rust-lang · jieyouxu · Jul 30, 2026 · Jul 30, 2026 · Jul 30, 2026 · Jul 30, 2026
diff --git a/compiler/rustc_attr_parsing/src/attributes/unroll.rs b/compiler/rustc_attr_parsing/src/attributes/unroll.rs
@@ -6,7 +6,8 @@ use super::prelude::*;
 
 pub(crate) struct UnrollParser;
 impl SingleAttributeParser for UnrollParser {
-    const PATH: &[Symbol] = &[sym::unroll];
+    // FIXME(#159429): temporarily renamed to mitigate `#[unroll]` nameres ambiguity.
+    const PATH: &[Symbol] = &[sym::rustc_unroll];
     const ALLOWED_TARGETS: AllowedTargets<'_> = AllowedTargets::AllowList(&[
         Allow(Target::Loop),
         Allow(Target::ForLoop),

diff --git a/compiler/rustc_feature/src/builtin_attrs.rs b/compiler/rustc_feature/src/builtin_attrs.rs
@@ -217,10 +217,12 @@ pub static BUILTIN_ATTRIBUTES: &[Symbol] = &[
     // - https://github.com/rust-lang/rust/issues/153629
     sym::splat,
 
-    // The `#[unroll]` attribute.
+    // The `#[rustc_unroll]` attribute.
     //
     // - https://github.com/rust-lang/rust/pull/156816
-    sym::unroll,
+    //
+    // FIXME(#159429): temporarily renamed to mitigate `#[unroll]` nameres ambiguity
+    sym::rustc_unroll,
 
     // `#[instrument_fn = "on|off"]` to insert or inhibit instrumentation function
     // calls inside a function, usually around the prologue.

diff --git a/compiler/rustc_hir/src/attrs/data_structures.rs b/compiler/rustc_hir/src/attrs/data_structures.rs
@@ -1706,7 +1706,8 @@ pub enum AttributeKind {
         limit: Limit,
     },
 
-    /// Represents `#[unroll]`
+    /// Represents `#[rustc_unroll]`
+    // FIXME(#159429): temporarily renamed from `#[unroll]` to mitigate nameres ambiguity
     Unroll(UnrollAttr),
 
     /// Represents `#[unstable_feature_bound]`.

diff --git a/compiler/rustc_span/src/symbol.rs b/compiler/rustc_span/src/symbol.rs
@@ -1867,6 +1867,8 @@ symbols! {
         rustc_test_marker,
         rustc_then_this_would_need,
         rustc_trivial_field_reads,
+        // FIXME(#159429): temporary rename to avoid `#[unroll]` nameres ambiguity
+        rustc_unroll,
         rustc_unsafe_specialization_marker,
         rustdoc,
         rustdoc_internals,
@@ -2248,7 +2250,6 @@ symbols! {
         unreachable_display,
         unreachable_macro,
         unrestricted_attribute_tokens,
-        unroll,
         unsafe_attributes,
         unsafe_binders,
         unsafe_block_in_unsafe_fn,

diff --git a/src/doc/unstable-book/src/language-features/loop-hints.md b/src/doc/unstable-book/src/language-features/loop-hints.md
@@ -6,18 +6,22 @@ The tracking issue for this feature is: [#156874]
 
 ------
 
+<!--
+FIXME(#159429): temporarily renamed `#[unroll]` to mitigate a nameres ambiguity
+-->
+
 Loop unrolling can be a powerful optimization but like inlining, it is sometimes useful to
 manually provide hints to optimizations.
 
-`#[unroll]` will encourage unrolling of a loop.
+`#[rustc_unroll]` will encourage unrolling of a loop.
 
-`#[unroll(full)]` is a stronger hint and can cause optimizations to completely ignore the code
+`#[rustc_unroll(full)]` is a stronger hint and can cause optimizations to completely ignore the code
 side growth from repeating a loop body.
 
-`#[unroll(never)]` is a strong hint to not unroll the loop at all. Note that other loop
+`#[rustc_unroll(never)]` is a strong hint to not unroll the loop at all. Note that other loop
 optimizations may still be applied.
 
