Rollup merge of #32682 - petrochenkov:field3, r=Manishearth

 The AST part of https://github.com/rust-lang/rust/pull/31937

Unlike HIR, AST still uses `Option` for field names because parser can't know field indexes reliably due to constructions like
```
struct S(#[cfg(false)] u8, u8); // The index of the second field changes from 1 during parsing to 0 after expansion.
```
and I wouldn't like to put the burden of renaming fields on expansion passes and syntax extensions.

plugin-[breaking-change] cc https://github.com/rust-lang/rust/issues/31645
r? @Manishearth

8 files changed, 47 insertions, 92 deletions

diff --git a/src/libsyntax/ast.rs b/src/libsyntax/ast.rs
index a441f2990cd..dbe7b078498 100644
--- a/src/libsyntax/ast.rs
+++ b/src/libsyntax/ast.rs
@@ -10,7 +10,6 @@
 
 // The Rust abstract syntax tree.
 
-pub use self::StructFieldKind::*;
 pub use self::TyParamBound::*;
 pub use self::UnsafeSource::*;
 pub use self::ViewPath_::*;
@@ -1877,46 +1876,15 @@ pub enum Visibility {
 }
 
 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, Hash, Debug)]
-pub struct StructField_ {
-    pub kind: StructFieldKind,
+pub struct StructField {
+    pub span: Span,
+    pub ident: Option<Ident>,
+    pub vis: Visibility,
     pub id: NodeId,
     pub ty: P<Ty>,
     pub attrs: Vec<Attribute>,
 }
 
-impl StructField_ {
-    pub fn ident(&self) -> Option<Ident> {
-        match self.kind {
-            NamedField(ref ident, _) => Some(ident.clone()),
-            UnnamedField(_) => None
-        }
-    }
-}
-
-pub type StructField = Spanned<StructField_>;
-
-#[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, Hash, Debug)]
-pub enum StructFieldKind {
-    NamedField(Ident, Visibility),
-    /// Element of a tuple-like struct
-    UnnamedField(Visibility),
-}
-
-impl StructFieldKind {
-    pub fn is_unnamed(&self) -> bool {
-        match *self {
-            UnnamedField(..) => true,
-            NamedField(..) => false,
-        }
-    }
-
-    pub fn visibility(&self) -> &Visibility {
-        match *self {
-            NamedField(_, ref vis) | UnnamedField(ref vis) => vis
-        }
-    }
-}
-
 /// Fields and Ids of enum variants and structs
 ///
 /// For enum variants: `NodeId` represents both an Id of the variant itself (relevant for all
diff --git a/src/libsyntax/ast_util.rs b/src/libsyntax/ast_util.rs
index 852b153044f..ffba9e824d4 100644
--- a/src/libsyntax/ast_util.rs
+++ b/src/libsyntax/ast_util.rs
@@ -95,12 +95,6 @@ pub fn impl_pretty_name(trait_ref: &Option<TraitRef>, ty: Option<&Ty>) -> Ident
     token::gensym_ident(&pretty[..])
 }
 
-pub fn struct_field_visibility(field: ast::StructField) -> Visibility {
-    match field.node.kind {
-        ast::NamedField(_, v) | ast::UnnamedField(v) => v
-    }
-}
-
 // ______________________________________________________________________
 // Enumerating the IDs which appear in an AST
 
@@ -269,7 +263,7 @@ impl<'a, 'v, O: IdVisitingOperation> Visitor<'v> for IdVisitor<'a, O> {
     }
 
     fn visit_struct_field(&mut self, struct_field: &StructField) {
-        self.operation.visit_id(struct_field.node.id);
+        self.operation.visit_id(struct_field.id);
         visit::walk_struct_field(self, struct_field)
     }
 
diff --git a/src/libsyntax/config.rs b/src/libsyntax/config.rs
index 9acb1805cdd..4554a280e5f 100644
--- a/src/libsyntax/config.rs
+++ b/src/libsyntax/config.rs
@@ -180,12 +180,12 @@ fn fold_struct<F>(cx: &mut Context<F>, vdata: ast::VariantData) -> ast::VariantD
     match vdata {
         ast::VariantData::Struct(fields, id) => {
             ast::VariantData::Struct(fields.into_iter().filter(|m| {
-                (cx.in_cfg)(&m.node.attrs)
+                (cx.in_cfg)(&m.attrs)
             }).collect(), id)
         }
         ast::VariantData::Tuple(fields, id) => {
             ast::VariantData::Tuple(fields.into_iter().filter(|m| {
-                (cx.in_cfg)(&m.node.attrs)
+                (cx.in_cfg)(&m.attrs)
             }).collect(), id)
         }
         ast::VariantData::Unit(id) => ast::VariantData::Unit(id)
@@ -434,7 +434,7 @@ impl<'v, 'a, 'b> visit::Visitor<'v> for StmtExprAttrFeatureVisitor<'a, 'b> {
     }
 
