Rollup merge of #34764 - pnkfelix:attrs-on-generic-formals, r=eddyb

 First step for #34761

6 files changed, 95 insertions, 10 deletions

diff --git a/src/libsyntax/ast.rs b/src/libsyntax/ast.rs
index 9364cec8ddd..fcf2d32ded9 100644
--- a/src/libsyntax/ast.rs
+++ b/src/libsyntax/ast.rs
@@ -121,6 +121,7 @@ impl fmt::Debug for Lifetime {
 /// A lifetime definition, e.g. `'a: 'b+'c+'d`
 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, Hash, Debug)]
 pub struct LifetimeDef {
+    pub attrs: ThinVec<Attribute>,
     pub lifetime: Lifetime,
     pub bounds: Vec<Lifetime>
 }
@@ -370,6 +371,7 @@ pub type TyParamBounds = P<[TyParamBound]>;
 
 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, Hash, Debug)]
 pub struct TyParam {
+    pub attrs: ThinVec<Attribute>,
     pub ident: Ident,
     pub id: NodeId,
     pub bounds: TyParamBounds,
diff --git a/src/libsyntax/ext/build.rs b/src/libsyntax/ext/build.rs
index 08bedd794f6..bdbc45471bb 100644
--- a/src/libsyntax/ext/build.rs
+++ b/src/libsyntax/ext/build.rs
@@ -73,6 +73,7 @@ pub trait AstBuilder {
     fn typaram(&self,
                span: Span,
                id: ast::Ident,
+               attrs: Vec<ast::Attribute>,
                bounds: ast::TyParamBounds,
                default: Option<P<ast::Ty>>) -> ast::TyParam;
 
@@ -83,6 +84,7 @@ pub trait AstBuilder {
     fn lifetime_def(&self,
                     span: Span,
                     name: ast::Name,
+                    attrs: Vec<ast::Attribute>,
                     bounds: Vec<ast::Lifetime>)
                     -> ast::LifetimeDef;
 
@@ -452,11 +454,13 @@ impl<'a> AstBuilder for ExtCtxt<'a> {
     fn typaram(&self,
                span: Span,
                id: ast::Ident,
+               attrs: Vec<ast::Attribute>,
                bounds: ast::TyParamBounds,
                default: Option<P<ast::Ty>>) -> ast::TyParam {
         ast::TyParam {
             ident: id,
             id: ast::DUMMY_NODE_ID,
+            attrs: attrs.into(),
             bounds: bounds,
             default: default,
             span: span
@@ -503,9 +507,11 @@ impl<'a> AstBuilder for ExtCtxt<'a> {
     fn lifetime_def(&self,
                     span: Span,
                     name: ast::Name,
+                    attrs: Vec<ast::Attribute>,
                     bounds: Vec<ast::Lifetime>)
                     -> ast::LifetimeDef {
         ast::LifetimeDef {
+            attrs: attrs.into(),
             lifetime: self.lifetime(span, name),
             bounds: bounds
         }
diff --git a/src/libsyntax/feature_gate.rs b/src/libsyntax/feature_gate.rs
index 88835fc868a..079d7175822 100644
--- a/src/libsyntax/feature_gate.rs
+++ b/src/libsyntax/feature_gate.rs
@@ -303,6 +303,9 @@ declare_features! (
     // Used to identify the `compiler_builtins` crate
     // rustc internal
     (active, compiler_builtins, "1.13.0", None),
+
+    // Allows attributes on lifetime/type formal parameters in generics (RFC 1327)
+    (active, generic_param_attrs, "1.11.0", Some(34761)),
 );
 
 declare_features! (
@@ -1220,6 +1223,24 @@ impl<'a> Visitor for PostExpansionVisitor<'a> {
 
         visit::walk_vis(self, vis)
     }
+
+    fn visit_generics(&mut self, g: &ast::Generics) {
+        for t in &g.ty_params {
+            if !t.attrs.is_empty() {
+                gate_feature_post!(&self, generic_param_attrs, t.attrs[0].span,
+                                   "attributes on type parameter bindings are experimental");
+            }
+        }
+        visit::walk_generics(self, g)
+    }
+
+    fn visit_lifetime_def(&mut self, lifetime_def: &ast::LifetimeDef) {
+        if !lifetime_def.attrs.is_empty() {
+            gate_feature_post!(&self, generic_param_attrs, lifetime_def.attrs[0].span,
+                               "attributes on lifetime bindings are experimental");
+        }
+        visit::walk_lifetime_def(self, lifetime_def)
+    }
 }
 
