Fix split index calculation in check_type_alias_where_clause_location

compiler/rustc_ast/src/ast.rs

@@ -3429,7 +3429,9 @@ pub struct TyAliasWhereClauses {
     /// The index in `TyAlias.generics.where_clause.predicates` that would split
     /// into predicates from the where clause before the equals sign and the ones
     /// from the where clause after the equals sign.
-    pub split: usize,
+    pub before_count: usize,
+    /// The count of the clauses that appear before the equals sign and have attrbutes.
+    pub before_with_attr_count: usize,
 }
 
 #[derive(Clone, Encodable, Decodable, Debug)]

compiler/rustc_ast/src/mut_visit.rs

@@ -1091,7 +1091,7 @@ fn walk_generics<T: MutVisitor>(vis: &mut T, generics: &mut Generics) {
 }
 
 fn walk_ty_alias_where_clauses<T: MutVisitor>(vis: &mut T, tawcs: &mut TyAliasWhereClauses) {
-    let TyAliasWhereClauses { before, after, split: _ } = tawcs;
+    let TyAliasWhereClauses { before, after, before_count: _, before_with_attr_count: _ } = tawcs;
     let TyAliasWhereClause { has_where_token: _, span: span_before } = before;
     let TyAliasWhereClause { has_where_token: _, span: span_after } = after;
     vis.visit_span(span_before);

compiler/rustc_ast_passes/src/ast_validation.rs

@@ -136,8 +136,10 @@ impl<'a> AstValidator<'a> {
             return Ok(());
         }
 
+        let split =
+            ty_alias.where_clauses.before_count - ty_alias.where_clauses.before_with_attr_count;
         let (before_predicates, after_predicates) =
-            ty_alias.generics.where_clause.predicates.split_at(ty_alias.where_clauses.split);
+            ty_alias.generics.where_clause.predicates.split_at(split);
         let span = ty_alias.where_clauses.before.span;
 
         let sugg = if !before_predicates.is_empty() || !ty_alias.where_clauses.after.has_where_token

compiler/rustc_ast_pretty/src/pprust/state/item.rs

@@ -125,7 +125,7 @@ impl<'a> State<'a> {
         defaultness: ast::Defaultness,
     ) {
         let (before_predicates, after_predicates) =
-            generics.where_clause.predicates.split_at(where_clauses.split);
+            generics.where_clause.predicates.split_at(where_clauses.before_count);
         self.head("");
         self.print_visibility(vis);
         self.print_defaultness(defaultness);

compiler/rustc_parse/src/parser/item.rs

@@ -1024,7 +1024,12 @@ impl<'a> Parser<'a> {
                 has_where_token: after_where_clause.has_where_token,
                 span: after_where_clause.span,
             },
-            split: before_where_clause.predicates.len(),
+            before_count: before_where_clause.predicates.len(),
+            before_with_attr_count: before_where_clause
+                .predicates
+                .iter()
+                .filter(|p| !p.attrs.is_empty())
+                .count(),
         };
         let mut predicates = before_where_clause.predicates;
         predicates.extend(after_where_clause.predicates);

src/tools/rustfmt/src/items.rs

@@ -1768,7 +1768,7 @@ fn rewrite_ty<R: Rewrite>(
     let (before_where_predicates, after_where_predicates) = generics
         .where_clause
         .predicates
-        .split_at(where_clauses.split);
+        .split_at(where_clauses.before_count);
     result.push_str(&format!("{}type ", format_visibility(context, vis)));
     let ident_str = rewrite_ident(context, ident);
 

tests/ui/where-clauses/cfg-attr-issue-138010-1.rs

@@ -0,0 +1,30 @@
+#![feature(lazy_type_alias)]
+//~^ WARNING: the feature `lazy_type_alias` is incomplete and may not be safe to use and/or cause compiler crashes [incomplete_features]
+
+trait TraitA {}
+trait TraitB {}
+
+fn this(_x: &()) {}
+
+fn needs_copy<T>() {
+    type F<T>
+    where
+        //~^ ERROR: where clauses are not allowed before the type for type aliases
+        #[cfg(a)]
+        //~^ ERROR: attributes in `where` clause are unstable
+        //~| WARNING: unexpected `cfg` condition name: `a`
+        T: TraitA,
+        #[cfg(b)]
+        //~^ ERROR: attributes in `where` clause are unstable
+        //~| WARNING: unexpected `cfg` condition name: `b`
+        T: TraitB,
+        ():,
+        ():,
+    = T;
+    let x: () = ();
+    this(&x);
+}
+
+fn main() {
+    needs_copy::<()>();
+}

