Rollup merge of #34339 - jseyfried:thin_vec, r=petrochenkov,Manishearth

Generalize and abstract `ThinAttributes` to `ThinVec<Attribute>`.

src/libsyntax/parse/mod.rs

@@ -675,6 +675,7 @@ mod tests {
     use tokenstream::{self, TokenTree};
     use util::parser_testing::{string_to_tts, string_to_parser};
     use util::parser_testing::{string_to_expr, string_to_item, string_to_stmt};
+    use util::ThinVec;
 
     // produce a syntax_pos::span
     fn sp(a: u32, b: u32) -> Span {
@@ -696,7 +697,7 @@ mod tests {
                         ),
                     }),
                     span: sp(0, 1),
-                    attrs: None,
+                    attrs: ThinVec::new(),
                    }))
     }
 
@@ -719,7 +720,7 @@ mod tests {
                             )
                         }),
                     span: sp(0, 6),
-                    attrs: None,
+                    attrs: ThinVec::new(),
                    }))
     }
 
@@ -835,10 +836,10 @@ mod tests {
                             ),
                         }),
                         span:sp(7,8),
-                        attrs: None,
+                        attrs: ThinVec::new(),
                     }))),
                     span:sp(0,8),
-                    attrs: None,
+                    attrs: ThinVec::new(),
                    }))
     }
 
@@ -858,7 +859,7 @@ mod tests {
                                ),
                             }),
                            span: sp(0,1),
-                           attrs: None})),
+                           attrs: ThinVec::new()})),
                        id: ast::DUMMY_NODE_ID,
                        span: sp(0,1)}))
 
@@ -953,7 +954,7 @@ mod tests {
                                                         ),
                                                       }),
                                                 span: sp(17,18),
-                                                attrs: None,})),
+                                                attrs: ThinVec::new()})),
                                             id: ast::DUMMY_NODE_ID,
                                             span: sp(17,19)}),
                                         expr: None,