Rollup merge of rust-lang#43501 - topecongiro:span-to-whereclause, r=nrc

Add Span to ast::WhereClause

This PR adds `Span` field to `ast::WhereClause`. The motivation here is to make rustfmt's life easier when recovering comments before and after where clause.
r? @nrc

Author: Mark-Simulacrum

src/libsyntax/ast.rs

@@ -336,6 +336,7 @@ impl Default for Generics {
             where_clause: WhereClause {
                 id: DUMMY_NODE_ID,
                 predicates: Vec::new(),
+                span: DUMMY_SP,
             },
             span: DUMMY_SP,
         }
@@ -347,6 +348,7 @@ impl Default for Generics {
 pub struct WhereClause {
     pub id: NodeId,
     pub predicates: Vec<WherePredicate>,
+    pub span: Span,
 }
 
 /// A single predicate in a `where` clause

src/libsyntax/fold.rs

@@ -737,14 +737,15 @@ pub fn noop_fold_generics<T: Folder>(Generics {ty_params, lifetimes, where_claus
 }
 
 pub fn noop_fold_where_clause<T: Folder>(
-                              WhereClause {id, predicates}: WhereClause,
+                              WhereClause {id, predicates, span}: WhereClause,
                               fld: &mut T)
                               -> WhereClause {
     WhereClause {
         id: fld.new_id(id),
         predicates: predicates.move_map(|predicate| {
             fld.fold_where_predicate(predicate)
-        })
+        }),
+        span: span,
     }
 }
 

src/libsyntax/parse/mod.rs

@@ -892,6 +892,7 @@ mod tests {
                                         where_clause: ast::WhereClause {
                                             id: ast::DUMMY_NODE_ID,
                                             predicates: Vec::new(),
+                                            span: syntax_pos::DUMMY_SP,
                                         },
                                         span: syntax_pos::DUMMY_SP,
                                     },

src/libsyntax/parse/parser.rs

@@ -4302,6 +4302,7 @@ impl<'a> Parser<'a> {
                 where_clause: WhereClause {
                     id: ast::DUMMY_NODE_ID,
                     predicates: Vec::new(),
+                    span: syntax_pos::DUMMY_SP,
                 },
                 span: span_lo.to(self.prev_span),
             })
@@ -4369,11 +4370,13 @@ impl<'a> Parser<'a> {
         let mut where_clause = WhereClause {
             id: ast::DUMMY_NODE_ID,
             predicates: Vec::new(),
+            span: syntax_pos::DUMMY_SP,
         };
 
         if !self.eat_keyword(keywords::Where) {
             return Ok(where_clause);
         }
+        let lo = self.prev_span;
 
         // This is a temporary future proofing.
         //
@@ -4451,6 +4454,7 @@ impl<'a> Parser<'a> {
             }
         }
 
+        where_clause.span = lo.to(self.prev_span);
         Ok(where_clause)
     }
 

src/libsyntax/print/pprust.rs

@@ -1041,6 +1041,7 @@ impl<'a> State<'a> {
                     where_clause: ast::WhereClause {
                         id: ast::DUMMY_NODE_ID,
                         predicates: Vec::new(),
+                        span: syntax_pos::DUMMY_SP,
                     },
                     span: syntax_pos::DUMMY_SP,
                 };
@@ -2983,6 +2984,7 @@ impl<'a> State<'a> {
             where_clause: ast::WhereClause {
                 id: ast::DUMMY_NODE_ID,
                 predicates: Vec::new(),
+                span: syntax_pos::DUMMY_SP,
             },
             span: syntax_pos::DUMMY_SP,
         };

src/libsyntax_ext/deriving/generic/ty.rs

@@ -216,6 +216,7 @@ fn mk_generics(lifetimes: Vec<ast::LifetimeDef>, ty_params: Vec<ast::TyParam>, s
         where_clause: ast::WhereClause {
             id: ast::DUMMY_NODE_ID,
             predicates: Vec::new(),
+            span: span,
         },
         span: span,
     }