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

12 files changed, 44 insertions, 39 deletions

diff --git a/src/libsyntax_ext/asm.rs b/src/libsyntax_ext/asm.rs
index 8edd0e1ae38..b8e89c3ecf8 100644
--- a/src/libsyntax_ext/asm.rs
+++ b/src/libsyntax_ext/asm.rs
@@ -11,7 +11,7 @@ use syntax::ext::base::{self, *};
 use syntax::feature_gate;
 use syntax::parse::{self, token};
 use syntax::ptr::P;
-use syntax::symbol::Symbol;
+use syntax::symbol::{Symbol, sym};
 use syntax::ast::AsmDialect;
 use syntax_pos::Span;
 use syntax::tokenstream;
@@ -39,7 +39,7 @@ impl State {
     }
 }
 
-const OPTIONS: &[&str] = &["volatile", "alignstack", "intel"];
+const OPTIONS: &[Symbol] = &[sym::volatile, sym::alignstack, sym::intel];
 
 pub fn expand_asm<'cx>(cx: &'cx mut ExtCtxt<'_>,
                        sp: Span,
@@ -47,7 +47,7 @@ pub fn expand_asm<'cx>(cx: &'cx mut ExtCtxt<'_>,
                        -> Box<dyn base::MacResult + 'cx> {
     if !cx.ecfg.enable_asm() {
         feature_gate::emit_feature_err(&cx.parse_sess,
-                                       "asm",
+                                       sym::asm,
                                        sp,
                                        feature_gate::GateIssue::Language,
                                        feature_gate::EXPLAIN_ASM);
@@ -233,13 +233,13 @@ fn parse_inline_asm<'a>(
             Options => {
                 let (option, _) = p.parse_str()?;
 
-                if option == "volatile" {
+                if option == sym::volatile {
                     // Indicates that the inline assembly has side effects
                     // and must not be optimized out along with its outputs.
                     volatile = true;
-                } else if option == "alignstack" {
+                } else if option == sym::alignstack {
                     alignstack = true;
-                } else if option == "intel" {
+                } else if option == sym::intel {
                     dialect = AsmDialect::Intel;
                 } else {
                     cx.span_warn(p.prev_span, "unrecognized option");
diff --git a/src/libsyntax_ext/concat_idents.rs b/src/libsyntax_ext/concat_idents.rs
index 8c9eb4bf2d8..77c53f402cc 100644
--- a/src/libsyntax_ext/concat_idents.rs
+++ b/src/libsyntax_ext/concat_idents.rs
@@ -6,7 +6,7 @@ use syntax::feature_gate;
 use syntax::parse::token;
 use syntax::ptr::P;
 use syntax_pos::Span;
-use syntax_pos::symbol::Symbol;
+use syntax_pos::symbol::{Symbol, sym};
 use syntax::tokenstream::TokenTree;
 
 pub fn expand_syntax_ext<'cx>(cx: &'cx mut ExtCtxt<'_>,
@@ -15,7 +15,7 @@ pub fn expand_syntax_ext<'cx>(cx: &'cx mut ExtCtxt<'_>,
                               -> Box<dyn base::MacResult + 'cx> {
     if !cx.ecfg.enable_concat_idents() {
         feature_gate::emit_feature_err(&cx.parse_sess,
-                                       "concat_idents",
+                                       sym::concat_idents,
                                        sp,
                                        feature_gate::GateIssue::Language,
                                        feature_gate::EXPLAIN_CONCAT_IDENTS);
diff --git a/src/libsyntax_ext/deriving/clone.rs b/src/libsyntax_ext/deriving/clone.rs
index b347092e1bc..1b0d572324a 100644
--- a/src/libsyntax_ext/deriving/clone.rs
+++ b/src/libsyntax_ext/deriving/clone.rs
@@ -7,7 +7,7 @@ use syntax::attr;
 use syntax::ext::base::{Annotatable, ExtCtxt};
 use syntax::ext::build::AstBuilder;
 use syntax::ptr::P;
-use syntax::symbol::{Symbol, keywords};
+use syntax::symbol::{Symbol, keywords, sym};
 use syntax_pos::Span;
 
