Implment #[cfg] and #[cfg_attr] in where clauses

Author: frank-king

compiler/rustc_ast/src/ast.rs

@@ -417,6 +417,7 @@ impl WhereClause {
 /// A single predicate in a where-clause.
 #[derive(Clone, Encodable, Decodable, Debug)]
 pub struct WherePredicate {
+    pub attrs: AttrVec,
     pub kind: WherePredicateKind,
     pub id: NodeId,
     pub span: Span,
@@ -431,6 +432,8 @@ pub enum WherePredicateKind {
     RegionPredicate(WhereRegionPredicate),
     /// An equality predicate (unsupported).
     EqPredicate(WhereEqPredicate),
+    /// A macro invocation,
+    MacCall(P<MacCall>),
 }
 
 /// A type bound.

compiler/rustc_ast/src/ast_traits.rs

@@ -11,7 +11,7 @@ use crate::tokenstream::LazyAttrTokenStream;
 use crate::{
     Arm, AssocItem, AttrItem, AttrKind, AttrVec, Attribute, Block, Crate, Expr, ExprField,
     FieldDef, ForeignItem, GenericParam, Item, NodeId, Param, Pat, PatField, Path, Stmt, StmtKind,
-    Ty, Variant, Visibility,
+    Ty, Variant, Visibility, WherePredicate,
 };
 
 /// A utility trait to reduce boilerplate.
@@ -79,6 +79,7 @@ impl_has_node_id!(
     Stmt,
     Ty,
     Variant,
+    WherePredicate,
 );
 
 impl<T: AstDeref<Target: HasNodeId>> HasNodeId for T {
@@ -127,7 +128,16 @@ macro_rules! impl_has_tokens_none {
 }
 
 impl_has_tokens!(AssocItem, AttrItem, Block, Expr, ForeignItem, Item, Pat, Path, Ty, Visibility);
-impl_has_tokens_none!(Arm, ExprField, FieldDef, GenericParam, Param, PatField, Variant);
+impl_has_tokens_none!(
+    Arm,
+    ExprField,
+    FieldDef,
+    GenericParam,
+    Param,
+    PatField,
+    Variant,
+    WherePredicate
+);
 
 impl<T: AstDeref<Target: HasTokens>> HasTokens for T {
     fn tokens(&self) -> Option<&LazyAttrTokenStream> {
@@ -285,6 +295,7 @@ impl_has_attrs!(
     Param,
     PatField,
     Variant,
+    WherePredicate,
 );
 impl_has_attrs_none!(Attribute, AttrItem, Block, Pat, Path, Ty, Visibility);
 

compiler/rustc_ast/src/mut_visit.rs

@@ -338,8 +338,11 @@ pub trait MutVisitor: Sized {
         walk_where_clause(self, where_clause);
     }
 
-    fn visit_where_predicate(&mut self, where_predicate: &mut WherePredicate) {
-        walk_where_predicate(self, where_predicate)
+    fn flat_map_where_predicate(
+        &mut self,
+        where_predicate: WherePredicate,
+    ) -> SmallVec<[WherePredicate; 1]> {
+        walk_flat_map_where_predicate(self, where_predicate)
     }
 
     fn visit_where_predicate_kind(&mut self, kind: &mut WherePredicateKind) {
@@ -1105,15 +1108,20 @@ fn walk_ty_alias_where_clauses<T: MutVisitor>(vis: &mut T, tawcs: &mut TyAliasWh
 
 fn walk_where_clause<T: MutVisitor>(vis: &mut T, wc: &mut WhereClause) {
     let WhereClause { has_where_token: _, predicates, span } = wc;
-    visit_thin_vec(predicates, |predicate| vis.visit_where_predicate(predicate));
+    predicates.flat_map_in_place(|predicate| vis.flat_map_where_predicate(predicate));
     vis.visit_span(span);
 }
 
-pub fn walk_where_predicate<T: MutVisitor>(vis: &mut T, pred: &mut WherePredicate) {
-    let WherePredicate { kind, id, span } = pred;
+pub fn walk_flat_map_where_predicate<T: MutVisitor>(
+    vis: &mut T,
+    mut pred: WherePredicate,
+) -> SmallVec<[WherePredicate; 1]> {
+    let WherePredicate { attrs, kind, id, span } = &mut pred;
     vis.visit_id(id);
+    visit_attrs(vis, attrs);
     vis.visit_where_predicate_kind(kind);
     vis.visit_span(span);
+    smallvec![pred]
 }
 
