Rollup merge of rust-lang#66895 - Centril:rustc_feature, r=oli-obk

Feature gating *declarations* => new crate `rustc_feature`

This PR moves the data-oriented parts of feature gating into its own crate, `rustc_feature`.
The parts consist of some data types as well as `accepted`, `active`, `removed`, and `builtin_attrs`.

Feature gate checking itself remains in `syntax::feature_gate::check`. The parts which define how to emit feature gate errors could probably be moved to `rustc_errors` or to the new `rustc_session` crate introduced in rust-lang#66878. The visitor itself could probably be moved as a pass in `rustc_passes` depending on how the dependency edges work out.

The PR also contains some drive-by cleanup of feature gate checking. As such, the PR probably best read commit-by-commit.

r? @oli-obk
cc @petrochenkov
cc @Mark-Simulacrum

Cargo.lock

@@ -3199,6 +3199,7 @@ dependencies = [
  "rustc_data_structures",
  "rustc_error_codes",
  "rustc_errors",
+ "rustc_feature",
  "rustc_fs_util",
  "rustc_index",
  "rustc_macros",
@@ -3574,6 +3575,7 @@ dependencies = [
  "rustc_data_structures",
  "rustc_error_codes",
  "rustc_errors",
+ "rustc_feature",
  "rustc_interface",
  "rustc_lint",
  "rustc_metadata",
@@ -3607,6 +3609,15 @@ dependencies = [
  "unicode-width",
 ]
 
+[[package]]
+name = "rustc_feature"
+version = "0.0.0"
+dependencies = [
+ "lazy_static 1.3.0",
+ "rustc_data_structures",
+ "syntax_pos",
+]
+
 [[package]]
 name = "rustc_fs_util"
 version = "0.0.0"
@@ -3682,6 +3693,7 @@ dependencies = [
  "rustc",
  "rustc_data_structures",
  "rustc_error_codes",
+ "rustc_feature",
  "rustc_index",
  "rustc_target",
  "syntax",
@@ -3786,6 +3798,7 @@ dependencies = [
  "rustc_data_structures",
  "rustc_error_codes",
  "rustc_errors",
+ "rustc_feature",
  "rustc_lexer",
  "rustc_target",
  "smallvec 1.0.0",
@@ -3802,6 +3815,7 @@ dependencies = [
  "rustc_data_structures",
  "rustc_error_codes",
  "rustc_errors",
+ "rustc_feature",
  "rustc_index",
  "rustc_parse",
  "rustc_target",
@@ -3844,6 +3858,7 @@ dependencies = [
  "rustc_data_structures",
  "rustc_error_codes",
  "rustc_errors",
+ "rustc_feature",
  "rustc_metadata",
  "smallvec 1.0.0",
  "syntax",
@@ -4442,6 +4457,7 @@ dependencies = [
  "rustc_data_structures",
  "rustc_error_codes",
  "rustc_errors",
+ "rustc_feature",
  "rustc_index",
  "rustc_lexer",
  "rustc_macros",
@@ -4458,6 +4474,7 @@ dependencies = [
  "log",
  "rustc_data_structures",
  "rustc_errors",
+ "rustc_feature",
  "rustc_lexer",
  "rustc_parse",
  "serialize",
@@ -4475,6 +4492,7 @@ dependencies = [
  "rustc_data_structures",
  "rustc_error_codes",
  "rustc_errors",
+ "rustc_feature",
  "rustc_parse",
  "rustc_target",
  "smallvec 1.0.0",

src/librustc/Cargo.toml

@@ -22,6 +22,7 @@ rustc-rayon = "0.3.0"
 rustc-rayon-core = "0.3.0"
 polonius-engine  = "0.10.0"
 rustc_apfloat = { path = "../librustc_apfloat" }
+rustc_feature = { path = "../librustc_feature" }
 rustc_target = { path = "../librustc_target" }
 rustc_macros = { path = "../librustc_macros" }
 rustc_data_structures = { path = "../librustc_data_structures" }

src/librustc/arena.rs

@@ -101,7 +101,7 @@ macro_rules! arena_types {
             [few] resolve_lifetimes: rustc::middle::resolve_lifetime::ResolveLifetimes,
             [few] lint_levels: rustc::lint::LintLevelMap,
             [few] stability_index: rustc::middle::stability::Index<'tcx>,
-            [few] features: syntax::feature_gate::Features,
+            [few] features: rustc_feature::Features,
             [few] all_traits: Vec<rustc::hir::def_id::DefId>,
             [few] privacy_access_levels: rustc::middle::privacy::AccessLevels,
             [few] target_features_whitelist: rustc_data_structures::fx::FxHashMap<

src/librustc/ich/impls_syntax.rs

@@ -4,7 +4,6 @@
 use crate::ich::StableHashingContext;
 
 use syntax::ast;
-use syntax::feature_gate;
 use syntax_pos::SourceFile;
 
 use crate::hir::def_id::{DefId, CrateNum, CRATE_DEF_INDEX};
@@ -156,7 +155,7 @@ fn stable_normalized_pos(np: ::syntax_pos::NormalizedPos,
 }
 