 pub fn expand_deriving_clone(cx: &mut ExtCtxt<'_>,
@@ -37,7 +37,7 @@ pub fn expand_deriving_clone(cx: &mut ExtCtxt<'_>,
             match annitem.node {
                 ItemKind::Struct(_, Generics { ref params, .. }) |
                 ItemKind::Enum(_, Generics { ref params, .. }) => {
-                    if attr::contains_name(&annitem.attrs, "rustc_copy_clone_marker") &&
+                    if attr::contains_name(&annitem.attrs, sym::rustc_copy_clone_marker) &&
                         !params.iter().any(|param| match param.kind {
                             ast::GenericParamKind::Type { .. } => true,
                             _ => false,
diff --git a/src/libsyntax_ext/deriving/generic/mod.rs b/src/libsyntax_ext/deriving/generic/mod.rs
index e5939e396e5..a13dc07085f 100644
--- a/src/libsyntax_ext/deriving/generic/mod.rs
+++ b/src/libsyntax_ext/deriving/generic/mod.rs
@@ -191,7 +191,7 @@ use syntax::ext::build::AstBuilder;
 use syntax::source_map::{self, respan};
 use syntax::util::map_in_place::MapInPlace;
 use syntax::ptr::P;
-use syntax::symbol::{Symbol, keywords};
+use syntax::symbol::{Symbol, keywords, sym};
 use syntax::parse::ParseSess;
 use syntax_pos::{DUMMY_SP, Span};
 
@@ -426,7 +426,7 @@ impl<'a> TraitDef<'a> {
                     }
                 };
                 let is_always_copy =
-                    attr::contains_name(&item.attrs, "rustc_copy_clone_marker") &&
+                    attr::contains_name(&item.attrs, sym::rustc_copy_clone_marker) &&
                     has_no_type_params;
                 let use_temporaries = is_packed && is_always_copy;
 
@@ -464,8 +464,8 @@ impl<'a> TraitDef<'a> {
                 attrs.extend(item.attrs
                     .iter()
                     .filter(|a| {
-                        ["allow", "warn", "deny", "forbid", "stable", "unstable"]
-                            .contains(&a.name_or_empty().get())
+                        [sym::allow, sym::warn, sym::deny, sym::forbid, sym::stable, sym::unstable]
+                            .contains(&a.name_or_empty())
                     })
                     .cloned());
                 push(Annotatable::Item(P(ast::Item { attrs: attrs, ..(*newitem).clone() })))
diff --git a/src/libsyntax_ext/deriving/mod.rs b/src/libsyntax_ext/deriving/mod.rs
index fff54814a38..c27de692d88 100644
--- a/src/libsyntax_ext/deriving/mod.rs
+++ b/src/libsyntax_ext/deriving/mod.rs
@@ -6,7 +6,7 @@ use syntax::ext::base::{Annotatable, ExtCtxt, SyntaxExtension, Resolver};
 use syntax::ext::build::AstBuilder;
 use syntax::ext::hygiene::{Mark, SyntaxContext};
 use syntax::ptr::P;
-use syntax::symbol::Symbol;
+use syntax::symbol::{Symbol, sym};
 use syntax_pos::Span;
 
