Unrolled build for #144080

Rollup merge of #144080 - jieyouxu:realign, r=BoxyUwU

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

Mitigates beta regression #143834 after a beta backport.

### Background on the beta regression

The name resolution regression arises due to #142507 adding a new feature-gated built-in attribute named `#[align]`. However, unfortunately even [introducing new feature-gated unstable built-in attributes can break user code](https://www.github.com/rust-lang/rust/issues/134963) such as

```rs
macro_rules! align {
    () => {
        /* .. */
    };
}

pub(crate) use align; // `use` here becomes ambiguous
```

### Mitigation approach

This PR renames `#[align]` to `#[rustc_align]` to mitigate the beta regression by:

1. Undoing the introduction of a new built-in attribute with a common name, i.e. `#[align]`.
2. Renaming `#[align]` to `#[rustc_align]`. The renamed attribute being `rustc_align` will not introduce new stable breakages, as attributes beginning with `rustc` are reserved and perma-unstable. This does mean existing nightly code using `fn_align` feature will additionally need to specify `#![feature(rustc_attrs)]`.

This PR is very much a short-term mitigation to alleviate time pressure from having to fully fix the current limitation of inevitable name resolution regressions that would arise from adding any built-in attributes. Long-term solutions are discussed in [#t-lang > namespacing macro attrs to reduce conflicts with new adds](https://rust-lang.zulipchat.com/#narrow/channel/213817-t-lang/topic/namespacing.20macro.20attrs.20to.20reduce.20conflicts.20with.20new.20adds/with/529249622).

### Alternative mitigation options

[Various mitigation options were considered during the compiler triage meeting](#143834 (comment)), and those consideration are partly reproduced here:

- Reverting the PR doesn't seem very minimal/trivial, and carries risks of its own.
- Rename to a less-common but aim-to-stabilization name is itself not safe nor convenient, because (1) that risks introducing new regressions (i.e. ambiguity against the new name), and (2) lang would have to FCP the new name hastily for the mitigation to land timely and have a chance to be backported. This also makes the path towards stabilization annoying.
- Rename the attribute to a rustc attribute, which will be perma-unstable and does not cause new ambiguities in stable code.
    - This alleviates the time pressure to address *this* regression, or for lang to have to rush an FCP for some new name that can still break user code.
    - This avoids backing out a whole implementation.

### Review advice

This PR is best reviewed commit-by-commit.

- Commit 1 adds a test `tests/ui/attributes/fn-align-nameres-ambiguity-143834.rs` which demonstrates the current name resolution regression re. `align`. This test fails against current master.
- Commit 2 carries out the renames and test reblesses. Notably, commit 2 will cause `tests/ui/attributes/fn-align-nameres-ambiguity-143834.rs` to change from fail (nameres regression) to pass.

This PR, if the approach still seems acceptable, will need a beta-backport to address the beta regression.

Author: rust-timer

compiler/rustc_attr_data_structures/src/attributes.rs

@@ -234,6 +234,7 @@ pub enum CfgEntry {
 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]`.

compiler/rustc_attr_parsing/src/attributes/codegen_attrs.rs

@@ -177,7 +177,8 @@ impl<S: Stage> AttributeParser<S> for NakedParser {
             sym::instruction_set,
             sym::repr,
             sym::rustc_std_internal_symbol,
-            sym::align,
+            // FIXME(#82232, #143834): temporarily renamed to mitigate `#[align]` nameres ambiguity
+            sym::rustc_align,
             // obviously compatible with self
             sym::naked,
             // documentation

compiler/rustc_attr_parsing/src/attributes/repr.rs

@@ -274,7 +274,7 @@ 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>(

compiler/rustc_feature/src/builtin_attrs.rs

@@ -490,7 +490,8 @@ 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),

compiler/rustc_middle/src/middle/codegen_fn_attrs.rs

@@ -70,6 +70,7 @@ 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.

compiler/rustc_parse/src/validate_attr.rs

@@ -294,7 +294,9 @@ pub fn check_builtin_meta_item(
                 | sym::rustc_paren_sugar
                 | sym::type_const
                 | sym::repr
-                | sym::align
+                // FIXME(#82232, #143834): temporarily renamed to mitigate `#[align]` nameres
+                // ambiguity
+                | sym::rustc_align
                 | sym::deprecated
                 | sym::optimize
                 | sym::pointee

compiler/rustc_passes/messages.ftl

@@ -14,15 +14,15 @@ passes_abi_of =
     fn_abi_of({$fn_name}) = {$fn_abi}
 
 passes_align_attr_application =
-    `#[align(...)]` should be applied to a function item
+    `#[rustc_align(...)]` should be applied to a function item
     .label = not a function item
 
 passes_align_on_fields =
     attribute should be applied to a function or method
     .warn = {-passes_previously_accepted}
 
 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 =
@@ -605,7 +605,7 @@ 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

compiler/rustc_passes/src/check_attr.rs

@@ -1970,6 +1970,7 @@ 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,

compiler/rustc_span/src/symbol.rs

@@ -1809,6 +1809,8 @@ 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,

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() {