 
-impl<'tcx> HashStable<StableHashingContext<'tcx>> for feature_gate::Features {
+impl<'tcx> HashStable<StableHashingContext<'tcx>> for rustc_feature::Features {
     fn hash_stable(&self, hcx: &mut StableHashingContext<'tcx>, hasher: &mut StableHasher) {
         // Unfortunately we cannot exhaustively list fields here, since the
         // struct is macro generated.

src/librustc/lint/levels.rs

@@ -232,13 +232,13 @@ impl<'a> LintLevelsBuilder<'a> {
                             // don't have any lint names (`#[level(reason = "foo")]`)
                             if let ast::LitKind::Str(rationale, _) = name_value.kind {
                                 if !self.sess.features_untracked().lint_reasons {
-                                    feature_gate::emit_feature_err(
+                                    feature_gate::feature_err(
                                         &self.sess.parse_sess,
                                         sym::lint_reasons,
                                         item.span,
-                                        feature_gate::GateIssue::Language,
                                         "lint reasons are experimental"
-                                    );
+                                    )
+                                    .emit();
                                 }
                                 reason = Some(rationale);
                             } else {

src/librustc/middle/stability.rs

@@ -13,11 +13,12 @@ use crate::ty::query::Providers;
 use crate::middle::privacy::AccessLevels;
 use crate::session::{DiagnosticMessageId, Session};
 use errors::DiagnosticBuilder;
+use rustc_feature::GateIssue;
 use syntax::symbol::{Symbol, sym};
 use syntax_pos::{Span, MultiSpan};
 use syntax::ast::{Attribute, CRATE_NODE_ID};
 use syntax::errors::Applicability;
-use syntax::feature_gate::{GateIssue, emit_feature_err};
+use syntax::feature_gate::{feature_err, feature_err_issue};
 use syntax::attr::{self, Stability, Deprecation, RustcDeprecation};
 use crate::ty::{self, TyCtxt};
 use crate::util::nodemap::{FxHashSet, FxHashMap};
@@ -512,9 +513,8 @@ pub fn report_unstable(
         if is_soft {
             soft_handler(lint::builtin::SOFT_UNSTABLE, span, &msg)
         } else {
-            emit_feature_err(
-                &sess.parse_sess, feature, span, GateIssue::Library(issue), &msg
-            );
+            feature_err_issue(&sess.parse_sess, feature, span, GateIssue::Library(issue), &msg)
+                .emit();
         }
     }
 }
@@ -842,15 +842,19 @@ impl Visitor<'tcx> for Checker<'tcx> {
                 let ty = self.tcx.type_of(def_id);
 
                 if adt_def.has_dtor(self.tcx) {
-                    emit_feature_err(&self.tcx.sess.parse_sess,
-                                     sym::untagged_unions, item.span, GateIssue::Language,
-                                     "unions with `Drop` implementations are unstable");
+                    feature_err(
+                        &self.tcx.sess.parse_sess, sym::untagged_unions, item.span,
+                        "unions with `Drop` implementations are unstable"
+                    )
+                    .emit();
                 } else {
                     let param_env = self.tcx.param_env(def_id);
                     if !param_env.can_type_implement_copy(self.tcx, ty).is_ok() {
-                        emit_feature_err(&self.tcx.sess.parse_sess,
-                                         sym::untagged_unions, item.span, GateIssue::Language,
-                                         "unions with non-`Copy` fields are unstable");
+                        feature_err(
+                            &self.tcx.sess.parse_sess, sym::untagged_unions, item.span,
+                            "unions with non-`Copy` fields are unstable"
+                        )
+                        .emit();
                     }
                 }
             }

src/librustc/query/mod.rs

@@ -1130,7 +1130,7 @@ rustc_queries! {
             desc { |tcx| "estimating size for `{}`", tcx.def_path_str(def.def_id()) }
         }
 