 pub fn walk_where_predicate_kind<T: MutVisitor>(vis: &mut T, kind: &mut WherePredicateKind) {
@@ -1134,6 +1142,7 @@ pub fn walk_where_predicate_kind<T: MutVisitor>(vis: &mut T, kind: &mut WherePre
             vis.visit_ty(lhs_ty);
             vis.visit_ty(rhs_ty);
         }
+        WherePredicateKind::MacCall(m) => vis.visit_mac_call(m),
     }
 }
 

compiler/rustc_ast/src/visit.rs

@@ -833,7 +833,8 @@ pub fn walk_where_predicate<'a, V: Visitor<'a>>(
     visitor: &mut V,
     predicate: &'a WherePredicate,
 ) -> V::Result {
-    let WherePredicate { kind, id: _, span: _ } = predicate;
+    let WherePredicate { attrs, kind, id: _, span: _ } = predicate;
+    walk_list!(visitor, visit_attribute, attrs);
     visitor.visit_where_predicate_kind(kind)
 }
 
@@ -859,6 +860,9 @@ pub fn walk_where_predicate_kind<'a, V: Visitor<'a>>(
             try_visit!(visitor.visit_ty(lhs_ty));
             try_visit!(visitor.visit_ty(rhs_ty));
         }
+        WherePredicateKind::MacCall(mac) => {
+            try_visit!(visitor.visit_mac_call(mac));
+        }
     }
     V::Result::output()
 }

compiler/rustc_ast_lowering/src/item.rs

@@ -1727,6 +1727,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
     fn lower_where_predicate(&mut self, pred: &WherePredicate) -> hir::WherePredicate<'hir> {
         let hir_id = self.lower_node_id(pred.id);
         let span = self.lower_span(pred.span);
+        self.lower_attrs(hir_id, &pred.attrs);
         let kind = self.arena.alloc(match &pred.kind {
             WherePredicateKind::BoundPredicate(WhereBoundPredicate {
                 bound_generic_params,
@@ -1761,6 +1762,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
                         .lower_ty(rhs_ty, ImplTraitContext::Disallowed(ImplTraitPosition::Bound)),
                 })
             }
+            WherePredicateKind::MacCall(_) => panic!("macro shouldn't exist here"),
         });
         hir::WherePredicate { hir_id, span, kind }
     }

compiler/rustc_ast_passes/src/feature_gate.rs

@@ -515,6 +515,7 @@ pub fn check_crate(krate: &ast::Crate, sess: &Session, features: &Features) {
     gate_all!(unsafe_binders, "unsafe binder types are experimental");
     gate_all!(contracts, "contracts are incomplete");
     gate_all!(contracts_internals, "contract internal machinery is for internal use only");
+    gate_all!(where_clause_attrs, "attributes in `where` clause are unstable");
 
     if !visitor.features.never_patterns() {
         if let Some(spans) = spans.get(&sym::never_patterns) {

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

@@ -735,7 +735,8 @@ impl<'a> State<'a> {
     }
 
     pub fn print_where_predicate(&mut self, predicate: &ast::WherePredicate) {
-        let ast::WherePredicate { kind, id: _, span: _ } = predicate;
+        let ast::WherePredicate { attrs, kind, id: _, span: _ } = predicate;
+        self.print_outer_attributes(attrs);
         match kind {
             ast::WherePredicateKind::BoundPredicate(where_bound_predicate) => {
                 self.print_where_bound_predicate(where_bound_predicate);
@@ -760,6 +761,12 @@ impl<'a> State<'a> {
                 self.word_space("=");
                 self.print_type(rhs_ty);
             }
+            ast::WherePredicateKind::MacCall(m) => {
+                self.print_mac(m);
+                if m.args.need_semicolon() {
+                    self.word(";");
+                }
+            }
         }
     }
 

compiler/rustc_builtin_macros/src/deriving/coerce_pointee.rs

@@ -300,13 +300,15 @@ pub(crate) fn expand_deriving_coerce_pointee(
                 to_ty: &s_ty,
                 rewritten: false,
             };
-            let mut predicate = ast::WherePredicate {
-                kind: ast::WherePredicateKind::BoundPredicate(bound.clone()),
-                span: predicate.span,
-                id: ast::DUMMY_NODE_ID,
-            };
-            substitution.visit_where_predicate(&mut predicate);
+            let mut kind = ast::WherePredicateKind::BoundPredicate(bound.clone());
+            substitution.visit_where_predicate_kind(&mut kind);
             if substitution.rewritten {
+                let predicate = ast::WherePredicate {
+                    attrs: predicate.attrs.clone(),
+                    kind,
+                    span: predicate.span,
+                    id: ast::DUMMY_NODE_ID,
+                };
                 impl_generics.where_clause.predicates.push(predicate);
             }
         }
@@ -388,8 +390,8 @@ impl<'a> ast::mut_visit::MutVisitor for TypeSubstitution<'a> {
         }
     }
 
