Auto merge of #60630 - nnethercote:use-Symbol-more, r=petrochenkov

Use `Symbol` more

A `Symbol` can be equated with a string (e.g. `&str`). This involves a
TLS lookup to get the chars (and a Mutex lock in a parallel compiler)
and then a char-by-char comparison. This functionality is convenient but
avoids one of the main benefits of `Symbol`s, which is fast equality
comparisons.

This PR removes the `Symbol`/string equality operations, forcing a lot
of existing string occurrences to become `Symbol`s. Fortunately, these
are almost all static strings (many are attribute names) and we can add
static `Symbol`s as necessary, and very little extra interning occurs.
The benefits are (a) a slight speedup (possibly greater in a parallel
compiler), and (b) the code is a lot more principled about `Symbol` use.
The main downside is verbosity, particularly with more `use
syntax::symbol::symbols` items.

r? @Zoxc

5 files changed, 44 insertions, 39 deletions

diff --git a/src/libsyntax/ext/base.rs b/src/libsyntax/ext/base.rs
index cc19acb61ad..0a88d2f8824 100644
--- a/src/libsyntax/ext/base.rs
+++ b/src/libsyntax/ext/base.rs
@@ -10,7 +10,7 @@ use crate::mut_visit::{self, MutVisitor};
 use crate::parse::{self, parser, DirectoryOwnership};
 use crate::parse::token;
 use crate::ptr::P;
-use crate::symbol::{keywords, Ident, Symbol};
+use crate::symbol::{keywords, Ident, Symbol, sym};
 use crate::ThinVec;
 use crate::tokenstream::{self, TokenStream};
 
@@ -871,7 +871,7 @@ impl<'a> ExtCtxt<'a> {
         let mut last_macro = None;
         loop {
             if ctxt.outer().expn_info().map_or(None, |info| {
-                if info.format.name() == "include" {
+                if info.format.name() == sym::include {
                     // Stop going up the backtrace once include! is encountered
                     return None;
                 }
diff --git a/src/libsyntax/ext/derive.rs b/src/libsyntax/ext/derive.rs
index 6df369133d0..a24e09f127e 100644
--- a/src/libsyntax/ext/derive.rs
+++ b/src/libsyntax/ext/derive.rs
@@ -4,7 +4,7 @@ use crate::source_map::{hygiene, ExpnInfo, ExpnFormat};
 use crate::ext::base::ExtCtxt;
 use crate::ext::build::AstBuilder;
 use crate::parse::parser::PathStyle;
-use crate::symbol::Symbol;
+use crate::symbol::{Symbol, sym};
 
 use syntax_pos::Span;
 
@@ -13,7 +13,7 @@ use rustc_data_structures::fx::FxHashSet;
 pub fn collect_derives(cx: &mut ExtCtxt<'_>, attrs: &mut Vec<ast::Attribute>) -> Vec<ast::Path> {
     let mut result = Vec::new();
     attrs.retain(|attr| {
-        if attr.path != "derive" {
+        if attr.path != sym::derive {
             return true;
         }
         if !attr.is_meta_item_list() {
diff --git a/src/libsyntax/ext/expand.rs b/src/libsyntax/ext/expand.rs
index 82358679c0e..a286fd83e3c 100644
--- a/src/libsyntax/ext/expand.rs
+++ b/src/libsyntax/ext/expand.rs
@@ -14,7 +14,7 @@ use crate::parse::token::{self, Token};
 use crate::parse::parser::Parser;
 use crate::ptr::P;
 use crate::symbol::Symbol;
-use crate::symbol::keywords;
+use crate::symbol::{keywords, sym};
 use crate::tokenstream::{TokenStream, TokenTree};
 use crate::visit::{self, Visitor};
 use crate::util::map_in_place::MapInPlace;
@@ -356,7 +356,7 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
                     self.collect_invocations(fragment, &[])
                 } else if let InvocationKind::Attr { attr: None, traits, item, .. } = invoc.kind {
                     if !item.derive_allowed() {
-                        let attr = attr::find_by_name(item.attrs(), "derive")
+                        let attr = attr::find_by_name(item.attrs(), sym::derive)
                             .expect("`derive` attribute should exist");
                         let span = attr.span;
                         let mut err = self.cx.mut_span_err(span,
@@ -376,7 +376,7 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
                     }
 
