Mitigate #[align] name resolution ambiguity regression with a rename

jieyouxu · cuviper · commit 2e832047c6bf · 2025-07-24T11:02:01.000-07:00
From `#[align]` -> `#[rustc_align]`. Attributes starting with `rustc` are always perma-unstable and feature-gated by `feature(rustc_attrs)`. See regression RUST-143834. For the underlying problem where even introducing new feature-gated unstable built-in attributes can break user code such as ```rs macro_rules! align { () => { /* .. */ }; } pub(crate) use align; // `use` here becomes ambiguous ``` refer to RUST-134963. Since the `#[align]` attribute is still feature-gated by `feature(fn_align)`, we can rename it as a mitigation. Note that `#[rustc_align]` will obviously mean that current unstable user code using `feature(fn_aling)` will need additionally `feature(rustc_attrs)`, but this is a short-term mitigation to buy time, and is expected to be changed to a better name with less collision potential. See <https://rust-lang.zulipchat.com/#narrow/channel/238009-t-compiler.2Fmeetings/topic/.5Bweekly.5D.202025-07-17/near/529290371> where mitigation options were considered. (cherry picked from commit 69b71e4)
diff --git a/compiler/rustc_attr_data_structures/src/attributes.rs b/compiler/rustc_attr_data_structures/src/attributes.rs
@@ -184,6 +184,7 @@ impl Deprecation {
 pub enum AttributeKind {
     // tidy-alphabetical-start
     /// Represents `#[align(N)]`.
+    // FIXME(#82232, #143834): temporarily renamed to mitigate `#[align]` nameres ambiguity
     Align { align: Align, span: Span },
 
     /// Represents `#[rustc_allow_const_fn_unstable]`.
diff --git a/compiler/rustc_attr_parsing/src/attributes/repr.rs b/compiler/rustc_attr_parsing/src/attributes/repr.rs
@@ -273,7 +273,7 @@ fn parse_alignment(node: &LitKind) -> Result<Align, &'static str> {
 pub(crate) struct AlignParser(Option<(Align, Span)>);
 
 impl AlignParser {
-    const PATH: &'static [Symbol] = &[sym::align];
+    const PATH: &'static [Symbol] = &[sym::rustc_align];
     const TEMPLATE: AttributeTemplate = template!(List: "<alignment in bytes>");
 
     fn parse<'c, S: Stage>(
diff --git a/compiler/rustc_feature/src/builtin_attrs.rs b/compiler/rustc_feature/src/builtin_attrs.rs
@@ -495,7 +495,8 @@ pub static BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
     ),
     ungated!(no_link, Normal, template!(Word), WarnFollowing, EncodeCrossCrate::No),
     ungated!(repr, Normal, template!(List: "C"), DuplicatesOk, EncodeCrossCrate::No),
-    gated!(align, Normal, template!(List: "alignment"), DuplicatesOk, EncodeCrossCrate::No, fn_align, experimental!(align)),
+    // FIXME(#82232, #143834): temporarily renamed to mitigate `#[align]` nameres ambiguity
+    gated!(rustc_align, Normal, template!(List: "alignment"), DuplicatesOk, EncodeCrossCrate::No, fn_align, experimental!(rustc_align)),
     ungated!(unsafe(Edition2024) export_name, Normal, template!(NameValueStr: "name"), FutureWarnPreceding, EncodeCrossCrate::No),
     ungated!(unsafe(Edition2024) link_section, Normal, template!(NameValueStr: "name"), FutureWarnPreceding, EncodeCrossCrate::No),
     ungated!(unsafe(Edition2024) no_mangle, Normal, template!(Word), WarnFollowing, EncodeCrossCrate::No),
diff --git a/compiler/rustc_middle/src/middle/codegen_fn_attrs.rs b/compiler/rustc_middle/src/middle/codegen_fn_attrs.rs
@@ -48,6 +48,7 @@ pub struct CodegenFnAttrs {
     /// switching between multiple instruction sets.
     pub instruction_set: Option<InstructionSetAttr>,
     /// The `#[align(...)]` attribute. Determines the alignment of the function body.
+    // FIXME(#82232, #143834): temporarily renamed to mitigate `#[align]` nameres ambiguity
     pub alignment: Option<Align>,
     /// The `#[patchable_function_entry(...)]` attribute. Indicates how many nops should be around
     /// the function entry.
diff --git a/compiler/rustc_parse/src/validate_attr.rs b/compiler/rustc_parse/src/validate_attr.rs
@@ -289,7 +289,8 @@ fn emit_malformed_attribute(
             | sym::rustc_force_inline
             | sym::rustc_confusables
             | sym::repr
-            | sym::align
+            // FIXME(#82232, #143834): temporarily renamed to mitigate `#[align]` nameres ambiguity
+            | sym::rustc_align
             | sym::deprecated
             | sym::optimize
             | sym::cold
diff --git a/compiler/rustc_passes/messages.ftl b/compiler/rustc_passes/messages.ftl
@@ -14,7 +14,7 @@ passes_abi_of =
     fn_abi_of({$fn_name}) = {$fn_abi}
 
