Downgrade string_lit_as_bytes to nursery

[dtolnay]

Between #1402 (regarding to_owned) and #4494 (regarding impl Read), as well as other confusion I've seen hit in my work codebase involving string_lit_as_bytes ("...".as_bytes().into()), I don't think this lint is at a quality to be enabled by default.

I would consider re-enabling this lint after it is updated to understand when the surrounding type information is sufficient to unsize b"..." to &[u8] without causing a type error.

As currently implemented, this lint is pushing people to write &b"_"[..] which is not an improvement over "_".as_bytes() as far as I am concerned.

---

changelog: Remove string_lit_as_bytes from default set of enabled lints

[rust-highfive]

r? @matthiaskrgr

(rust_highfive has picked a reviewer for you, use r? to override)

[dtolnay]

CI failure appears unrelated.

error[E0061]: this function takes 2 arguments but 3 arguments were supplied
  --> clippy_lints/src/redundant_clone.rs:89:14
   |
89 |             .into_engine(cx.tcx, mir, def_id.to_def_id())
   |              ^^^^^^^^^^^ ------  ---  ------------------ supplied 3 arguments
   |              |
   |              expected 2 arguments

[dtolnay]

• Rebased on Rustup #6126 to maybe fix the build.

[dtolnay]

Passed!

[ebroto]

I agree that the suggestion is broken so it seems fair to downgrade it.

Could you please add a small note in the Known problems section explaining why it's in the nursery?

[dtolnay]

Added documentation of known problems.

Known Problems:

"str".as_bytes() and the suggested replacement of b"str" are not equivalent because they have different types. The former is &[u8] while the latter is &[u8; 3]. That means in general they will have a different set of methods and different trait implementations.

fn f(v: Vec<u8>) {}

f("...".as_bytes().to_owned()); // works
f(b"...".to_owned()); // does not work, because arg is [u8; 3] not Vec<u8>

fn g(r: impl std::io::Read) {}

g("...".as_bytes()); // works
g(b"..."); // does not work

The actual equivalent of "str".as_bytes() with the same type is not b"str" but &b"str"[..], which is a great deal of punctuation and not more readable than a function call.

[ebroto]

@bors r+

Thanks for the nice explanation of the problem

[bors]

📌 Commit c81bea4 has been approved by ebroto

[bors]

⌛ Testing commit c81bea4 with merge 265e484...

[bors]

☀️ Test successful - checks-action_dev_test, checks-action_remark_test, checks-action_test
Approved by: ebroto
Pushing 265e484 to master...