 macro path_local($x:ident) {
@@ -139,7 +139,7 @@ fn call_intrinsic(cx: &ExtCtxt<'_>,
     let intrinsic_allowed_via_allow_internal_unstable = cx
         .current_expansion.mark.expn_info().unwrap()
         .allow_internal_unstable.map_or(false, |features| features.iter().any(|&s|
-            s == "core_intrinsics"
+            s == sym::core_intrinsics
         ));
     if intrinsic_allowed_via_allow_internal_unstable {
         span = span.with_ctxt(cx.backtrace());
diff --git a/src/libsyntax_ext/format.rs b/src/libsyntax_ext/format.rs
index 24fbc9b6caf..9e54c0634b6 100644
--- a/src/libsyntax_ext/format.rs
+++ b/src/libsyntax_ext/format.rs
@@ -12,7 +12,7 @@ use syntax::ext::build::AstBuilder;
 use syntax::feature_gate;
 use syntax::parse::token;
 use syntax::ptr::P;
-use syntax::symbol::Symbol;
+use syntax::symbol::{Symbol, sym};
 use syntax::tokenstream;
 use syntax_pos::{MultiSpan, Span, DUMMY_SP};
 
@@ -711,12 +711,12 @@ pub fn expand_format_args_nl<'cx>(
     //if !ecx.ecfg.enable_allow_internal_unstable() {
 
     // For some reason, the only one that actually works for `println` is the first check
-    if !sp.allows_unstable("format_args_nl") // the span is marked as `#[allow_insternal_unsable]`
+    if !sp.allows_unstable(sym::format_args_nl) // the span is marked `#[allow_insternal_unsable]`
         && !ecx.ecfg.enable_allow_internal_unstable()  // NOTE: when is this enabled?
         && !ecx.ecfg.enable_format_args_nl()  // enabled using `#[feature(format_args_nl]`
     {
         feature_gate::emit_feature_err(&ecx.parse_sess,
-                                       "format_args_nl",
+                                       sym::format_args_nl,
                                        sp,
                                        feature_gate::GateIssue::Language,
                                        feature_gate::EXPLAIN_FORMAT_ARGS_NL);
diff --git a/src/libsyntax_ext/global_asm.rs b/src/libsyntax_ext/global_asm.rs
index 2baf530aeda..3f2853e4b0e 100644
--- a/src/libsyntax_ext/global_asm.rs
+++ b/src/libsyntax_ext/global_asm.rs
@@ -16,12 +16,12 @@ use syntax::ext::base::{self, *};
 use syntax::feature_gate;
 use syntax::parse::token;
 use syntax::ptr::P;
-use syntax::symbol::Symbol;
+use syntax::symbol::{Symbol, sym};
 use syntax_pos::Span;
 use syntax::tokenstream;
 use smallvec::smallvec;
 
-pub const MACRO: &str = "global_asm";
+pub const MACRO: Symbol = sym::global_asm;
 
 pub fn expand_global_asm<'cx>(cx: &'cx mut ExtCtxt<'_>,
                               sp: Span,
diff --git a/src/libsyntax_ext/log_syntax.rs b/src/libsyntax_ext/log_syntax.rs
index 658ce98d268..1be3990837c 100644
--- a/src/libsyntax_ext/log_syntax.rs
+++ b/src/libsyntax_ext/log_syntax.rs
@@ -2,6 +2,7 @@ use syntax::ext::base;
 use syntax::feature_gate;
 use syntax::print;
 use syntax::tokenstream;
+use syntax::symbol::sym;
 use syntax_pos;
 
 pub fn expand_syntax_ext<'cx>(cx: &'cx mut base::ExtCtxt<'_>,
@@ -10,7 +11,7 @@ pub fn expand_syntax_ext<'cx>(cx: &'cx mut base::ExtCtxt<'_>,
                               -> Box<dyn base::MacResult + 'cx> {
     if !cx.ecfg.enable_log_syntax() {
         feature_gate::emit_feature_err(&cx.parse_sess,
-                                       "log_syntax",
+                                       sym::log_syntax,
                                        sp,
                                        feature_gate::GateIssue::Language,
                                        feature_gate::EXPLAIN_LOG_SYNTAX);
diff --git a/src/libsyntax_ext/proc_macro_decls.rs b/src/libsyntax_ext/proc_macro_decls.rs
index f0390ba3d40..5ced1400acb 100644
--- a/src/libsyntax_ext/proc_macro_decls.rs
+++ b/src/libsyntax_ext/proc_macro_decls.rs
@@ -13,12 +13,16 @@ use syntax::mut_visit::MutVisitor;
 use syntax::parse::ParseSess;
 use syntax::ptr::P;
 use syntax::symbol::Symbol;
-use syntax::symbol::keywords;
+use syntax::symbol::{keywords, sym};
 use syntax::visit::{self, Visitor};
 