                     let mut item = self.fully_configure(item);
-                    item.visit_attrs(|attrs| attrs.retain(|a| a.path != "derive"));
+                    item.visit_attrs(|attrs| attrs.retain(|a| a.path != sym::derive));
                     let mut item_with_markers = item.clone();
                     add_derived_markers(&mut self.cx, item.span(), &traits, &mut item_with_markers);
                     let derives = derives.entry(invoc.expansion_data.mark).or_default();
@@ -510,7 +510,7 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
         if invoc.fragment_kind == AstFragmentKind::ForeignItems &&
            !self.cx.ecfg.macros_in_extern_enabled() {
             if let SyntaxExtension::NonMacroAttr { .. } = *ext {} else {
-                emit_feature_err(&self.cx.parse_sess, "macros_in_extern",
+                emit_feature_err(&self.cx.parse_sess, sym::macros_in_extern,
                                  invoc.span(), GateIssue::Language,
                                  "macro invocations in `extern {}` blocks are experimental");
             }
@@ -636,7 +636,7 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
             Annotatable::Item(ref item) => {
                 match item.node {
                     ItemKind::Mod(_) if self.cx.ecfg.proc_macro_hygiene() => return,
-                    ItemKind::Mod(_) => ("modules", "proc_macro_hygiene"),
+                    ItemKind::Mod(_) => ("modules", sym::proc_macro_hygiene),
                     _ => return,
                 }
             }
@@ -645,8 +645,8 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
             Annotatable::ForeignItem(_) => return,
             Annotatable::Stmt(_) |
             Annotatable::Expr(_) if self.cx.ecfg.proc_macro_hygiene() => return,
-            Annotatable::Stmt(_) => ("statements", "proc_macro_hygiene"),
-            Annotatable::Expr(_) => ("expressions", "proc_macro_hygiene"),
+            Annotatable::Stmt(_) => ("statements", sym::proc_macro_hygiene),
+            Annotatable::Expr(_) => ("expressions", sym::proc_macro_hygiene),
         };
         emit_feature_err(
             self.cx.parse_sess,
@@ -681,7 +681,7 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
                 if let ast::ItemKind::MacroDef(_) = i.node {
                     emit_feature_err(
                         self.parse_sess,
-                        "proc_macro_hygiene",
+                        sym::proc_macro_hygiene,
                         self.span,
                         GateIssue::Language,
                         "procedural macros cannot expand to macro definitions",
@@ -724,13 +724,13 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
                 // don't stability-check macros in the same crate
                 // (the only time this is null is for syntax extensions registered as macros)
                 if def_site_span.map_or(false, |def_span| !crate_span.contains(def_span))
-                    && !span.allows_unstable(&feature.as_str())
+                    && !span.allows_unstable(feature)
                     && this.cx.ecfg.features.map_or(true, |feats| {
                     // macro features will count as lib features
                     !feats.declared_lib_features.iter().any(|&(feat, _)| feat == feature)
                 }) {
                     let explain = format!("macro {}! is unstable", path);
-                    emit_feature_err(this.cx.parse_sess, &*feature.as_str(), span,
+                    emit_feature_err(this.cx.parse_sess, feature, span,
                                      GateIssue::Library(Some(issue)), &explain);
                     this.cx.trace_macros_diag();
                 }
@@ -885,7 +885,7 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
         }
         emit_feature_err(
             self.cx.parse_sess,
-            "proc_macro_hygiene",
+            sym::proc_macro_hygiene,
             span,
             GateIssue::Language,
             &format!("procedural macros cannot be expanded to {}", kind),
@@ -1109,7 +1109,7 @@ impl<'a, 'b> InvocationCollector<'a, 'b> {
                        -> Option<ast::Attribute> {
         let attr = attrs.iter()
                         .position(|a| {
-                            if a.path == "derive" {
+                            if a.path == sym::derive {
                                 *after_derive = true;
                             }
                             !attr::is_known(a) && !is_builtin_attr(a)
@@ -1117,8 +1117,8 @@ impl<'a, 'b> InvocationCollector<'a, 'b> {
                         .map(|i| attrs.remove(i));
         if let Some(attr) = &attr {
             if !self.cx.ecfg.enable_custom_inner_attributes() &&
-               attr.style == ast::AttrStyle::Inner && attr.path != "test" {
-                emit_feature_err(&self.cx.parse_sess, "custom_inner_attributes",
+               attr.style == ast::AttrStyle::Inner && attr.path != sym::test {
+                emit_feature_err(&self.cx.parse_sess, sym::custom_inner_attributes,
                                  attr.span, GateIssue::Language,
                                  "non-builtin inner attributes are unstable");
             }
@@ -1167,7 +1167,7 @@ impl<'a, 'b> InvocationCollector<'a, 'b> {
             self.check_attribute_inner(attr, features);
 