     fn visit_struct_field(&mut self, s: &'v ast::StructField) {
-        if node_survives_cfg(&s.node.attrs, self.config) {
+        if node_survives_cfg(&s.attrs, self.config) {
             visit::walk_struct_field(self, s);
         }
     }
diff --git a/src/libsyntax/ext/build.rs b/src/libsyntax/ext/build.rs
index 0eb42f17f68..a4e5b68277d 100644
--- a/src/libsyntax/ext/build.rs
+++ b/src/libsyntax/ext/build.rs
@@ -1007,12 +1007,14 @@ impl<'a> AstBuilder for ExtCtxt<'a> {
 
     fn variant(&self, span: Span, name: Ident, tys: Vec<P<ast::Ty>> ) -> ast::Variant {
         let fields: Vec<_> = tys.into_iter().map(|ty| {
-            Spanned { span: ty.span, node: ast::StructField_ {
+            ast::StructField {
+                span: ty.span,
                 ty: ty,
-                kind: ast::UnnamedField(ast::Visibility::Inherited),
+                ident: None,
+                vis: ast::Visibility::Inherited,
                 attrs: Vec::new(),
                 id: ast::DUMMY_NODE_ID,
-            }}
+            }
         }).collect();
 
         let vdata = if fields.is_empty() {
diff --git a/src/libsyntax/fold.rs b/src/libsyntax/fold.rs
index 46bcb8067a3..46191b95f81 100644
--- a/src/libsyntax/fold.rs
+++ b/src/libsyntax/fold.rs
@@ -847,15 +847,13 @@ pub fn noop_fold_poly_trait_ref<T: Folder>(p: PolyTraitRef, fld: &mut T) -> Poly
 }
 
 pub fn noop_fold_struct_field<T: Folder>(f: StructField, fld: &mut T) -> StructField {
-    let StructField {node: StructField_ {id, kind, ty, attrs}, span} = f;
-    Spanned {
-        node: StructField_ {
-            id: fld.new_id(id),
-            kind: kind,
-            ty: fld.fold_ty(ty),
-            attrs: fold_attrs(attrs, fld),
-        },
-        span: fld.new_span(span)
+    StructField {
+        span: fld.new_span(f.span),
+        id: fld.new_id(f.id),
+        ident: f.ident.map(|ident| fld.fold_ident(ident)),
+        vis: f.vis,
+        ty: fld.fold_ty(f.ty),
+        attrs: fold_attrs(f.attrs, fld),
     }
 }
 
diff --git a/src/libsyntax/parse/parser.rs b/src/libsyntax/parse/parser.rs
index 89a504e1ebd..28e4682f66b 100644
--- a/src/libsyntax/parse/parser.rs
+++ b/src/libsyntax/parse/parser.rs
@@ -29,7 +29,6 @@ use ast::Local;
 use ast::MacStmtStyle;
 use ast::Mac_;
 use ast::{MutTy, Mutability};
-use ast::NamedField;
 use ast::{Pat, PatKind};
 use ast::{PolyTraitRef, QSelf};
 use ast::{Stmt, StmtKind};
@@ -38,7 +37,6 @@ use ast::StrStyle;
 use ast::SelfKind;
 use ast::{Delimited, SequenceRepetition, TokenTree, TraitItem, TraitRef};
 use ast::{Ty, TyKind, TypeBinding, TyParam, TyParamBounds};
-use ast::UnnamedField;
 use ast::{ViewPath, ViewPathGlob, ViewPathList, ViewPathSimple};
 use ast::{Visibility, WhereClause};
 use attr::{ThinAttributes, ThinAttributesExt, AttributesExt};
@@ -3847,12 +3845,14 @@ impl<'a> Parser<'a> {
         let name = self.parse_ident()?;
         self.expect(&token::Colon)?;
         let ty = self.parse_ty_sum()?;
-        Ok(spanned(lo, self.last_span.hi, ast::StructField_ {
-            kind: NamedField(name, pr),
+        Ok(StructField {
+            span: mk_sp(lo, self.last_span.hi),
+            ident: Some(name),
+            vis: pr,
             id: ast::DUMMY_NODE_ID,
             ty: ty,
             attrs: attrs,
-        }))
+        })
     }
 
