Implement --check-cfg option (RFC 3013)

Co-authored-by: Urgau <lolo.branstett@numericable.fr>
Co-authored-by: Marcelina Kościelnicka <mwk@0x04.net>

compiler/rustc_session/src/parse.rs

@@ -1,6 +1,7 @@
 //! Contains `ParseSess` which holds state living beyond what one `Parser` might.
 //! It also serves as an input to the parser itself.
 
+use crate::config::CheckCfg;
 use crate::lint::{BufferedEarlyLint, BuiltinLintDiagnostics, Lint, LintId};
 use rustc_ast::node_id::NodeId;
 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
@@ -18,6 +19,7 @@ use std::str;
 /// The set of keys (and, optionally, values) that define the compilation
 /// environment of the crate, used to drive conditional compilation.
 pub type CrateConfig = FxHashSet<(Symbol, Option<Symbol>)>;
+pub type CrateCheckConfig = CheckCfg<Symbol>;
 
 /// Collected spans during parsing for places where a certain feature was
 /// used and should be feature gated accordingly in `check_crate`.
@@ -117,6 +119,7 @@ pub struct ParseSess {
     pub span_diagnostic: Handler,
     pub unstable_features: UnstableFeatures,
     pub config: CrateConfig,
+    pub check_config: CrateCheckConfig,
     pub edition: Edition,
     pub missing_fragment_specifiers: Lock<FxHashMap<Span, NodeId>>,
     /// Places where raw identifiers were used. This is used to avoid complaining about idents
@@ -162,6 +165,7 @@ impl ParseSess {
             span_diagnostic: handler,
             unstable_features: UnstableFeatures::from_environment(None),
             config: FxHashSet::default(),
+            check_config: CrateCheckConfig::default(),
             edition: ExpnId::root().expn_data().edition,
             missing_fragment_specifiers: Default::default(),
             raw_identifier_spans: Lock::new(Vec::new()),