AST: Refactor type alias where clauses

compiler/rustc_ast/src/ast.rs

@@ -403,9 +403,10 @@ impl Default for Generics {
 /// A where-clause in a definition.
 #[derive(Clone, Encodable, Decodable, Debug)]
 pub struct WhereClause {
-    /// `true` if we ate a `where` token: this can happen
-    /// if we parsed no predicates (e.g. `struct Foo where {}`).
-    /// This allows us to pretty-print accurately.
+    /// `true` if we ate a `where` token.
+    ///
+    /// This can happen if we parsed no predicates, e.g., `struct Foo where {}`.
+    /// This allows us to pretty-print accurately and provide correct suggestion diagnostics.
     pub has_where_token: bool,
     pub predicates: ThinVec<WherePredicate>,
     pub span: Span,
@@ -3017,18 +3018,29 @@ pub struct Trait {
 ///
 /// If there is no where clause, then this is `false` with `DUMMY_SP`.
 #[derive(Copy, Clone, Encodable, Decodable, Debug, Default)]
-pub struct TyAliasWhereClause(pub bool, pub Span);
+pub struct TyAliasWhereClause {
+    pub has_where_token: bool,
+    pub span: Span,
+}
+
+/// The span information for the two where clauses on a `TyAlias`.
+#[derive(Copy, Clone, Encodable, Decodable, Debug, Default)]
+pub struct TyAliasWhereClauses {
+    /// Before the equals sign.
+    pub before: TyAliasWhereClause,
+    /// After the equals sign.
+    pub after: TyAliasWhereClause,
+    /// 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,
+}
 
 #[derive(Clone, Encodable, Decodable, Debug)]
 pub struct TyAlias {
     pub defaultness: Defaultness,
     pub generics: Generics,
-    /// The span information for the two where clauses (before equals, after equals)
-    pub where_clauses: (TyAliasWhereClause, TyAliasWhereClause),
-    /// The index in `generics.where_clause.predicates` that would split into
-    /// predicates from the where clause before the equals and the predicates
-    /// from the where clause after the equals
-    pub where_predicates_split: usize,
+    pub where_clauses: TyAliasWhereClauses,
     pub bounds: GenericBounds,
     pub ty: Option<P<Ty>>,
 }

compiler/rustc_ast/src/mut_visit.rs

@@ -1079,8 +1079,8 @@ pub fn noop_visit_item_kind<T: MutVisitor>(kind: &mut ItemKind, vis: &mut T) {
         }) => {
             visit_defaultness(defaultness, vis);
             vis.visit_generics(generics);
-            vis.visit_span(&mut where_clauses.0.1);
-            vis.visit_span(&mut where_clauses.1.1);
+            vis.visit_span(&mut where_clauses.before.span);
+            vis.visit_span(&mut where_clauses.after.span);
             visit_bounds(bounds, vis);
             visit_opt(ty, |ty| vis.visit_ty(ty));
         }
@@ -1163,8 +1163,8 @@ pub fn noop_flat_map_assoc_item<T: MutVisitor>(
         }) => {
             visit_defaultness(defaultness, visitor);
             visitor.visit_generics(generics);
-            visitor.visit_span(&mut where_clauses.0.1);
-            visitor.visit_span(&mut where_clauses.1.1);
+            visitor.visit_span(&mut where_clauses.before.span);
+            visitor.visit_span(&mut where_clauses.after.span);
             visit_bounds(bounds, visitor);
             visit_opt(ty, |ty| visitor.visit_ty(ty));
         }
@@ -1257,8 +1257,8 @@ pub fn noop_flat_map_foreign_item<T: MutVisitor>(
         }) => {
             visit_defaultness(defaultness, visitor);
             visitor.visit_generics(generics);
-            visitor.visit_span(&mut where_clauses.0.1);
-            visitor.visit_span(&mut where_clauses.1.1);
+            visitor.visit_span(&mut where_clauses.before.span);
+            visitor.visit_span(&mut where_clauses.after.span);
             visit_bounds(bounds, visitor);
             visit_opt(ty, |ty| visitor.visit_ty(ty));
         }