-`#[unroll(N)]` is a hint to unroll `N` iterations of the loop.
+`#[rustc_unroll(N)]` is a hint to unroll `N` iterations of the loop.
 
 In all cases these are just hints and may be ignored. But unlike function inlining hints,
 loops tend to be heavily modified during compilation, which can make obeying hints challenging.

diff --git a/tests/codegen-llvm/loop-attrs/unroll-for-metadata.rs b/tests/codegen-llvm/loop-attrs/unroll-for-metadata.rs
@@ -15,7 +15,7 @@ unsafe extern "C" {
 pub fn unroll_hint() {
     // CHECK-LABEL: @unroll_hint
     // CHECK: !llvm.loop ![[HINT:[0-9]+]]
-    #[unroll]
+    #[rustc_unroll]
     for _ in 0..10 {
         unsafe { maybe_has_side_effect() }
     }
@@ -25,7 +25,7 @@ pub fn unroll_hint() {
 pub fn unroll_full() {
     // CHECK-LABEL: @unroll_full
     // CHECK: !llvm.loop ![[FULL:[0-9]+]]
-    #[unroll(full)]
+    #[rustc_unroll(full)]
     for _ in 0..10 {
         unsafe { maybe_has_side_effect() }
     }
@@ -35,7 +35,7 @@ pub fn unroll_full() {
 pub fn unroll_never() {
     // CHECK-LABEL: @unroll_never
     // CHECK: !llvm.loop ![[DISABLE:[0-9]+]]
-    #[unroll(never)]
+    #[rustc_unroll(never)]
     for _ in 0..10 {
         unsafe { maybe_has_side_effect() }
     }
@@ -45,7 +45,7 @@ pub fn unroll_never() {
 pub fn unroll_count() {
     // CHECK-LABEL: @unroll_count
     // CHECK: !llvm.loop ![[COUNT:[0-9]+]]
-    #[unroll(5)]
+    #[rustc_unroll(5)]
     for _ in 0..10 {
         unsafe { maybe_has_side_effect() }
     }

diff --git a/tests/codegen-llvm/loop-attrs/unroll-for-works.rs b/tests/codegen-llvm/loop-attrs/unroll-for-works.rs
@@ -11,7 +11,7 @@ unsafe extern "C" {
 pub fn unroll_full() {
     // CHECK-LABEL: @unroll_full
     // CHECK-COUNT-512: tail call void @maybe_has_side_effect()
-    #[unroll(full)]
+    #[rustc_unroll(full)]
     for _ in 0..512 {
         unsafe { maybe_has_side_effect() }
     }
@@ -22,7 +22,7 @@ pub fn unroll_never() {
     // CHECK-LABEL: @unroll_never
     // CHECK: tail call void @maybe_has_side_effect()
     // CHECK-NOT: tail call void @maybe_has_side_effect()
-    #[unroll(never)]
+    #[rustc_unroll(never)]
     for _ in 0..3 {
         unsafe { maybe_has_side_effect() }
     }
@@ -32,7 +32,7 @@ pub fn unroll_never() {
 pub fn unroll_count() {
     // CHECK-LABEL: @unroll_count
     // CHECK-COUNT-5: tail call void @maybe_has_side_effect()
-    #[unroll(5)]
+    #[rustc_unroll(5)]
     for _ in 0..10 {
         unsafe { maybe_has_side_effect() }
     }

diff --git a/tests/codegen-llvm/loop-attrs/unroll-loop-metadata.rs b/tests/codegen-llvm/loop-attrs/unroll-loop-metadata.rs
@@ -17,7 +17,7 @@ pub fn unroll_hint() {
     // CHECK-LABEL: @unroll_hint
     // CHECK: !llvm.loop ![[HINT:[0-9]+]]
     let mut i = 0;
-    #[unroll]
+    #[rustc_unroll]
     loop {
         unsafe { maybe_has_side_effect() }
         i += 1;
@@ -35,7 +35,7 @@ pub fn unroll_full() {
     // CHECK-LABEL: @unroll_full
     // CHECK: !llvm.loop ![[FULL:[0-9]+]]
     let mut i = 0;
-    let _return = (#[unroll(full)]
+    let _return = (#[rustc_unroll(full)]
     loop {
         unsafe { maybe_has_side_effect() }
         i += 1;
@@ -50,7 +50,7 @@ pub fn unroll_never() {
     // CHECK-LABEL: @unroll_never
     // CHECK: !llvm.loop ![[DISABLE:[0-9]+]]
     let mut i = 0;
-    let _return = (1 + #[unroll(never)]
+    let _return = (1 + #[rustc_unroll(never)]
     loop {
         unsafe { maybe_has_side_effect() }
         i += 1;
@@ -65,7 +65,7 @@ pub fn unroll_count() {
     // CHECK-LABEL: @unroll_count
     // CHECK: !llvm.loop ![[COUNT:[0-9]+]]
     let mut i = 0;
-    #[unroll(5)]
+    #[rustc_unroll(5)]
     loop {
         unsafe { maybe_has_side_effect() }
         i += 1;

