Rollup merge of #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 #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

2 files changed, 6 insertions, 7 deletions

diff --git a/src/librustc/session/config.rs b/src/librustc/session/config.rs
index 6733250e1e8..fbfae721bbe 100644
--- a/src/librustc/session/config.rs
+++ b/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);
diff --git a/src/librustc/session/mod.rs b/src/librustc/session/mod.rs
index 0b9d04ca6a3..87c7e5a82a3 100644
--- a/src/librustc/session/mod.rs
+++ b/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);
     }