compiler/rustc_ast_lowering/src/item.rs

@@ -33,19 +33,20 @@ pub(super) struct ItemLowerer<'a, 'hir> {
 /// clause if it exists.
 fn add_ty_alias_where_clause(
     generics: &mut ast::Generics,
-    mut where_clauses: (TyAliasWhereClause, TyAliasWhereClause),
+    mut where_clauses: TyAliasWhereClauses,
     prefer_first: bool,
 ) {
     if !prefer_first {
-        where_clauses = (where_clauses.1, where_clauses.0);
-    }
-    if where_clauses.0.0 || !where_clauses.1.0 {
-        generics.where_clause.has_where_token = where_clauses.0.0;
-        generics.where_clause.span = where_clauses.0.1;
-    } else {
-        generics.where_clause.has_where_token = where_clauses.1.0;
-        generics.where_clause.span = where_clauses.1.1;
+        (where_clauses.before, where_clauses.after) = (where_clauses.after, where_clauses.before);
     }
+    let where_clause =
+        if where_clauses.before.has_where_token || !where_clauses.after.has_where_token {
+            where_clauses.before
+        } else {
+            where_clauses.after
+        };
+    generics.where_clause.has_where_token = where_clause.has_where_token;
+    generics.where_clause.span = where_clause.span;
 }
 
 impl<'a, 'hir> ItemLowerer<'a, 'hir> {

compiler/rustc_ast_passes/src/ast_validation.rs

@@ -139,14 +139,14 @@ impl<'a> AstValidator<'a> {
         ty_alias: &TyAlias,
     ) -> Result<(), errors::WhereClauseBeforeTypeAlias> {
         let before_predicates =
-            ty_alias.generics.where_clause.predicates.split_at(ty_alias.where_predicates_split).0;
+            ty_alias.generics.where_clause.predicates.split_at(ty_alias.where_clauses.split).0;
 
         if ty_alias.ty.is_none() || before_predicates.is_empty() {
             return Ok(());
         }
 
         let mut state = State::new();
-        if !ty_alias.where_clauses.1.0 {
+        if !ty_alias.where_clauses.after.has_where_token {
             state.space();
             state.word_space("where");
         } else {
@@ -161,13 +161,13 @@ impl<'a> AstValidator<'a> {
             state.print_where_predicate(p);
         }
 
-        let span = ty_alias.where_clauses.0.1;
+        let span = ty_alias.where_clauses.before.span;
         Err(errors::WhereClauseBeforeTypeAlias {
             span,
             sugg: errors::WhereClauseBeforeTypeAliasSugg {
                 left: span,
                 snippet: state.s.eof(),
-                right: ty_alias.where_clauses.1.1.shrink_to_hi(),
+                right: ty_alias.where_clauses.after.span.shrink_to_hi(),
             },
         })
     }
@@ -457,8 +457,7 @@ impl<'a> AstValidator<'a> {
     fn check_foreign_ty_genericless(
         &self,
         generics: &Generics,
-        before_where_clause: &TyAliasWhereClause,
-        after_where_clause: &TyAliasWhereClause,
+        where_clauses: &TyAliasWhereClauses,
     ) {
         let cannot_have = |span, descr, remove_descr| {
             self.dcx().emit_err(errors::ExternTypesCannotHave {
@@ -473,14 +472,14 @@ impl<'a> AstValidator<'a> {
             cannot_have(generics.span, "generic parameters", "generic parameters");
         }
 
-        let check_where_clause = |where_clause: &TyAliasWhereClause| {
-            if let TyAliasWhereClause(true, where_clause_span) = where_clause {
-                cannot_have(*where_clause_span, "`where` clauses", "`where` clause");
+        let check_where_clause = |where_clause: TyAliasWhereClause| {
+            if where_clause.has_where_token {
+                cannot_have(where_clause.span, "`where` clauses", "`where` clause");
             }
         };
 
