From eea6f23a0ed67fd8c6b8e1b02cda3628fee56b2f Mon Sep 17 00:00:00 2001
From: Nicholas Nethercote <nnethercote@mozilla.com>
Date: Thu, 24 Oct 2019 06:33:12 +1100
Subject: Make doc comments cheaper with `AttrKind`.

`AttrKind` is a new type with two variants, `Normal` and `DocComment`. It's a
big performance win (over 10% in some cases) because `DocComment` lets doc
comments (which are common) be represented very cheaply.

`Attribute` gets some new helper methods to ease the transition:
- `has_name()`: check if the attribute name matches a single `Symbol`; for
  `DocComment` variants it succeeds if the symbol is `sym::doc`.
- `is_doc_comment()`: check if it has a `DocComment` kind.
- `{get,unwrap}_normal_item()`: extract the item from a `Normal` variant;
  panic otherwise.

Fixes #60935.
---
 src/libsyntax/parse/parser/attr.rs |  7 +++----
 src/libsyntax/parse/parser/item.rs | 12 +++++++-----
 2 files changed, 10 insertions(+), 9 deletions(-)

(limited to 'src/libsyntax/parse/parser')

diff --git a/src/libsyntax/parse/parser/attr.rs b/src/libsyntax/parse/parser/attr.rs
index 188a144cac9..1c292661f24 100644
--- a/src/libsyntax/parse/parser/attr.rs
+++ b/src/libsyntax/parse/parser/attr.rs
@@ -43,7 +43,7 @@ impl<'a> Parser<'a> {
                     just_parsed_doc_comment = false;
                 }
                 token::DocComment(s) => {
-                    let attr = attr::mk_sugared_doc_attr(s, self.token.span);
+                    let attr = attr::mk_doc_comment(s, self.token.span);
                     if attr.style != ast::AttrStyle::Outer {
                         let mut err = self.fatal("expected outer doc comment");
                         err.note("inner doc comments like this (starting with \
@@ -150,10 +150,9 @@ impl<'a> Parser<'a> {
         };
 
         Ok(ast::Attribute {
-            item,
+            kind: ast::AttrKind::Normal(item),
             id: attr::mk_attr_id(),
             style,
-            is_sugared_doc: false,
             span,
         })
     }
@@ -229,7 +228,7 @@ impl<'a> Parser<'a> {
                 }
                 token::DocComment(s) => {
                     // We need to get the position of this token before we bump.
-                    let attr = attr::mk_sugared_doc_attr(s, self.token.span);
+                    let attr = attr::mk_doc_comment(s, self.token.span);
                     if attr.style == ast::AttrStyle::Inner {
                         attrs.push(attr);
                         self.bump();
diff --git a/src/libsyntax/parse/parser/item.rs b/src/libsyntax/parse/parser/item.rs
index 5b60e7e6dba..cc6235c6fc7 100644
--- a/src/libsyntax/parse/parser/item.rs
+++ b/src/libsyntax/parse/parser/item.rs
@@ -3,8 +3,8 @@ use super::diagnostics::{Error, dummy_arg, ConsumeClosingDelim};
 
 use crate::maybe_whole;
 use crate::ptr::P;
-use crate::ast::{self, DUMMY_NODE_ID, Ident, Attribute, AttrStyle, AnonConst, Item, ItemKind};
-use crate::ast::{ImplItem, ImplItemKind, TraitItem, TraitItemKind, UseTree, UseTreeKind};
+use crate::ast::{self, DUMMY_NODE_ID, Ident, Attribute, AttrKind, AttrStyle, AnonConst, Item};
+use crate::ast::{ItemKind, ImplItem, ImplItemKind, TraitItem, TraitItemKind, UseTree, UseTreeKind};
 use crate::ast::{PathSegment, IsAuto, Constness, IsAsync, Unsafety, Defaultness};
 use crate::ast::{Visibility, VisibilityKind, Mutability, FnHeader, ForeignItem, ForeignItemKind};
 use crate::ast::{Ty, TyKind, Generics, GenericBounds, TraitRef, EnumDef, VariantData, StructField};
@@ -483,12 +483,14 @@ impl<'a> Parser<'a> {
     /// Emits an expected-item-after-attributes error.
     fn expected_item_err(&mut self, attrs: &[Attribute]) -> PResult<'a,  ()> {
         let message = match attrs.last() {
-            Some(&Attribute { is_sugared_doc: true, .. }) => "expected item after doc comment",
-            _ => "expected item after attributes",
+            Some(&Attribute { kind: AttrKind::DocComment(_), .. }) =>
+                "expected item after doc comment",
+            _ =>
+                "expected item after attributes",
         };
 
         let mut err = self.diagnostic().struct_span_err(self.prev_span, message);
-        if attrs.last().unwrap().is_sugared_doc {
+        if attrs.last().unwrap().is_doc_comment() {
             err.span_label(self.prev_span, "this doc comment doesn't document anything");
         }
         Err(err)
-- 
cgit 1.4.1-3-g733a5