     /// Emit an expected item after attributes error.
@@ -5246,13 +5246,16 @@ impl<'a> Parser<'a> {
             |p| {
                 let attrs = p.parse_outer_attributes()?;
                 let lo = p.span.lo;
-                let struct_field_ = ast::StructField_ {
-                    kind: UnnamedField(p.parse_visibility()?),
+                let vis = p.parse_visibility()?;
+                let ty = p.parse_ty_sum()?;
+                Ok(StructField {
+                    span: mk_sp(lo, p.span.hi),
+                    vis: vis,
+                    ident: None,
                     id: ast::DUMMY_NODE_ID,
-                    ty: p.parse_ty_sum()?,
+                    ty: ty,
                     attrs: attrs,
-                };
-                Ok(spanned(lo, p.span.hi, struct_field_))
+                })
             })?;
 
         Ok(fields)
diff --git a/src/libsyntax/print/pprust.rs b/src/libsyntax/print/pprust.rs
index a8f28ed3d9e..e2b1d2f5e7a 100644
--- a/src/libsyntax/print/pprust.rs
+++ b/src/libsyntax/print/pprust.rs
@@ -1407,14 +1407,9 @@ impl<'a> State<'a> {
                 self.commasep(
                     Inconsistent, struct_def.fields(),
                     |s, field| {
-                        match field.node.kind {
-                            ast::NamedField(..) => panic!("unexpected named field"),
-                            ast::UnnamedField(ref vis) => {
-                                s.print_visibility(vis)?;
-                                s.maybe_print_comment(field.span.lo)?;
-                                s.print_type(&field.node.ty)
-                            }
-                        }
+                        s.print_visibility(&field.vis)?;
+                        s.maybe_print_comment(field.span.lo)?;
+                        s.print_type(&field.ty)
                     }
                 )?;
                 self.pclose()?;
@@ -1432,19 +1427,14 @@ impl<'a> State<'a> {
             self.hardbreak_if_not_bol()?;
 
             for field in struct_def.fields() {
-                match field.node.kind {
-                    ast::UnnamedField(..) => panic!("unexpected unnamed field"),
-                    ast::NamedField(ident, ref visibility) => {
-                        self.hardbreak_if_not_bol()?;
-                        self.maybe_print_comment(field.span.lo)?;
-                        self.print_outer_attributes(&field.node.attrs)?;
-                        self.print_visibility(visibility)?;
-                        self.print_ident(ident)?;
-                        self.word_nbsp(":")?;
-                        self.print_type(&field.node.ty)?;
-                        word(&mut self.s, ",")?;
-                    }
-                }
+                self.hardbreak_if_not_bol()?;
+                self.maybe_print_comment(field.span.lo)?;
+                self.print_outer_attributes(&field.attrs)?;
+                self.print_visibility(&field.vis)?;
+                self.print_ident(field.ident.unwrap())?;
+                self.word_nbsp(":")?;
+                self.print_type(&field.ty)?;
+                word(&mut self.s, ",")?;
             }
 
             self.bclose(span)
diff --git a/src/libsyntax/visit.rs b/src/libsyntax/visit.rs
index 1251f9bfe13..839bbf4805d 100644
--- a/src/libsyntax/visit.rs
+++ b/src/libsyntax/visit.rs
@@ -619,9 +619,9 @@ pub fn walk_struct_def<'v, V: Visitor<'v>>(visitor: &mut V,
 
 pub fn walk_struct_field<'v, V: Visitor<'v>>(visitor: &mut V,
                                              struct_field: &'v StructField) {
-    walk_opt_ident(visitor, struct_field.span, struct_field.node.ident());
-    visitor.visit_ty(&struct_field.node.ty);
-    walk_list!(visitor, visit_attribute, &struct_field.node.attrs);
+    walk_opt_ident(visitor, struct_field.span, struct_field.ident);
+    visitor.visit_ty(&struct_field.ty);
+    walk_list!(visitor, visit_attribute, &struct_field.attrs);
 }
 
 pub fn walk_block<'v, V: Visitor<'v>>(visitor: &mut V, block: &'v Block) {