diff --git a/tests/codegen-llvm/loop-attrs/unroll-while-metadata.rs b/tests/codegen-llvm/loop-attrs/unroll-while-metadata.rs
@@ -16,7 +16,7 @@ pub fn unroll_hint() {
     // CHECK-LABEL: @unroll_hint
     // CHECK: !llvm.loop ![[HINT:[0-9]+]]
     let mut i = 0;
-    #[unroll]
+    #[rustc_unroll]
     while i < 10 {
         unsafe { maybe_has_side_effect() }
         i += 1;
@@ -28,7 +28,7 @@ pub fn unroll_full() {
     // CHECK-LABEL: @unroll_full
     // CHECK: !llvm.loop ![[FULL:[0-9]+]]
     let mut i = 0;
-    #[unroll(full)]
+    #[rustc_unroll(full)]
     while i < 10 {
         unsafe { maybe_has_side_effect() }
         i += 1;
@@ -40,7 +40,7 @@ pub fn unroll_never() {
     // CHECK-LABEL: @unroll_never
     // CHECK: !llvm.loop ![[DISABLE:[0-9]+]]
     let mut i = 0;
-    #[unroll(never)]
+    #[rustc_unroll(never)]
     while i < 10 {
         unsafe { maybe_has_side_effect() }
         i += 1;
@@ -52,7 +52,7 @@ pub fn unroll_count() {
     // CHECK-LABEL: @unroll_count
     // CHECK: !llvm.loop ![[COUNT:[0-9]+]]
     let mut i = 0;
-    #[unroll(5)]
+    #[rustc_unroll(5)]
     while i < 10 {
         unsafe { maybe_has_side_effect() }
         i += 1;

diff --git a/tests/ui/attributes/unroll/invalid-unroll.rs b/tests/ui/attributes/unroll/invalid-unroll.rs
@@ -2,18 +2,18 @@
 #![crate_type = "lib"]
 
 pub fn main() {
-    #[unroll(please)] //~ ERROR malformed `unroll` attribute input
+    #[rustc_unroll(please)] //~ ERROR malformed `rustc_unroll` attribute input
     for _ in 0..10 {}
 
-    #[unroll("never")] //~ ERROR malformed `unroll` attribute input
+    #[rustc_unroll("never")] //~ ERROR malformed `rustc_unroll` attribute input
     for _ in 0..10 {}
 
-    #[unroll()] //~ ERROR malformed `unroll` attribute input
+    #[rustc_unroll()] //~ ERROR malformed `rustc_unroll` attribute input
     for _ in 0..10 {}
 
-    #[unroll(-1)] //~ ERROR expected a literal
+    #[rustc_unroll(-1)] //~ ERROR expected a literal
     for _ in 0..10 {}
 
-    #[unroll(1.5)] //~ ERROR malformed `unroll` attribute input
+    #[rustc_unroll(1.5)] //~ ERROR malformed `rustc_unroll` attribute input
     for _ in 0..10 {}
 }
diff --git a/tests/ui/attributes/unroll/invalid-unroll.stderr b/tests/ui/attributes/unroll/invalid-unroll.stderr
@@ -1,46 +1,46 @@
-error[E0539]: malformed `unroll` attribute input
+error[E0539]: malformed `rustc_unroll` attribute input
   --> $DIR/invalid-unroll.rs:5:7
    |
-LL |     #[unroll(please)]
-   |       ^^^^^^^------^
-   |              |
-   |              valid arguments are `full` or `never`
+LL |     #[rustc_unroll(please)]
+   |       ^^^^^^^^^^^^^------^
+   |                    |
+   |                    valid arguments are `full` or `never`
 