-        query features_query(_: CrateNum) -> &'tcx feature_gate::Features {
+        query features_query(_: CrateNum) -> &'tcx rustc_feature::Features {
             eval_always
             desc { "looking up enabled feature gates" }
         }

src/librustc/session/config.rs

@@ -7,6 +7,7 @@ use crate::session::{early_error, early_warn, Session};
 use crate::session::search_paths::SearchPath;
 
 use rustc_data_structures::fx::FxHashSet;
+use rustc_feature::UnstableFeatures;
 
 use rustc_target::spec::{LinkerFlavor, MergeFunctions, PanicStrategy, RelroLevel};
 use rustc_target::spec::{Target, TargetTriple};
@@ -16,7 +17,6 @@ use syntax::ast;
 use syntax::source_map::{FileName, FilePathMapping};
 use syntax::edition::{Edition, EDITION_NAME_LIST, DEFAULT_EDITION};
 use syntax::symbol::{sym, Symbol};
-use syntax::feature_gate::UnstableFeatures;
 
 use errors::emitter::HumanReadableErrorType;
 use errors::{ColorConfig, FatalError, Handler};
@@ -2701,7 +2701,7 @@ pub fn parse_crate_types_from_list(list_list: Vec<String>) -> Result<Vec<CrateTy
 
 pub mod nightly_options {
     use getopts;
-    use syntax::feature_gate::UnstableFeatures;
+    use rustc_feature::UnstableFeatures;
     use super::{ErrorOutputType, OptionStability, RustcOptGroup};
     use crate::session::early_error;
 
@@ -2850,9 +2850,9 @@ mod dep_tracking {
     use super::{CrateType, DebugInfo, ErrorOutputType, OptLevel, OutputTypes,
                 Passes, Sanitizer, LtoCli, LinkerPluginLto, SwitchWithOptPath,
                 SymbolManglingVersion};
+    use rustc_feature::UnstableFeatures;
     use rustc_target::spec::{MergeFunctions, PanicStrategy, RelroLevel, TargetTriple};
     use syntax::edition::Edition;
-    use syntax::feature_gate::UnstableFeatures;
 
     pub trait DepTrackingHash {
         fn hash(&self, hasher: &mut DefaultHasher, error_format: ErrorOutputType);

src/librustc/session/mod.rs

@@ -21,7 +21,6 @@ use errors::emitter::{Emitter, EmitterWriter};
 use errors::emitter::HumanReadableErrorType;
 use errors::annotate_snippet_emitter_writer::{AnnotateSnippetEmitterWriter};
 use syntax::edition::Edition;
-use syntax::feature_gate;
 use errors::json::JsonEmitter;
 use syntax::source_map;
 use syntax::sess::ParseSess;
@@ -86,7 +85,7 @@ pub struct Session {
     /// `rustc_codegen_llvm::back::symbol_names` module for more information.
     pub crate_disambiguator: Once<CrateDisambiguator>,
 
-    features: Once<feature_gate::Features>,
+    features: Once<rustc_feature::Features>,
 
     /// The maximum recursion limit for potentially infinitely recursive
     /// operations such as auto-dereference and monomorphization.
@@ -470,11 +469,11 @@ impl Session {
     /// DO NOT USE THIS METHOD if there is a TyCtxt available, as it circumvents
     /// dependency tracking. Use tcx.features() instead.
     #[inline]
-    pub fn features_untracked(&self) -> &feature_gate::Features {
+    pub fn features_untracked(&self) -> &rustc_feature::Features {
         self.features.get()
     }
 
-    pub fn init_features(&self, features: feature_gate::Features) {
+    pub fn init_features(&self, features: rustc_feature::Features) {
         self.features.set(features);
     }
 

src/librustc/ty/context.rs

@@ -72,7 +72,6 @@ use rustc_macros::HashStable;
 use syntax::ast;
 use syntax::attr;
 use syntax::source_map::MultiSpan;
-use syntax::feature_gate;
 use syntax::symbol::{Symbol, kw, sym};
 use syntax_pos::Span;
 use syntax::expand::allocator::AllocatorKind;
@@ -1312,7 +1311,7 @@ impl<'tcx> TyCtxt<'tcx> {
         self.cstore.allocator_kind()
     }
 
-    pub fn features(self) -> &'tcx feature_gate::Features {
+    pub fn features(self) -> &'tcx rustc_feature::Features {
         self.features_query(LOCAL_CRATE)
     }
 

src/librustc/ty/query/mod.rs

@@ -56,7 +56,6 @@ use std::any::type_name;
 use syntax_pos::{Span, DUMMY_SP};
 use syntax::attr;
 use syntax::ast;
-use syntax::feature_gate;
 use syntax::symbol::Symbol;
 
