Merge pull request #1905 from ehuss/used

Update `used` to use the attribute template

Author: traviscross

src/abi.md

@@ -9,57 +9,60 @@ See *[extern functions]* for information on specifying the ABI for exporting
 functions. See *[external blocks]* for information on specifying the ABI for
 linking external libraries.
 
+<!-- template:attributes -->
 r[abi.used]
 ## The `used` attribute
 
 r[abi.used.intro]
-The *`used` attribute* can only be applied to [`static` items]. This [attribute] forces the
-compiler to keep the variable in the output object file (.o, .rlib, etc. excluding final binaries)
-even if the variable is not used, or referenced, by any other item in the crate.
-However, the linker is still free to remove such an item.
+The *`used` [attribute]* forces a [static] to be kept in the output object file (.o, .rlib, etc., excluding final binaries) even if it's never used or referenced by any other item in the crate. The linker, however, is still free to remove it.
+
+> [!EXAMPLE]
+> ```rust
+> // lib.rs
+>
+> // This is kept because of `#[used]`.
+> #[used]
+> static S1: u8 = 0;
+>
+> // This is removable because it's unused.
+> #[allow(dead_code)]
+> static S2: u8 = 0;
+>
+> // This is kept because it's publicly reachable.
+> pub static S3: u8 = 0;
+>
+> // This is kept because it's referenced by a publicly
+> // reachable function.
+> static S4: u8 = 0;
+> #[unsafe(no_mangle)] pub fn f4() -> &'static u8 { &S4 }
+>
+> // This is removable because it's referenced only by a
+> // private, unused (dead) function.
+> static S5: u8 = 0;
+> #[allow(dead_code)]
+> fn f5() -> &'static u8 { &S5 }
+> ```
+>
+> ```console
+> $ rustc -O --emit=obj --crate-type=rlib lib.rs
+> $ LC_ALL=C nm -C lib.o
+> 0000000000000000 R lib::S1
+> 0000000000000000 R lib::S3
+> 0000000000000000 r lib::S4
+> 0000000000000000 T f4
+> ```
+
+r[abi.used.syntax]
+The `used` attribute uses the [MetaWord] syntax.
+
+r[abi.used.allowed-positions]
+The `used` attribute may only be applied to [`static` items].
+
+r[abi.used.duplicates]
+Only the first use of `used` on an item has effect.
 
-Below is an example that shows under what conditions the compiler keeps a `static` item in the
-output object file.
-
-``` rust
-// foo.rs
-
-// This is kept because of `#[used]`:
-#[used]
-static FOO: u32 = 0;
-
-// This is removable because it is unused:
-#[allow(dead_code)]
-static BAR: u32 = 0;
-
-// This is kept because it is publicly reachable:
-pub static BAZ: u32 = 0;
-
-// This is kept because it is referenced by a public, reachable function:
-static QUUX: u32 = 0;
-
-pub fn quux() -> &'static u32 {
-    &QUUX
-}
-
-// This is removable because it is referenced by a private, unused (dead) function:
-static CORGE: u32 = 0;
-
-#[allow(dead_code)]
-fn corge() -> &'static u32 {
-    &CORGE
-}
-```
-
-``` console
-$ rustc -O --emit=obj --crate-type=rlib foo.rs
-
-$ nm -C foo.o
-0000000000000000 R foo::BAZ
-0000000000000000 r foo::FOO
-0000000000000000 R foo::QUUX
-0000000000000000 T foo::quux
-```
+> [!NOTE]
+> `rustc` lints against any use following the first.
 
 r[abi.no_mangle]
 ## The `no_mangle` attribute
@@ -149,10 +152,10 @@ r[abi.export_name.edition2024]
 > [!EDITION-2024]
 > Before the 2024 edition it is allowed to use the `export_name` attribute without the `unsafe` qualification.
 
-[`static` items]: items/static-items.md
 [attribute]: attributes.md
 [extern functions]: items/functions.md#extern-function-qualifier
 [external blocks]: items/external-blocks.md
 [function]: items/functions.md
 [item]: items.md
+[`static` items]: items.static
 [static]: items/static-items.md