tests/ui/where-clauses/cfg-attr-issue-138010-1.stderr

@@ -0,0 +1,70 @@
+error: where clauses are not allowed before the type for type aliases
+  --> $DIR/cfg-attr-issue-138010-1.rs:11:5
+   |
+LL | /     where
+LL | |
+LL | |         #[cfg(a)]
+...  |
+LL | |         ():,
+LL | |         ():,
+   | |____________^
+   |
+   = note: see issue #89122 <https://github.com/rust-lang/rust/issues/89122> for more information
+help: move it to the end of the type declaration
+   |
+LL ~     
+LL ~     = T where ():, ():;
+   |
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/cfg-attr-issue-138010-1.rs:13:9
+   |
+LL |         #[cfg(a)]
+   |         ^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/cfg-attr-issue-138010-1.rs:17:9
+   |
+LL |         #[cfg(b)]
+   |         ^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+warning: the feature `lazy_type_alias` is incomplete and may not be safe to use and/or cause compiler crashes
+  --> $DIR/cfg-attr-issue-138010-1.rs:1:12
+   |
+LL | #![feature(lazy_type_alias)]
+   |            ^^^^^^^^^^^^^^^
+   |
+   = note: see issue #112792 <https://github.com/rust-lang/rust/issues/112792> for more information
+   = note: `#[warn(incomplete_features)]` on by default
+
+warning: unexpected `cfg` condition name: `a`
+  --> $DIR/cfg-attr-issue-138010-1.rs:13:15
+   |
+LL |         #[cfg(a)]
+   |               ^ help: found config with similar value: `target_feature = "a"`
+   |
+   = help: expected names are: `FALSE` and `test` and 31 more
+   = help: to expect this configuration use `--check-cfg=cfg(a)`
+   = note: see <https://doc.rust-lang.org/nightly/rustc/check-cfg.html> for more information about checking conditional configuration
+   = note: `#[warn(unexpected_cfgs)]` on by default
+
+warning: unexpected `cfg` condition name: `b`
+  --> $DIR/cfg-attr-issue-138010-1.rs:17:15
+   |
+LL |         #[cfg(b)]
+   |               ^
+   |
+   = help: to expect this configuration use `--check-cfg=cfg(b)`
+   = note: see <https://doc.rust-lang.org/nightly/rustc/check-cfg.html> for more information about checking conditional configuration
+
+error: aborting due to 3 previous errors; 3 warnings emitted
+
+For more information about this error, try `rustc --explain E0658`.

tests/ui/where-clauses/cfg-attr-issue-138010-2.rs

@@ -0,0 +1,33 @@
+#![feature(where_clause_attrs, cfg_boolean_literals, lazy_type_alias)]
+#![expect(incomplete_features)]
+
+struct Foo;
+trait Trait {}
+
+impl Trait for Foo {}
+
+type MixedWhereBounds1
+where //~ ERROR: where clauses are not allowed before the type for type aliases
+    #[cfg(true)]
+    Foo: Trait,
+= Foo
+where
+    (): Sized;
+
+type MixedWhereBounds2
+where //~ ERROR: where clauses are not allowed before the type for type aliases
+    #[cfg(false)]
+    Foo: Trait,
+= Foo
+where
+    (): Sized;
+
+type MixedWhereBounds3
+where
+//~^ ERROR: where clauses are not allowed before the type for type aliases
+    Foo: Trait,
+= Foo
+where
+    (): Sized;
+
+fn main() {}

tests/ui/where-clauses/cfg-attr-issue-138010-2.stderr

@@ -0,0 +1,39 @@
+error: where clauses are not allowed before the type for type aliases
+  --> $DIR/cfg-attr-issue-138010-2.rs:10:1
+   |
+LL | / where
+LL | |     #[cfg(true)]
+LL | |     Foo: Trait,
+   | |_______________^ help: remove this `where`
+   |
+   = note: see issue #89122 <https://github.com/rust-lang/rust/issues/89122> for more information
+
+error: where clauses are not allowed before the type for type aliases
+  --> $DIR/cfg-attr-issue-138010-2.rs:18:1
+   |
+LL | / where
+LL | |     #[cfg(false)]
+LL | |     Foo: Trait,
+   | |_______________^ help: remove this `where`
+   |
+   = note: see issue #89122 <https://github.com/rust-lang/rust/issues/89122> for more information
+
+error: where clauses are not allowed before the type for type aliases
+  --> $DIR/cfg-attr-issue-138010-2.rs:26:1
+   |
+LL | / where
+LL | |
+LL | |     Foo: Trait,
+   | |_______________^
+   |
+   = note: see issue #89122 <https://github.com/rust-lang/rust/issues/89122> for more information
+help: move it to the end of the type declaration
+   |
+LL + 
+LL | = Foo
+LL | where
+LL ~     (): Sized, Foo: Trait;
+   |
+
+error: aborting due to 3 previous errors
+