-    fn visit_where_predicate(&mut self, where_predicate: &mut ast::WherePredicate) {
-        match &mut where_predicate.kind {
+    fn visit_where_predicate_kind(&mut self, kind: &mut ast::WherePredicateKind) {
+        match kind {
             rustc_ast::WherePredicateKind::BoundPredicate(bound) => {
                 bound
                     .bound_generic_params
@@ -400,7 +402,8 @@ impl<'a> ast::mut_visit::MutVisitor for TypeSubstitution<'a> {
                 }
             }
             rustc_ast::WherePredicateKind::RegionPredicate(_)
-            | rustc_ast::WherePredicateKind::EqPredicate(_) => {}
+            | rustc_ast::WherePredicateKind::EqPredicate(_)
+            | rustc_ast::WherePredicateKind::MacCall(_) => {}
         }
     }
 }

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

@@ -690,6 +690,7 @@ impl<'a> TraitDef<'a> {
         // and similarly for where clauses
         where_clause.predicates.extend(generics.where_clause.predicates.iter().map(|clause| {
             ast::WherePredicate {
+                attrs: clause.attrs.clone(),
                 kind: clause.kind.clone(),
                 id: ast::DUMMY_NODE_ID,
                 span: clause.span.with_ctxt(ctxt),
@@ -747,8 +748,12 @@ impl<'a> TraitDef<'a> {
                         };
 
                         let kind = ast::WherePredicateKind::BoundPredicate(predicate);
-                        let predicate =
-                            ast::WherePredicate { kind, id: ast::DUMMY_NODE_ID, span: self.span };
+                        let predicate = ast::WherePredicate {
+                            attrs: ThinVec::new(),
+                            kind,
+                            id: ast::DUMMY_NODE_ID,
+                            span: self.span,
+                        };
                         where_clause.predicates.push(predicate);
                     }
                 }

compiler/rustc_expand/src/base.rs

@@ -52,6 +52,7 @@ pub enum Annotatable {
     Param(ast::Param),
     FieldDef(ast::FieldDef),
     Variant(ast::Variant),
+    WherePredicate(ast::WherePredicate),
     Crate(ast::Crate),
 }
 
@@ -70,6 +71,7 @@ impl Annotatable {
             Annotatable::Param(p) => p.span,
             Annotatable::FieldDef(sf) => sf.span,
             Annotatable::Variant(v) => v.span,
+            Annotatable::WherePredicate(wp) => wp.span,
             Annotatable::Crate(c) => c.spans.inner_span,
         }
     }
@@ -88,6 +90,7 @@ impl Annotatable {
             Annotatable::Param(p) => p.visit_attrs(f),
             Annotatable::FieldDef(sf) => sf.visit_attrs(f),
             Annotatable::Variant(v) => v.visit_attrs(f),
+            Annotatable::WherePredicate(wp) => wp.visit_attrs(f),
             Annotatable::Crate(c) => c.visit_attrs(f),
         }
     }
@@ -106,6 +109,7 @@ impl Annotatable {
             Annotatable::Param(p) => visitor.visit_param(p),
             Annotatable::FieldDef(sf) => visitor.visit_field_def(sf),
             Annotatable::Variant(v) => visitor.visit_variant(v),
+            Annotatable::WherePredicate(wp) => visitor.visit_where_predicate(wp),
             Annotatable::Crate(c) => visitor.visit_crate(c),
         }
     }
@@ -127,6 +131,7 @@ impl Annotatable {
             | Annotatable::Param(..)
             | Annotatable::FieldDef(..)
             | Annotatable::Variant(..)
+            | Annotatable::WherePredicate(..)
             | Annotatable::Crate(..) => panic!("unexpected annotatable"),
         }
     }
@@ -222,6 +227,13 @@ impl Annotatable {
         }
     }
 
+    pub fn expect_where_predicate(self) -> ast::WherePredicate {
+        match self {
+            Annotatable::WherePredicate(wp) => wp,
+            _ => panic!("expected where predicate"),
+        }
+    }
+
     pub fn expect_crate(self) -> ast::Crate {
         match self {
             Annotatable::Crate(krate) => krate,
@@ -445,6 +457,10 @@ pub trait MacResult {
         None
     }
 
+    fn make_where_predicates(self: Box<Self>) -> Option<SmallVec<[ast::WherePredicate; 1]>> {
+        None
+    }
+
     fn make_crate(self: Box<Self>) -> Option<ast::Crate> {
         // Fn-like macros cannot produce a crate.
         unreachable!()