-error[E0539]: malformed `unroll` attribute input
+error[E0539]: malformed `rustc_unroll` attribute input
   --> $DIR/invalid-unroll.rs:8:7
    |
-LL |     #[unroll("never")]
-   |       ^^^^^^^-------^
-   |              |
-   |              valid arguments are `full` or `never`
+LL |     #[rustc_unroll("never")]
+   |       ^^^^^^^^^^^^^-------^
+   |                    |
+   |                    valid arguments are `full` or `never`
 
-error[E0805]: malformed `unroll` attribute input
+error[E0805]: malformed `rustc_unroll` attribute input
   --> $DIR/invalid-unroll.rs:11:7
    |
-LL |     #[unroll()]
-   |       ^^^^^^--
-   |             |
-   |             expected an argument here
+LL |     #[rustc_unroll()]
+   |       ^^^^^^^^^^^^--
+   |                   |
+   |                   expected an argument here
 
 error: expected a literal (`1u8`, `1.0f32`, `"string"`, etc.) here, found expression
-  --> $DIR/invalid-unroll.rs:14:14
+  --> $DIR/invalid-unroll.rs:14:20
    |
-LL |     #[unroll(-1)]
-   |              ^^ expressions are not allowed here
+LL |     #[rustc_unroll(-1)]
+   |                    ^^ expressions are not allowed here
    |
 help: negative numbers are not literals, try removing the `-` sign
    |
-LL -     #[unroll(-1)]
-LL +     #[unroll(1)]
+LL -     #[rustc_unroll(-1)]
+LL +     #[rustc_unroll(1)]
    |
 
-error[E0539]: malformed `unroll` attribute input
+error[E0539]: malformed `rustc_unroll` attribute input
   --> $DIR/invalid-unroll.rs:17:7
    |
-LL |     #[unroll(1.5)]
-   |       ^^^^^^^---^
-   |              |
-   |              valid arguments are `full` or `never`
+LL |     #[rustc_unroll(1.5)]
+   |       ^^^^^^^^^^^^^---^
+   |                    |
+   |                    valid arguments are `full` or `never`
 
 error: aborting due to 5 previous errors
 

diff --git a/tests/ui/feature-gates/feature-gate-loop-hints.rs b/tests/ui/feature-gates/feature-gate-loop-hints.rs
@@ -1,4 +1,4 @@
 fn main() {
-    #[unroll] //~ ERROR the `unroll` attribute is an experimental feature
+    #[rustc_unroll] //~ ERROR the `rustc_unroll` attribute is an experimental feature
     for _ in 0..10 {}
 }
diff --git a/tests/ui/feature-gates/feature-gate-loop-hints.stderr b/tests/ui/feature-gates/feature-gate-loop-hints.stderr
@@ -1,8 +1,8 @@
-error[E0658]: the `unroll` attribute is an experimental feature
+error[E0658]: the `rustc_unroll` attribute is an experimental feature
   --> $DIR/feature-gate-loop-hints.rs:2:7
    |
-LL |     #[unroll]
-   |       ^^^^^^
+LL |     #[rustc_unroll]
+   |       ^^^^^^^^^^^^
    |
    = note: see issue #156874 <https://github.com/rust-lang/rust/issues/156874> for more information
    = help: add `#![feature(loop_hints)]` to the crate attributes to enable

diff --git a/tests/ui/feature-gates/feature-gate-rustc-attrs.stderr b/tests/ui/feature-gates/feature-gate-rustc-attrs.stderr
@@ -33,6 +33,12 @@ error: cannot find attribute `rustc_unknown` in this scope
    |
 LL | #[rustc_unknown]
    |   ^^^^^^^^^^^^^
+   |
+help: a built-in attribute with a similar name exists
+   |
+LL - #[rustc_unknown]
+LL + #[rustc_unroll]
+   |
 
 error[E0658]: use of an internal attribute
   --> $DIR/feature-gate-rustc-attrs.rs:20:3