 #[macro_use]

src/librustc_codegen_llvm/lib.rs

@@ -30,6 +30,7 @@ extern crate libc;
 #[macro_use] extern crate rustc;
 extern crate rustc_target;
 #[macro_use] extern crate rustc_data_structures;
+extern crate rustc_feature;
 extern crate rustc_index;
 extern crate rustc_incremental;
 extern crate rustc_codegen_utils;

src/librustc_codegen_llvm/llvm_util.rs

@@ -6,7 +6,7 @@ use rustc::session::config::PrintRequest;
 use rustc_target::spec::{MergeFunctions, PanicStrategy};
 use libc::c_int;
 use std::ffi::CString;
-use syntax::feature_gate::UnstableFeatures;
+use rustc_feature::UnstableFeatures;
 use syntax::symbol::sym;
 
 use std::str;

src/librustc_driver/Cargo.toml

@@ -19,6 +19,7 @@ rustc_target = { path = "../librustc_target" }
 rustc_lint = { path = "../librustc_lint" }
 rustc_data_structures = { path = "../librustc_data_structures" }
 errors = { path = "../librustc_errors", package = "rustc_errors" }
+rustc_feature = { path = "../librustc_feature" }
 rustc_metadata = { path = "../librustc_metadata" }
 rustc_mir = { path = "../librustc_mir" }
 rustc_parse = { path = "../librustc_parse" }

src/librustc_driver/lib.rs

@@ -44,7 +44,7 @@ use errors::{PResult, registry::Registry};
 use rustc_interface::interface;
 use rustc_interface::util::get_codegen_sysroot;
 use rustc_data_structures::sync::SeqCst;
-
+use rustc_feature::{find_gated_cfg, UnstableFeatures};
 use rustc_serialize::json::ToJson;
 
 use std::borrow::Cow;
@@ -61,10 +61,9 @@ use std::str;
 use std::time::Instant;
 
 use syntax::ast;
-use syntax::source_map::FileLoader;
-use syntax::feature_gate::{GatedCfg, UnstableFeatures};
-use syntax::symbol::sym;
-use syntax_pos::{DUMMY_SP, FileName};
+use syntax_pos::source_map::FileLoader;
+use syntax_pos::symbol::sym;
+use syntax_pos::FileName;
 
 pub mod pretty;
 mod args;
@@ -684,12 +683,6 @@ impl RustcDefaultCalls {
                         .is_nightly_build();
 
                     let mut cfgs = sess.parse_sess.config.iter().filter_map(|&(name, ref value)| {
-                        let gated_cfg = GatedCfg::gate(&ast::MetaItem {
-                            path: ast::Path::from_ident(ast::Ident::with_dummy_span(name)),
-                            kind: ast::MetaItemKind::Word,
-                            span: DUMMY_SP,
-                        });
-
                         // Note that crt-static is a specially recognized cfg
                         // directive that's printed out here as part of
                         // rust-lang/rust#37406, but in general the
@@ -700,10 +693,11 @@ impl RustcDefaultCalls {
                         // through to build scripts.
                         let value = value.as_ref().map(|s| s.as_str());
                         let value = value.as_ref().map(|s| s.as_ref());
-                        if name != sym::target_feature || value != Some("crt-static") {
-                            if !allow_unstable_cfg && gated_cfg.is_some() {
-                                return None
-                            }
+                        if (name != sym::target_feature || value != Some("crt-static"))
+                            && !allow_unstable_cfg
+                            && find_gated_cfg(|cfg_sym| cfg_sym == name).is_some()
+                        {
+                            return None;
                         }
 
                         if let Some(value) = value {

src/librustc_feature/Cargo.toml

@@ -0,0 +1,15 @@
+[package]
+authors = ["The Rust Project Developers"]
+name = "rustc_feature"
+version = "0.0.0"
+edition = "2018"
+
+[lib]
+name = "rustc_feature"
+path = "lib.rs"
+doctest = false
+
+[dependencies]
+rustc_data_structures = { path = "../librustc_data_structures" }
+lazy_static = "1.0.0"
+syntax_pos = { path = "../libsyntax_pos" }

src/libsyntax/feature_gate/accepted.rs → src/librustc_feature/accepted.rs

@@ -1,7 +1,7 @@
 //! List of the accepted feature gates.
 
-use crate::symbol::sym;
 use super::{State, Feature};
+use syntax_pos::symbol::sym;
 
 macro_rules! declare_features {
     ($(