 passes_align_should_be_repr_align =
-    `#[align(...)]` is not supported on {$item} items
+    `#[rustc_align(...)]` is not supported on {$item} items
     .suggestion = use `#[repr(align(...))]` instead
 
 passes_allow_incoherent_impl =
@@ -589,7 +589,7 @@ passes_repr_align_greater_than_target_max =
 
 passes_repr_align_should_be_align =
     `#[repr(align(...))]` is not supported on {$item} items
-    .help = use `#[align(...)]` instead
+    .help = use `#[rustc_align(...)]` instead
 
 passes_repr_conflicting =
     conflicting representation hints
diff --git a/compiler/rustc_passes/src/check_attr.rs b/compiler/rustc_passes/src/check_attr.rs
@@ -662,7 +662,8 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
             sym::naked,
             sym::instruction_set,
             sym::repr,
-            sym::align,
+            // FIXME(#82232, #143834): temporarily renamed to mitigate `#[align]` nameres ambiguity
+            sym::rustc_align,
             sym::rustc_std_internal_symbol,
             // documentation
             sym::doc,
@@ -1996,6 +1997,7 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
     }
 
     /// Checks if the `#[align]` attributes on `item` are valid.
+    // FIXME(#82232, #143834): temporarily renamed to mitigate `#[align]` nameres ambiguity
     fn check_align(&self, span: Span, target: Target, align: Align, repr_span: Span) {
         match target {
             Target::Fn | Target::Method(_) => {}
diff --git a/compiler/rustc_span/src/symbol.rs b/compiler/rustc_span/src/symbol.rs
@@ -1806,6 +1806,8 @@ symbols! {
         rust_out,
         rustc,
         rustc_abi,
+        // FIXME(#82232, #143834): temporary name to mitigate `#[align]` nameres ambiguity
+        rustc_align,
         rustc_allocator,
         rustc_allocator_zeroed,
         rustc_allow_const_fn_unstable,
diff --git a/src/tools/miri/tests/pass/fn_align.rs b/src/tools/miri/tests/pass/fn_align.rs
@@ -1,15 +1,19 @@
 //@compile-flags: -Zmin-function-alignment=8
+
+// FIXME(rust-lang/rust#82232, rust-lang/rust#143834): temporarily renamed to mitigate `#[align]`
+// nameres ambiguity
+#![feature(rustc_attrs)]
 #![feature(fn_align)]
 
 // When a function uses `align(N)`, the function address should be a multiple of `N`.
 
-#[align(256)]
+#[rustc_align(256)]
 fn foo() {}
 
-#[align(16)]
+#[rustc_align(16)]
 fn bar() {}
 
-#[align(4)]
+#[rustc_align(4)]
 fn baz() {}
 
 fn main() {
diff --git a/tests/codegen/align-fn.rs b/tests/codegen/align-fn.rs
@@ -1,44 +1,46 @@
 //@ compile-flags: -C no-prepopulate-passes -Z mir-opt-level=0
 
 #![crate_type = "lib"]
+// FIXME(#82232, #143834): temporarily renamed to mitigate `#[align]` nameres ambiguity
+#![feature(rustc_attrs)]
 #![feature(fn_align)]
 
 // CHECK: align 16
 #[no_mangle]
-#[align(16)]
+#[rustc_align(16)]
 pub fn fn_align() {}
 
 pub struct A;
 
 impl A {
     // CHECK: align 16
     #[no_mangle]
-    #[align(16)]
+    #[rustc_align(16)]
     pub fn method_align(self) {}
 
     // CHECK: align 16
     #[no_mangle]
-    #[align(16)]
+    #[rustc_align(16)]
     pub fn associated_fn() {}
 }
 
 trait T: Sized {
     fn trait_fn() {}
 
     // CHECK: align 32
-    #[align(32)]
+    #[rustc_align(32)]
     fn trait_method(self) {}
 }
 
 impl T for A {
     // CHECK: align 16
     #[no_mangle]
-    #[align(16)]
+    #[rustc_align(16)]
     fn trait_fn() {}
 