             // macros are expanded before any lint passes so this warning has to be hardcoded
-            if attr.path == "derive" {
+            if attr.path == sym::derive {
                 self.cx.struct_span_warn(attr.span, "`#[derive]` does nothing on macro invocations")
                     .note("this may become a hard error in a future release")
                     .emit();
@@ -1352,7 +1352,7 @@ impl<'a, 'b> MutVisitor for InvocationCollector<'a, 'b> {
                 let inline_module = item.span.contains(inner) || inner.is_dummy();
 
                 if inline_module {
-                    if let Some(path) = attr::first_attr_value_str_by_name(&item.attrs, "path") {
+                    if let Some(path) = attr::first_attr_value_str_by_name(&item.attrs, sym::path) {
                         self.cx.current_expansion.directory_ownership =
                             DirectoryOwnership::Owned { relative: None };
                         module.directory.push(&*path.as_str());
@@ -1485,19 +1485,19 @@ impl<'a, 'b> MutVisitor for InvocationCollector<'a, 'b> {
     fn visit_attribute(&mut self, at: &mut ast::Attribute) {
         // turn `#[doc(include="filename")]` attributes into `#[doc(include(file="filename",
         // contents="file contents")]` attributes
-        if !at.check_name("doc") {
+        if !at.check_name(sym::doc) {
             return noop_visit_attribute(at, self);
         }
 
         if let Some(list) = at.meta_item_list() {
-            if !list.iter().any(|it| it.check_name("include")) {
+            if !list.iter().any(|it| it.check_name(sym::include)) {
                 return noop_visit_attribute(at, self);
             }
 
             let mut items = vec![];
 
             for mut it in list {
-                if !it.check_name("include") {
+                if !it.check_name(sym::include) {
                     items.push({ noop_visit_meta_list_item(&mut it, self); it });
                     continue;
                 }
diff --git a/src/libsyntax/ext/source_util.rs b/src/libsyntax/ext/source_util.rs
index 549de1628eb..e1cb90d9e71 100644
--- a/src/libsyntax/ext/source_util.rs
+++ b/src/libsyntax/ext/source_util.rs
@@ -4,7 +4,7 @@ use crate::ext::build::AstBuilder;
 use crate::parse::{self, token, DirectoryOwnership};
 use crate::print::pprust;
 use crate::ptr::P;
-use crate::symbol::Symbol;
+use crate::symbol::{Symbol, sym};
 use crate::tokenstream;
 
 use smallvec::SmallVec;
@@ -44,7 +44,7 @@ pub fn expand_column(cx: &mut ExtCtxt<'_>, sp: Span, tts: &[tokenstream::TokenTr
 /* __rust_unstable_column!(): expands to the current column number */
 pub fn expand_column_gated(cx: &mut ExtCtxt<'_>, sp: Span, tts: &[tokenstream::TokenTree])
                   -> Box<dyn base::MacResult+'static> {
-    if sp.allows_unstable("__rust_unstable_column") {
+    if sp.allows_unstable(sym::__rust_unstable_column) {
         expand_column(cx, sp, tts)
     } else {
         cx.span_fatal(sp, "the __rust_unstable_column macro is unstable");
diff --git a/src/libsyntax/ext/tt/macro_rules.rs b/src/libsyntax/ext/tt/macro_rules.rs
index a53cc2fe661..06651750de7 100644
--- a/src/libsyntax/ext/tt/macro_rules.rs
+++ b/src/libsyntax/ext/tt/macro_rules.rs
@@ -13,7 +13,7 @@ use crate::parse::{Directory, ParseSess};
 use crate::parse::parser::Parser;
 use crate::parse::token::{self, NtTT};
 use crate::parse::token::Token::*;
-use crate::symbol::Symbol;
+use crate::symbol::{Symbol, keywords, sym};
 use crate::tokenstream::{DelimSpan, TokenStream, TokenTree};
 
 use errors::FatalError;
@@ -376,7 +376,7 @@ pub fn compile(
     });
 
     if body.legacy {
-        let allow_internal_unstable = attr::find_by_name(&def.attrs, "allow_internal_unstable")
+        let allow_internal_unstable = attr::find_by_name(&def.attrs, sym::allow_internal_unstable)
             .map(|attr| attr
                 .meta_item_list()
                 .map(|list| list.iter()
@@ -399,11 +399,11 @@ pub fn compile(
                     vec![Symbol::intern("allow_internal_unstable_backcompat_hack")].into()
                 })
             );
-        let allow_internal_unsafe = attr::contains_name(&def.attrs, "allow_internal_unsafe");
+        let allow_internal_unsafe = attr::contains_name(&def.attrs, sym::allow_internal_unsafe);
         let mut local_inner_macros = false;
-        if let Some(macro_export) = attr::find_by_name(&def.attrs, "macro_export") {
+        if let Some(macro_export) = attr::find_by_name(&def.attrs, sym::macro_export) {
             if let Some(l) = macro_export.meta_item_list() {
-                local_inner_macros = attr::list_contains_name(&l, "local_inner_macros");
+                local_inner_macros = attr::list_contains_name(&l, sym::local_inner_macros);
             }
         }
 
