolchain `nightly-2025-05-14-x86_64-unknown-linux-gnu`
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.02s
--
warning: the receiver implements the required traits
   --> src/sugg.rs:672:43
    |
672 |             self.span_suggestion(span, msg.to_string(), format!("{attr}\n{indent}"), applicability);
    |                                           ^^^^^^^^^^^^ help: remove this
    |
--
warning: the receiver implements the required traits
   --> src/sugg.rs:693:43
    |
693 |             self.span_suggestion(span, msg.to_string(), format!("{new_item}\n{indent}"), applicability);
    |                                           ^^^^^^^^^^^^ help: remove this

warning: the receiver implements the required traits
   --> src/sugg.rs:710:46
    |
710 |         self.span_suggestion(remove_span, msg.to_string(), "", applicability);
    |                                              ^^^^^^^^^^^^ help: remove this

warning: `clippy_utils` (lib) generated 3 warnings (run `cargo fix --lib -p clippy_utils` to apply 3 suggestions)
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.01s
Building workspace metadata entry `unnecessary_conversion_for_trait`
    Finished `release` profile [optimized] target(s) in 0.08s
Checking with toolchain `nightly-2025-05-14-x86_64-unknown-linux-gnu`
warning: the receiver implements the required traits
  --> src/almost_complete_range.rs:63:34
   |
63 | ...                   "..=".to_owned(),
   |                            ^^^^^^^^^^^ help: remove this
   |
--
warning: the receiver implements the required traits
   --> src/matches/single_match.rs:130:51
    |
130 |             diag.span_suggestion(expr.span, help, sugg.to_string(), app);
    |                                                   ^^^^^^^^^^^^^^^^ help: use: `&sugg`

warning: the receiver implements the required traits
   --> src/matches/single_match.rs:186:48
    |
186 |         diag.span_suggestion(expr.span, "try", sugg.to_string(), app);
    |                                                ^^^^^^^^^^^^^^^^ help: use: `&sugg`

warning: the receiver implements the required traits
   --> src/matches/single_match.rs:400:21
    |
400 |                 pats.iter(),
    |                     ^^^^^^^ help: remove this

warning: the receiver implements the required traits
   --> src/methods/open_options.rs:192:38
    |
192 |                     ".truncate(true)".to_string(),
    |                                      ^^^^^^^^^^^^ help: remove this

warning: the receiver implements the required traits
  --> src/methods/vec_resize_to_zero.rs:42:30
   |
42 |                     "clear()".to_string(),
   |                              ^^^^^^^^^^^^ help: remove this

warning: the receiver implements the required traits
   --> src/misc.rs:295:44
    |
295 |             "used underscore-prefixed item".to_string(),
    |                                            ^^^^^^^^^^^^ help: remove this

warning: the receiver implements the required traits
   --> src/misc.rs:297:71
    |
297 |                 diag.span_note(definition_span, "item is defined here".to_string());
    |                                                                       ^^^^^^^^^^^^ help: remove this

warning: the receiver implements the required traits
   --> src/misc.rs:340:47
    |
340 |             "used underscore-prefixed binding".to_string(),
    |                                               ^^^^^^^^^^^^ help: remove this

warning: the receiver implements the required traits
   --> src/misc.rs:342:74
    |
342 |                 diag.span_note(definition_span, "binding is defined here".to_string());
    |                                                                          ^^^^^^^^^^^^ help: remove this

warning: the receiver implements the required traits
  --> src/misc_early/zero_prefixed_literal.rs:19:33
   |
19 |                 trimmed_lit_snip.to_string(),
   |                                 ^^^^^^^^^^^^ help: remove this

warning: the receiver implements the required traits
   --> src/needless_pass_by_ref_mut.rs:282:55
    |
282 | ...                   "consider changing to".to_string(),
    |                                             ^^^^^^^^^^^^ help: remove this

warning: the receiver implements the required traits
  --> src/redundant_pub_crate.rs:69:30
   |
69 |                         "pub".to_string(),
   |                              ^^^^^^^^^^^^ help: remove this

warning: the receiver implements the required traits
   --> src/std_instead_of_core.rs:147:41
    |
147 | ...                   replace_with.to_string(),
    |                                   ^^^^^^^^^^^^ help: remove this

warning: the receiver implements the required traits
  --> src/transmute/transmute_int_to_bool.rs:33:25
   |
33 |                         sugg::make_binop(ast::BinOpKind::Ne, &arg, &zero).to_string(),
   |                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: use: `&sugg::make_binop(ast::BinOpKind::Ne, &arg, &zero)`

warning: the receiver implements the required traits
  --> src/transmute/transmutes_expressible_as_ptr_casts.rs:29:29
   |
29 |                 .as_ty(to_ty.to_string())
   |                             ^^^^^^^^^^^^ help: remove this

warning: the receiver implements the required traits
  --> src/transmute/transmutes_expressible_as_ptr_casts.rs:33:25
   |
33 |             .as_ty(to_ty.to_string())
   |                         ^^^^^^^^^^^^ help: remove this

warning: the receiver implements the required traits
  --> src/transmute/useless_transmute.rs:59:76
   |
59 |                         diag.span_suggestion(e.span, "try", arg.as_ty(to_ty.to_string()), Applicability::Unspecified);
   |                                                                            ^^^^^^^^^^^^ help: remove this

warning: the receiver implements the required traits
  --> src/unnecessary_box_returns.rs:95:33
   |
95 |                         boxed_ty.to_string(),
   |                                 ^^^^^^^^^^^^ help: remove this

warning: `clippy_lints` (lib) generated 19 warnings (run `cargo fix --lib -p clippy_lints` to apply 19 suggestions)
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.03s
Building workspace metadata entry `unnecessary_conversion_for_trait`
    Finished `release` profile [optimized] target(s) in 0.08s
Checking with toolchain `nightly-2025-05-14-x86_64-unknown-linux-gnu`
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.01s
--
warning: the inner argument implements the required traits
   --> src/driver.rs:229:29
    |
229 |                 args.extend(vec!["--sysroot".into(), sys_root]);
    |                             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
--
warning: `clippy` (bin "clippy-driver") generated 1 warning
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.05s

[dswij]

That'd be highly welcomed! @smoelius