     // CHECK: align 16
     #[no_mangle]
-    #[align(16)]
+    #[rustc_align(16)]
     fn trait_method(self) {}
 }
 
@@ -51,20 +53,20 @@ pub fn foo() {
 // CHECK-LABEL: align_specified_twice_1
 // CHECK-SAME: align 64
 #[no_mangle]
-#[align(32)]
-#[align(64)]
+#[rustc_align(32)]
+#[rustc_align(64)]
 pub fn align_specified_twice_1() {}
 
 // CHECK-LABEL: align_specified_twice_2
 // CHECK-SAME: align 128
 #[no_mangle]
-#[align(128)]
-#[align(32)]
+#[rustc_align(128)]
+#[rustc_align(32)]
 pub fn align_specified_twice_2() {}
 
 // CHECK-LABEL: align_specified_twice_3
 // CHECK-SAME: align 256
 #[no_mangle]
-#[align(32)]
-#[align(256)]
+#[rustc_align(32)]
+#[rustc_align(256)]
 pub fn align_specified_twice_3() {}
diff --git a/tests/codegen/min-function-alignment.rs b/tests/codegen/min-function-alignment.rs
@@ -4,6 +4,8 @@
 //@ [align1024] compile-flags: -Zmin-function-alignment=1024
 
 #![crate_type = "lib"]
+// FIXME(#82232, #143834): temporarily renamed to mitigate `#[align]` nameres ambiguity
+#![feature(rustc_attrs)]
 #![feature(fn_align)]
 
 // functions without explicit alignment use the global minimum
@@ -18,7 +20,7 @@ pub fn no_explicit_align() {}
 // align16: align 16
 // align1024: align 1024
 #[no_mangle]
-#[align(8)]
+#[rustc_align(8)]
 pub fn lower_align() {}
 
 // the higher value of min-function-alignment and the align attribute wins out
@@ -27,7 +29,7 @@ pub fn lower_align() {}
 // align16: align 32
 // align1024: align 1024
 #[no_mangle]
-#[align(32)]
+#[rustc_align(32)]
 pub fn higher_align() {}
 
 // cold functions follow the same rules as other functions
diff --git a/tests/codegen/naked-fn/aligned.rs b/tests/codegen/naked-fn/aligned.rs
@@ -3,12 +3,15 @@
 //@ ignore-arm no "ret" mnemonic
 
 #![crate_type = "lib"]
+// FIXME(#82232, #143834): temporarily renamed to mitigate `#[align]` nameres ambiguity
+#![feature(rustc_attrs)]
 #![feature(fn_align)]
+
 use std::arch::naked_asm;
 
 // CHECK: .balign 16
 // CHECK-LABEL: naked_empty:
-#[align(16)]
+#[rustc_align(16)]
 #[no_mangle]
 #[unsafe(naked)]
 pub extern "C" fn naked_empty() {
diff --git a/tests/codegen/naked-fn/min-function-alignment.rs b/tests/codegen/naked-fn/min-function-alignment.rs
@@ -2,6 +2,8 @@
 //@ needs-asm-support
 //@ ignore-arm no "ret" mnemonic
 
+// FIXME(#82232, #143834): temporarily renamed to mitigate `#[align]` nameres ambiguity
+#![feature(rustc_attrs)]
 #![feature(fn_align)]
 #![crate_type = "lib"]
 
@@ -16,15 +18,15 @@ pub extern "C" fn naked_no_explicit_align() {
 
 // CHECK: .balign 16
 #[no_mangle]
-#[align(8)]
+#[rustc_align(8)]
 #[unsafe(naked)]
 pub extern "C" fn naked_lower_align() {
     core::arch::naked_asm!("ret")
 }
 
 // CHECK: .balign 32
 #[no_mangle]
-#[align(32)]
+#[rustc_align(32)]
 #[unsafe(naked)]
 pub extern "C" fn naked_higher_align() {
     core::arch::naked_asm!("ret")
diff --git a/tests/ui/asm/naked-with-invalid-repr-attr.rs b/tests/ui/asm/naked-with-invalid-repr-attr.rs
@@ -1,5 +1,9 @@
 //@ needs-asm-support
+
+// FIXME(#82232, #143834): temporarily renamed to mitigate `#[align]` nameres ambiguity
+#![feature(rustc_attrs)]
 #![feature(fn_align)]
+
 #![crate_type = "lib"]
 use std::arch::naked_asm;
 