@@ -426,7 +426,7 @@ pub fn compile(
             edition,
         }
     } else {
-        let is_transparent = attr::contains_name(&def.attrs, "rustc_transparent_macro");
+        let is_transparent = attr::contains_name(&def.attrs, sym::rustc_transparent_macro);
 
         SyntaxExtension::DeclMacro {
             expander,
@@ -467,7 +467,7 @@ fn check_lhs_no_empty_seq(sess: &ParseSess, tts: &[quoted::TokenTree]) -> bool {
             TokenTree::Sequence(span, ref seq) => {
                 if seq.separator.is_none() && seq.tts.iter().all(|seq_tt| {
                     match *seq_tt {
-                        TokenTree::MetaVarDecl(_, _, id) => id.name == "vis",
+                        TokenTree::MetaVarDecl(_, _, id) => id.name == sym::vis,
                         TokenTree::Sequence(_, ref sub_seq) =>
                             sub_seq.op == quoted::KleeneOp::ZeroOrMore
                             || sub_seq.op == quoted::KleeneOp::ZeroOrOne,
@@ -1046,7 +1046,8 @@ fn is_in_follow(tok: &quoted::TokenTree, frag: &str) -> IsInFollow {
                 match *tok {
                     TokenTree::Token(_, ref tok) => match *tok {
                         FatArrow | Comma | Eq | BinOp(token::Or) => IsInFollow::Yes,
-                        Ident(i, false) if i.name == "if" || i.name == "in" => IsInFollow::Yes,
+                        Ident(i, false) if i.name == keywords::If.name() ||
+                                           i.name == keywords::In.name() => IsInFollow::Yes,
                         _ => IsInFollow::No(tokens),
                     },
                     _ => IsInFollow::No(tokens),
@@ -1063,10 +1064,12 @@ fn is_in_follow(tok: &quoted::TokenTree, frag: &str) -> IsInFollow {
                         OpenDelim(token::DelimToken::Bracket) |
                         Comma | FatArrow | Colon | Eq | Gt | BinOp(token::Shr) | Semi |
                         BinOp(token::Or) => IsInFollow::Yes,
-                        Ident(i, false) if i.name == "as" || i.name == "where" => IsInFollow::Yes,
+                        Ident(i, false) if i.name == keywords::As.name() ||
+                                           i.name == keywords::Where.name() => IsInFollow::Yes,
                         _ => IsInFollow::No(tokens),
                     },
-                    TokenTree::MetaVarDecl(_, _, frag) if frag.name == "block" => IsInFollow::Yes,
+                    TokenTree::MetaVarDecl(_, _, frag) if frag.name == sym::block =>
+                        IsInFollow::Yes,
                     _ => IsInFollow::No(tokens),
                 }
             },
@@ -1089,16 +1092,18 @@ fn is_in_follow(tok: &quoted::TokenTree, frag: &str) -> IsInFollow {
                 match *tok {
                     TokenTree::Token(_, ref tok) => match *tok {
                         Comma => IsInFollow::Yes,
-                        Ident(i, is_raw) if is_raw || i.name != "priv" => IsInFollow::Yes,
+                        Ident(i, is_raw) if is_raw || i.name != keywords::Priv.name() =>
+                            IsInFollow::Yes,
                         ref tok => if tok.can_begin_type() {
                             IsInFollow::Yes
                         } else {
                             IsInFollow::No(tokens)
                         }
                     },
-                    TokenTree::MetaVarDecl(_, _, frag) if frag.name == "ident"
-                                                       || frag.name == "ty"
-                                                       || frag.name == "path" => IsInFollow::Yes,
+                    TokenTree::MetaVarDecl(_, _, frag) if frag.name == sym::ident
+                                                       || frag.name == sym::ty
+                                                       || frag.name == sym::path =>
+                        IsInFollow::Yes,
                     _ => IsInFollow::No(tokens),
                 }
             },