 use syntax_pos::{Span, DUMMY_SP};
 
-const PROC_MACRO_KINDS: [&str; 3] = ["proc_macro_derive", "proc_macro_attribute", "proc_macro"];
+const PROC_MACRO_KINDS: [Symbol; 3] = [
+    sym::proc_macro_derive,
+    sym::proc_macro_attribute,
+    sym::proc_macro
+];
 
 struct ProcMacroDerive {
     trait_name: ast::Name,
@@ -139,7 +143,7 @@ impl<'a> CollectProcMacros<'a> {
 
         let attributes_attr = list.get(1);
         let proc_attrs: Vec<_> = if let Some(attr) = attributes_attr {
-            if !attr.check_name("attributes") {
+            if !attr.check_name(sym::attributes) {
                 self.handler.span_err(attr.span(), "second argument must be `attributes`")
             }
             attr.meta_item_list().unwrap_or_else(|| {
@@ -231,7 +235,7 @@ impl<'a> CollectProcMacros<'a> {
 impl<'a> Visitor<'a> for CollectProcMacros<'a> {
     fn visit_item(&mut self, item: &'a ast::Item) {
         if let ast::ItemKind::MacroDef(..) = item.node {
-            if self.is_proc_macro_crate && attr::contains_name(&item.attrs, "macro_export") {
+            if self.is_proc_macro_crate && attr::contains_name(&item.attrs, sym::macro_export) {
                 let msg =
                     "cannot export macro_rules! macros from a `proc-macro` crate type currently";
                 self.handler.span_err(item.span, msg);
@@ -304,11 +308,11 @@ impl<'a> Visitor<'a> for CollectProcMacros<'a> {
             return;
         }
 
-        if attr.check_name("proc_macro_derive") {
+        if attr.check_name(sym::proc_macro_derive) {
             self.collect_custom_derive(item, attr);
-        } else if attr.check_name("proc_macro_attribute") {
+        } else if attr.check_name(sym::proc_macro_attribute) {
             self.collect_attr_proc_macro(item);
-        } else if attr.check_name("proc_macro") {
+        } else if attr.check_name(sym::proc_macro) {
             self.collect_bang_proc_macro(item);
         };
 
diff --git a/src/libsyntax_ext/test.rs b/src/libsyntax_ext/test.rs
index 0fa5cd64360..86ae6ab5fec 100644
--- a/src/libsyntax_ext/test.rs
+++ b/src/libsyntax_ext/test.rs
@@ -7,7 +7,7 @@ use syntax::ext::hygiene::{self, Mark, SyntaxContext};
 use syntax::attr;
 use syntax::ast;
 use syntax::print::pprust;
-use syntax::symbol::Symbol;
+use syntax::symbol::{Symbol, sym};
 use syntax_pos::{DUMMY_SP, Span};
 use syntax::source_map::{ExpnInfo, MacroAttribute};
 use std::iter;
@@ -206,15 +206,15 @@ enum ShouldPanic {
 }
 
 fn should_ignore(i: &ast::Item) -> bool {
-    attr::contains_name(&i.attrs, "ignore")
+    attr::contains_name(&i.attrs, sym::ignore)
 }
 
 fn should_fail(i: &ast::Item) -> bool {
-    attr::contains_name(&i.attrs, "allow_fail")
+    attr::contains_name(&i.attrs, sym::allow_fail)
 }
 
 fn should_panic(cx: &ExtCtxt<'_>, i: &ast::Item) -> ShouldPanic {
-    match attr::find_by_name(&i.attrs, "should_panic") {
+    match attr::find_by_name(&i.attrs, sym::should_panic) {
         Some(attr) => {
             let ref sd = cx.parse_sess.span_diagnostic;
 