@@ -21,7 +25,7 @@ extern "C" fn example2() {
 
 #[repr(C)]
 //~^ ERROR attribute should be applied to a struct, enum, or union [E0517]
-#[align(16)]
+#[rustc_align(16)]
 #[unsafe(naked)]
 extern "C" fn example3() {
     //~^ NOTE not a struct, enum, or union
diff --git a/tests/ui/asm/naked-with-invalid-repr-attr.stderr b/tests/ui/asm/naked-with-invalid-repr-attr.stderr
@@ -1,5 +1,5 @@
 error[E0517]: attribute should be applied to a struct, enum, or union
-  --> $DIR/naked-with-invalid-repr-attr.rs:6:8
+  --> $DIR/naked-with-invalid-repr-attr.rs:10:8
    |
 LL |   #[repr(C)]
    |          ^
@@ -11,7 +11,7 @@ LL | | }
    | |_- not a struct, enum, or union
 
 error[E0517]: attribute should be applied to a struct, enum, or union
-  --> $DIR/naked-with-invalid-repr-attr.rs:14:8
+  --> $DIR/naked-with-invalid-repr-attr.rs:18:8
    |
 LL |   #[repr(transparent)]
    |          ^^^^^^^^^^^
@@ -23,7 +23,7 @@ LL | | }
    | |_- not a struct, enum, or union
 
 error[E0517]: attribute should be applied to a struct, enum, or union
-  --> $DIR/naked-with-invalid-repr-attr.rs:22:8
+  --> $DIR/naked-with-invalid-repr-attr.rs:26:8
    |
 LL |   #[repr(C)]
    |          ^
@@ -35,7 +35,7 @@ LL | | }
    | |_- not a struct, enum, or union
 
 error[E0517]: attribute should be applied to a struct, enum, or union
-  --> $DIR/naked-with-invalid-repr-attr.rs:32:8
+  --> $DIR/naked-with-invalid-repr-attr.rs:36:8
    |
 LL |   #[repr(C, packed)]
    |          ^
@@ -48,7 +48,7 @@ LL | | }
    | |_- not a struct, enum, or union
 
 error[E0517]: attribute should be applied to a struct or union
-  --> $DIR/naked-with-invalid-repr-attr.rs:32:11
+  --> $DIR/naked-with-invalid-repr-attr.rs:36:11
    |
 LL |   #[repr(C, packed)]
    |             ^^^^^^
@@ -61,7 +61,7 @@ LL | | }
    | |_- not a struct or union
 
 error[E0517]: attribute should be applied to an enum
-  --> $DIR/naked-with-invalid-repr-attr.rs:42:8
+  --> $DIR/naked-with-invalid-repr-attr.rs:46:8
    |
 LL |   #[repr(u8)]
    |          ^^
diff --git a/tests/ui/attributes/fn-align-nameres-ambiguity-143834.rs b/tests/ui/attributes/fn-align-nameres-ambiguity-143834.rs
@@ -1,21 +1,19 @@
-//~ NOTE `align` could refer to a built-in attribute
-
 // Anti-regression test to demonstrate that at least we mitigated breakage from adding a new
 // `#[align]` built-in attribute.
+//
+// See https://github.com/rust-lang/rust/issues/143834.
+
+//@ check-pass
 
 // Needs edition >= 2018 macro use behavior.
 //@ edition: 2018
 
 macro_rules! align {
-    //~^ NOTE `align` could also refer to the macro defined here
     () => {
         /* .. */
     };
 }
 
 pub(crate) use align;
-//~^ ERROR `align` is ambiguous
-//~| NOTE ambiguous name
-//~| NOTE ambiguous because of a name conflict with a builtin attribute
 
 fn main() {}
diff --git a/tests/ui/attributes/fn-align-nameres-ambiguity-143834.stderr b/tests/ui/attributes/fn-align-nameres-ambiguity-143834.stderr
diff --git a/tests/ui/attributes/malformed-fn-align.rs b/tests/ui/attributes/malformed-fn-align.rs
diff --git a/tests/ui/attributes/malformed-fn-align.stderr b/tests/ui/attributes/malformed-fn-align.stderr
diff --git a/tests/ui/feature-gates/feature-gate-fn_align.rs b/tests/ui/feature-gates/feature-gate-fn_align.rs
diff --git a/tests/ui/feature-gates/feature-gate-fn_align.stderr b/tests/ui/feature-gates/feature-gate-fn_align.stderr