-        check_where_clause(before_where_clause);
-        check_where_clause(after_where_clause);
+        check_where_clause(where_clauses.before);
+        check_where_clause(where_clauses.after);
     }
 
     fn check_foreign_kind_bodyless(&self, ident: Ident, kind: &str, body: Option<Span>) {
@@ -1121,9 +1120,9 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
                     if let Err(err) = self.check_type_alias_where_clause_location(ty_alias) {
                         self.dcx().emit_err(err);
                     }
-                } else if where_clauses.1.0 {
+                } else if where_clauses.after.has_where_token {
                     self.dcx().emit_err(errors::WhereClauseAfterTypeAlias {
-                        span: where_clauses.1.1,
+                        span: where_clauses.after.span,
                         help: self.session.is_nightly_build().then_some(()),
                     });
                 }
@@ -1153,7 +1152,7 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
                 self.check_defaultness(fi.span, *defaultness);
                 self.check_foreign_kind_bodyless(fi.ident, "type", ty.as_ref().map(|b| b.span));
                 self.check_type_no_bounds(bounds, "`extern` blocks");
-                self.check_foreign_ty_genericless(generics, &where_clauses.0, &where_clauses.1);
+                self.check_foreign_ty_genericless(generics, where_clauses);
                 self.check_foreign_item_ascii_only(fi.ident);
             }
             ForeignItemKind::Static(_, _, body) => {

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

@@ -43,15 +43,13 @@ impl<'a> State<'a> {
                 defaultness,
                 generics,
                 where_clauses,
-                where_predicates_split,
                 bounds,
                 ty,
             }) => {
                 self.print_associated_type(
                     ident,
                     generics,
                     *where_clauses,
-                    *where_predicates_split,
                     bounds,
                     ty.as_deref(),
                     vis,
@@ -108,15 +106,14 @@ impl<'a> State<'a> {
         &mut self,
         ident: Ident,
         generics: &ast::Generics,
-        where_clauses: (ast::TyAliasWhereClause, ast::TyAliasWhereClause),
-        where_predicates_split: usize,
+        where_clauses: ast::TyAliasWhereClauses,
         bounds: &ast::GenericBounds,
         ty: Option<&ast::Ty>,
         vis: &ast::Visibility,
         defaultness: ast::Defaultness,
     ) {
         let (before_predicates, after_predicates) =
-            generics.where_clause.predicates.split_at(where_predicates_split);
+            generics.where_clause.predicates.split_at(where_clauses.split);
         self.head("");
         self.print_visibility(vis);
         self.print_defaultness(defaultness);
@@ -127,13 +124,13 @@ impl<'a> State<'a> {
             self.word_nbsp(":");
             self.print_type_bounds(bounds);
         }
-        self.print_where_clause_parts(where_clauses.0.0, before_predicates);
+        self.print_where_clause_parts(where_clauses.before.has_where_token, before_predicates);
         if let Some(ty) = ty {
             self.space();
             self.word_space("=");
             self.print_type(ty);
         }
-        self.print_where_clause_parts(where_clauses.1.0, after_predicates);
+        self.print_where_clause_parts(where_clauses.after.has_where_token, after_predicates);
         self.word(";");
         self.end(); // end inner head-block
         self.end(); // end outer head-block
@@ -249,15 +246,13 @@ impl<'a> State<'a> {
                 defaultness,
                 generics,
                 where_clauses,
-                where_predicates_split,
                 bounds,
                 ty,
             }) => {
                 self.print_associated_type(
                     item.ident,
                     generics,
                     *where_clauses,
-                    *where_predicates_split,
                     bounds,
                     ty.as_deref(),
                     &item.vis,
@@ -536,15 +531,13 @@ impl<'a> State<'a> {
                 defaultness,
                 generics,
                 where_clauses,
-                where_predicates_split,
                 bounds,
                 ty,
             }) => {
                 self.print_associated_type(
                     ident,
                     generics,
                     *where_clauses,
-                    *where_predicates_split,
                     bounds,
                     ty.as_deref(),
                     vis,

compiler/rustc_builtin_macros/src/deriving/generic/mod.rs

@@ -595,11 +595,7 @@ impl<'a> TraitDef<'a> {
                 kind: ast::AssocItemKind::Type(Box::new(ast::TyAlias {
                     defaultness: ast::Defaultness::Final,
                     generics: Generics::default(),
-                    where_clauses: (
-                        ast::TyAliasWhereClause::default(),
-                        ast::TyAliasWhereClause::default(),
-                    ),
-                    where_predicates_split: 0,
+                    where_clauses: ast::TyAliasWhereClauses::default(),
                     bounds: Vec::new(),
                     ty: Some(type_def.to_ty(cx, self.span, type_ident, generics)),
                 })),

compiler/rustc_parse/src/parser/item.rs

@@ -970,11 +970,17 @@ impl<'a> Parser<'a> {
 
         let after_where_clause = self.parse_where_clause()?;
 