 pub fn get_features(span_handler: &Handler, krate_attrs: &[ast::Attribute]) -> Features {
diff --git a/src/libsyntax/fold.rs b/src/libsyntax/fold.rs
index 05adfc43056..08c0637b2d9 100644
--- a/src/libsyntax/fold.rs
+++ b/src/libsyntax/fold.rs
@@ -662,8 +662,13 @@ pub fn noop_fold_ty_param_bound<T>(tpb: TyParamBound, fld: &mut T)
 }
 
 pub fn noop_fold_ty_param<T: Folder>(tp: TyParam, fld: &mut T) -> TyParam {
-    let TyParam {id, ident, bounds, default, span} = tp;
+    let TyParam {attrs, id, ident, bounds, default, span} = tp;
+    let attrs: Vec<_> = attrs.into();
     TyParam {
+        attrs: attrs.into_iter()
+            .flat_map(|x| fld.fold_attribute(x).into_iter())
+            .collect::<Vec<_>>()
+            .into(),
         id: fld.new_id(id),
         ident: ident,
         bounds: fld.fold_bounds(bounds),
@@ -687,7 +692,12 @@ pub fn noop_fold_lifetime<T: Folder>(l: Lifetime, fld: &mut T) -> Lifetime {
 
 pub fn noop_fold_lifetime_def<T: Folder>(l: LifetimeDef, fld: &mut T)
                                          -> LifetimeDef {
+    let attrs: Vec<_> = l.attrs.into();
     LifetimeDef {
+        attrs: attrs.into_iter()
+            .flat_map(|x| fld.fold_attribute(x).into_iter())
+            .collect::<Vec<_>>()
+            .into(),
         lifetime: fld.fold_lifetime(l.lifetime),
         bounds: fld.fold_lifetimes(l.bounds),
     }
diff --git a/src/libsyntax/parse/parser.rs b/src/libsyntax/parse/parser.rs
index b3fa8a2a5b0..9b6002b2469 100644
--- a/src/libsyntax/parse/parser.rs
+++ b/src/libsyntax/parse/parser.rs
@@ -1179,7 +1179,7 @@ impl<'a> Parser<'a> {
         let lo = self.span.lo;
 
         let (name, node) = if self.eat_keyword(keywords::Type) {
-            let TyParam {ident, bounds, default, ..} = self.parse_ty_param()?;
+            let TyParam {ident, bounds, default, ..} = self.parse_ty_param(vec![])?;
             self.expect(&token::Semi)?;
             (ident, TraitItemKind::Type(bounds, default))
         } else if self.is_const_item() {
@@ -1910,10 +1910,22 @@ impl<'a> Parser<'a> {
 
     /// Parses `lifetime_defs = [ lifetime_defs { ',' lifetime_defs } ]` where `lifetime_def  =
     /// lifetime [':' lifetimes]`
-    pub fn parse_lifetime_defs(&mut self) -> PResult<'a, Vec<ast::LifetimeDef>> {
-
+    ///
+    /// If `followed_by_ty_params` is None, then we are in a context
+    /// where only lifetime parameters are allowed, and thus we should
+    /// error if we encounter attributes after the bound lifetimes.
+    ///
+    /// If `followed_by_ty_params` is Some(r), then there may be type
+    /// parameter bindings after the lifetimes, so we should pass
+    /// along the parsed attributes to be attached to the first such
+    /// type parmeter.
+    pub fn parse_lifetime_defs(&mut self,
+                               followed_by_ty_params: Option<&mut Vec<ast::Attribute>>)
+                               -> PResult<'a, Vec<ast::LifetimeDef>>
+    {
         let mut res = Vec::new();
         loop {
+            let attrs = self.parse_outer_attributes()?;
             match self.token {
                 token::Lifetime(_) => {
                     let lifetime = self.parse_lifetime()?;
@@ -1923,11 +1935,20 @@ impl<'a> Parser<'a> {
                         } else {
                             Vec::new()
                         };
-                    res.push(ast::LifetimeDef { lifetime: lifetime,
+                    res.push(ast::LifetimeDef { attrs: attrs.into(),
+                                                lifetime: lifetime,
                                                 bounds: bounds });
                 }
 
                 _ => {
+                    if let Some(recv) = followed_by_ty_params {
+                        assert!(recv.is_empty());
+                        *recv = attrs;
+                    } else {
+                        let msg = "trailing attribute after lifetime parameters";
+                        return Err(self.fatal(msg));
+                    }
+                    debug!("parse_lifetime_defs ret {:?}", res);
                     return Ok(res);
                 }
             }
@@ -4228,7 +4249,7 @@ impl<'a> Parser<'a> {
     }
 
     /// Matches typaram = IDENT (`?` unbound)? optbounds ( EQ ty )?
-    fn parse_ty_param(&mut self) -> PResult<'a, TyParam> {
+    fn parse_ty_param(&mut self, preceding_attrs: Vec<ast::Attribute>) -> PResult<'a, TyParam> {
         let span = self.span;
         let ident = self.parse_ident()?;
 
