Auto merge of rust-lang#6117 - dtolnay:string_lit_as_bytes, r=ebroto

Downgrade string_lit_as_bytes to nursery

Between rust-lang#1402 (regarding `to_owned`) and rust-lang#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

Author: bors

clippy_lints/src/lib.rs

@@ -1477,7 +1477,6 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
         LintId::of(&single_component_path_imports::SINGLE_COMPONENT_PATH_IMPORTS),
         LintId::of(&slow_vector_initialization::SLOW_VECTOR_INITIALIZATION),
         LintId::of(&stable_sort_primitive::STABLE_SORT_PRIMITIVE),
-        LintId::of(&strings::STRING_LIT_AS_BYTES),
         LintId::of(&suspicious_trait_impl::SUSPICIOUS_ARITHMETIC_IMPL),
         LintId::of(&suspicious_trait_impl::SUSPICIOUS_OP_ASSIGN_IMPL),
         LintId::of(&swap::ALMOST_SWAPPED),
@@ -1619,7 +1618,6 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
         LintId::of(&returns::LET_AND_RETURN),
         LintId::of(&returns::NEEDLESS_RETURN),
         LintId::of(&single_component_path_imports::SINGLE_COMPONENT_PATH_IMPORTS),
-        LintId::of(&strings::STRING_LIT_AS_BYTES),
         LintId::of(&tabs_in_doc_comments::TABS_IN_DOC_COMMENTS),
         LintId::of(&to_digit_is_some::TO_DIGIT_IS_SOME),
         LintId::of(&try_err::TRY_ERR),
@@ -1831,6 +1829,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
         LintId::of(&needless_borrow::NEEDLESS_BORROW),
         LintId::of(&path_buf_push_overwrite::PATH_BUF_PUSH_OVERWRITE),
         LintId::of(&redundant_pub_crate::REDUNDANT_PUB_CRATE),
+        LintId::of(&strings::STRING_LIT_AS_BYTES),
         LintId::of(&transmute::USELESS_TRANSMUTE),
         LintId::of(&use_self::USE_SELF),
     ]);

clippy_lints/src/strings.rs

@@ -69,7 +69,27 @@ declare_clippy_lint! {
     /// **Why is this bad?** Byte string literals (e.g., `b"foo"`) can be used
     /// instead. They are shorter but less discoverable than `as_bytes()`.
     ///
-    /// **Known Problems:** None.
+    /// **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.
+    ///
+    /// ```compile_fail
+    /// 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.
     ///
     /// **Example:**
     /// ```rust
@@ -80,7 +100,7 @@ declare_clippy_lint! {
     /// let bs = b"a byte string";
     /// ```
     pub STRING_LIT_AS_BYTES,
-    style,
+    nursery,
     "calling `as_bytes` on a string literal instead of using a byte string literal"
 }
 

src/lintlist/mod.rs

@@ -2161,7 +2161,7 @@ pub static ref ALL_LINTS: Vec<Lint> = vec![
     },
     Lint {
         name: "string_lit_as_bytes",
-        group: "style",
+        group: "nursery",
         desc: "calling `as_bytes` on a string literal instead of using a byte string literal",
         deprecation: None,
         module: "strings",