-        let where_clauses = (
-            TyAliasWhereClause(before_where_clause.has_where_token, before_where_clause.span),
-            TyAliasWhereClause(after_where_clause.has_where_token, after_where_clause.span),
-        );
-        let where_predicates_split = before_where_clause.predicates.len();
+        let where_clauses = TyAliasWhereClauses {
+            before: TyAliasWhereClause {
+                has_where_token: before_where_clause.has_where_token,
+                span: before_where_clause.span,
+            },
+            after: TyAliasWhereClause {
+                has_where_token: after_where_clause.has_where_token,
+                span: after_where_clause.span,
+            },
+            split: before_where_clause.predicates.len(),
+        };
         let mut predicates = before_where_clause.predicates;
         predicates.extend(after_where_clause.predicates);
         let where_clause = WhereClause {
@@ -993,7 +999,6 @@ impl<'a> Parser<'a> {
                 defaultness,
                 generics,
                 where_clauses,
-                where_predicates_split,
                 bounds,
                 ty,
             })),

src/tools/rustfmt/src/items.rs

@@ -1651,8 +1651,7 @@ struct TyAliasRewriteInfo<'c, 'g>(
     &'c RewriteContext<'c>,
     Indent,
     &'g ast::Generics,
-    (ast::TyAliasWhereClause, ast::TyAliasWhereClause),
-    usize,
+    ast::TyAliasWhereClauses,
     symbol::Ident,
     Span,
 );
@@ -1672,23 +1671,14 @@ pub(crate) fn rewrite_type_alias<'a, 'b>(
         ref bounds,
         ref ty,
         where_clauses,
-        where_predicates_split,
     } = *ty_alias_kind;
     let ty_opt = ty.as_ref();
     let (ident, vis) = match visitor_kind {
         Item(i) => (i.ident, &i.vis),
         AssocTraitItem(i) | AssocImplItem(i) => (i.ident, &i.vis),
         ForeignItem(i) => (i.ident, &i.vis),
     };
-    let rw_info = &TyAliasRewriteInfo(
-        context,
-        indent,
-        generics,
-        where_clauses,
-        where_predicates_split,
-        ident,
-        span,
-    );
+    let rw_info = &TyAliasRewriteInfo(context, indent, generics, where_clauses, ident, span);
     let op_ty = opaque_ty(ty);
     // Type Aliases are formatted slightly differently depending on the context
     // in which they appear, whether they are opaque, and whether they are associated.
@@ -1724,19 +1714,11 @@ fn rewrite_ty<R: Rewrite>(
     vis: &ast::Visibility,
 ) -> Option<String> {
     let mut result = String::with_capacity(128);
-    let TyAliasRewriteInfo(
-        context,
-        indent,
-        generics,
-        where_clauses,
-        where_predicates_split,
-        ident,
-        span,
-    ) = *rw_info;
+    let TyAliasRewriteInfo(context, indent, generics, where_clauses, ident, span) = *rw_info;
     let (before_where_predicates, after_where_predicates) = generics
         .where_clause
         .predicates
-        .split_at(where_predicates_split);
+        .split_at(where_clauses.split);
     if !after_where_predicates.is_empty() {
         return None;
     }
@@ -1771,7 +1753,7 @@ fn rewrite_ty<R: Rewrite>(
     let where_clause_str = rewrite_where_clause(
         context,
         before_where_predicates,
-        where_clauses.0.1,
+        where_clauses.before.span,
         context.config.brace_style(),
         Shape::legacy(where_budget, indent),
         false,
@@ -1795,7 +1777,7 @@ fn rewrite_ty<R: Rewrite>(
         let comment_span = context
             .snippet_provider
             .opt_span_before(span, "=")
-            .map(|op_lo| mk_sp(where_clauses.0.1.hi(), op_lo));
+            .map(|op_lo| mk_sp(where_clauses.before.span.hi(), op_lo));
 
         let lhs = match comment_span {
             Some(comment_span)