@@ -4242,6 +4263,7 @@ impl<'a> Parser<'a> {
         };
 
         Ok(TyParam {
+            attrs: preceding_attrs.into(),
             ident: ident,
             id: ast::DUMMY_NODE_ID,
             bounds: bounds,
@@ -4262,11 +4284,27 @@ impl<'a> Parser<'a> {
         let span_lo = self.span.lo;
 
         if self.eat(&token::Lt) {
-            let lifetime_defs = self.parse_lifetime_defs()?;
+            // Upon encountering attribute in generics list, we do not
+            // know if it is attached to lifetime or to type param.
+            //
+            // Solution: 1. eagerly parse attributes in tandem with
+            // lifetime defs, 2. store last set of parsed (and unused)
+            // attributes in `attrs`, and 3. pass in those attributes
+            // when parsing formal type param after lifetime defs.
+            let mut attrs = vec![];
+            let lifetime_defs = self.parse_lifetime_defs(Some(&mut attrs))?;
             let mut seen_default = false;
+            let mut post_lifetime_attrs = Some(attrs);
             let ty_params = self.parse_seq_to_gt(Some(token::Comma), |p| {
                 p.forbid_lifetime()?;
-                let ty_param = p.parse_ty_param()?;
+                // Move out of `post_lifetime_attrs` if present. O/w
+                // not first type param: parse attributes anew.
+                let attrs = match post_lifetime_attrs.as_mut() {
+                    None => p.parse_outer_attributes()?,
+                    Some(attrs) => mem::replace(attrs, vec![]),
+                };
+                post_lifetime_attrs = None;
+                let ty_param = p.parse_ty_param(attrs)?;
                 if ty_param.default.is_some() {
                     seen_default = true;
                 } else if seen_default {
@@ -4276,6 +4314,12 @@ impl<'a> Parser<'a> {
                 }
                 Ok(ty_param)
             })?;
+            if let Some(attrs) = post_lifetime_attrs {
+                if !attrs.is_empty() {
+                    self.span_err(attrs[0].span,
+                                  "trailing attribute after lifetime parameters");
+                }
+            }
             Ok(ast::Generics {
                 lifetimes: lifetime_defs,
                 ty_params: ty_params,
@@ -4423,7 +4467,7 @@ impl<'a> Parser<'a> {
                     let bound_lifetimes = if self.eat_keyword(keywords::For) {
                         // Higher ranked constraint.
                         self.expect(&token::Lt)?;
-                        let lifetime_defs = self.parse_lifetime_defs()?;
+                        let lifetime_defs = self.parse_lifetime_defs(None)?;
                         self.expect_gt()?;
                         lifetime_defs
                     } else {
@@ -4991,7 +5035,7 @@ impl<'a> Parser<'a> {
     fn parse_late_bound_lifetime_defs(&mut self) -> PResult<'a, Vec<ast::LifetimeDef>> {
         if self.eat_keyword(keywords::For) {
             self.expect(&token::Lt)?;
-            let lifetime_defs = self.parse_lifetime_defs()?;
+            let lifetime_defs = self.parse_lifetime_defs(None)?;
             self.expect_gt()?;
             Ok(lifetime_defs)
         } else {
diff --git a/src/libsyntax/visit.rs b/src/libsyntax/visit.rs
index 49f3a729f16..7fb3e5c6bee 100644
--- a/src/libsyntax/visit.rs
+++ b/src/libsyntax/visit.rs
@@ -201,6 +201,7 @@ pub fn walk_lifetime<V: Visitor>(visitor: &mut V, lifetime: &Lifetime) {
 pub fn walk_lifetime_def<V: Visitor>(visitor: &mut V, lifetime_def: &LifetimeDef) {
     visitor.visit_lifetime(&lifetime_def.lifetime);
     walk_list!(visitor, visit_lifetime, &lifetime_def.bounds);
+    walk_list!(visitor, visit_attribute, &*lifetime_def.attrs);
 }
 
 pub fn walk_poly_trait_ref<V>(visitor: &mut V, trait_ref: &PolyTraitRef, _: &TraitBoundModifier)
@@ -474,6 +475,7 @@ pub fn walk_generics<V: Visitor>(visitor: &mut V, generics: &Generics) {
         visitor.visit_ident(param.span, param.ident);
         walk_list!(visitor, visit_ty_param_bound, &param.bounds);
         walk_list!(visitor, visit_ty, &param.default);
+        walk_list!(visitor, visit_attribute, &*param.attrs);
     }
     walk_list!(visitor, visit_lifetime_def, &generics.lifetimes);
     for predicate in &generics.where_clause.predicates {