@@ -222,7 +222,7 @@ fn should_panic(cx: &ExtCtxt<'_>, i: &ast::Item) -> ShouldPanic {
                 // Handle #[should_panic(expected = "foo")]
                 Some(list) => {
                     let msg = list.iter()
-                        .find(|mi| mi.check_name("expected"))
+                        .find(|mi| mi.check_name(sym::expected))
                         .and_then(|mi| mi.meta_item())
                         .and_then(|mi| mi.value_str());
                     if list.len() != 1 || msg.is_none() {
@@ -247,7 +247,7 @@ fn should_panic(cx: &ExtCtxt<'_>, i: &ast::Item) -> ShouldPanic {
 }
 
 fn has_test_signature(cx: &ExtCtxt<'_>, i: &ast::Item) -> bool {
-    let has_should_panic_attr = attr::contains_name(&i.attrs, "should_panic");
+    let has_should_panic_attr = attr::contains_name(&i.attrs, sym::should_panic);
     let ref sd = cx.parse_sess.span_diagnostic;
     if let ast::ItemKind::Fn(ref decl, ref header, ref generics, _) = i.node {
         if header.unsafety == ast::Unsafety::Unsafe {
diff --git a/src/libsyntax_ext/test_case.rs b/src/libsyntax_ext/test_case.rs
index 1ed1ab0a07b..802037f6d22 100644
--- a/src/libsyntax_ext/test_case.rs
+++ b/src/libsyntax_ext/test_case.rs
@@ -14,7 +14,7 @@ use syntax::ext::build::AstBuilder;
 use syntax::ext::hygiene::{self, Mark, SyntaxContext};
 use syntax::ast;
 use syntax::source_map::respan;
-use syntax::symbol::Symbol;
+use syntax::symbol::{Symbol, sym};
 use syntax_pos::{DUMMY_SP, Span};
 use syntax::source_map::{ExpnInfo, MacroAttribute};
 use syntax::feature_gate;
@@ -27,7 +27,7 @@ pub fn expand(
 ) -> Vec<Annotatable> {
     if !ecx.ecfg.enable_custom_test_frameworks() {
         feature_gate::emit_feature_err(&ecx.parse_sess,
-                                       "custom_test_frameworks",
+                                       sym::custom_test_frameworks,
                                        attr_sp,
                                        feature_gate::GateIssue::Language,
                                        feature_gate::EXPLAIN_CUSTOM_TEST_FRAMEWORKS);
diff --git a/src/libsyntax_ext/trace_macros.rs b/src/libsyntax_ext/trace_macros.rs
index 4d35daf3de9..eca658cb547 100644
--- a/src/libsyntax_ext/trace_macros.rs
+++ b/src/libsyntax_ext/trace_macros.rs
@@ -1,6 +1,6 @@
 use syntax::ext::base::{self, ExtCtxt};
 use syntax::feature_gate;
-use syntax::symbol::keywords;
+use syntax::symbol::{keywords, sym};
 use syntax_pos::Span;
 use syntax::tokenstream::TokenTree;
 
@@ -10,7 +10,7 @@ pub fn expand_trace_macros(cx: &mut ExtCtxt<'_>,
                            -> Box<dyn base::MacResult + 'static> {
     if !cx.ecfg.enable_trace_macros() {
         feature_gate::emit_feature_err(&cx.parse_sess,
-                                       "trace_macros",
+                                       sym::trace_macros,
                                        sp,
                                        feature_gate::GateIssue::Language,
                                        feature_gate::EXPLAIN_TRACE_MACROS);